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Project Specific Discussions => Filters/Equalizers => Topic started by: ruffrecords on May 08, 2011, 08:29:31 AM

Title: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 08, 2011, 08:29:31 AM
Place holder for answers to questions related to building the Poor Man's Pultec EQP1-A.

Edit:  Added BOM and other documentation info:

There is no specific BOM except the switches are laid out for Lorlin types or their equivalent. Below is a link to  the latest schematic. It shows component values for a series of recommended frequencies but there is no reason you cannot use your own and calculate the capacitor values using the spreadsheet I provided in the original thread. As far as component choice is concerned, a lot depends on what accuracy you want and hence what tolerance of components you will need. It also depends on what range of values of capacitor are available where you are.

http://www.ianbell.ukfsn.org/pics/PMEQP1-AMKII.png (http://www.ianbell.ukfsn.org/pics/PMEQP1-AMKII.png)

Here is the corresponding list of calculated and recommended practical capacitor values:

http://www.ianbell.ukfsn.org/pics/CapValues.pdf (http://www.ianbell.ukfsn.org/pics/CapValues.pdf)

Edit: Here is the schematic showing how the Hi and Lo PCBs are wired together to make the complete EQ (except the 56K is actually on the PCB now):

http://www.ianbell.ukfsn.org/pics/wiringsm.jpeg (http://www.ianbell.ukfsn.org/pics/wiringsm.jpeg)

Now, that schematic assumes you put the lo cut capacitors in the C1 to C6 postitons on the PCB. Many people have put the boost capacitors in the C1 to C6 positions (I did myself). If you did this you need to wire up the two EQ PCBs accoring to this schematic:

http://www.ianbell.ukfsn.org/pics/alteq/hookupsm.jpg (http://www.ianbell.ukfsn.org/pics/alteq/hookupsm.jpg)

Here is the PCB layout showing the component positions:

http://www.ianbell.ukfsn.org/pics/PMEQP1ApcbV4.png (http://www.ianbell.ukfsn.org/pics/PMEQP1ApcbV4.png)


And here is the system diagram showing how the EQ mates with the input transformer, an EQ In/OUT switch and the gain make up amplifier.

http://www.ianbell.ukfsn.org/pics/EQSystem.png (http://www.ianbell.ukfsn.org/pics/EQSystem.png)

An finally here is a link to a circuit for a possible tube gain make up stage.

http://www.ianbell.ukfsn.org/pics/PMTGMsm.jpeg (http://www.ianbell.ukfsn.org/pics/PMTGMsm.jpeg)

Edit: plus the hookup diagram showing how all the various bits fit together is appended as a pdf file.

Edit: April 2012: And here is a link to a hookup that shows how to wire the EQ to the tube gain make up and PCB and its power supply:

http://www.ianbell.ukfsn.org/pics/alteq/2-wirescaled.jpeg (http://www.ianbell.ukfsn.org/pics/alteq/2-wirescaled.jpeg)

Edit: PLus here is the link to the BOM for the recommended design including the tube gain make up and its power supply:

http://www.ianbell.ukfsn.org/pics/alteq/partslist.xls (http://www.ianbell.ukfsn.org/pics/alteq/partslist.xls)

Edit Aug 2012. We now have the benefit of Chicago Dave's excellent colour hook up diagrams for the EQP1A and for the mid boost/cut add-on:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/DavesPMEQP-1A%20Hookup%20Diagram.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/DavesPMEQP-1A%20Hookup%20Diagram.pdf)

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/DavesPoor%20Mid%20Hookup.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/DavesPoor%20Mid%20Hookup.pdf)

Thanks Dave.


Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 08, 2011, 11:53:52 AM
Place holder for construction tips.

1. Fit resistors and capacitors to PCB first. If you fit the switch first it is very hard to support the caps while they are soldered in. I found this out the hard way.

2. Try to use 50V or 63V caps. 100V caps are fine but some WIMA 100V types are very fat even for quite small values.

3. Caps can be fitted to either side of the PCB. The PCB is laid out for two skinny caps per switch position. if you need to fit a fat one and a skinny one then fit the fat one on the rear of the PCB.

4. If you need to fit a fat cap at one of the switch positions where the caps are near the edge of the PCB then fit the fat cap on the inner of the two positions otherwise it will overlap the edge of the PCB and it may be more difficult to fit into a 1U high space.

5. Panasonic do a nice range of compact 5mm pitch 5% tolerance film caps.

http://uk.farnell.com/jsp/search/browse.jsp?N=500006+1000229+5700009+5156429+5087885+5586183+5087944&Ntk=PLS_MAN_BRAND_NAME&Ntt=panasonic&Ntx=&No=0&getResults=true&appliedparametrics=true&locale=en_UK&catalogId=&prevNValues=500006+1000229+5700009+5156429+5087885+5586183+5087944+5087494+5586078&filtersHidden=false&appliedHidden=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D500006%2B1000229%26Ntk%3DPLS_MAN_BRAND_NAME%26Ntt%3Dpanasonic%26Ntx%3D%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26catalogId%3D%26prevNValues%3D500006%2B1000229 (http://uk.farnell.com/jsp/search/browse.jsp?N=500006+1000229+5700009+5156429+5087885+5586183+5087944&Ntk=PLS_MAN_BRAND_NAME&Ntt=panasonic&Ntx=&No=0&getResults=true&appliedparametrics=true&locale=en_UK&catalogId=&prevNValues=500006+1000229+5700009+5156429+5087885+5586183+5087944+5087494+5586078&filtersHidden=false&appliedHidden=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D500006%2B1000229%26Ntk%3DPLS_MAN_BRAND_NAME%26Ntt%3Dpanasonic%26Ntx%3D%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26catalogId%3D%26prevNValues%3D500006%2B1000229)




Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ej_whyte on May 08, 2011, 12:41:19 PM
Here are my stepped pot calcs, might be useful to have them in here.

Cheers
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 10, 2011, 12:07:04 PM
Here is a snap of the Hi (left) and Lo (right) switch assemblies complete. What appear to be resistors on the Lo PCB are zero ohm resistors for the links.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ej_whyte on May 10, 2011, 12:24:49 PM
What about the small jumper next to the 56k resistor? i thought that had to be done on the low pcb?

Cheers
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 10, 2011, 02:41:44 PM
What about the small jumper next to the 56k resistor? i thought that had to be done on the low pcb?

Cheers

You are right, it does. You may not be able to see it in the picture but what I did was simply use the leg of the resistor to make the link under the PCB.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 10, 2011, 05:26:07 PM
I just noticed a potential error in wiring sketch I did (copied below). When I built the two PCBs I put the boost components in the C1 thru' C6 positions and the cut components in the C7 thru' C12 positions. If you do that and wire it up according to the sketch below it will not work properly because the Lo boost caps get connected to the lo cut pot and vice versa. I'll do an updated version and post it tomorrow if I can. In the meantime if you replace T1 and T2 with T3 and T4 and then replace T3 and T4 with T1 and T2 it should work fine.

Cheers

Ian


(http://www.ianbell.ukfsn.org/pics/wiringsm.jpeg)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 11, 2011, 09:24:29 AM
Here is an updated version of the hook up diagram. I have also noted the position of the counter-clockwise setting (off) of each pot.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: baadc0de on May 11, 2011, 10:18:24 AM
I followed a bit in the main thread that spawned this, but I wasn't entirely sure, so I'll ask here.. what about the inductor? I think there's a place for it and I see L1 populated on the PCB. I've built an ordinary EQP in the past and it had a multi-tapped inductors, so what's the function of this one here, can one omit it, what kind of value does/should it have, etc.?

Sorry if this is a really newb question, I guess it indicates just what a hack I am :D
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 11, 2011, 11:38:27 AM
I followed a bit in the main thread that spawned this, but I wasn't entirely sure, so I'll ask here.. what about the inductor? I think there's a place for it and I see L1 populated on the PCB. I've built an ordinary EQP in the past and it had a multi-tapped inductors, so what's the function of this one here, can one omit it, what kind of value does/should it have, etc.?

It was put in as a bit of an after thought simply because there was space on the PCB for a small one and somebody asked if I would include it on the layout. It just allows a small inductor to be used at one frequency setting only. You don't need to fit it and you can just  short it out.

If you look half way down this page:

http://www.groupdiy.com/index.php?topic=43859.60 (http://www.groupdiy.com/index.php?topic=43859.60)

you will see what I said about possible inductor values.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on May 12, 2011, 01:29:22 PM
Got my boards.
Is there a specific Bom or are we looking at the schematic:(http://www.ianbell.ukfsn.org/pics/PMEQP1-A.png)
Thanks.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 12, 2011, 04:13:26 PM
Got my boards.
Is there a specific Bom or are we looking at the schematic.
Thanks.

There is no specific BOM except the switches are laid out for Lorlin types or their equivalent. Below is a link to  the latest schematic. It shows component values for a series of recommended frequencies but there is no reason you cannot use your own and calculate the capacitor values using the spreadsheet I provided in the original thread. As far as component choice is concerned, a lot depends on what accuracy you want and hence what tolerance of components you will need. it also depends on what range of values of capacitor are available where you are.

http://www.ianbell.ukfsn.org/pics/PMEQP1-AMKII.png (http://www.ianbell.ukfsn.org/pics/PMEQP1-AMKII.png)

Here is the corresponding list of calculated and recommended practical capacitor values:

http://www.ianbell.ukfsn.org/pics/CapValues.pdf (http://www.ianbell.ukfsn.org/pics/CapValues.pdf)

And here is the system diagram showing how the EQ mates with the input transformer, an EQ In/OUT switch and the gain make up amplifier.

http://www.ianbell.ukfsn.org/pics/EQSystem.png (http://www.ianbell.ukfsn.org/pics/EQSystem.png)

An finally here is a link to a circuit for a possible tube gain make up stage.

http://www.ianbell.ukfsn.org/pics/PMTGMsm.jpeghttp://

Cheers

Ian






Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: CJ on May 12, 2011, 09:46:01 PM
we have this Peerles S 217 D all blueprinted,

who needs one?

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: shabtek on May 12, 2011, 10:02:58 PM
CJ!!!           I need 1.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: buschfsu on May 13, 2011, 09:08:22 AM
CJ 2 plzzzzz
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 13, 2011, 07:04:59 PM
Here's a pic of my lash up prototype on the bench. I am pleased to say it appears to work as advertised. The Lo PCB is at the bottom. Notice the larger caps fitted to the rear of the PCB.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: gemini86 on May 13, 2011, 09:10:25 PM
that's quite the mish-mash of pots you have there...

Just curious though, where does one get 470k/47k/4.7K pots in the US?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 14, 2011, 07:06:16 AM
that's quite the mish-mash of pots you have there...

Just curious though, where does one get 470k/47k/4.7K pots in the US?

Someone else had this problem in the original thread. It seem 5K, 50K and 500K are more common in the USA so I would suggest you use those values and tweak the capacitor values accordingly. If you check the original thread you should find that the person who originally asked the question tweaked the spreadsheet for those values of pot in order to calculate new cap values. I promised to update the spreadsheet so you could feed in different pot values and I have now done this. Just for you I have set the initial values to 5k etc.  All you have to do is set the Hi Cut pot value and the spreadsheet calculates the other pot values and all the capacitor values (except for the inductor ones). If you set the Hi Cut pot to 1000 for example you get very close to the classic Pultec circuit.

For those interested in using the single inductor position, the spreadsheet now also includes a section that calculates the required L and series C values for a variety of frequencies for a Q of 0.6.

http://www.ianbell.ukfsn.org/pics/capcalc.xls (http://www.ianbell.ukfsn.org/pics/capcalc.xls)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: baadc0de on May 14, 2011, 10:09:35 AM
Thanks Ian for doing this..

If I understand correctly, the inductor only kicks in at one specific frequency stop (probably the highest?) and if you populate it if you can then calculate an alternative capacitor for that stop and have a Q of 0.6 at that point?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 14, 2011, 10:45:03 AM
Thanks Ian for doing this..

If I understand correctly, the inductor only kicks in at one specific frequency stop (probably the highest?) and if you populate it if you can then calculate an alternative capacitor for that stop and have a Q of 0.6 at that point?

That's right. I think it happens to be in the left most position of the switch so if you want to make it the highest frequency then your frequencies will have to increase as you switch anti-clockwise.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: baadc0de on May 14, 2011, 11:43:57 AM
Thanks for the explanation.. I'll just leave it out then I suppose, or maybe have one funky 3kHz setting for that Ampeg SVT yowl..
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: gemini86 on May 14, 2011, 12:19:43 PM
that's quite the mish-mash of pots you have there...

Just curious though, where does one get 470k/47k/4.7K pots in the US?

Someone else had this problem in the original thread. It seem 5K, 50K and 500K are more common in the USA so I would suggest you use those values and tweak the capacitor values accordingly. If you check the original thread you should find that the person who originally asked the question tweaked the spreadsheet for those values of pot in order to calculate new cap values. I promised to update the spreadsheet so you could feed in different pot values and I have now done this. Just for you I have set the initial values to 5k etc.  All you have to do is set the Hi Cut pot value and the spreadsheet calculates the other pot values and all the capacitor values (except for the inductor ones). If you set the Hi Cut pot to 1000 for example you get very close to the classic Pultec circuit.

For those interested in using the single inductor position, the spreadsheet now also includes a section that calculates the required L and series C values for a variety of frequencies for a Q of 0.6.

http://www.ianbell.ukfsn.org/pics/capcalc.xls (http://www.ianbell.ukfsn.org/pics/capcalc.xls)

Cheers

Ian


yeah that was me, Ian... I'm still curious why they seem to be uncommon in the US. I found that Newark has stock though, for anyone who wants to build to your recommended cap values.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 14, 2011, 02:06:28 PM
Thanks for the explanation.. I'll just leave it out then I suppose, or maybe have one funky 3kHz setting for that Ampeg SVT yowl..

No problem. You need to short it out rather than leave it out though.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 14, 2011, 02:11:50 PM

yeah that was me, Ian... I'm still curious why they seem to be uncommon in the US. I found that Newark has stock though, for anyone who wants to build to your recommended cap values.

I have no idea why 4K7, 47K and 470K pots should be hard to find in the US. Maybe its because, although most passive parts are these days made in the Far East, pots still tend to be made locally. I know I use Omeg pots made here in the UK.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: gemini86 on May 15, 2011, 12:28:58 AM
I tend to use alpha, cause their cheap and mouser stocks them. They're from Japan, i think?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 15, 2011, 06:10:06 PM
I tend to use alpha, cause their cheap and mouser stocks them. They're from Japan, i think?

I think they are Taiwanese. The switches I use in this project are made by Alpha and the data sheet says their company name is "Taiwan Alpha Electronic Co".

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: gemini86 on May 15, 2011, 08:37:08 PM
those are the ones...

Well, I've found that newark has 47/470/4.7 pots in stock, just their search function is not as filter-able? anyway, thanks again for this great project, Ian.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: AudioHammer on May 16, 2011, 01:35:40 PM
Does anyone else get this issue when opening the Capacitor Calc spreadsheet?  I am using Excel 2003 and 2007 versions running on WinXP.

Excel found unreadable content in 'capcalc.xls'. Do you want to recover the contents of this workbook?

Clicked 'Yes" and got the following:

Excel recovered your formulas and cell values, but some data may have been lost.

When I open the spreadsheet with the recovery option, I check the formulas which seem to be wrong:

Hi Cut
Cell  I9   5000   Log      
Hi Boost
Cell I10   50000   Lin      
Low Cut
Cell I11   500000   Log      
Low Boost
Cell I12   50000   Lin   


Low Boost/Cut
   C cut(nF)
=1/(2*3.14*I10*B8*0.000000001)      Formula references I10 cell which is Hi Boost 50k Linear Pot.  Should this be I11 cell instead?

Hi Boost/Cut
   Cboost(nF)
=1/(2*3.14*47000*C24*0.000000001)           Should this formula reference I10 cell instead of being hard coded to 47000?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 16, 2011, 02:40:19 PM
Does anyone else get this issue when opening the Capacitor Calc spreadsheet?  I am using Excel 2003 and 2007 versions running on WinXP.

Low Boost/Cut
   C cut(nF)
=1/(2*3.14*I10*B8*0.000000001)      Formula references I10 cell which is Hi Boost 50k Linear Pot.  Should this be I11 cell instead?

Strictly speaking the time constant of the low cut cap and the 56K Lo bump resistor should be used here. I have created a new version of the spreadsheet which calculates the Bump R and uses it to calc the low cut caps - it is called capcalc3.xls http://www.ianbell.ukfsn.org/pics/capcalc3.xls (http://www.ianbell.ukfsn.org/pics/capcalc3.xls)

Quote
Hi Boost/Cut
   Cboost(nF)
=1/(2*3.14*47000*C24*0.000000001)           Should this formula reference I10 cell instead of being hard coded to 47000?

Yes it should be I10. The new capcalc 3 reflects this change.

Sorry for the errors.

Note, the original is an Open Office spreadsheet (.ods) so I have uploaded this too (it is just called capcalc.ods) http://www.ianbell.ukfsn.org/pics/capcalc.ods (http://www.ianbell.ukfsn.org/pics/capcalc.ods)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 17, 2011, 04:35:29 PM
I have measured the frequency response of my prototype and it seems to perform pretty much as expected. Here are the Lo frequency measurments. You can clearly see the Pultec 'bump' with simultaneous max boost and cut.


http://www.ianbell.ukfsn.org/pics/LFresponse.pdf (http://www.ianbell.ukfsn.org/pics/LFresponse.pdf)


Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pigsnoot on June 08, 2011, 05:57:03 PM
Hey ian

I've been searching for the parts list everywhere! I forgot in wich thread it was....I guess it wouldn't be bad if it would be mentioned somewhere in this thread....?

I can get almost everything from the schematics posted here, but it is nice and easy if you would mention all the parts in a list...

Sorry if I missed it somewhere!  :)

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 09, 2011, 05:39:19 AM
Hey ian

I've been searching for the parts list everywhere! I forgot in wich thread it was....I guess it wouldn't be bad if it would be mentioned somewhere in this thread....?

I can get almost everything from the schematics posted here, but it is nice and easy if you would mention all the parts in a list...

Sorry if I missed it somewhere!  :)



I have added all the documentation to the very first post of this thread so it is easy to find.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: safe as milk on June 13, 2011, 08:58:11 AM
hi
thanks for these great little boards
i got all 8 stuffed caps/switches yesterday whilst that rain was
coming down... :o

how do i go about loading the input trafo's so that the eq
gets it's prefered impedance?

cheers
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 13, 2011, 03:35:41 PM
hi
thanks for these great little boards
i got all 8 stuffed caps/switches yesterday whilst that rain was
coming down... :o

how do i go about loading the input trafo's so that the eq
gets it's prefered impedance?

cheers


The EQ pretty much does it itself. All you really need is a 12K across the 10K:10K bridging input transformer to make its total load close to the desired 10K so whatever you drive it with 'sees' a 10K load. The EQ really likes a nice low source driving it but most of today's gear has an output resistance of a few hundred ohms at most which will be reflected straight through the transformer and will be what the EQ 'sees'. The original Pultec was much more picky about the impedance that drove it simply because the Q of the LC filters depends directly on it. We don't have and inductors so it is not really an issue.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Biasrocks on June 14, 2011, 09:40:45 AM
we have this Peerles S 217 D all blueprinted,
who needs one?

CJ

I'd love to have one.

Mark
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: safe as milk on June 14, 2011, 03:06:36 PM
hi
thanks for the information ian.
what are your thoughts on placing the eq in the feedback loop
of whatever op amp i end up using? where a vol/trim pot would normally be.

cheers

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 14, 2011, 06:44:59 PM
hi
thanks for the information ian.
what are your thoughts on placing the eq in the feedback loop
of whatever op amp i end up using? where a vol/trim pot would normally be.

cheers



In a nutshell, don't ;-) This is a passive EQ and is definitely not intended to be included as part of a feedback network. Not only that but if it did work at all, because it is in a feedback circuit, it would do the inverse of what you expect so the boost controls would cut and vice versa.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: safe as milk on June 15, 2011, 03:50:03 PM
cheers
i think i was getting mixed up with placing it between 2 op-amps?
i do have a tendency to type first ask questions later!

thanks again for your advice ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 15, 2011, 04:28:04 PM
cheers
i think i was getting mixed up with placing it between 2 op-amps?

Between 2 op amps is fine. The first would act as a line in buffer and could provide a  balanced input and a nice low impedance drive to the passive EQ. The second could be used as a gain make up amplifier.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on June 27, 2011, 07:40:17 AM
is possible to use:
5k instead 4k7
50k instead 47k
500k instead 470k?
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: gemini86 on June 27, 2011, 10:31:56 AM
your cap values may need adjustment, but yes.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Hank Dussen on June 27, 2011, 12:52:10 PM
is possible to use:
5k instead 4k7
50k instead 47k
500k instead 470k?

As Gemini says: cap values will be slightly different. See the spreadsheet Ian posted halfway the previous page.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 12, 2011, 04:47:13 PM
Here are the results of my measurements of the HF response of the poor man's EQP1-A. I made them some time ago but lost them. Fortunately I found them this morning. As expected there is a small broad bump with max boost and cut

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 19, 2011, 06:30:52 PM
Hi, I bought a pair of Lorlin 6 pos. switches, well, actually 12 pos., but you can limit them to 6 positions.
Are those usable on this project?

Also I`ve noticed that the switches doesn`t have a pin in "C", just a hole, should I open them and solder a little piece of wire to it or somenthing like that?

And L1 will be fine just making a bridge?

Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 20, 2011, 03:36:52 AM
Another question...

The Pots have to be normal or reversed?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 20, 2011, 05:33:41 AM
Hi, I bought a pair of Lorlin 6 pos. switches, well, actually 12 pos., but you can limit them to 6 positions.
Are those usable on this project?

Probably not. You need two pole 6 way switches. I think the ones you have are single pole 12 way
Quote
Also I`ve noticed that the switches doesn`t have a pin in "C", just a hole, should I open them and solder a little piece of wire to it or somenthing like that?

Again, that is most likely because they are single pole 12 way types. I am afraid you have purchased the wrong type of switch.

Quote
And L1 will be fine just making a bridge?

Yes.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 20, 2011, 05:34:51 AM
Another question...

The Pots have to be normal or reversed?

Normal.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 20, 2011, 08:46:24 AM
Thanks ruffrecords

Surely I`ve bought the wrong switches  :-\ well, trial and error way

Another thing, I understand in the low pcb C1 & C1 A are for 20 Hz Cut, and C12 & C12 A are for 20Hz Boost, and so on, am I ok or wrong? (Actually I Think I`ve populated one of the low boards mirror`ed)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 20, 2011, 06:55:08 PM
Another thing, I understand in the low pcb C1 & C1 A are for 20 Hz Cut, and C12 & C12 A are for 20Hz Boost, and so on, am I ok or wrong?

Which side you use for boost and which for cut is entirely up to you. However, the wiring schematic showing how the switch PCBs are wired together (which I have now added to the first post in this thread) does assume the Lo Cut capacitors start at the C1 position. These are fitted from C1 to C6. The Boost capacitors then start from C7 (for 20Hz) and continue up to C12.

I have also added a link to the PCB layout to the first post in this thread.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on July 21, 2011, 03:02:14 AM

I can't decide on whether to build dual mono unit or a stereo unit. For a stereo unit with a single set of controls I believe this monacor switch for frequency selection should work; http://www.electricalmate.co.uk/proddetail.php?prod=11480

Also for the Boost/Att control it seems that, from what I can gather log pots(mono or dual) will not match closely enough for decent stereo operation in which case a 2pole/12position stepped switch like this perhaps would work; http://www.electricalmate.co.uk/proddetail.php?prod=11470

I'm sure most people would prefer dual mono units, but I might sacrifice individual channel usage for the convenience of simultaneous control.
If you can recommend alternatives to the switches above please do.

Matt
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 21, 2011, 06:19:28 AM

I can't decide on whether to build dual mono unit or a stereo unit. For a stereo unit with a single set of controls I believe this monacor switch for frequency selection should work; http://www.electricalmate.co.uk/proddetail.php?prod=11480

Yes, you need a 4 pole 6 way and that switch fits the bill and it has a keen price too.
Quote
Also for the Boost/Att control it seems that, from what I can gather log pots(mono or dual) will not match closely enough for decent stereo operation in which case a 2pole/12position stepped switch like this perhaps would work; http://www.electricalmate.co.uk/proddetail.php?prod=11470

For repeatability, stepped pots are preferable and for stereo matching they are almost essential. 12 positions should be plenty. Of course there is a one pole 12 way version of the Lorlin for anyone who wants to do single channel switched pots.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 22, 2011, 08:51:07 PM
For repeatability, stepped pots are preferable and for stereo matching they are almost essential. 12 positions should be plenty. Of course there is a one pole 12 way version of the Lorlin for anyone who wants to do single channel switched pots.

Cheers

Ian

How could I calculate the resistor values for 12 pos. pot? What`s the formula?

Also I have some non shorting switches, how bad would it be to use them?

Thanks


D.Hanfri
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 26, 2011, 09:43:30 AM
Ok, I`ve found the resistors value for the stepped switches in the second post..., sorry for the question

I`ve been also buying parts for the psu and I got 4 IN4007 instead of IN5007. The guy at the shop told they`re equivalent, but I`d like to be sure.

And for the 47pF cap, it`s only 63v. will this work or should I get a 100 v. cap?

Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 26, 2011, 11:36:45 AM
Ok, I`ve found the resistors value for the stepped switches in the second post..., sorry for the question

I`ve been also buying parts for the psu and I got 4 IN4007 instead of IN5007. The guy at the shop told they`re equivalent, but I`d like to be sure.

1N4007 diodes will be fine.
Quote
And for the 47pF cap, it`s only 63v. will this work or should I get a 100 v. cap?


That should be 47uF (microFarads) - sorry that's my poor writing. It does need to be 100V working as the voltage across is is approximately 75 volts so a 63V will not do. The other capacitors in the PSU are 220 microFarads. They need to be at least 400V dc working types.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 26, 2011, 12:19:56 PM
Great.

Thanks!

I`ll post some pics later
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 26, 2011, 06:31:17 PM
Should the caps of the psu be electrolityc?

The only electrolityc I got is the 100uF and I put the - leg down as we look the schem, is this ok or not?

And a Pair of pics.

Thanks to everyone sharing info on this project and to ruffrecords for designing it.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 26, 2011, 06:32:09 PM
The tube gain stage (waiting for tubes & sockets)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on July 26, 2011, 06:39:55 PM
sorry dirtyhanfri
where I can find the tube gain stage PCB?
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 27, 2011, 02:31:17 AM
sorry dirtyhanfri
where I can find the tube gain stage PCB?
Thanks

I got them from ruffrecords, but don`t know if there`s any left....
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 27, 2011, 12:22:25 PM
Should the caps of the psu be electrolityc?

The only electrolityc I got is the 100uF and I put the - leg down as we look the schem, is this ok or not?

Yes, all the PSU caps are electrolytic.  In all cases the - leg is connected to 0V. The 220uF from the cathode of the bottom triode to ground is also electrolytic - it should be 50V working type or better.

The 4.7uF from the top triode cathode to the transformer is NOT an electrolytic. It should be a 450V working metal film type.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 28, 2011, 11:29:50 AM
Yes, all the PSU caps are electrolytic.  In all cases the - leg is connected to 0V. The 220uF from the cathode of the bottom triode to ground is also electrolytic - it should be 50V working type or better.

The 4.7uF from the top triode cathode to the transformer is NOT an electrolytic. It should be a 450V working metal film type.

Cheers

Ian

I understand you mean the two 2u2 caps in the Make up gain Pcb? I got a pair of 250v, should I change them?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 28, 2011, 03:33:19 PM

I understand you mean the two 2u2 caps in the Make up gain Pcb? I got a pair of 250v, should I change them?

That is correct. They really do need to be 400V working so I recommend you change them.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on July 29, 2011, 05:06:08 AM
Sorry where i can find the right  pot in Europe? (4k7 - 47k log - 470k log)
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kante1603 on July 29, 2011, 05:23:11 AM
Sorry where i can find the right  pot in Europe? (4k7 - 47k log - 470k log)
Thanks
Hi, here in germany it´s easy,e.g. Reichelt.
Look here:

http://www.reichelt.de/?ACTION=2;GROUPID=3135;SHOW=1;SID=11TfPHtH8AAAIAAFsZIxsee1eadf0815ceb8aecd183fa1d3eebfd

Best regards,

Udo.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 29, 2011, 06:13:41 AM
Sorry where i can find the right  pot in Europe? (4k7 - 47k log - 470k log)
Thanks

Farnell should do them:

http://it.farnell.com/ (http://it.farnell.com/)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 30, 2011, 08:03:58 AM
I just got my first face and rear pannels, designed by me, cutted & drilled by my homie Baresi (Thanks man)

Now I´m dealing with stepped switches...

It´ s too bad to connect resistors in series to get the right value?

I should solder the 12 switch pins to a leg of a resistor, and the other end?

I´ve been looking around and didn´t found anything clear.

Thanks.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 30, 2011, 09:02:04 AM
Pics of the pannels

(http://img705.imageshack.us/img705/7982/29072011459.jpg)

(http://img29.imageshack.us/img29/9899/29072011460.jpg)

(http://img38.imageshack.us/img38/3820/29072011461.jpg)

Waiting for black paint and white lettering
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 30, 2011, 04:25:43 PM
Now I´m dealing with stepped switches...

It´ s too bad to connect resistors in series to get the right value?

I should solder the 12 switch pins to a leg of a resistor, and the other end?

It is OK to connect resistors in series to get the right value.

It is common practice to wire the resistors directly to switch pins.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 30, 2011, 04:39:52 PM
And the other side of the resistors?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 31, 2011, 06:39:30 AM
And the other side of the resistors?

I am not sure what you mean. For a stepped resistor switch you would normally wire the resistors across adjacent pins on the switch. You calculate the resistor values such that the sum from the start position is the required value at each switch position.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 31, 2011, 08:17:50 AM
And the other side of the resistors?

I am not sure what you mean. For a stepped resistor switch you would normally wire the resistors across adjacent pins on the switch. You calculate the resistor values such that the sum from the start position is the required value at each switch position.

Cheers

Ian

Ok thanks, I´m gonna make some research about this.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 01, 2011, 04:28:44 AM
Ok, I think I got it...


I have to solder the 12 resistors across the pins, and then (as I can understand looking at the "hookupsm.jpg" you posted at the top of the topic) I have to wire T1 to Pin 12, T2 to Pin "A" in the High Boost Switch, right? (If I`m ok with this I understand the other switches)

And, for linear stepped switches; maybe it`s obvious, but I`d like to be sure, Total R / Nº of steps - 1

For 4K7 with 12 steps It should be 4700 / 11 = 427,27

Is it ok? or I`m wrong?

Thanks, and sorry my poor english, its frustrating when don`t know how to say exactly what you want to say.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 01, 2011, 06:09:46 AM
Ok, I think I got it...


I have to solder the 12 resistors across the pins, and then (as I can understand looking at the "hookupsm.jpg" you posted at the top of the topic) I have to wire T1 to Pin 12, T2 to Pin "A" in the High Boost Switch, right? (If I`m ok with this I understand the other switches)

That seems about right. The pin A on the switch resistor is the wiper of the pot. I think pin1 of the switch will be the anti-clockwise position of the switch resistor so T1 would go to pin 1 and T2 to pin A for the Hi boost.

Quote
And, for linear stepped switches; maybe it`s obvious, but I`d like to be sure, Total R / Nº of steps - 1

For 4K7 with 12 steps It should be 4700 / 11 = 427,27

Is it ok? or I`m wrong?

OK. 12 steps means 11 resistors so each is R/11. how to say exactly what you want to say.

And your English is very good!

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 01, 2011, 06:34:57 PM
Ok, Thanks

Fisrt of all, a pic of almost everything soldered (only the linear stepped switches left)

(http://img69.imageshack.us/img69/5333/01082011463.jpg)


Now a pair of questions...

The Psu could be enough to feed a 2 channel version?

What about the heaters? I just left this for the end because I have no idea what is this about, something like this?

(http://www.kabytes.com/wp-content/uploads/2007/05/disipador-calor.jpg)

Thanks, you`re great ruffrecords!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on August 01, 2011, 06:40:44 PM
heaters?? are 6.3V that most of tubes need to function properly...its not a heatsink
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 02, 2011, 09:08:56 AM
Now a pair of questions...

The Psu could be enough to feed a 2 channel version?

What about the heaters? I just left this for the end because I have no idea what is this about, something like this?

Yes the PSU will feed two channels provided you use a mains transformer with enough current capability.

As others have said, the heaters are in the tubes themselves. They are what glows red. They need a 6.3V ac supply at 0.6amps each if you use the 6CG7 tube. You can normally obtain a single transformer with separate 6.3V ac and HT windings.

If this is your first ever tube [project then please be very careful. Very high voltages are involved and the tubes themselves get very hot.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 02, 2011, 10:02:00 AM
Thanks for the advice

Of course I´m being as carefull as I can, and I´m specially worried about the power supply (I understand basics of electricity and know where don´t touch). I just soldered the power supply comps to a perfored board and wired point  to point. I wont make it run untill I´m totally sure, I don´t want to die in my first project ;)

Thanks again for the advice, and don´t worry, I ´ ll be careful.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 08, 2011, 06:39:29 PM
Hi, I think It`s time to think in the wiring while waiting for the tube and a pair of caps.

Many doubts...

-In the make up gain stage schematic;  HT+ in the Power Supply HT goes to HT in the gain stage PCB? In the Schematic too, "TO HEATERS" Goes to H1 & H2 in The gain stage Pcb? If It`s ok, where should I connect the "6.3 V AC" points of the Schematic?

-P In & P Out in the Gain Stage Pcb are for the Pad circuit? I`d like to get over the whole circuit (Gain stage included) with the "EQ In-Out" Switch, like a Bypass, should I install any jumper?

-In & IG in the Gain Stage Pcb are for the Input?

-PG Is for 0V? Chassis?

-** Point in the Gain Stage Pcb is wired to chassis?

-If I`m gonna use unbalanced inputs and outputs, ¿I need to use transformers?


Maybe If I`m totally wrong about this…

Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 08, 2011, 07:03:12 PM
Hi, I think It`s time to think in the wiring while waiting for the tube and a pair of caps.

Many doubts...

-In the make up gain stage schematic;  HT+ in the Power Supply HT goes to HT in the gain stage PCB? In the Schematic too, "TO HEATERS" Goes to H1 & H2 in The gain stage Pcb?

Yes and yes.

Quote
If It`s ok, where should I connect the "6.3 V AC" points of the Schematic?

That needs to come from the mains transformer secondary.

Quote
-P In & P Out in the Gain Stage Pcb are for the Pad circuit?

Yes.

Quote
I`d like to get over the whole circuit (Gain stage included) with the "EQ In-Out" Switch, like a Bypass, should I install any jumper?

I am not sure what you mean here. Do you want an EQ in/out switch?

Quote
-In & IG in the Gain Stage Pcb are for the Input?

-PG Is for 0V? Chassis?

-** Point in the Gain Stage Pcb is wired to chassis?

I have noticed some inconsistencies between the system diagram, the gain make up schematic and system diagram. I will draw it all on one sheet of paper to make it clear.

Quote
-If I`m gonna use unbalanced inputs and outputs, ¿I need to use transformers?

No, you do not need to use transformers.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 09, 2011, 03:25:13 AM
Quote
If It`s ok, where should I connect the "6.3 V AC" points of the Schematic?

That needs to come from the mains transformer secondary.

Quote


Yes.



I think I don´t get it, should I geg a toroid transformer with 6.3v ac secondary? Then... 2 power inputs? One for the psu and one for the psu? Surely not.... But I don´t fully understand it.

Thanks for your patience
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 09, 2011, 06:51:39 AM


I think I don´t get it, should I geg a toroid transformer with 6.3v ac secondary? Then... 2 power inputs? One for the psu and one for the psu? Surely not.... But I don´t fully understand it.

Thanks for your patience

No problem. Both the 250V ac and the 6.3V ac should be supplied by secondary windings of a transformer. DO NOT UNDER ANY CIRCUMSTANCES CONNECT THE PSU DIRECTLY TO THE MAINS.

Suitable transformers are available from many suppliers and I am sure there will be one in Italy.

On another forum I have been helping someone from Italy design a tube mixer. I have emailed him and asked him if he will help you out. If he agrees I will PM you his email.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Hank Dussen on August 09, 2011, 07:14:03 AM
You could for example use this power transfo:
http://www.musikding.de/index.php/cat/c276_Power-transformer.html (http://www.musikding.de/index.php/cat/c276_Power-transformer.html)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 09, 2011, 08:50:05 AM
Ok, I´ ll get an old transformer I´ve got around and measure the secondarys current, if it´ s usable I´ ll go on, if not, I´ll look for a transformer in a local shop.

Any help will be welcome, but I think you believe I´m from Italy, actually I´m from Spain. But I´m really thankful of all your help.

I´ m gonna get the transformer and wire everything, get sure it looks ok and then plug it, I´ll be careful. Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 09, 2011, 08:55:40 AM
Ok, I´ ll get an old transformer I´ve got around and measure the secondarys current, if it´ s usable I´ ll go on, if not, I´ll look for a transformer in a local shop.

Any help will be welcome, but I think you believe I´m from Italy, actually I´m from Spain. But I´m really thankful of all your help.

Oops, my mistake. Sorry about that. LOL

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 09, 2011, 06:59:36 PM
I have added to the first post in this thread an overall hookup diagram for the power supply, tube gain make up and EQ showing how one channel all fits together. I have used the pin names used on the tube gain make up PCb to hopefully avoid confusion and shown how screened cable should be used from the output of the EQ to the input of the gain make up amplifier. I repeat it here for convenience.

Cheers

Ian

Edit: Corrected version attached..
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 10, 2011, 06:46:17 AM
You could for example use this power transfo:
http://www.musikding.de/index.php/cat/c276_Power-transformer.html (http://www.musikding.de/index.php/cat/c276_Power-transformer.html)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 10, 2011, 09:54:54 AM
Wrong Post Before

Thanks for the useful link Hank Dussen, I`ll get that transformer

Also I`ll get a pair of tube sockets, these seems to be ok, but I`d like to be sure

http://www.musikding.de/product_info.php/info/p1196_Socket-noval-print.html



Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 10, 2011, 11:15:04 AM
Also I`ll get a pair of tube sockets, these seems to be ok, but I`d like to be sure

http://www.musikding.de/product_info.php/info/p1196_Socket-noval-print.html

They look exactly like the ones I use.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 11, 2011, 05:52:38 PM
I have had several requests for a basic parts list for the poor man's Pultec EQP1A and the poor man's tube gain make up stage so I have put one together. Since people will be buying all over the world I have not specified part numbers but there should be enough description to find the right parts wherever you live. The only things not inlcuded are the input and output connectors, the EQ in/out switch and the Sowter output transformer. The EQ capacitors list is the smallest number for the suggested hi and lo  frequencies and I have shown the position of each on the PCBs.

http://www.ianbell.ukfsn.org/pics/alteq/partslist.xls (http://www.ianbell.ukfsn.org/pics/alteq/partslist.xls)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Lowfreq on October 08, 2011, 11:19:45 PM
Have many people have completed this project? I saw lots of boards get snapped up, but not so many reports on the final product. :o

I'm finishing up a stereo unit, and I've used Lundahl 1521s on the input and then I've used the PPA I/O boards for the make up gain with JLM 99v opamps. I used polystyrene caps in the hi boost and whatever I could get my hands on for the other sections. (A mixture of the polys....prop.....ester.....styrenes.....)

The front panel is ugly at this stage, so no photos just yet, but I have to say that the hi boost on this eq is just lovely. :)
I've been inserting it on same vocal tracks (both mono & stereo) and I think it's gonna get used there a lot from now on.

Fantastic project :D :D
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 09, 2011, 10:26:31 AM
Have many people have completed this project? I saw lots of boards get snapped up, but not so many reports on the final product. :o

I know at least one group member has completed a project using them because he PM'd me some pics.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: gemini86 on October 09, 2011, 07:59:26 PM
pics or it didn't happen....

:D

I plan on doing a p2p or 500 version in the future, but have other projects to complete first.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on October 16, 2011, 08:08:50 PM
Hi everyone,

I'm starting to collect parts for a dual mono build and would like to order transformers (planning on going with Ian's tube makeup gain stage). In the interests of affordability, I'm thinking of these Edcors for the ins and outs:

http://www.edcorusa.com/products/156-xsm600-600.aspx
http://www.edcorusa.com/products/161-xsm10k-10k.aspx

There seems to be a wide range of opinion on these products. Anyone care to offer an opinion on how they might serve here?

For power, I'm thinking of this toroid from Antek (their 250V secondary model is out of stock - might this work instead?):

http://www.antekinc.com/details.php?p=638

Happy to entertain other options and would be curious to hear what North Americans have been using for powering their builds, and as alternatives to the Sowters for in and outs.

Thanks

Ralph
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 17, 2011, 06:11:26 PM
Hi everyone,

I'm starting to collect parts for a dual mono build and would like to order transformers (planning on going with Ian's tube makeup gain stage). In the interests of affordability, I'm thinking of these Edcors for the ins and outs:

http://www.edcorusa.com/products/156-xsm600-600.aspx
http://www.edcorusa.com/products/161-xsm10k-10k.aspx

There seems to be a wide range of opinion on these products. Anyone care to offer an opinion on how they might serve here?

The 600:600 for the output has a primary inductance on only 3H. This is so low that the resultant  bass response will be both poor and distorted.

The 10K:10K for the input has a primary inductance of 25H which has an impedance of 10K at 64Hz. This means that as long as your source impedance is in fact 1K or less then this transformer will be fine at the input.  In fact it would probably do at the output too since it can take 50V rms which is +36dBu.

Quote
For power, I'm thinking of this toroid from Antek (their 250V secondary model is out of stock - might this work instead?):

http://www.antekinc.com/details.php?p=638

That should be fine. The tube gain make up stage is not particularly sensitive to HT voltage and the prototype was built with a mains transformer with a 240V ac secondary.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on October 18, 2011, 05:22:36 AM
It might be interesting for you pm-eqp1 people to check this thread and join the discussion: http://www.groupdiy.com/index.php?topic=45475.new;topicseen#new (http://www.groupdiy.com/index.php?topic=45475.new;topicseen#new). Ian is having something nice up his sleeve again!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ChrisPbass on October 18, 2011, 09:01:50 AM
It might be interesting for you pm-eqp1 people to check this thread and join the discussion: http://www.groupdiy.com/index.php?topic=45475.new;topicseen#new (http://www.groupdiy.com/index.php?topic=45475.new;topicseen#new). Ian is having something nice up his sleeve again!

Well bang goes the idea of a stereo PM in a 1U case! :)  Well not really, but I was just working on a front panel design last night for my stereo version so will do that first. I have extra boards so may either do another stereo with valve make up gain (1st build is with PPA's doa make up) or possibly try this new 'enhanced' version. We are entering into the realms of it no longer being a poor man's Pultec though are we not?! :) Excuse my ignorance, but how much of a different 'flavour' would this add compared to the original eqp1? I suppose it would be a bit of an eqp1 and meq5 hybrid...good work anyway  and looking forward to the outcome :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on October 18, 2011, 06:36:18 PM
Me too.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Holger on December 18, 2011, 07:35:59 AM
I found some time to (almost) finish mine.
I used JLM Dingos for I/O, I'm currently experimenting with different DOAs and transformers.
Needs some clean up here and there, but it works good.

(http://audiofor.tv/diy/pmeqp/front.jpg)

(http://audiofor.tv/diy/pmeqp/guts.jpg)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 18, 2011, 02:05:58 PM
I found some time to (almost) finish mine.

Well done. it is good to see pics of the finished EQ. How did you do the front panel?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Holger on December 18, 2011, 02:37:21 PM
...How did you do the front panel?

It's custom painted. Frank/NRGRecording did the engraving.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ChrisPbass on December 18, 2011, 08:55:46 PM
Nice job Holger, have you fitted a bypass on each channel?
Cheers
Chris
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Holger on December 19, 2011, 03:01:13 AM
Nice job Holger, have you fitted a bypass on each channel?
Cheers
Chris
Yes, utilising the Dingo relay bypass.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ChrisPbass on December 19, 2011, 07:54:07 AM
Thanks Holger, wasn't familiar with the dingo Io kit...just had a look on the jlm site.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: e.oelberg on December 20, 2011, 06:39:11 AM
How much makup gain do you need for that EQ ?

thanks, Nicholas
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 20, 2011, 07:22:26 AM
How much makup gain do you need for that EQ ?

thanks, Nicholas

It needs a little over 20dB and less than 26dB so a gain make up amplifier with 26dB of gain and a preset pot in front of it is normally used.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mus1k_freak on December 27, 2011, 09:19:37 PM
if anyones interested here's a link to my mouser cart for this build, i had to use 5k, 50k and 500k pots instead of the 4.7k 47k and 470k, otherwise i kept everything else the same just to keep it simple. nothing in the cart for the tube make up stage just the eq with bypass switch http://www.mouser.com:80/ProjectManager/ProjectDetail.aspx?AccessID=cbfa3d750d
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 07, 2012, 12:05:36 PM
if anyones interested here's a link to my mouser cart for this build, i had to use 5k, 50k and 500k pots instead of the 4.7k 47k and 470k, otherwise i kept everything else the same just to keep it simple. nothing in the cart for the tube make up stage just the eq with bypass switch http://www.mouser.com:80/ProjectManager/ProjectDetail.aspx?AccessID=cbfa3d750d

I just had a look at this and unless I am mistaken it looks like you have ordered a 1 pole 12 way switch (CK2372) instead of the 2 pole 6 way (CK2373you need for the hi/lo EQ.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on January 08, 2012, 07:33:18 AM
Hi Ian

Iam sourting for the gain make up stage now, and what are:
preset pot   VR2   1K Lin   
preset pot   VR1   470K Lin   
 
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 08, 2012, 07:43:50 AM
Hi Ian

Iam sourting for the gain make up stage now, and what are:
preset pot   VR2   1K Lin   
preset pot   VR1   470K Lin

VR2 is the adjustment for the pad and VR1 is the adjustment to set the overall gain to unity. The system attached system diagram shows how they are connected:

http://www.ianbell.ukfsn.org/pics/EQSystem.png (http://www.ianbell.ukfsn.org/pics/EQSystem.png)

Cheers

Ian

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on January 08, 2012, 07:47:48 AM
so that could be something like this, even though it does not state lineair?

http://www.reichelt.de/Miniaturtrimmer/75H-1-0K/index.html?;ACTION=3;LA=2;ARTICLE=3475;GROUPID=3131;artnr=75H+1%2C0K;SID=12Twg8738AAAIAAFK8aRgffe5c225175f44e6d02d3f5e3cb32f64 (http://www.reichelt.de/Miniaturtrimmer/75H-1-0K/index.html?;ACTION=3;LA=2;ARTICLE=3475;GROUPID=3131;artnr=75H+1%2C0K;SID=12Twg8738AAAIAAFK8aRgffe5c225175f44e6d02d3f5e3cb32f64)

and for these:
fixed   100nF   100nF   400V Polyester   
fixed   2.2uF   2.2uF   400V Polyester   
fixed   2.2uF   2.2uF   400V Polyester   
Am I looking for ac or dc? I am a bit spooked with all the stories about danger with tubes....

edit: I am guessing DC, since AC is stated seperately elsewhere on the xls file.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: bernbrue on January 08, 2012, 08:04:58 AM
Am I looking for ac or dc? I am a bit spooked with all the stories about danger with tubes....

Hi Erik,
tubes are lovely things. They even glow to show you that they are giving their best. They are just a little bit hungry in terms of current. Don´t be scared.
regards
Bernd
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on January 08, 2012, 08:07:21 AM
hmmm ok.. going from scared to very careful then! :-)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 08, 2012, 12:17:56 PM
so that could be something like this, even though it does not state lineair?

http://www.reichelt.de/Miniaturtrimmer/75H-1-0K/index.html?;ACTION=3;LA=2;ARTICLE=3475;GROUPID=3131;artnr=75H+1%2C0K;SID=12Twg8738AAAIAAFK8aRgffe5c225175f44e6d02d3f5e3cb32f64 (http://www.reichelt.de/Miniaturtrimmer/75H-1-0K/index.html?;ACTION=3;LA=2;ARTICLE=3475;GROUPID=3131;artnr=75H+1%2C0K;SID=12Twg8738AAAIAAFK8aRgffe5c225175f44e6d02d3f5e3cb32f64)

That looks OK. You just need to check it will physically fit onto the PCB. The spacing I used fits a range of standard preset pots.

Quote
and for these:
fixed   100nF   100nF   400V Polyester   
fixed   2.2uF   2.2uF   400V Polyester   
fixed   2.2uF   2.2uF   400V Polyester   
Am I looking for ac or dc? I am a bit spooked with all the stories about danger with tubes....

edit: I am guessing DC, since AC is stated seperately elsewhere on the xls file.
Yes, 400V dc is what you need.

You do need to be careful where you put your fingers with tubes. There are very high voltages involved which can give you a nasty electrical shock. Just take extra care.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on January 15, 2012, 08:30:02 AM
Hi All

I have decided to go with stepped pots for all boost / cut pots. So I am trying to calculate the appropriate R values. I have a few questions on them:

1. could someone verify what I have so far?
2. What are the values for the posh mid boost/cut pots? And are those 1 pole or two pole swithes?

Cheers

Erik


Ok, Iam going to read more on this and then come up with my actual question...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on January 16, 2012, 11:29:15 AM
I've prepared stepped pots using the R values posted on page 1, post 3.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on January 16, 2012, 11:40:23 AM
Is there a difference between a "normal" log pot and the 40db one mentioned in post #3? I have received an excel sheet from SilentArts, and that gives me different values...

And btw, does anyone know the values of the boost/cut pots for the posh mid sections? Or (oh men I am getting confused now, forgive me) do I need two deck 12 pos switches to have different values for the resistors for boost and cut? (makes sense I think... my poor brain)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 16, 2012, 12:42:22 PM
A normal linear pot obviously has 50% of the total resistance between wiper and top and 50% between wiper and bottom connection when the pot is at the mid way position giving a nominal
6dB attenuation at the mid point. For a normal log pot, at the mid way position there is 90% of the total resistance between the wiper and the top and 10% between the wiper and the bottom giving a nominal 20dB attenuation at the mid point. So for a log switch to look like a log pot you need to aim for 20dB at the mid point. So if you have an 11 way switch this would be at position 6 with 4dB attenuation per step:

1 0dB
2 4dB
3 8dB
4 12dB
5 16dB
6 20dB  middle
7 24dB
8 28dB
9 32dB
10 36dB
11 40dB or infinity

Normal you want your pot to give infinite attenuation when turned fully anti clockwise so you usually make the last switch position do this.

Notice that in principal there is now reason why you have to have 20dB at the mid point - this is just normal practice. With a switch pot you could make it 30dB and have 6dB steps.

For EQ designs, you often do not want a potential divider but a variable resistance and you choose a log or lin pot depending on which gives a more or less equal change of boost/cut as the pot is rotated. In general though, neither a lin or a log law is exactly right for this and you generally choose depending on which give closest to half the boost/cut at the mid point of the pot. If you then decide to use a switch pot instead you could calculate the exact values to give exactly the same dB  boost/cut for each step. I have not done this for the poor man's EQP.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on January 16, 2012, 12:50:19 PM
clear, thank you!

And what about the properties / values of the boost / cut pots in the poshmen's? (the two different mid ranges with one boost / cut pot per band with on off on switch)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on February 04, 2012, 01:53:46 PM
I am for a few days in Poland and surviving the cold by finally working on the pm eqp1. Of course running in problems right away... Can't read all my docs here... So who knows the relation between the r1-r5 on the power board and the values in the parts list excell file? And what precautions should I take with the 1n4007s? Electrostatic precautions the sticker says... But not how!

Cheers from -18!

Erik
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 05, 2012, 11:52:36 AM
clear, thank you!

And what about the properties / values of the boost / cut pots in the poshmen's? (the two different mid ranges with one boost / cut pot per band with on off on switch)

Exactly the same as the poor man's.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 05, 2012, 12:00:29 PM
I am for a few days in Poland and surviving the cold by finally working on the pm eqp1. Of course running in problems right away... Can't read all my docs here... So who knows the relation between the r1-r5 on the power board and the values in the parts list excell file? And what precautions should I take with the 1n4007s? Electrostatic precautions the sticker says... But not how!

Cheers from -18!

Erik

The power supply schematic was done just for this project on the assumption that people would build it point to point as it is so simple. The  power supply PCB uses the same circuit but was designed for a different project so its numbering is different.

R1, R2 and R3 are the 1K 1watt resistors. R4 is 220K and R5 is 75K.

You do not need to take any anti-static precautions with 1N4007 diodes.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 06, 2012, 07:31:42 PM
I've been reading this and the other associated threads for this project for about 6 hours and I'm just as confused as when I started today.
I can stare at the diagrams and it just doesn't make sense to me for some reason. I feel like I have Poor Man's EQP-1A block or something. I don't even know where to start with my questions  :-[

Edit: I think I'm starting to get it a little
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on February 06, 2012, 08:07:23 PM
I'm putting together my order and came up with 3 questions. If anyone would advise it'd be appreciated. 1. The switches for the frequencies, are we to use shorting or non shorting? Also if anyone has a part # they've had success with would be nice. 2. Being that the tube pcb has no mounting holes I was curious of your solution. 3. I found omeg pots with the hard to find values easily in Europe, has anyone have a source for the correct values in the states regardless of brand?

Thank you fellow members,
Brice
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 06, 2012, 08:57:29 PM
I'm putting together my order and came up with 3 questions. If anyone would advise it'd be appreciated. 1. The switches for the frequencies, are we to use shorting or non shorting? Also if anyone has a part # they've had success with would be nice. 2. Being that the tube pcb has no mounting holes I was curious of your solution. 3. I found omeg pots with the hard to find values easily in Europe, has anyone have a source for the correct values in the states regardless of brand?

Thank you fellow members,
Brice
1. I read in one of the other threads associated with this that it didn't matter as the caps had to charge up when you change frequencies
2.Drill it and the chassis and use screws and standoffs
3. Newark in one (a US company) which is part of the element 14 company or whatever stocks them but upon reading the fine print,they come from Farnell UK (another element 14 company) so there is a $20 handling charge and they're non returnable. The US option is to use 5K, 50K, & 500K and tweak the cap values accordingly. You can use Ian's capcalc spreadsheet and plug this in to get the values if you can get it to open (I had a file corrupted error when opening on Excel 2011 Mac and Excel 2007 Windows)

Good Luck!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on February 06, 2012, 10:39:20 PM
Thank you for the response the pcb mount question I suppose I should have also mentioned I I wt
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on February 07, 2012, 05:19:00 AM
I've been reading this and the other associated threads for this project for about 6 hours and I'm just as confused as when I started today.
I can stare at the diagrams and it just doesn't make sense to me for some reason. I feel like I have Poor Man's EQP-1A block or something. I don't even know where to start with my questions  :-[

Edit: I think I'm starting to get it a little

No reason to feel stupid. I have done just a very few number of other projects but this one is a weird one. Technically it is very simple. But conceptually Otis somewhat difficult to grasp. Also, the information is scattered through out a number of threads. And also, Ian is a very very clever guy, and his answers seem to require some amount of technical knowledge to actually grasp. I literally spend about 30 hours sourcing for this project. And still 10% of my items is wrong. The good news is, so far Ian is answering all my stupid questions thoroughly and friendly. Eve the ones I asked per mail because I did not want everyone to see I still did not get it. So keep struggling, keep asking questions, and be So proud when you finish!
I am trying to put together a document as a sort of beginners guide to posh/poor eq, but progress is slow.

Cheers

Erik
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 07, 2012, 12:34:21 PM
Erik,
Thanks for your kind words sir! You are a gentleman and a scholar!

UPDATE!!!!!
SOme of you may know that I've been having trouble with the capcalc.xls file that is posted around in the different threads.
I have gotten it to open in Excel 2007 in windows on my Parallels virtualizer but it opens with errors and I specifically remember reading that Ian said it calculates to 2 decimal points. Well opening (with errors) the file calculates to as many decimal points as the cell size allows.
I can confirm that it will open correctly in Google Docs!

Still trying my best-
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 07, 2012, 12:59:42 PM
Question:
When sourcing, is it better to use a combination of cap values to get the total value needed for one frequency point?
I see in Ian's partslist that he uses two cap values  (i.e. 4K C2=10nF + CA=2.2nF) to get the total value needed (12nF)?

EDIT: Would this transformer work for the PSU?
http://www.antekinc.com/details.php?p=671

EDIT#2: If this trafo worked for the mains, what resistors would I have to change? (Dumb a** alert!)
http://www.antekinc.com/details.php?p=638

Still confused-
Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 07, 2012, 01:55:44 PM
Poor Man's Tube Stage:
Is there a build thread for this?
I'm seeing a spot for a 220K resistor that's not on the parts list spreadsheet, do I populate this or short it out?

EDIT: Does anyone know a U.S. source for a good PCB mount tube socket for this board?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on February 07, 2012, 01:56:56 PM
If there is a build thread, this is it!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 07, 2012, 02:14:32 PM
If there is a build thread, this is it!

Haha!
So I'm staring at the PMEQP1AHookup.pdf and I'm wondering is the eq In/Out switch a DPST?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on February 07, 2012, 03:50:04 PM
Got my tubes and sockets at Tube Depot. Also a good source for knobs.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on February 07, 2012, 08:01:08 PM
So I'm staring at the PMEQP1AHookup.pdf and I'm wondering is the eq In/Out switch a DPST?

DPDT,  the input signal is one common point to be directed through the EQ or through the pad resistors and at the same time the output signal as the other common, taken from the EQ out or the pad out.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 07, 2012, 11:50:35 PM
So this pic could be how I would wire the EQ In/Out switch to do that?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on February 08, 2012, 08:09:39 PM
T2 in place of where you have T3, T3 is connected to the circuit ground using the screen of the cable and connected to the IG pad of the gainstage.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 09, 2012, 12:55:32 AM
T2 in place of where you have T3, T3 is connected to the circuit ground using the screen of the cable and connected to the IG pad of the gainstage.

Thanks!. I have such an incredibly hard time understanding schematic style diagrams. It's my diy Achilles Heel. I'm trying to create a layout diagram based on Ian's hookup so I'm sure I will have plenty of questions.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 09, 2012, 12:02:27 PM
Well it's another day of feeling stupid but if I don't ask I will never know.
I'm looking at the parts list that Ian posted and I'm wondering a couple things;
In the EQP-1A section, under resistors, it says:
fixed          hi boost R1              5K Lin            0.25W 1%

Is that a typo? R1 on the board is for an axial not a trimmer

Also, it says hi boost R1, hi cut R2, and lo cut R3. Does that mean when I'm populating the hi boost board I put a 5K in the R1 position and jumper  R2 & R3?
Conversely, if I'm building the lo cut board, I populate R3 with a 60K and jumper R1 & R2?

Thanks for the help
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on February 09, 2012, 12:25:46 PM
Yes, "lin" appears to be a typo, although Ian's xls spreadsheet calls for a fixed value of 4K7 for R1, not 5K.

If you look about half way down page 1 of this thread, you'll see that Ian's jpegs of his populated boards use jumpers (0ohm resistors) in the positions you've mentioned. For the low board, Ian's example is on the back of the PCB.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on February 09, 2012, 12:37:54 PM

Also, it says hi boost R1, hi cut R2, and lo cut R3. Does that mean when I'm populating the hi boost board I put a 5K in the R1 position and jumper  R2 & R3?
Conversely, if I'm building the lo cut board, I populate R3 with a 60K and jumper R1 & R2?

Thanks for the help

The Hi-boost and Hi-cut would presumably be on the same board so R1 4.7k, R2 470R and jumper R3.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 09, 2012, 06:34:13 PM
Yes, "lin" appears to be a typo, although Ian's xls spreadsheet calls for a fixed value of 4K7 for R1, not 5K.

If you look about half way down page 1 of this thread, you'll see that Ian's jpegs of his populated boards use jumpers (0ohm resistors) in the positions you've mentioned. For the low board, Ian's example is on the back of the PCB.

Thanks! I think I accidentally changed that (5K Lin) when I was changing the pot values for the standard U.S. pots. I have read this whole thread and I did see Ian's pics, I just wanted to ask the question to double check as I'm trying to wrap my brain around this project and I'm definitely still a noob.

The Hi-boost and Hi-cut would presumably be on the same board so R1 4.7k, R2 470R and jumper R3.

Thanks MatthisD. I think that I'm just over thinking it. That was a stupid mistake on my part  :)

On the Low board it would be R3=60K (for using U.S. value pots) and jumper R1 & R2?

I had asked this question earlier - Is it better to use two capacitors per frequency to get the necessary value or are two areas provided to use 2 caps to get an odd value (like a value you might not be able to find in 1 cap)?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on February 09, 2012, 08:23:54 PM

Thanks MatthisD. I think that I'm just over thinking it. That was a stupid mistake on my part  :)

On the Low board it would be R3=60K (for using U.S. value pots) and jumper R1 & R2?

I had asked this question earlier - Is it better to use two capacitors per frequency to get the necessary value or are two areas provided to use 2 caps to get an odd value (like a value you might not be able to find in 1 cap)?

No problem, thats right for the Lo PCB.

You can see below the capacitor values and choose for yourself whether to use 1 or 2 for each frequency.
http://www.ianbell.ukfsn.org/pics/CapValues.pdf
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 09, 2012, 08:37:41 PM

Thanks MatthisD. I think that I'm just over thinking it. That was a stupid mistake on my part  :)

On the Low board it would be R3=60K (for using U.S. value pots) and jumper R1 & R2?

I had asked this question earlier - Is it better to use two capacitors per frequency to get the necessary value or are two areas provided to use 2 caps to get an odd value (like a value you might not be able to find in 1 cap)?

No problem, thats right for the Lo PCB.

You can see below the capacitor values and choose for yourself whether to use 1 or 2 for each frequency.
http://www.ianbell.ukfsn.org/pics/CapValues.pdf
Thanks!
I have downloaded this. I was asking as I want to use some different frequencies on the hi section of the eq. So I'm assuming that it's best to get the value closest to what is needed whether it be achieved with one cap or two.
I appreciate all your help! I'm starting to get it a little more.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 20, 2012, 11:30:47 PM
So, if I'm using the US standard 5K, 50K, 500K pots and a 60K for lo cut R3 do I need to change out the Hi Boost R1 and Hi Cut R2?

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on February 21, 2012, 01:34:34 AM
Hi Dave, check the magic .xls file on page 2, it will give you the capacitor values for your pots.
Matt
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 21, 2012, 04:44:03 PM
Hi Dave, check the magic .xls file on page 2, it will give you the capacitor values for your pots.
Matt

MatthisD,
Thanks for the reply. I have used the capcalc.xls to get the cap values. My question was about the resistor values for Hi Boost R1 (4K7) and Hi Cut R2 (470R). I'm assuming that since they aren't on the capcalc.xls as an value that changes when using the US pots their values stay the same.

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 21, 2012, 06:40:28 PM
So, if I'm using the US standard 5K, 50K, 500K pots and a 60K for lo cut R3 do I need to change out the Hi Boost R1 and Hi Cut R2?

Dave

Probably not. These resistors are designed to set the the maximum boost/cut that can be applied, ensure the input impedance does not drop significantly below 10K ohms and set the frequency at which the the cut and boost response begins to shelve. As such they are not critical but since you have increased the value of all the pots by 6.4% you could increase these two resistors by the same amount to maintain the same ratios.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on February 25, 2012, 05:28:53 PM
I'm having a hard time understanding the psu pcb for the tube gain stage. Now I understand the bom list Ian offered in the first post, but I am unsure where the connections are on the pcb, as in where do I connect the psu to the tube pcb? Is it the 75v that is b+ and the heater is heater and the unmarked square is the ground?

ALSO..what are people in north America using for psu transformers? If i am correct we need a 120ac to 250vac 25ma & 6.3vac 1.2a? If I found a tranny with higher amps is that okay or will I need to modify my values.? Anyone?

Thank you,
Brice
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on February 25, 2012, 05:38:45 PM
Would this work or is there a cheaper option? http://angela.com/hammondpowertransformer269ax.aspx
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 26, 2012, 12:53:04 PM
I'm having a hard time understanding the psu pcb for the tube gain stage. Now I understand the bom list Ian offered in the first post, but I am unsure where the connections are on the pcb, as in where do I connect the psu to the tube pcb? Is it the 75v that is b+ and the heater is heater and the unmarked square is the ground?

Sorry, this is my fault. I did not use a consistent annotation thoughout. You need to tie up the:

 tube gain make up stage circuit diagram http://www.ianbell.ukfsn.org/pics/PMTGMsm.jpeg (http://www.ianbell.ukfsn.org/pics/PMTGMsm.jpeg)
with the system diagram http://www.ianbell.ukfsn.org/pics/EQSystem.png (http://www.ianbell.ukfsn.org/pics/EQSystem.png)
and the PCB as follows:

Point A on the circuit corresponds to point A on the system diagram and to pad Pout on the PCB
Point B on the circuit corresponds to point B on the system diagram and to pad Pin on the PCB
Pad PG on the PCB is the local ground connection for Pin and Pout and should be used for the screens of the cables going from Pin and Pout to the EQ  bypass switch.

Point C on the circuit corresponds to point C on the system diagram and to pad In on the PCB
Pad 1G on the PCB is the local ground connection for the screened cable that connect Pad In to the EQ bypass switch and then on to the output of the equaliser itself.

The HT+ on the circuit diagram connects directly to the HT pad on the PCB
The  connections labelled heaters connect directly to the pads labelled  H1 and H2 on the PCB.
The Pad labelled ** on the PCB is the tube gain make up start earth point and should be connected directly to the 0V of the power supply as shown on the circuit diagram.

Hope that clears things up a bit.
Quote
ALSO..what are people in north America using for psu transformers? If i am correct we need a 120ac to 250vac 25ma & 6.3vac 1.2a? If I found a tranny with higher amps is that okay or will I need to modify my values.? Anyone?

Thank you,
Brice

Higher output amps is OK, the circuit will just take what is needs and no more.

As to what to use in the US I am sure someone asked this before and they found a reasonably priced toroidal transformer that would be ideal for the job but at the moment I cannot remeber the make.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 26, 2012, 12:54:32 PM
Would this work or is there a cheaper option? http://angela.com/hammondpowertransformer269ax.aspx

Yes, that would work but as I mentioned in my other post I think there is a cheaper/smaller toroid that will do the job.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 26, 2012, 01:48:20 PM

As to what to use in the US I am sure someone asked this before and they found a reasonably priced toroidal transformer that would be ideal for the job but at the moment I cannot remeber the make.

Cheers

Ian

I had asked about using this transformer in one of my many emails to Ian

http://www.antekinc.com/details.php?p=638

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 26, 2012, 02:26:19 PM

As to what to use in the US I am sure someone asked this before and they found a reasonably priced toroidal transformer that would be ideal for the job but at the moment I cannot remeber the make.

Cheers

Ian

I had asked about using this transformer in one of my many emails to Ian

http://www.antekinc.com/details.php?p=638

Dave

That's the one!! I knew it began with an A.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on February 26, 2012, 03:40:11 PM
Thank you both of you!

Dave can you guide me in how you wired the antek transformer for us voltages? I see it has 2x115v primary. I also noticed it only provides 240v, is that enough?

Thanks again
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 26, 2012, 07:26:49 PM
240V is plenty.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 27, 2012, 01:40:30 AM
Thank you both of you!

Dave can you guide me in how you wired the antek transformer for us voltages? I see it has 2x115v primary. I also noticed it only provides 240v, is that enough?

Thanks again
Sure. What kind of IEC inlet are you using? Is it one with a built in fuse?
EDIT: You just have to tie the 2 red wires together and hook them to the "hot" AC in and the 2 black wires hook to the "cold" AC in. If you tell me what IEC inlet you're using I'll make you a diagram
Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on February 27, 2012, 12:51:16 PM
Thank you! It's just a standard 3 prong north American type and I have a separate fuse holder. I'm sure the diagram will help alot of people. Much appreciated!

Brice
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 27, 2012, 03:58:44 PM
Here you go
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on February 28, 2012, 12:55:26 PM
I'm sorry keep asking questions, but I'll never learn if I dont. Would you mind making a diagram for hooking up the secondary leads to the psu pcb? I just don't know what to do with the extra wires and voltages ie there are two 6.3v. All help is much appreciated!

Brice
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 28, 2012, 03:38:05 PM
I'm sorry keep asking questions, but I'll never learn if I dont. Would you mind making a diagram for hooking up the secondary leads to the psu pcb? I just don't know what to do with the extra wires and voltages ie there are two 6.3v. All help is much appreciated!

Brice
Brice,
I'm more than happy to make you a diagram. I didn't get a PSU PCB from Ian as he was out of them. Send me an email so I can send you a pic of what I think the PSU PCB looks like as I don't know if Ian wants me to post a pic of his PCB in here (he sent me a PSU PCB pic in an email and I want to see if it's the one you're using.

email: wave(dot)audio(at)gmail(dot)com

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on February 28, 2012, 04:58:15 PM
If it is the one he told you of it is the same with 470uf values for the 4 big caps and it needs some diodes of the number 1N4608 or something alike. Any way I'm sure it is the same. My email is Brice**perusse at hotmail dot com. No spaces between words. So if you have an idea any simple diagram regardless of psu pcb would help, mainly I simply have no clue what to do with the extra leads and voltages. Do I join them to the same co nection as the other or cut them and seal them? I don't know but I appreciate your effort.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 28, 2012, 07:16:49 PM
Brice,
Here is my crappy diagram. I hope it helps. On this I drew the second 6.3VAC secondary as being capped off and not used but you could very well use it to power a 6.3V Fender style jewel lamp for a power on indicator on the front panel.
Anyway good luck, and feel free to ask any other questions. God knows, I've asked my share :-)

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 29, 2012, 12:34:31 PM
Nice diagram. Well done. What did you use to create it?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 29, 2012, 12:38:33 PM
Nice diagram. Well done. What did you use to create it?

Cheers

Ian
Thanks Ian.
I use Adobe Illustrator for these and my homebrew etch files.  So I was correct in connecting one of the 6.3VAC secondary wires (in one pair) to the 75V hole on the PCB? In my etch file (I sent you in an email) I made it with 6.3VAC in and out terminals with the in connected to the 75V spot.
I'm going to make an overall PMEQP-1A hookup diagram so I'm sure you will be getting questions about that!

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 29, 2012, 06:01:43 PM
Nice diagram. Well done. What did you use to create it?

Cheers

Ian
Thanks Ian.
I use Adobe Illustrator for these and my homebrew etch files.  So I was correct in connecting one of the 6.3VAC secondary wires (in one pair) to the 75V hole on the PCB? In my etch file (I sent you in an email) I made it with 6.3VAC in and out terminals with the in connected to the 75V spot.
I'm going to make an overall PMEQP-1A hookup diagram so I'm sure you will be getting questions about that!

Dave

Yes, you were correct in connecting one of 6.3VAC wires to the +75V hole. That 75V is for heater elevation.

I was thinking of doing an overall hookup diagram but since you just volunteered I am happy to let you do it and I'll check it for you!

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on February 29, 2012, 06:53:35 PM
Thanks Ian,
I think it will be great practice in my never ending struggle of reading schematics.

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on March 02, 2012, 11:31:27 PM
Thanks again. I've been studying this whole layout and I love the challenge. Sure glad I have good people to help!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 03, 2012, 06:15:20 AM
Here is a hand drawn sketch if what I think you need. I am sure you can make it look much better.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on March 03, 2012, 04:36:11 PM
Ian,
Thanks for the sketch. It really helps.
One question: I also have the PMEQP1A Hookup pdf and in that diagram there is no 12K resistor strapped across the input transformer secondary before the EQ in/out switch. Was that overlooked in the PMEQP1A hookup pdf?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 03, 2012, 06:48:34 PM
Ian,
Thanks for the sketch. It really helps.
One question: I also have the PMEQP1A Hookup pdf and in that diagram there is no 12K resistor strapped across the input transformer secondary before the EQ in/out switch. Was that overlooked in the PMEQP1A hookup pdf?

Yes, you are right, it was overlooked in the Hookup pdf. The idea was to make the nominal load on the transformer close to 10K and with the 12K across the secondary it is close to 10K when all the pots are in the off position (no boost or cut). As soon as you apply some EQ the load impedance drops at some frequencies (the ones you boost) and rises at other (the ones you cut) but that's just a property of passive EQ.

For most sources  (where the driving impedance is much lower than 10K) it doesn't really matter.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: WNStudios on March 08, 2012, 04:11:19 PM
Looking through the schematics and my boxes of salvaged parts.

Does it have to be a 6CG7 tube?
I got 3x 6DJ8/ECC88 Philips ones and 2x 6BL8/ECF80's Philips.
I'm going with the pcb and BOM that's provided by Ian and it would just be nice if those old guys would get some use after all these years.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 09, 2012, 05:55:45 AM
Looking through the schematics and my boxes of salvaged parts.

Does it have to be a 6CG7 tube?
I got 3x 6DJ8/ECC88 Philips ones and 2x 6BL8/ECF80's Philips.
I'm going with the pcb and BOM that's provided by Ian and it would just be nice if those old guys would get some use after all these years.

You could use the 6DJ8/ECC88 tubes but you would have to reduce the HT to no more  than about 250V but that is just a matter of using larger dropper resistors in the power supply. YOu might need to change bias resistors too. I'll look into it. Note the gain would be much higher than with a 6CG7.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: WNStudios on March 09, 2012, 10:32:46 AM
You could use the 6DJ8/ECC88 tubes but you would have to reduce the HT to no more  than about 250V but that is just a matter of using larger dropper resistors in the power supply. YOu might need to change bias resistors too. I'll look into it. Note the gain would be much higher than with a 6CG7.

Cheers

Ian

I've found a toroid readily availible for me that has a secondary of 185V, would that be way under what i need? I was thinking a stereo unit at first but i think i will do two seperate units so it would only run 1 makeup stage. "Primary 230V, secondary 185V 0,04A and 6.3V 1,4A." to be exact. If it's much higher, could i simply put an output pot on there, or even an output transformer just to tame it?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 09, 2012, 12:45:15 PM
You could use the 6DJ8/ECC88 tubes but you would have to reduce the HT to no more  than about 250V but that is just a matter of using larger dropper resistors in the power supply. YOu might need to change bias resistors too. I'll look into it. Note the gain would be much higher than with a 6CG7.

Cheers

Ian

I've found a toroid readily availible for me that has a secondary of 185V, would that be way under what i need? I was thinking a stereo unit at first but i think i will do two seperate units so it would only run 1 makeup stage. "Primary 230V, secondary 185V 0,04A and 6.3V 1,4A." to be exact. If it's much higher, could i simply put an output pot on there, or even an output transformer just to tame it?

That should work fine because by the time it has been rectified it will be around 260 volts and you would aim to lose about 30 volts across the RC filters which gives you 230 volts which should be fine..

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: WNStudios on March 09, 2012, 05:28:51 PM
Thank you very much for your help Ian! Really looking forward to this project. Hopefully a couple of questions will be cleared when i got the pcb's and i'm sure some other will pop up :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on March 11, 2012, 07:04:18 PM
I'm considering using a inductor for the top bell position. Using Ian's list I gather I'll need a 50mH, however I cannot find that value in any usable size. Can I use a 47mH?

Also if I am using an inductor should place the capacitors in that positions or short them out or do nothing at all? And if I don't use an inductor should I short the position?

Thanks for all the help,
Brice
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 12, 2012, 01:47:46 PM
I'm considering using a inductor for the top bell position. Using Ian's list I gather I'll need a 50mH, however I cannot find that value in any usable size. Can I use a 47mH?

Also if I am using an inductor should place the capacitors in that positions or short them out or do nothing at all? And if I don't use an inductor should I short the position?

Thanks for all the help,
Brice

47mH is close enough. You need to include appropriate value capacitors to create the bell at the frequency you want. If you do not use the inductor you do need to replace it with a shorting link.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: WNStudios on March 13, 2012, 10:54:46 AM
Got the PCB's today Ian, extremely fast! Thank you! Will start populating them with what i have today.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: adeptusmajor on April 07, 2012, 11:36:03 AM
First, I apologize if this has already been discussed here...

I am finally starting to move forward with this project, started sourcing components the other day.

I noticed that the values of the diodes and electrolytic caps for the power supply are different on the schematic and bom from the values silk screened on the board itself.

Should I stick with the bom and schematic, or should I up the values to what is printed on the board? I am building a two channel unit if that makes a difference.

Thanks.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 07, 2012, 04:37:08 PM
First, I apologize if this has already been discussed here...

I am finally starting to move forward with this project, started sourcing components the other day.

I noticed that the values of the diodes and electrolytic caps for the power supply are different on the schematic and bom from the values silk screened on the board itself.

Should I stick with the bom and schematic, or should I up the values to what is printed on the board? I am building a two channel unit if that makes a difference.

Thanks.

The power supply PCB was originally designed for another project that needed larger value smoothing capacitors. You should use the values in the circuit diagram/BOM. Also, the diodes on the PCB were for a higher power supply, but for just two channels regular 1N4007 diodes will be fine.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: adeptusmajor on April 07, 2012, 09:00:18 PM
That's what I figured. Just had to be sure.

Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on April 08, 2012, 05:06:36 PM
Anyone finish there's? It'd be great to see some photos!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on April 13, 2012, 11:04:39 AM
What type switch is needed for the eq in&out? I assumed double pole, double throw. Wanted to double check. Also is that the same type for power on-off switch?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on April 13, 2012, 11:28:16 AM
What type switch is needed for the eq in&out? I assumed double pole, double throw. Wanted to double check. Also is that the same type for power on-off switch?
DPDT for EQ in/out. You can use an SPST for the power switch

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on April 16, 2012, 12:42:23 AM
On the psu I see that I need a 100nf film with 250 "ac".. Is this correct? If so is there a special type of cap that is necessary or will any film work assuming it'll handle 250v? Part #?

Thanks,
Brice
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 16, 2012, 05:45:47 AM
On the psu I see that I need a 100nf film with 250 "ac".. Is this correct? If so is there a special type of cap that is necessary or will any film work assuming it'll handle 250v? Part #?

Thanks,
Brice

This is connected across the 240V ac HT winding hence the 250V ac rating. You need remember this means the peak voltage across this cap will be over 350V dc so you could use any film cap rated at 400V dc. However, there are filem caps designed especially for this job and rated at 250V ac or 275V ac.  A goo choice would be this one:

http://uk.farnell.com/vishay-roederstein/f17724102000/capacitor-100nf-275v/dp/1612243 (http://uk.farnell.com/vishay-roederstein/f17724102000/capacitor-100nf-275v/dp/1612243)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on April 25, 2012, 07:02:04 PM
Ian,
So I got my hands on some cool surplus 18 pos switches and I'm going to make stepped pots for everything. I saw the post on page one about this (in 12 steps). My question is: when using the resistor calculator what values in db should I use? EJ_whyte used -40 for his max attenuation (first step) on his 470K log. Is that a correct place to start? Could it be more?
Please be aware that this is the first time I have attempted something like this and I'm still a noob in general (you know that though).

One more thing, on the mid boards thread you mentioned the three position switch for the boost/cut selector. Do you know of a part number for a switch like that I could use for reference?

Thanks,
Dave

p.s. I'm still planning on finishing the hookup diagram I've just had to put it on the back burner for a little while  ;)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 26, 2012, 03:43:11 PM
Ian,
So I got my hands on some cool surplus 18 pos switches and I'm going to make stepped pots for everything. I saw the post on page one about this (in 12 steps). My question is: when using the resistor calculator what values in db should I use? EJ_whyte used -40 for his max attenuation (first step) on his 470K log. Is that a correct place to start? Could it be more?
Please be aware that this is the first time I have attempted something like this and I'm still a noob in general (you know that though).

Even or 18 steps, -40 would be a good place to start. The calculator should then divide that into equal steps.

Quote
One more thing, on the mid boards thread you mentioned the three position switch for the boost/cut selector. Do you know of a part number for a switch like that I could use for reference?

Thanks,
Dave


Any of these will do:

http://uk.farnell.com/jsp/search/browse.jsp?N=2031+203716+110145882+110177139&Ntk=gensearch&Ntt=spdt+toggle&Ntx=mode+matchallpartial&No=0&getResults=true&appliedparametrics=true&locale=en_UK&divisionLocale=en_UK&catalogId=&skipManufacturer=false&skipParametricAttributeId=&prevNValues=2031+203716+110145882&mm=1001953||,1002918||,&filtersHidden=false&appliedHidden=false&autoApply=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D2031%2B203716%26Ntk%3Dgensearch%26Ntt%3Dspdt%2Btoggle%26Ntx%3Dmode%2Bmatchallpartial%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26divisionLocale%3Den_UK%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D2031%2B203716 (http://uk.farnell.com/jsp/search/browse.jsp?N=2031+203716+110145882+110177139&Ntk=gensearch&Ntt=spdt+toggle&Ntx=mode+matchallpartial&No=0&getResults=true&appliedparametrics=true&locale=en_UK&divisionLocale=en_UK&catalogId=&skipManufacturer=false&skipParametricAttributeId=&prevNValues=2031+203716+110145882&mm=1001953||,1002918||,&filtersHidden=false&appliedHidden=false&autoApply=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D2031%2B203716%26Ntk%3Dgensearch%26Ntt%3Dspdt%2Btoggle%26Ntx%3Dmode%2Bmatchallpartial%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26divisionLocale%3Den_UK%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D2031%2B203716)

You just need a spdt On-Off-On toggle switch.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on April 26, 2012, 03:57:17 PM
Thanks Ian,
I want equal steps for a linear pot but the log pots need a curved response, right?

This will work for the switches, right?

http://www.mouser.com/ProductDetail/NKK-Switches/M2113TCFW01-RO/?qs=gndqSz9ohutnKt0mR5dl7oTaLWHsOuSQ%2f%2fZ9J67D6Xk%3d


Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 26, 2012, 04:28:49 PM
Thanks Ian,
I want equal steps for a linear pot but the log pots need a curved response, right?

Spot on.

Quote
This will work for the switches, right?

http://www.mouser.com/ProductDetail/NKK-Switches/M2113TCFW01-RO/?qs=gndqSz9ohutnKt0mR5dl7oTaLWHsOuSQ%2f%2fZ9J67D6Xk%3d


Dave

They look fine to me. I assume the illumination is just on all the time.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on April 26, 2012, 04:52:07 PM
Ian,
I'm looking at those switches as they are red in one position and green in the other. No illumination in the off position.

Is there any guidelines for what curve to use for the log response? There is a chart on the Goldpoint website for 24 position but I need to break that down to 16

http://www.goldpt.com/r_series.html

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 26, 2012, 05:55:48 PM
Ian,
I'm looking at those switches as they are red in one position and green in the other. No illumination in the off position.

Is there any guidelines for what curve to use for the log response? There is a chart on the Goldpoint website for 24 position but I need to break that down to 16

http://www.goldpt.com/r_series.html

Dave

OK, the first thing to remember is that all these sites and calculators are for making volume controls. As often as not they make the attenuation steps equal until you reach the end when of course they turn right off.

That's not quite what you want in an equaliser. For a start, the range of boost and cut is less than 20dB. We are more interested in the law of the pot so we get equal dBs of boost of cut per step rather than its attenuation in dB. A regular log pot attenuates by 20dB (one tenth) at the mid point . This means 90% of its value is from the wiper to the top and 10% from the wiper to the bottom. You should arrange your log switches to do the same but this corresponds to half the boost cut or around 10dB.

Confused? You should be because I am.

The bottom line is there is I am not sure if there is an easy and obvious way to design a stepped equaliser switch using programs/techniques/formulae intended for volume controls. What I really need to do is run the simulation of the EQ and work out the resistor values for 1dB and 2dB steps of boost or cut or for 10 or 20 steps all of which is quite a bit of work.

Anyway, I have just spent a few minutes going over the original design thread where ej white first suggested using stepped pots and it seems we did agree that it was best to set the range to 40dB on the basis that equal steps must make the mid point at 20dB as we require.

What we nned is a calculator to work out the values for us and I just found one here:

http://www.quadesl.com/attenuator.html (http://www.quadesl.com/attenuator.html)

Just put in the resistance in ohms (470000 for 470K) select the number of steps and set the final attenuation as 40dB. Use the fixed logarithmic slope. I just ran this for 470K with 18 steps and rounding to the nearest resistor values I get:

1. 110K
2. 86K
3. 68K
4. 47K
5. 39K
6. 27K
7. 22K
8. 15K
9. 12K
10. 10K
11. 7K5
12. 5K6
13. 4K3
14. 3K3
15. 2K4
16. 2K
17.1K5


Hope that helps.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on April 26, 2012, 06:54:25 PM
Ian,
Thanks! I actually came across this calculator in my quest for info on this project but it didn't work in Firefox on my mac.
I had to use Chrome on my Parallels PC (sigh).

So for the record, I should be cool with using the calculator on that site to find the values for my log "pots" and then just dividing the total resistance by the number of steps for my linear "pots"

Since I'm doing the stepped switches I have the opportunity to use the pot values in your design as opposed to the US vales (i.e. 5K, 50K, 500K)
Does it really matter which pot values I use provided I compensate via changing the capacitor values (and resistor) using your capcalc spreadsheet?
I ask as I have already painstakingly sourced the needed components based on the US pot values.

Once again, thanks for all your help!
Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 27, 2012, 05:25:14 AM
Ian,
Thanks! I actually came across this calculator in my quest for info on this project but it didn't work in Firefox on my mac.
I had to use Chrome on my Parallels PC (sigh).

So for the record, I should be cool with using the calculator on that site to find the values for my log "pots" and then just dividing the total resistance by the number of steps for my linear "pots"

Yes.
Quote

Since I'm doing the stepped switches I have the opportunity to use the pot values in your design as opposed to the US vales (i.e. 5K, 50K, 500K)
Does it really matter which pot values I use provided I compensate via changing the capacitor values (and resistor) using your capcalc spreadsheet?
I ask as I have already painstakingly sourced the needed components based on the US pot values.

The exact pot values are not critical so long as they remain in the same ratio to each other and you change the capacitor values appropriately.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on April 28, 2012, 03:32:40 PM
Ian,
So would the switch be wired up so that the max resistance  (i.e 470K) is at the CW or CCW position?
Conversely, does the answer repeat for all the pots (i.e. is the answer is CW then the 4.7K Lin switch exhibits the max resistance in the CW position as well)

Thanks for your help!
Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 28, 2012, 06:30:57 PM
Ian,
So would the switch be wired up so that the max resistance  (i.e 470K) is at the CW or CCW position?

Max resistance should be with the 470K (lo cut) pot at the fully CW position.

Quote
Conversely, does the answer repeat for all the pots (i.e. is the answer is CW then the 4.7K Lin switch exhibits the max resistance in the CW position as well)

Thanks for your help!
Dave

The direction of rotation of all for pots is shown on the attached schematic (which is also included in the first post of this thread).

I would advise you to download and print all the documents listed in the first post.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on April 28, 2012, 08:59:29 PM
Ian,
Thanks for the info. I actually have already downloaded every document and pic throughout both threads.
I think maybe I'm over thinking this.
Maybe I need to start with understanding the relationship of the info I get from the calculator to the assembling of the switch.
(I apologize for the penny not dropping yet!)
So according to the numbers you posted above:
1. 110K
2. 86K
3. 68K
4. 47K
5. 39K
6. 27K
7. 22K
8. 15K
9. 12K
10. 10K
11. 7K5
12. 5K6
13. 4K3
14. 3K3
15. 2K4
16. 2K
17.1K5

It all adds up to roughly 470K, but would step #1 be the first step rotating CW from a starting point of full anti-CW? Or would that be backwards?

Confused as ever,
Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 29, 2012, 09:23:44 AM

It all adds up to roughly 470K, but would step #1 be the first step rotating CW from a starting point of full anti-CW? Or would that be backwards?

Confused as ever,
Dave

I am not surprised you are confused. Once again, unfortunately, this calculator is for a volume control so it is not immediately obvious how you use it for EQ.

Anyway, to cut a long story short, with it fully clockwise we want about 470K and when it has been turned from there to the half way point we want about one tenth of that and sure enough if we add up the values from 9 thru 15 we get just over 50K. So, as you rightly guess it is backwards. We want it backwards which means you wire the 110K between positions 18 and 17, the 86K between positions 17 and 16 and so on (where position 18 is the fully clockwise position).

Hope that helps!!!

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on April 30, 2012, 12:32:49 PM
This goes a long ways to explaining why I've been having such problems getting mine going! I've wired everything up bass-ackwards and didn't take an attenuation of 40dB into account, using Harpo's calculator instead. Obviously, my values were very different. Ooops....

Before I make up another eight switches, I wonder if someone could check this attachment and see if I understand this correctly. I'm using 12-pos. switches, and the calculator Ian has suggested. Will this work?

Ralph

[Edit: removed attachment]
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on April 30, 2012, 01:14:07 PM
I'm probably not the person who should be chiming in on this but looking at your pdf, if viewing the switch from the rear shouldn't your pin 1 be on the left side?

As far as I'm understanding it, the chart you have seems correct but like I said....

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on April 30, 2012, 02:37:28 PM
Did I mention that my 18 pos switches are concentric? I also found some seriously cool old Daka-Ware concentric knobs

(http://farm8.staticflickr.com/7039/7129090655_62279702c8.jpg) (http://www.flickr.com/photos/wavedealer/7129090655/)


Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 30, 2012, 03:44:30 PM
I'm probably not the person who should be chiming in on this but looking at your pdf, if viewing the switch from the rear shouldn't your pin 1 be on the left side?

As far as I'm understanding it, the chart you have seems correct but like I said....

Dave

I agree. When fully CCW pin2 should be connected to pin 3.Drawing of pot looks as if it is from the front not the rear.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 30, 2012, 03:45:30 PM
Did I mention that my 18 pos switches are concentric? I also found some seriously cool old Daka-Ware concentric knobs

(http://farm8.staticflickr.com/7039/7129090655_62279702c8.jpg) (http://www.flickr.com/photos/wavedealer/7129090655/)


Dave

Those are some really cool dual concentric switches. Where can I get me some??

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on April 30, 2012, 04:27:02 PM
Okay, one more time (sorry). Like this?

[Edit: removed attachment]
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 30, 2012, 04:59:59 PM
Okay, one more time (sorry). Like this?

I think you changed both the circuit and the pot view so it is still wrong. You need the circuit from the first and the pot view from the second I think. Awww, my head hurts.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on April 30, 2012, 06:11:13 PM
Welcome to the perpetual state of confusion that has been dogging my heels since trying to get this right. Sorry - I hope it's not catching...

Okay, one last try...

Ralph
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kante1603 on April 30, 2012, 06:49:38 PM
Did I mention that my 18 pos switches are concentric? I also found some seriously cool old Daka-Ware concentric knobs.


Dave
Woooooaaaahhhhh....now that looks really vintage Dave.I wonder how small the inner pot is and if you need much force to turn it.

Very nice,congrats,

Udo.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on May 01, 2012, 02:18:56 AM
Ralph- PDF ver3 looks right to me  :)

Udo - The inner (smaller) knob is 3/4" or 19mm (for you Europeans). I've worked the switches a little and they are nice and stiff but don't require much force to turn  :D

My plan is to make a stereo version with concentric stepped controls for the boost/cut and one set of controls for the frequency select (2P6W dual deck switches) Everything will be wired off board

EDIT: I have removed the layout diagram for some editing I will repost when finished

Ian - I emailed you some links  8)

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 01, 2012, 06:15:44 AM
Ralph- PDF ver3 looks right to me  :)

I think he's got it!


And thanks for the links Dave.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on May 01, 2012, 09:52:26 AM
Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 04, 2012, 11:57:59 AM
Just a quick note to let everyone know that as I have run out of EQP1A PCBs I have just placed an order for a hundred as I still get asked for them occasionally  (PM me). I have also ordered some prototypes of a new Pultec 3 band PCB that combines the poor man's EQP1A and the mid boost/cut mod onto a single PCB. It takes PCB mounting Grayhill switches and off board pots.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on May 05, 2012, 01:46:57 AM
Ian,
That single PCB idea sounds cool! I can't wait to see it!

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on May 05, 2012, 05:31:22 AM
I'm In too for that single pcb

P.D. Finally I got all the parts for the PMEQP1A, and started wiring it. I got not many time to work on it, but I'd like to get this thing working before the summer.

Been lurking this thread lately. Finally I will unbalance the inputs with IC's and use OEP's for the outputs.

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 05, 2012, 06:42:08 AM
I'm In too for that single pcb

P.D. Finally I got all the parts for the PMEQP1A, and started wiring it. I got not many time to work on it, but I'd like to get this thing working before the summer.

Been lurking this thread lately. Finally I will unbalance the inputs with IC's and use OEP's for the outputs.

What will you be using for gain make up?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 05, 2012, 06:54:25 AM
Attached is a schematic for the new single PCB based Pultec 3 band EQ. As you can see, the hi boost is as in the original Pultec EQP1A using an inductor. However, I have arranged the circuit so that just by changing capacitor values and shorting out the inductor pins you can build it just like the original poor man's Pultec. As in the poor man's there are 6 hi and 6 lo frequencies and I have added the mid boost/cut option with a set of frequencies chosen from the Pultec MEQ5. The PCB is laid out for Grayhill PCB mounting switches which are quite expensive but you can easily wire up to off board cheaper types.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 05, 2012, 07:04:16 AM
Here is a pic of the single PCB Pultec 3 band EQ. The hi boost/cut switch is front left with it capacitors behind i and the (optional) inductor behind it. The mid bboost/cut switch is centre front with it capacitors behind it and the inductor behind them. On the righ front is the lo boost/cut switch with its capacitors behind it and behind that is the pad you need for the EQ in/out switching.

There are no pots on the PCB just the switches which are on exactly the same centres as the Helios EQ version of this PCB. All the pot connections are wired to a triangular shaped trim pot pad footprint in an attempt to make it fairly obvious how to wire each one up to its associated pot.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on May 05, 2012, 11:06:54 AM
Wow! Very elegant. If I weren't almost done, I'd be first in line. Brilliant as usual, Ian.
Kudos.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on May 05, 2012, 02:22:24 PM
Ian,
Awesome work as usual!
The 100K resistor between the 4K7 and 0V wasn't on the other mid schematics. I'm assuming it should be there (so I can include it in my layout)?

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on May 05, 2012, 02:49:03 PM
GREAT IAN!!!
I'm IN!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 05, 2012, 03:30:39 PM
Ian,
Awesome work as usual!
The 100K resistor between the 4K7 and 0V wasn't on the other mid schematics. I'm assuming it should be there (so I can include it in my layout)?

Dave


The 100K is a nominal value, connected right across the input to the EQ, because this EQ PCB can be used in a number of ways. If you use it just as in the poor man's where it is driven direct from a 10K:10K bridging transformer then you can set it to 12K as in the original to help ensure the transformer sees the right load. If you use it as part of the EZ Tube Mixer then it will probably be driven from a 10K fader so there is no requirement for it to see a specific load and then you would use 100K.

Hope that makes sense.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on May 05, 2012, 07:14:10 PM
Strangely enough Ian, it makes perfect sense! There are all kinds of pennies dropping over here lately thanks to your patience and ability to explain everything to me!

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on May 12, 2012, 09:02:14 AM
Is there enough space to drill our own mounting holes at the corners? not at the inductor one I know.

Regarding the Q max resistor, is it selected for the particular inductance/capacitor combination? and is the range of the sharp/broad setting reduced as a result?

Are you using the 1H tap of the inductor for the 3K setting and a 2.8nF capacitor(s). I had looked at using the poorman in original Pultec form a while back but thought for the 3K setting I could use 600mH/4.7n combination with a 10k Q pot.
Thanks.




Here is a pic of the single PCB Pultec 3 band EQ. The hi boost/cut switch is front left with it capacitors behind i and the (optional) inductor behind it. The mid bboost/cut switch is centre front with it capacitors behind it and the inductor behind them. On the righ front is the lo boost/cut switch with its capacitors behind it and behind that is the pad you need for the EQ in/out switching.

There are no pots on the PCB just the switches which are on exactly the same centres as the Helios EQ version of this PCB. All the pot connections are wired to a triangular shaped trim pot pad footprint in an attempt to make it fairly obvious how to wire each one up to its associated pot.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 12, 2012, 06:50:59 PM
Is there enough space to drill our own mounting holes at the corners? not at the inductor one I know.

There should be. If you are not using the PCB mounted switches then you should be able to place mounting holes near SHi and Slo. There's also room for one between the two inductors and one near the pad circuit. I nearly put mounting holes in on the PCB layout but I thought that if I did then someone would want them somewhere else.

Quote
Regarding the Q max resistor, is it selected for the particular inductance/capacitor combination? and is the range of the sharp/broad setting reduced as a result?

It depends really on the inductor as its resistance sets the maximum Q. In the original Pultec this resistor did not exist and the maximum Q turns out to be around 3. I put this in to allow for inductors with lower series resistance that might need padding out to get the Q closer to the original. You can also use this in the poor man's version of the hi boost as the resistor in series with the wiper of the pot.

Quote
Are you using the 1H tap of the inductor for the 3K setting and a 2.8nF capacitor(s). I had looked at using the poorman in original Pultec form a while back but thought for the 3K setting I could use 600mH/4.7n combination with a 10k Q pot.
Thanks.

The 1H tap (F) on the inductor is not used at all so the 3K setting would be as you propose.

Cheers

Ian

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on May 13, 2012, 10:36:18 AM

It depends really on the inductor as its resistance sets the maximum Q. In the original Pultec this resistor did not exist and the maximum Q turns out to be around 3. I put this in to allow for inductors with lower series resistance that might need padding out to get the Q closer to the original. You can also use this in the poor man's version of the hi boost as the resistor in series with the wiper of the pot.



The 1H tap (F) on the inductor is not used at all so the 3K setting would be as you propose.

Cheers

Ian


Ok, and would the inductor resistance need to be proportionately higher, as are the pot values compared to the original or is the Q independent of circuit impedance? I'm going to wind the inductor so I can work out the resistance from the core AL value/wire gauge combination but I'm just a bit unsure of the impedance/Q relationship.
It'd be great to get a few of the PCBs if and when you have them available.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on May 15, 2012, 02:03:47 PM
I'm just a bit unsure of the impedance/Q relationship.


I think I understand it a bit better now, with a resistance of 370ohms (including inductor resistance) the max Q is about 3 for 600mH/4.7n. I'm not sure if thats right, I can try it with a 150mH inductor for the 12Khz and see what it looks like.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 15, 2012, 03:29:51 PM
I'm just a bit unsure of the impedance/Q relationship.


I think I understand it a bit better now, with a resistance of 370ohms (including inductor resistance) the max Q is about 3 for 600mH/4.7n. I'm not sure if thats right, I can try it with a 150mH inductor for the 12Khz and see what it looks like.

The Q of the circuit depends on two factors. The first is the total resistance across the LC resonant circuit. This includes the resistance of the inductor itself but also resistances in the rest of the EQ circuit and the source and load resistances. It is not at all easy to work out what this total resistance is and it will vary as the other controls are altered and with different source and load resistances. The designers job is to try to make the overall circuit resistance as constant as possible and to be affected only a little by other controls and source/load resistances.

The other factor is the characteristic impedance of the LC circuit which is the impedance represented by the L and the C at resonance and for the inductor is equal to Xr = 2*pi*f*L where f is the resonant frequency and L the inductance. If the total resistance across the LC circuit is Rt then the Q is just Xr/Rt.

To keep the Q constant you therefore need to try to keep the characteristic impedance constant which really means a separate LC combination for each frequency. This is rarely practicable and so most passive EQs compromise by using one inductor for several frequencies. The Helios LC bass boost does this with a single value inductor and a switched capacitor. The Q gets higher as the frequency gets higher but the bandwidth at each setting is constant. For this reason this is sometime called a constant bandwidth EQ.

Hope that helps.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on May 16, 2012, 01:05:49 PM
Thanks for explaining, with a separate LC for each frequency you can maintain the Q and if doing this the value of the Qmax resistor becomes a more simple choice.

With higher impedance in your version means that Xr has to be raised for Xr/Rt to be similar to the original. If you raise Xr by lowering the capacitor/raising L then the cap value for the high frequencies gets very small, would that be why you've used a 10k pot instead of any higher?
Sorry to drag it out!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 16, 2012, 03:41:37 PM
With higher impedance in your version means that Xr has to be raised for Xr/Rt to be similar to the original. If you raise Xr by lowering the capacitor/raising L then the cap value for the high frequencies gets very small,


Correct.
Quote

would that be why you've used a 10k pot instead of any higher?
Sorry to drag it out!

If you compare my circuit values with the original Pultec EQP1A ones you will see that just about everything has been changed by a factor of  about 4.7. The inductors are about 4.7 times bigger and the capacitors about 4.7 times smaller. In the same way, the treble boost pot has been increased 4.7 times from 10K to 47K. The original Pultec Q pot was 2.5K which times 4.7 is actually 11.75K so 10K is the nearest most common value pot to use.

In the original Pultec there is no Qmax resistor so the maximum Q is determined by the circuit resistance and the inductor resistance.

Now inductance is proportional to turns squared so if you double the turns the inductance goes up by four times. But resistance is proportional to the number of turns so if you double the turns you only double the resistance which would therefore lead to a higher Q. However, to get more turns on you often use thinner wire which has a higher resistance which lowers the Q. The bottom line is we have no way of knowing if the resistance of present day inductors using my design has scaled such that the Q remains the same as the original. Given modern materials are likely to provide more inductance per turn then it is likely that they have a higher Q. So the   Q max resistor is included to compensate for this improvement and to try to limit the maximum Q to the same as the original.

Having said all that, it is highly likely that the maximum Q is determined largely by the circuit resistances external to the inductor so I expect the Q max resistor could in most cases be set to zero and no one would notice the difference. It is in there just in case.

The Q pot achieves maximum Q at minimum resistance and minimum Q at its maximum resistance.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: surfkat on May 17, 2012, 11:27:54 PM
I would like to build a few of these with unbalanced in and out so I can hang them off of the unbalanced channel inserts on my Soundcraft Delta console. I am thinking of using a jfet input opamp for a gain stage (TL071, OPA134). I understand I need about 24dB of gain.

Do I need to have a buffer amp for the input or can I plug the insert send directly into the passive EQ? I could easily use a dual opamp and have 1/2 for a input buffer if needed.

Will I need a coupling capacitor after the gain stage? Looking at the schematic for my board, the first component in line after the insert return is a 47uF electrolytic.

Thanks for any thoughts and/or suggestions.

Special thanks to Ian for all the work he has put into this project.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 18, 2012, 04:19:50 PM
I would like to build a few of these with unbalanced in and out so I can hang them off of the unbalanced channel inserts on my Soundcraft Delta console. I am thinking of using a jfet input opamp for a gain stage (TL071, OPA134). I understand I need about 24dB of gain.

That's about right.

Quote
Do I need to have a buffer amp for the input or can I plug the insert send directly into the passive EQ? I could easily use a dual opamp and have 1/2 for a input buffer if needed.

Soundcraft insert points generally have a nice low send source impedance so I would say you should be able to drive the EQ directly.

Quote
Will I need a coupling capacitor after the gain stage? Looking at the schematic for my board, the first component in line after the insert return is a 47uF electrolytic.

You almost certainly do not need one but there is always the possibility your circuit develops a fault which might possibly damage the Soundcraft. So to be safe I would include an output electrolytic capacitor followed by a resistor to ground (10K would do)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on June 04, 2012, 10:40:02 PM
I've been using the EQ with some different options for gain makeup that each seem to work well.
EQ output - Jensen DI transformer - API preamp
EQ output - Bo Hansen DI with Jensen as above - API preamp
EQ output - API(3124+) Hi-Z input which is specified as 470K impedance.

The first two I couldn't tell apart tonally with the gain also equal between the two. With the DI buffer load (1M) on the EQ I measured the low boost 47K pot to be 25k total Resistance, with just the DI transformer load(200k approx) it measured 17.3K total. I'm wondering if theres something wrong or if thats just the load in parallel with the circuit impedance in parallel with the low boost pot.

The third way was tested at a friend's studio and I didn't have a meter with me. He ran it through Waves 'Q-clone' plugin which displayed the response curves and they were as expected. At the moment its on a wooden panel, a 1/4 inch output jack and there is some noise but so far it sounds great with either of the above for gain makeup, I've yet to try it with the PM's tube gain makeup.







Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 05, 2012, 06:35:25 PM
The first two I couldn't tell apart tonally with the gain also equal between the two. With the DI buffer load (1M) on the EQ I measured the low boost 47K pot to be 25k total Resistance, with just the DI transformer load(200k approx) it measured 17.3K total. I'm wondering if theres something wrong or if thats just the load in parallel with the circuit impedance in parallel with the low boost pot.

That's probably about right. If you have a transformer at the input its secondary dc resistance is quite low so the input end of the high boost pot is effectively connected to ground at dc So you have the 47K of the hi boost pot in series with the 4K7 of the hi cut pot, in parallel with the 47K of the lo boost pot which is about 25K.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 11, 2012, 05:58:53 PM
Some Work In Progress...

(http://img841.imageshack.us/img841/3287/p1010176k.jpg)

I've wired one channel, hope everything is fine....

(http://img338.imageshack.us/img338/6898/p1010168y.jpg)

The PSU (More about it below...)

(http://img594.imageshack.us/img594/83/p1010171yu.jpg)

The (nice) tubes...

(http://img20.imageshack.us/img20/9328/p1010169n.jpg)

Recicled box from a dead sh*tty hifi-amp...

Now, the problems....

I've fired up the psu, with nothing connected to it, (Also I forget the "A" Connection to chassis as I noticed later...) and while I was trying to measure V at the outputs, the transformer started getting hot, smelling too bad and smoke going out from it...., after it, I turned it off, unsoldered the psu from the transformer, fired it up again and no no voltages coming out of it.... No fuses were used at that moment... I know...

Could it be because I didn't connect the 0V of the psu to the chassis?

The transformer was correctly connected to mains power...

Any ideas about that?
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 11, 2012, 06:25:51 PM
Sorry to hear about your smoking transformer. This should not be caused by not connecting the 0V of the PSU to the chassis so don't worry about that. It sounds like one of the secondaries was shorted somehow.

Many mains transformers have a built in thermal fuse as a safety measure to stop them causing a fire. Unfortunately it is like a fuse (it cannot be reset) and it is usually buried deep inside the transformer. Disconnect the transformer from everything and check the primary winding resistance. If it is open circuit then you have blown the thermal fuse I am afraid and the transformer is scrap.

Apart from that your build is looking good!

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 11, 2012, 06:37:29 PM

Apart from that your build is looking good!


Thanks!, I'm trying to give it the look it deserves... (almost one year working, ocasionally on this)

About the transformer, I'm a bit worried about the PSU home made pcb, maybe the 250v solder leads are so close?, disconnected from everything, my multimeter doesn't read continuity between them.... (I put electrician tape trying to prevent contact between traces and chassis, but I don't know if it does anything more than look like crap....)

Does the transformer atachent system need to be isolated from the chassis?

I will try to measure R between main leads, but I'm not so hopefull, I could hear some melting noise apart the smell, but one can never know...

Also I will check for continuity and other issues in the psu, thanks for the tips...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 11, 2012, 07:13:10 PM
About the transformer, I'm a bit worried about the PSU home made pcb, maybe the 250v solder leads are so close?, disconnected from everything, my multimeter doesn't read continuity between them.... (I put electrician tape trying to prevent contact between traces and chassis, but I don't know if it does anything more than look like crap....)

For HT that is probably not enough.I prefer to mont the HT PCB on insulated (nylon) pillars

Quote
Does the transformer atachent system need to be isolated from the chassis?

No, it does not need to be isolated from the chassis. However, if the chassis is steel (rather than aluminium) the transformer will sometimes hum if bolted direct to the chassis and sometimes magnetic interference can be transmitted from the mains transformer via the steel chassis to the input transformer which we do not want. For steel chassis I normally put a rubber grommet between the transformer and the chassis using its mounting bolts.
Quote
I will try to measure R between main leads, but I'm not so hopefull, I could hear some melting noise apart the smell, but one can never know...

Also I will check for continuity and other issues in the psu, thanks for the tips...

Good Luck.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 18, 2012, 07:02:43 AM
Finally, the transformer was dead  :-\

I've finished the wiring of everything, so just waiting the transformer to start trying voltages and such...

Any tips on trying the psu for not burning another transformer? I replaced the 4 diodes for a little bridge rectifier (400V), and I have one question, the pin labelled "+" goes to the 1Watt resistors and + pin of caps, right? And the pin labelled "-" goes to - side of the caps?

I will upload a photo showing the copper side of my home made pcb later and the wiring scheme I'm assuming...

Thanks

Edit: thanks for the correction Ian, I use to confuse both names...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 18, 2012, 11:24:21 AM
Finally, the transformer was dead  :-\

I've finished the wiring of everything, so just waiting the transformer to start trying voltages and such...

Any tips on trying the psu for not burning another transformer? I replaced the 4 diodes for a little regulator (400V), and I have one question, the pin labelled "+" goes to the 1Watt resistors and + pin of caps, right? And the pin labelled "-" goes to - side of the caps?

Yes, that is correct and I think you mean a bridge rectifier rather than a regulator.

The best tip I can give you is to try the HT supply on its own first before connecting it to the tubes. Just use a 300K 1 watt resistor across the output as a temporary load. Turn the power supply and check the output voltage across the 300K load is over 300 volts. Turn it off and leave it for at least 30 minutes to discharge the capacitors, then connect up to the tube gain make up stage.

Another tip is that sometime the inrush current into the first electrolytic capacitor causes the first 1K 1 watt resistor to get very hot and even sometime it will smoke. To be safe you should use a 2W or even  a 5W type here.

I look forward to more pics.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 19, 2012, 06:09:17 PM
Thanks for the tips

It is burning fuses, Is 500mA enough, right? I think I readed it somewhere here, but I'm not sure right now, even out of the metal case, over my wood board it gets shorted, but I can't see any electrical damage in any of the comps or the board, so I'm not sure

I realized my home etch pcb is so crappy, so I will not use it anymore, I will dessign a pcb using eagle (I was looking for time to learn using it, this looks like a nice chance) and will upload here when I got it, I'd like to make a nice job with this eq...

Thanks again for the tips
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on June 19, 2012, 07:03:52 PM
I think I had spec'ed a 250mA fuse for mine. I haven't tried it yet tho.
Can you post a photo of the etched side of your PSU board? Have you triple checked for any shorts that may be happening on the PSU board?

I have an etch file that I'm going to use and you can try it if you want to

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 20, 2012, 03:45:46 AM
I think I had spec'ed a 250mA fuse for mine. I haven't tried it yet tho.
Can you post a photo of the etched side of your PSU board? Have you triple checked for any shorts that may be happening on the PSU board?

I have an etch file that I'm going to use and you can try it if you want to

Dave

I could upload a picture but it's so ugly, and I made a few track cutting for adapt the rectifier, so it's uglier now...

Of course, i have checked everything (many times indeed) looking for shorts or something, but couldn't find anything.

That etch file would be great, thanks, this night I've been struggling with eagle, I almost got it, surely I will finish it for the learning process...

One question, the first capacitor, before the rectifier, should it be a electrolityc, right? the one I have is a small electrolitic, but labelled 100uF 250V, it seems strange to me, it much smaller than the other caps in the psu...

Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on June 20, 2012, 10:42:11 AM
I have a film cap for that position. It is 100nF not 100µF!

http://www.mouser.com/Search/ProductDetail.aspx?R=R413N31004000Kvirtualkey64600000virtualkey80-R413N31004000K

Here are the etch files I'm going to use

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 20, 2012, 04:56:19 PM
Great!, thanks a lot, that pcb looks easy to etch at home, big tracks and pads...

About the cap, Right now I'm not at the bench, so I can't check it but, I'd swear it's 100uF, so maybe I have misread the schematic sooo long....

Gonna work these days out of my city, I will report my advances the next week...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 20, 2012, 05:16:52 PM
I have a film cap for that position. It is 100nF not 100µF!

Dave

Yes, that should definitely NOT be an electrolytic but a plastic film type rated at 275VAC. The Mouser part Wave pointed to is just what you need.

I am surprised that electrolytic has not exploded! Not surprised you are getting blown fuses.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on June 20, 2012, 09:17:35 PM
Great!, thanks a lot, that pcb looks easy to etch at home, big tracks and pads...

About the cap, Right now I'm not at the bench, so I can't check it but, I'd swear it's 100uF, so maybe I have misread the schematic sooo long....

Gonna work these days out of my city, I will report my advances the next week...

It's definitely 100nF. I just looked at the schematic and the PSU board that Ian designed.

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on June 21, 2012, 09:10:17 AM

It is burning fuses, Is 500mA enough, right? I think I readed it somewhere here, but I'm not sure right now,



Try a 1amp fuse for a single tube gain stage, the heater current draw is 600ma alone.

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 21, 2012, 03:13:10 PM

It is burning fuses, Is 500mA enough, right? I think I readed it somewhere here, but I'm not sure right now,



Try a 1amp fuse for a single tube gain stage, the heater current draw is 600ma alone.

DirtyHanfri - is the fuse on the primary or secondary of the transformer??  You should fuse the primary and a 1 amp slow blow should be fine. You need to use a slow blow fuse because the inrush current to the heaters and the HT smoothing caps can be quite high.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on June 22, 2012, 07:20:02 AM
sorry for the stupid question
I'm using a 6.3V DC
When I connect to the H1 and H2 have to respect a polarity?
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 22, 2012, 08:47:20 AM
sorry for the stupid question
I'm using a 6.3V DC
When I connect to the H1 and H2 have to respect a polarity?
Thanks

No, the tube does not care about the polarity of the heaters. Connect them whichever way is most convenient.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on June 22, 2012, 09:47:21 AM
Sorry I've populated R1 and R2 on Hi PCB...
Jumper on R3?
If I don't use L1 I must use a jumper across it?
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 22, 2012, 05:16:52 PM
Sorry I've populated R1 and R2 on Hi PCB...
That is is correct.
Quote
Jumper on R3?
On Hi PCB there is NO R3 and NO jumper on it. R3 is fitted only on Lo PCB.
Quote
If I don't use L1 I must use a jumper across it?
Thanks

Yes, you should jumper L1 if you do not use it.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 23, 2012, 02:45:11 AM
Thanks for the advices about the cap, I guess I've been lucky with no cap explosion  :P

About the fuse, it's on the primary, in the IEC socket, actually it fits 2 fuses, one on each pin (except the earth one).

I will be working on that this weekend, hopefully everything will be fine, thanks again for the tips

Edit: just to say I've etched the psu and it was so easy, great! It was my first etch using my led isolation box, cheap and nice way to get my boards done and looking fine, I'm actually happy with this. I will populate it later and see what happens, thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 23, 2012, 11:39:49 AM
Tubes Glowing Nicely  ;D

I connected the psu to one of the Make up gain stages with a tube on it and fired it up, nothing exploded and the tube was glowing, then I unplugged it and measured voltage falling from 250v. to zero slowly (it took about 15 minutes actually). Then I plugged the other tube and everything nice too. Actually, I think the tubes were shining more than when I had only one tube....

Now, I'll start passing audio.

Thanks for all your advices!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on June 24, 2012, 02:55:04 PM
Tubes Glowing Nicely  ;D

I connected the psu to one of the Make up gain stages with a tube on it and fired it up, nothing exploded and the tube was glowing, then I unplugged it and measured voltage falling from 250v. to zero slowly (it took about 15 minutes actually). Then I plugged the other tube and everything nice too. Actually, I think the tubes were shining more than when I had only one tube....

Now, I'll start passing audio.

Thanks for all your advices!!!

Did you end up using my etch file for your PSU? I would love to see a pic of it and the rest of the unit!

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 24, 2012, 05:36:24 PM
Yes, I used it, thanks, very nice layout btw

This is the picture I have from the psu, I will make a better one when I dissasemble everything for clean everything inside

(http://img440.imageshack.us/img440/2226/p1010227zz.jpg)

The closed unit (and my left foot, just noticed)
(http://img441.imageshack.us/img441/9594/p1010209uu.jpg)

Almost everything inside
(http://img696.imageshack.us/img696/4893/p1010228bp.jpg)

Another View(http://img29.imageshack.us/img29/4217/p1010219bd.jpg)

Tubes on
(http://img824.imageshack.us/img824/1167/p1010233s.jpg)

Trimmers in a little piece of perf board, for easy access
(http://img713.imageshack.us/img713/6049/p1010224d.jpg)

Ground Star
(http://img59.imageshack.us/img59/3069/p1010229t.jpg)

This two last pictures really like me, two detaills that makes the build nicer .

I'm having some troubles, gonna work hard on the wiring, I just noticed there are 2 eq hook up schemes, gonna look that tomorrow...

The unit passes audio, both in bypass and eq in mode, but the eq doesn't work propperly (the High cut switch seems to be reversed, with max cut at pos 1.

Also, the trimmers look strange too...

I'm actually so happy, my first tube project, and everything looks better than expected (as opposed to my gssl...) also I have some new tools, like a Proxxon minidrill with an amazing vertical stand and my cheap and self made pcb isolation box wich makes me want to build more thigs...

This wouldn't be possible without all the wise advices I got in this forum, thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 24, 2012, 06:23:09 PM
It's great to see pictures of a project coming together. Congratulations.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 24, 2012, 06:35:07 PM
Just updated the documentation for the new 3 band Pultec PCB to include a BOM. New pdf is here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/3BandPultec/P3bandDoc.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/3BandPultec/P3bandDoc.pdf)


Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on June 24, 2012, 07:57:39 PM
Hey dirtyhanfri,
Nice unit. Good job so far. I made this diagram to help me out as well as others. I took it down earlier as I was going to add the mid section but I don't think you're using that so feel free to check it out

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 25, 2012, 02:56:57 AM
It's great to see pictures of a project coming together. Congratulations.

Thanks, you can feel so proud, without your advices i probably would have a electrical shock, for sure, also, nice EQ Ian!, it's being a funny and instructive project.

Hey dirtyhanfri,
Nice unit. Good job so far. I made this diagram to help me out as well as others. I took it down earlier as I was going to add the mid section but I don't think you're using that so feel free to check it out

Dave

Thanks, It's so clear, I will try it. I think I have reversed the pots wiring (I'm using stepped switches), maybe I'm misunderstanding something, just to be sure, fully counteclock wise, means pin 12, right? So, in the hook up diagram v2 by Ian (posted in the first post of this thread), the little dots are pin 12?

Also, In the input I have no transformers, will etch a balancing / unabancing amp based on 5532s I've seen in this forum, but at the moment just using the pin 2 of the input xlr's, 3 to gnd..Also I've found some wiring issues in my oeps, so right now, my unit is fully unbalanced, gonna focus on the eq and the in that kind of things.

I noticed the eq was so quiet with no audio going though it, almost no hum (again as opposed to my gssl), what I was worried about...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 25, 2012, 05:34:19 AM
I think I have reversed the pots wiring (I'm using stepped switches), maybe I'm misunderstanding something, just to be sure, fully counteclock wise, means pin 12,

Fully counter-clockwise usually means pin1.

Fully clockwise usually means pin 12.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 25, 2012, 05:37:10 AM
I reversed connection in pins 1 and 12 on one channel and it seems to be working fine as far as I can tell listening in my bench monitor...   ;D
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 25, 2012, 08:00:17 AM
I reversed connection in pins 1 and 12 on one channel and it seems to be working fine as far as I can tell listening in my bench monitor...   ;D

Sounds like you fixed it.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on June 25, 2012, 12:12:15 PM
give me some advice?

2 XSM 10k/10K
2 XSM 600/10k
2 Jensen 11p-1 10k/10k

What do you recommend to use as an input and an output?
thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 25, 2012, 03:18:23 PM
give me some advice?

2 XSM 10k/10K
2 XSM 600/10k
2 Jensen 11p-1 10k/10k

What do you recommend to use as an input and an output?
thanks

To be honest I am not very impressed by Edcor transformers so I would not really be able to recommend either of the ones you listed.

The Jensen will be fine for the input.

For the output the Jensen JT-112-LCF would be a good choice.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 25, 2012, 05:49:20 PM
Well I've tested one channel in a more or less accurate way (Channel EQ Analyzer in Logic Studio ???)

It works fine, but it looks like cutting a lot more than boosting, both in low & high freqs, actually it boost, but is way more evident the cut. I think boosting is the problem, gonna check that tomorrow.

Also, in eq-out mode, the level is much lower, and tweaking the trim doesn't make it as loud as with the eq enabled, I will check for wrong resistor values or something...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on June 25, 2012, 08:35:03 PM
thanks Ian for the suggestions
i 've also 2 x lundahl 1539
can they work well in this situation?
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 26, 2012, 12:52:52 PM
Well, Everything Looks better now, nice boost and cut, I was reversing the high boost and cut switches, also, the bypass issues are gone, but some hum in  the unit, gonna work on the wiring for tidy up a bit everything...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 26, 2012, 06:33:04 PM
Well, Everything Looks better now, nice boost and cut, I was reversing the high boost and cut switches, also, the bypass issues are gone, but some hum in  the unit, gonna work on the wiring for tidy up a bit everything...

What tubes are you using? Sometime NOS tubes have poor heater cathode isolation which shows up as hum. Do you have a steel enclosure? If you do you need to be careful that the power supply transformer does not get magnetically coupled to the input transformers.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on June 27, 2012, 03:00:42 AM
I'm not using input transformers by the moment, actually just taking + from the balanced input (I'd like to make a 2 channel ballancing/unballancing amp based on 5532's posted in this forum by audiox). The tubes are old RCA's, and I think the hum was related to the messy wiring inside the box.

Also I noticed when putting my hand near the wires going to the trimmers it makes some kind of noise, hoping it's nothing relevant qhen it's closed and racked, but, maybe is because the wire, I got for free a coil with hundreds of pure copper wire, like 1.2mm diameter and semi-rigid, ,maybe it's not the best wire to use in audio circuits?

Gonna work on the front panel today, photos coming soon
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 27, 2012, 01:48:56 PM
I'm not using input transformers by the moment, actually just taking + from the balanced input (I'd like to make a 2 channel ballancing/unballancing amp based on 5532's posted in this forum by audiox). The tubes are old RCA's, and I think the hum was related to the messy wiring inside the box.

Also I noticed when putting my hand near the wires going to the trimmers it makes some kind of noise, hoping it's nothing relevant qhen it's closed and racked, but, maybe is because the wire, I got for free a coil with hundreds of pure copper wire, like 1.2mm diameter and semi-rigid, ,maybe it's not the best wire to use in audio circuits?

Gonna work on the front panel today, photos coming soon

The audio signals going from the EQ output to and from the trimmers should be carried in screened wire as shown on the latest hook up diagram (attached). The dotted wires represent the screens of the cables.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: surfkat on June 27, 2012, 09:19:06 PM
I built a single channel of this EQ on a perfboard. It's unbalanced so I can patch it into the inserts on my mix board. The make up gain is a TL071 and this thing sounds great! I am making a second channel now to have a stereo pair. Thanks again to Ian for this project.

I came up with a simple mod which I tried on my prototype. I was thinking it would be cool if you could offset the frequency of the boost/cut. By adding a cap in parallel to the other caps the value of each individual cap on the 6 position switch is increased by the value of the parallel cap. Using a SPST switch on the parallel cap, I could compare the new offset freq with the original. I put a 3n3 cap on the hi boost which lowers the freq of the boost. When this is switched in, with the 6 position switch on 16k I can boost 8k and cut 16k. This sounds very musical to me. I also put a switchable 3n3 cap on the lo cut. This lowers the freq of the cut so when I boost 100hz I can cut around 50hz. This sounds like it tightens up the bass a bit.

I only tested this in mono so I am anxious to try it with a stereo pair of EQs. It's not a huge difference but for the cost of a cap and a switch it gives a bit more flexibility to this already great sounding EQ. Try it and let me know what you think.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on June 28, 2012, 07:02:23 AM
 surfkat , I think it's a great idea!
you can explain it better, maybe with a drawing?
thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: surfkat on June 28, 2012, 10:15:07 AM
This should explain it better.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on June 28, 2012, 01:13:48 PM
Many thanks surfkat
I'll try ....
Thanks Ian!!!
I just finished my Poor Man's Pultec
is beautiful
incredible sound
Thanks
Grazie
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 28, 2012, 04:00:32 PM
Hey Surfkat, nice idea!!

Ilfungo - glad  that you finally got it working and you like the sound of the EQ!!

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 28, 2012, 08:07:25 PM
Well, after coming to a bit of an impasse with this EQ and letting it sit for a month or so, I finally got it working, thanks to dirtyhanfri's question about R3 a page back. Thanks, guys, and thanks, Ian for a very satisfying project. Still need to tweak my make-up gain levels and do some more extensive testing, but my initial impression is very positive. Here are a few pictures for your amusement (forgive my messy wiring, but after the hell I went through getting it wired up, there's no way I'm going back to try to make it any prettier).

Cheers,

Ralph
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 28, 2012, 08:09:30 PM
Front panel closeup. I decided to call it an EQP-1A/5.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 28, 2012, 08:11:37 PM
Another angle. Using a final couple of coats of satin finish helped to cover up most (albeit not all) of the imperfections of my spray-bomb finish.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 28, 2012, 08:13:37 PM
The rear panel. Gotta love those knock-off greenlee punches (think they were q-max)!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 28, 2012, 08:15:30 PM
The guts, with a neat little row of Sowter transformers on the right.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 28, 2012, 08:19:41 PM
A good look at a single channel with Chrion's inductors. All of the rotaries with Dale resistors were my second shot at switches, because the first set were done up as volume pots. Live and learn...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 28, 2012, 08:22:45 PM
Ian's PSU (Thanks again, Ian: with the luck I was having a few months ago, I may well have killed myself trying to breadboard one!).
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 28, 2012, 08:31:37 PM
Tube gain make-up. Need to double-check these, since I only did a very rough adjustment, more or less by ear. Thanks again, Ian, for your generosity in sharing your wealth of experience, and putting such a fine EQ within reach. I'm sure it's going to see a lot of use. Thanks also to   everyone who has contributed to this thread and helped me through this build - the generosity and courtesy of the members of this forum is truly remarkable.

Ralph
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on June 28, 2012, 08:52:56 PM
Looks fantastic Ralph! Very nice, neat work. I think you're the first poshman builder I've seen so far.

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 28, 2012, 08:58:12 PM
Thanks very much, Dave, especially for your help in getting the switches and wiring sorted out - your diagram really came in handy. Did you ever get one done up that included the mid stage?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on June 28, 2012, 10:36:20 PM
I've got a diagram that shows the mid (only one of them) inserted into the hi and lo. It's not a complete overall hookup diagram just the pots and switches and one would use both diagrams for a complete picture.

Check it out

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 28, 2012, 10:50:06 PM
Nice. I'm sure it will come in handy for the next guy. I needed a bit of trial and error to figure out the mids - this would have been a time saver for me.  ::)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on June 29, 2012, 12:06:22 AM
Man I'm totally sorry  :(. I've had it finished for a while, but I kinda spaced on posting it. I just sent you a PM

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on June 29, 2012, 04:41:50 AM
wow... I am going to pick up this project again as well... now my monitor system is up and running... very, very, very nice work! Inspiring!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 29, 2012, 06:11:45 AM
I am impressed, especially with the metalwork. I wish I could do metalwork that good.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 29, 2012, 07:48:17 PM
Metalwork was the easiest part of the build for me! Wish I could get my head around the workings of a circuit as well as you!
Thanks for your comments, guys.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: bieckmusic on June 30, 2012, 08:59:30 AM
Rmaier Great job, impressive!!  :)   Were those lazertran decals, ingraved or screen-printed?  If lazertran which varnish did you use to get them to be see-through...  I've been having trouble getting my lazertran to show the background surface clearly...

thanks!
greg
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 30, 2012, 10:39:16 AM
Thanks, Greg. The front panel is made with waterslide decals, which I sprayed with a coat of clear gloss and then a coat of satin finish. After applying them to the panel, the whole thing got another topcoat of satin finish. Its not quite perfect, but it does help to make the decals a little less conspicuous.

Ralph
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: bieckmusic on June 30, 2012, 04:10:00 PM
Cool, what brand waterslide decals, (Inkjet?)  Did they have a clear or white background.  And what brand lacquers did you use.  My waterslide decals are coming out funky...

thanks so much for the tips!!  I think it's a good way to make a good looking and inexpensive panel   :)

best,
greg
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on June 30, 2012, 08:21:55 PM
The decals were made from clear inkjet decal paper I found at a vendor on Ebay: http://stores.ebay.com/Robins-Eggcetera?_trksid=p4340.l2563 (http://stores.ebay.com/Robins-Eggcetera?_trksid=p4340.l2563).

The lacquers were Rustoleum Painter's Touch Clear Gloss and Tremclad Rust Paint Clear Satin.

I've had trouble in the past with decals bleeding while soaking (like on my Studer front panel: http://www.groupdiy.com/index.php?topic=36522.200 (http://www.groupdiy.com/index.php?topic=36522.200). I had less trouble on this one because I made sure they had a good couple of coats of lacquer, and that I didn't soak the decals too long or overwork them when getting them in place on the panel.

What kind of funkiness are you running into?

Ralph
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: bieckmusic on July 01, 2012, 12:46:56 PM
Thanks for that! 
I think you answered my question...  I've been using Lazertran inkjet paper, and it's a white background that turns clear (supposedly) with an oil-based laquer.  Anyway it doesn't work, for me.  So I tried other methods and got it to look pretty good.  I'll order some of that label paper you're using and give it a go.  I also ran into the image bleeding and found if I use many super light coats of varnish, instead of a thicker coat is doesn't bleed.  Also, wiping off the extra water, and I put a light coat of alcohol under the label first.

My Mother in Law is a artist who's made prints and she showed me how to slide the decal off gently directy onto the panel, then press from the middle out to remove excess water.  That helped a little.  I think my biggest issues is the paper I'm using.
I think it's a good alternative to expensive front panels.

thanks for the info 8-)

greg
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on July 05, 2012, 07:09:01 AM
sorry
I do not remember where I found this layout ...
where can I find this PCB?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 05, 2012, 02:25:25 PM
sorry
I do not remember where I found this layout ...
where can I find this PCB?

It is the new combined 3 band Pultec PCB. It has the hi, lo and mid circuits of the poor man's Pultec all on one PCB plus you can also do an inductive hi boost just like the original EQP1A or wire it up as a poor man's. This PCB does however use expensive switches.

The documentation is here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/3BandPultec/ (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/3BandPultec/)

and you can buy it here:

http://www.groupdiy.com/index.php?topic=48986.0 (http://www.groupdiy.com/index.php?topic=48986.0)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on July 09, 2012, 06:43:53 PM
Ian,
I'm sourcing the resistors for my stepped switches and I've come across something.
The capcalc3.xls spreadsheet has the pots listed as:

Hi Cut             4700 Log
Hi Boost        47000 Lin
Low Cut       470000 Log
Low Boost      47000 Lin

Whereas the partslist.xls spreadsheet has them listed as:

Hi Cut             4700 Lin
Hi Boost        47000 Lin
Low Cut       470000 Log
Low Bosst      47000 Log

Which spreadsheet is accurate? I'm assuming the partslist is the accurate one as I also looked at the PMEQP1-AMKII.png from the first post and it shows both Hi pots to be Lin and both low pots to be Log but I want to be certain.

Thanks,
Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 10, 2012, 07:27:03 AM
The parts list is correct. Both the HI controls are linear and both the LO controls are log. Thanks for pointing that out. I will correct the capcalc spreadsheet.

Cheers

Ian

Edit:

I have uploaded a corrected version of capcalc.xls and I have also included the original LibreOffice file capcalc.ods for those using open source document standards.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/capcalc.xls (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/capcalc.xls)

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/capcalc.ods (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/capcalc.ods)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on July 11, 2012, 11:09:21 PM
The mid boost/cut pot is 47K Log, correct?

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on July 12, 2012, 12:04:50 AM
Yes (at least, that's what I used for both low mid and high mid boost/cut in my build). I had a bit more time to play with the EQ lately. God, it sounds really good!

Ralph
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on July 12, 2012, 12:35:18 AM
Great to hear Ralph!
Your build is very inspiring. I look at your pics almost every day and I'm progressing on my project because of yours.
I should be getting my first batch of parts from Mouser tomorrow to start building my stepped concentric switches.
Can't wait!
Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 12, 2012, 03:00:49 PM
The mid boost/cut pot is 47K Log, correct?

Dave

Yes, 47K log is what I have put on the schematic and also what I noted on the simulations. The problem is we really need one pot law for boost and another for cut. For boost a LIN pot is best and for cut an anti LOG pot is best and I guess I thought a log was a reasonable compromise. However, I have just done some more simulations at different pot positions and I think now that a LIN pot would be better. If you use a LIN pot then the boost and cut you get at 50% and 100% rotation are:

Rotation                Boost                Cut
50%                     7.5dB                1.2dB
100%                    15.6dB               14dB


As you can see the boost is spot on but nearly all the cut happens in the last 50%. I thought at first a log pot would cure this but it doesn't because the way the pot is wired means at 50% the pot will still be 90% of the pot total so the cut and boost will be even less.

So, on balance, I would now say the best bet for the mid cut/boost pot is to use a LIN type.

Thanks for getting me to think this through again and apologies to all those who have purchased log pots! (me included)

I will update the documentation.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on July 12, 2012, 06:48:52 PM
No wonder my mid cuts were so SUBTLE  ;D ;D ;D ;D ;D
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 12, 2012, 07:24:59 PM
No wonder my mid cuts were so SUBTLE  ;D ;D ;D ;D ;D

You could always try wiring your log pots as backwards reverse log pots. To do this you swap the wires going to the pot and also swap the pair of pot tags that are wired together. The pot now works backwards i.e. fully clockwise is off and anticlockwise is full boost/cut.. This should make the cut a bit smoother.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on July 12, 2012, 08:30:28 PM
Thanks, Ian, but I think I'll probably make up a new set of linear switches and see how they compare. 3rd time lucky?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 13, 2012, 06:13:43 AM
Thanks, Ian, but I think I'll probably make up a new set of linear switches and see how they compare. 3rd time lucky?

Fingers  crossed!!

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 13, 2012, 06:49:54 PM
I have updated the Pultec 3 band schematic to reflect the change of the mid boost/cut pot changing to a LIN type. I also added the values, type and CW direction to the Hi cut control.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/3BandPultec/pultec3bandcctv2scaled.JPG (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/3BandPultec/pultec3bandcctv2scaled.JPG)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on July 13, 2012, 09:06:50 PM
Gentlemen,
I have created a diagram for my stepped switches (I need these visual aids) and I'm wondering if you can give it a look and make sure that I'm going to do this right.
The switch is viewed from the front (shaft) side and I have labeled the connections as Pin 1 Anti CW...etc.

(http://farm8.staticflickr.com/7278/7565169540_3e334d7495.jpg) (http://www.flickr.com/photos/wavedealer/7565169540/)

So if looking at my diagram, if I were using this switch as the Hi Boost Lin pot (switch) then Pin1 would be connected to T1 of the High PCB.
Pin 2 would be connected to T2 of the High PCB. Pin 3 would be connected to Pin3 of the Hi Cut switch, correct?

Conversely, if this were the Lo Boost Log pot (switch), Pin 1 would be connected to T1 of the Lo PCB while Pin 2 would be jumpered to Pin 3 and Pin 3 would be connected to T2 of the Lo PCB as well as Pin 1 of the Hi Cut pot (switch).

Does this sound right? Basically I'm trying to make sure I'm connecting the wires correctly to the switch (pot).

Thanks
Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 14, 2012, 07:31:07 AM
Gentlemen,
I have created a diagram for my stepped switches (I need these visual aids) and I'm wondering if you can give it a look and make sure that I'm going to do this right.
The switch is viewed from the front (shaft) side and I have labeled the connections as Pin 1 Anti CW...etc.

So if looking at my diagram, if I were using this switch as the Hi Boost Lin pot (switch) then Pin1 would be connected to T1 of the High PCB.
Pin 2 would be connected to T2 of the High PCB. Pin 3 would be connected to Pin3 of the Hi Cut switch, correct?

Looks right to me.
Quote
Conversely, if this were the Lo Boost Log pot (switch), Pin 1 would be connected to T1 of the Lo PCB while Pin 2 would be jumpered to Pin 3 and Pin 3 would be connected to T2 of the Lo PCB as well as Pin 1 of the Hi Cut pot (switch).

That looks right too except to say that Pin1 and T1 are also connected to signal 0V.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 14, 2012, 07:54:01 AM
I have updated the poor man's id schematic to reflect the change to a LIN pot and also added a clockwise direction indication.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/PMEQMIDv1.1.png (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/PMEQMIDv1.1.png)


Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: irfrench on July 16, 2012, 09:29:03 AM
Hi,

First post for me.

Quick explanation:  Don't move house whilst DIYing - I have been really tight on money recently so couldn't afford the I/O transformers for this ace project.  After speaking with Ian these two circuits were contrived/built for I/O duties with the Poormans Pultec.

They are geared toward presenting the correct impedance at each stage, unbalance/balancing duties and variable makeup gain.  The circuits have been tested (powered by PeterCs Green PSU @ +/-15v) with the correct EQ curves confirmed.

The attached file is .zip with BOM, self-etch tracks and layout.  Save the file and rename to a .zip (file type not allowed for attachments).  You can open directly with rar/zip if you right-click and 'open with'.

Hope it's useful to someone,

Ian



EDIT: See post below for corrected version   ;)
 
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: surfkat on July 18, 2012, 09:06:17 PM
irfrench - thanks for that contribution. I would love to see schematics of these 2 circuits if possible. I am teaching myself to think in terms of schematics, I find it helps me understand better.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: irfrench on July 20, 2012, 05:31:28 AM
surfkat,

Sorry for the delay, the less enjoyable form of DIY has kicked in!   ::)

I've (hopefully) attached the schematic(s) for the I/O.  The circuits were inspired/used/copied/modified from the ESP site, chosen on their apparent suitability.  Ian - ruffrecords - then kindly suggested some tweaks and reading material re:impedance to gear the circuits to the requirements of the Poor Man's Pultec.

I hope it's useful.

Regards,
Ian

EDIT: See post below for corrected version    ;)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 20, 2012, 04:57:25 PM
Ian,

I am not sure if we covered this in our email discussions but there should be an extra 10K resistor on the input board between pin 3 of the input XLR and pin 3 of the TL072. Also R4 is not needed and should be replaced by a shorting link or zero ohm resistor.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: irfrench on July 23, 2012, 04:52:10 PM
Ian,

Ha ha, Thanks for getting back.  I'll update the schematic & layout to include those changes.  If you don't mind airing laundry in public - what do those changes provide/produce/prevent?

Thanks,
Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 23, 2012, 06:07:09 PM
Ian,

Ha ha, Thanks for getting back.  I'll update the schematic & layout to include those changes.  If you don't mind airing laundry in public - what do those changes provide/produce/prevent?

Thanks,
Ian

Adding the 10K at the input ensures that the gain for the inverting and non-inverting inputs is the same which is necessary for proper common mode noise rejection.

The 10K at the output just raises the output impedance to about 10K. The EQ prefers to be fed from as low an impedance as possible which removing the 10K at the output does.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: irfrench on July 25, 2012, 05:45:10 PM
Evening,

Sorry it's taken this long to tweak such a small thing.

Please see attached the revised docs, as before this has needed to be a .txt to be attached, but should be downloaded and renamed as a .rar.

The archive contains 6 files: layout, tracks and schematic for each input and output sections.

Thanks for your help Ian.


Regards,
Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 26, 2012, 03:36:15 PM
Schematics look OK now.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 28, 2012, 11:28:23 AM
My finally finished unit:

(http://img267.imageshack.us/img267/2040/p1010306v.jpg)

(http://img841.imageshack.us/img841/4707/p1010304d.jpg)

(http://img208.imageshack.us/img208/1826/p1010309dy.jpg)

Hope to don't open this box again in a couple years....
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 28, 2012, 11:59:47 AM
Love the logo!!!!

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kante1603 on July 28, 2012, 12:24:11 PM
...and I love chickenheads!

Congrats,have fun mixing with it!

Udo.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 28, 2012, 01:52:19 PM
...and I love chickenheads!

Congrats,have fun mixing with it!

Udo.

Love the logo!!!!

Cheers

Ian

Thanks to both, some friends use to call me Cheaper for it's english meaning (long story :D) and I decided to use it for my buildings

For sure, I'm having lot of fun with it
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on July 28, 2012, 06:32:40 PM
Ian,
I accidentally ordered 4x 470uf 400v caps for the tube gain stage PSU. Apparently I should of ordered 220uf. Will it have a significant effect if I use the 470uf caps or should I just order 4x220uf caps?

Thanks,
Brice
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 29, 2012, 06:51:29 AM
Ian,
I accidentally ordered 4x 470uf 400v caps for the tube gain stage PSU. Apparently I should of ordered 220uf. Will it have a significant effect if I use the 470uf caps or should I just order 4x220uf caps?

Thanks,
Brice

They will be fine. The original design of that PSU uses 470uF caps but that has enough smoothing to power an entire mixer. That's why I reduced the values to 220uF for the EQ as it only uses a couple of tubes. All it means it your HT will be even smoother than usual. You may well find that when you switch it off, the HT takes quite a long time to discharge (through the heater elevation resistors). Just be aware of this whilst you are constructing it else you might get a shock from the charge stored in the capacitors.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: rmaier on July 29, 2012, 01:20:22 PM
...and I love chickenheads!

Congrats,have fun mixing with it!

Udo.

Love the logo!!!!

Cheers

Ian

Thanks to both, some friends use to call me Cheaper for it's english meaning (long story :D) and I decided to use it for my buildings

For sure, I'm having lot of fun with it

Very cool build! I really like the look of the logo and labels. How were they done?

Ralph
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on July 29, 2012, 05:52:50 PM
I had a feeling it'd be okay but I never would take a chance with such a high voltage PSU or any PSU for that matter! Thanks Ian for the quick response. As soon as get my omeg pots from Germany I can finish this thing!

-Brice
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on July 30, 2012, 12:10:29 PM

Very cool build! I really like the look of the logo and labels. How were they done?

Ralph

It's all photoshop work printed in a vinyl sticker. Cheap and nice.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 01, 2012, 01:46:02 PM

Very cool build! I really like the look of the logo and labels. How were they done?

Ralph

It's all photoshop work printed in a vinyl sticker. Cheap and nice.

Do you use those vinyl stickers you can get in A4 sheets and print onto in a regular ink jet printer?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 04, 2012, 07:06:28 PM
No, I get it done with a plotter in a artwork shop
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 09, 2012, 05:01:33 PM
Chicago Dave has kindly donated his colour 3D hook up diagrams for the poor mans EQP1A and also for the mid cut/boost mod. I have added them to the first post in this thread:

http://www.groupdiy.com/index.php?topic=44213.msg553036#msg553036 (http://www.groupdiy.com/index.php?topic=44213.msg553036#msg553036)

but the are also now on my mini web site along with all the other documentation for this project here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/ (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/)

Thanks Dave.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on August 10, 2012, 03:26:13 PM
Great work Dave! You made it almost too easy!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on August 10, 2012, 06:35:26 PM
It's my pleasure to help out! I think Ian deserves all the credit. he has given us  a great project.
Now if I could just get the rest of my parts...

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 18, 2012, 04:37:11 AM
Hi

I realised yesterday that my unit doesn't work propperly.

In one channel, the Low cut switch acts like Hi cut. In pos 1 to 5 of the switch it doesn't seem too bad, I can't hear it cutting lows, maybe just a bit, but when I go above pos. 5 it starts working as a LPF, lowering everything above 2K. The Boost switch seems to work fine. The other channel works nicely.

I've rechecked the wiring between switches and it looks fine, the same in both channels, so I can't figure what's going on.

Another thing I noticed (I think by the OEP transformers) is a soft fall in frequency response above 10K, It's nice, usable in mixes.

Actually I can use it, because I never go as far in cutting lows, actually, I use the whole eq in a very subtle way, sometimes just bypassing the eq and runing the whole mix in it, and I really like it.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 18, 2012, 01:34:55 PM
Hi

I realised yesterday that my unit doesn't work propperly.

In one channel, the Low cut switch acts like Hi cut. In pos 1 to 5 of the switch it doesn't seem too bad, I can't hear it cutting lows, maybe just a bit, but when I go above pos. 5 it starts working as a LPF, lowering everything above 2K. The Boost switch seems to work fine. The other channel works nicely.

I've rechecked the wiring between switches and it looks fine, the same in both channels, so I can't figure what's going on.

That's a pity, especially as one channel works OK. I guess the next thing to check is the components on the boards of the channel that does not work. If the lo cut starts to act like a hi cut then that sounds like a wiring error with the capacitors not connected in parallel with the low cut pot as they should be.

Quote
Another thing I noticed (I think by the OEP transformers) is a soft fall in frequency response above 10K, It's nice, usable in mixes.

That's interesting. I have not heard of that before. One way to check is to turn all the boost and cut controls fully anti-clockwise. This should give you a near ruler flat frequency response. If you then switch between EQ in and EQ out, there should be no difference in sound.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on August 18, 2012, 04:53:11 PM
Hi

I realised yesterday that my unit doesn't work propperly.

In one channel, the Low cut switch acts like Hi cut. In pos 1 to 5 of the switch it doesn't seem too bad, I can't hear it cutting lows, maybe just a bit, but when I go above pos. 5 it starts working as a LPF, lowering everything above 2K. The Boost switch seems to work fine. The other channel works nicely.

I've rechecked the wiring between switches and it looks fine, the same in both channels, so I can't figure what's going on.

Another thing I noticed (I think by the OEP transformers) is a soft fall in frequency response above 10K, It's nice, usable in mixes.

Actually I can use it, because I never go as far in cutting lows, actually, I use the whole eq in a very subtle way, sometimes just bypassing the eq and runing the whole mix in it, and I really like it.

I imagine that when you use it like that (eq bypassed) that you're getting the nice "tubey" sound from the gain make up stage and the iron? Did you use Ian's tube make up PCB?

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 18, 2012, 07:13:40 PM
That's a pity, especially as one channel works OK. I guess the next thing to check is the components on the boards of the channel that does not work. If the lo cut starts to act like a hi cut then that sounds like a wiring error with the capacitors not connected in parallel with the low cut pot as they should be.


Maybe I've reversed the caps in the low board? Meaning, using boost caps as cut and viceversa?  I'll check the wiring anyway, it's a bit complicated so surely I'm overlooking something... Thanks for the advice!

That's interesting. I have not heard of that before. One way to check is to turn all the boost and cut controls fully anti-clockwise. This should give you a near ruler flat frequency response. If you then switch between EQ in and EQ out, there should be no difference in sound.

Cheers

Ian

Sorry, I explained myself bad, there's no difference in the sound bypassing the EQ with no boost or cut, I 'm reffereing to the whole unit sound, in logic studio channel eq analyzer it's a very soft fall, looks kinda natural, I didn't get surprised when I saw it (I've built a La-4 last year, using an OEP output transformer and it was about the same IIRC)


I imagine that when you use it like that (eq bypassed) that you're getting the nice "tubey" sound from the gain make up stage and the iron? Did you use Ian's tube make up PCB?

Dave

Yes and yes, but not sure if I would call tubey to the sound, I suspect the output transformers have a lot to do here, and I'm not a tube expert, but yes, it's really nice. I 've grown in digital, and now, when I hear this (and his partner my new gssl) is like "that sound" I couldn't get before, soft highs and big basses, having a really fun time now, this place is great!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 30, 2012, 05:00:32 PM
Hi

Today I had a bit of time to mess around with my unit.

I was thinking about what Ian said about the caps in parallel with the switch, so I looked the wiring and it was ok, then I put the low boards out of the front pannel and saw C12 was wrong, look the pic...

(http://img845.imageshack.us/img845/6898/p8300068.jpg)

Ooops  ;D

BTW, my unit looks a bit noisier, I got a measurement program for mac, and it measured noise at -72 & 66 db's around 50Hz, I think it can be improved with some nicer wiring...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 31, 2012, 06:28:09 AM
BTW, my unit looks a bit noisier, I got a measurement program for mac, and it measured noise at -72 & 66 db's around 50Hz, I think it can be improved with some nicer wiring...

Because of the relatively high impedance output from the EQ you need to take care of signal wiring and use screened wire as indicated on the hook up diagrams. You should also try to keep them as short as possible.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 17, 2012, 08:28:38 AM
I just had an order from someone who wanted to do separate frequency switches for bass boost and cut so he could also get 12 frequencies on each instead of the six in the regular poor man's. I had a look at the PCBs and the Lorlin switches and it looks like it can be done quite easily. The 12 way Lorlin has  a single wiper connected to the A pas on the PMEQP1A PCB and it will connect to caps C1 thru C12 as is goes through its 12 positions. The capacitor common for the first 6 is T1 and for the second six is T3 so you just strap these togher for 12 positions.

I have no idea if anyone else wants to do this but I thought it was worth passing on.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: TimS on September 17, 2012, 12:45:45 PM
I just had an order from someone who wanted to do separate frequency switches for bass boost and cut so he could also get 12 frequencies on each instead of the six in the regular poor man's. I had a look at the PCBs and the Lorlin switches and it looks like it can be done quite easily. The 12 way Lorlin has  a single wiper connected to the A pas on the PMEQP1A PCB and it will connect to caps C1 thru C12 as is goes through its 12 positions. The capacitor common for the first 6 is T1 and for the second six is T3 so you just strap these togher for 12 positions.

I have no idea if anyone else wants to do this but I thought it was worth passing on.

Cheers

Ian
I take it this can't be done with the 3-band pultec due to the wiring on the PCB?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 17, 2012, 01:20:57 PM
I just had an order from someone who wanted to do separate frequency switches for bass boost and cut so he could also get 12 frequencies on each instead of the six in the regular poor man's. I had a look at the PCBs and the Lorlin switches and it looks like it can be done quite easily. The 12 way Lorlin has  a single wiper connected to the A pas on the PMEQP1A PCB and it will connect to caps C1 thru C12 as is goes through its 12 positions. The capacitor common for the first 6 is T1 and for the second six is T3 so you just strap these togher for 12 positions.

I have no idea if anyone else wants to do this but I thought it was worth passing on.

Cheers

Ian
I take it this can't be done with the 3-band pultec due to the wiring on the PCB?

I am not sure. I don't think you could do it for the lo frequency because the lo boost caps have one end hard wired to the ground plane (0V). You might be able to do it with the hi boost/cut since the capacitor commons all go to the inductor pins or to the hi cut pot and the wiper you need goes to a 470R resistor which you could just omit. So with a bit of judicious track cutting you might do it.

Then again, the original individual poor man's PCBs give you a lot more flexibility to do this sort of thing. The 3Band was intended as much as anything to simplify construction by removing as much of the confusing inter-wiring as possible.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnnyscotch on September 18, 2012, 02:38:39 AM
has anyone found a good source for the switches on these boards in the US?

I'm just researching parts and not sure where to go for these......

cheers
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 18, 2012, 06:34:10 AM
has anyone found a good source for the switches on these boards in the US?

I'm just researching parts and not sure where to go for these......

cheers

The 2 pole 6 way used in the original poor man's EQP1A can be got from Farnell:

http://uk.farnell.com/lorlin/ck1050/switch-2pole-6-pos-0-15a-250v/dp/1123696 (http://uk.farnell.com/lorlin/ck1050/switch-2pole-6-pos-0-15a-250v/dp/1123696)

and also the 1 pole 12 way used for the mid add-on:

http://uk.farnell.com/lorlin/ck1049/switch-1pole-12-pos-0-15a-250v/dp/1123694 (http://uk.farnell.com/lorlin/ck1049/switch-1pole-12-pos-0-15a-250v/dp/1123694)

I expect Digiekey and Mouser will do them too.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on September 18, 2012, 03:16:23 PM
Mouser page for the Lorlin 2P6W switch

http://www.mouser.com/ProductDetail/Lorlin/CK1055/?qs=sGAEpiMZZMvNbjZ2WlReYu3hsbqI1iNk7sf%252bAWMyL2Y%3d

1P12W

http://www.mouser.com/ProductDetail/Lorlin/CK1034/?qs=sGAEpiMZZMvNbjZ2WlReYu3hsbqI1iNkKp9%2fpytA750%3d

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnnyscotch on September 19, 2012, 11:58:48 PM
Great, thanks!

Has anyone done any experimenting with trafos for this?

Less expensive options than the Sowters? I know Ian has said he is not a fan of the Edcors.......
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on September 20, 2012, 12:51:22 AM
I was looking at the Cinemag  CMOB-1L and the Cinemag CMLI-15/15B.
 I believe the pricing is:
CMLI-15/15B - $49.04
CMOB-1L       - $36.52

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnnyscotch on September 20, 2012, 01:55:14 AM
That's a bit better.

What is the problem with the Edcors? People seem to use them for a lot of projects. Is the nature of this build such that they just don't cut it? Or is it a preference thing?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 20, 2012, 07:19:01 AM
That's a bit better.

What is the problem with the Edcors? People seem to use them for a lot of projects. Is the nature of this build such that they just don't cut it? Or is it a preference thing?

It is basically an inductance thing - the Edcors generally don't have enough - more inductance means more wire and a bigger core and hence more expense.

At the input side, provided you drive it with pretty low source impedances, 100 ohms or less, you will probably be OK using an Edcor. If your source impedance tends to be higher then the lower inductance Edcors will lose bass response.

On the output side, the source impedance of my tube gain make up amp is about 1500 ohms so you really do need a good quality, high inductance = expensive output transformer. Of course, if you use an op amp gain make up this is not an issue.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: funkymonksf on September 20, 2012, 02:20:44 PM
That's a bummer. Im finishing my dual poor man eq w/ tube gainstage. And I'm using edcors. I decided it was worth the gamble since it only cost $45 for the entire set. I'll post my opinions on them when I fire it up.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 20, 2012, 03:23:39 PM
That's a bummer. Im finishing my dual poor man eq w/ tube gainstage. And I'm using edcors. I decided it was worth the gamble since it only cost $45 for the entire set. I'll post my opinions on them when I fire it up.

That would be useful information. You should have no problems from 100Hz upwards with normal sources and bridging loads. If you were able to measure the frequency response with the EQ out or set flat that would be very useful.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on September 20, 2012, 03:34:25 PM

 I believe the pricing is:

CMOB-1L       - $36.52

Dave

Is that an up to date price by any chance? it seems very cheap for a core like that!


If choosing an Edcor, the WSM15K/15K seems like the best match for the output although its listed as an input, the core size is more suitable as an output. Inductance is given as 15 henries, the low frequency response should be reasonable but the upper end may be a bit wonky even though the Edcor plot for the WSM15k/15K is near flat. Also I would wire it backwards so that the lower DCR winding is used as the primary and the higher DCR side as the secondary which should mean that the secondary winding surrounds the primary winding on the core.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: TimS on September 22, 2012, 12:22:56 AM
What sort of transformers would you recommend for someone wishing to make a completely passive unit from this circuit (with the idea of using a separate preamp for makeup gain)?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 22, 2012, 07:18:50 AM
What sort of transformers would you recommend for someone wishing to make a completely passive unit from this circuit (with the idea of using a separate preamp for makeup gain)?
This as discussed in some detail in the original thread in Drawing Board. Search to that thread and start reading at page 18.

Edit: Here's a link to it:  http://www.groupdiy.com/index.php?topic=43859.msg563485#msg563485 (http://www.groupdiy.com/index.php?topic=43859.msg563485#msg563485)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on September 25, 2012, 03:56:55 PM

 I believe the pricing is:

CMOB-1L       - $36.52

Dave

Is that an up to date price by any chance? it seems very cheap for a core like that!


If choosing an Edcor, the WSM15K/15K seems like the best match for the output although its listed as an input, the core size is more suitable as an output. Inductance is given as 15 henries, the low frequency response should be reasonable but the upper end may be a bit wonky even though the Edcor plot for the WSM15k/15K is near flat. Also I would wire it backwards so that the lower DCR winding is used as the primary and the higher DCR side as the secondary which should mean that the secondary winding surrounds the primary winding on the core.
That is the price for the 50/50 core not the high nickel. I'm not going to use the high nickel as I feel they are a little to clinical for my tastes
I was quoted that price in Feb I think.

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on September 26, 2012, 04:47:04 PM

That is the price for the 50/50 core not the high nickel. I'm not going to use the high nickel as I feel they are a little to clinical for my tastes
I was quoted that price in Feb I think.

Dave

Thanks Dave, I was going to ask if that was for both type. The shipping to EU makes it less viable but nice to know the price. I got a quote for the pushpull output but the price inc. shipping was quite a bit higher than Sowter's equivalent.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on September 26, 2012, 08:59:41 PM
Hey Matthis,
If it was me, I would get the Sowters if the price (with the shipping) was close. Ian did design the circuit with the Sowters in mind...
What is the shipping for the Cinemags?

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on September 26, 2012, 10:04:31 PM
About $50 for shipping for the original Pultec replacement so I presume it would be similar for CMOB-1L, I'm not actually in need of a pair but that price you posted caught my eye considering the core size! Thanks.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnnyscotch on September 29, 2012, 02:51:52 AM
Hey everyone, I'm building a 2 ch version with Ian's power supply board.

Will this work for the torroid: http://www.antekinc.com/details.php?p=637

It will be a US build (115v, etc...)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 29, 2012, 05:25:36 AM
Hey everyone, I'm building a 2 ch version with Ian's power supply board.

Will this work for the torroid: http://www.antekinc.com/details.php?p=637

It will be a US build (115v, etc...)

You really need one with a 240V secondary so this one would probably be better:

http://www.antekinc.com/details.php?p=638 (http://www.antekinc.com/details.php?p=638)

Edit: or even this one which is in stock at present. The HT will be lower because of the 200V secondary but it should be sufficient for a pair of channels.

http://www.antekinc.com/details.php?p=603 (http://www.antekinc.com/details.php?p=603)


Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnnyscotch on September 29, 2012, 10:31:32 PM
Thanks Ian,

I guess the 240v thing threw me. I'm still putting it all together in my head.

cheers
Eric
Hey everyone, I'm building a 2 ch version with Ian's power supply board.

Will this work for the torroid: http://www.antekinc.com/details.php?p=637

It will be a US build (115v, etc...)

You really need one with a 240V secondary so this one would probably be better:

http://www.antekinc.com/details.php?p=638 (http://www.antekinc.com/details.php?p=638)

Edit: or even this one which is in stock at present. The HT will be lower because of the 200V secondary but it should be sufficient for a pair of channels.

http://www.antekinc.com/details.php?p=603 (http://www.antekinc.com/details.php?p=603)


Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnnyscotch on October 07, 2012, 01:50:25 AM
OK, Sorry in advance.

I know this has been asked to death, but I just went through the whole thread again and I can't find a definitive answer for 2 questions:

1) Which pots need to be Log and which Lin? The diagrams, schematic, and information all seem to be at odds with each other.

2) Has anyone made up a parts list of the caps to use with US available pots (50K, etc...)?? I've downloaded and tried altering the available xcl files and I can't get them to work........
If anyone has got them to work, would you mind posting a pdf of the results?

cheers all
Eric
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 07, 2012, 09:24:10 AM
OK, Sorry in advance.

I know this has been asked to death, but I just went through the whole thread again and I can't find a definitive answer for 2 questions:

1) Which pots need to be Log and which Lin? The diagrams, schematic, and information all seem to be at odds with each other.

The hi pots are Lin and the lo pots are Log.
Quote

2) Has anyone made up a parts list of the caps to use with US available pots (50K, etc...)?? I've downloaded and tried altering the available xcl files and I can't get them to work........

There is only a 6% difference between the nominal UK and US types which is little more than the tolerances of the capacitors you will most likely use. When you add to his the fact that the tolerance on the value of most pots is at least 10% and often 20% then you might just as well use that same values of capacitors for both.


Edit, I have run the spreadsheet with US pot values and attached the results. You need to change the file extension to .xls.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnnyscotch on October 07, 2012, 07:06:36 PM
Thanks Ian, That's great,

 :) :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: atticmike on October 08, 2012, 02:55:12 PM
guys, what sets this build apart from the manley pultec?

also, would you help me figure out to alter the FREQ bands? like going 60, 70 and 120 in the lower register?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 08, 2012, 05:48:46 PM
guys, what sets this build apart from the manley pultec?

It's like 100 times cheaper.

Quote

also, would you help me figure out to alter the FREQ bands? like going 60, 70 and 120 in the lower register?

There's a spreadsheet in the documentation that let's you do this - check out the first post for links.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: atticmike on October 08, 2012, 10:32:23 PM
guys, what sets this build apart from the manley pultec?

It's like 100 times cheaper.

Quote

also, would you help me figure out to alter the FREQ bands? like going 60, 70 and 120 in the lower register?

There's a spreadsheet in the documentation that let's you do this - check out the first post for links.

Cheers

Ian

Alright.

Got a couple of questions left:

1. this one can by tube gain staged like the manley right?
2. which transformers would I have to get in order to be the closest to the manley as possible?
3. what will I end up spending for a single channel unit?
4. can i use specific greyhill instead of those mouser plastic towers?

Mike
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 09, 2012, 07:17:58 AM

Alright.

Got a couple of questions left:

1. this one can by tube gain staged like the manley right?

Yes it can. I have designed a poor man's tube gain make up stage for this project.

http://www.groupdiy.com/index.php?topic=43973.0 (http://www.groupdiy.com/index.php?topic=43973.0)

Quote

2. which transformers would I have to get in order to be the closest to the manley as possible?

The Manley only has one transformer - at the input. I know David Manley prefers Lundhall transformers so I suggest you use one of their 10K:10K input transformers at the input.

Quote
3. what will I end up spending for a single channel unit?
4. can i use specific greyhill instead of those mouser plastic towers?

Yes, you can use Grayhill switches if you wish but they will not fit the PCBs. If you want to use Grayhill switches then you will probably be better off using the PCB I designed for them. This PCB has the advantages that it simplifies a lot of the wiring, includes space for an HF inductor so you get the same bell response as the original, and it also includes a mid boost/cut section which is based on the Pultec MEQ5.

Excluding the variable items like enclosure, gain make up amp, transformer and power supply, the approximate costs per channel are:

1. Original design with low cost switches and no inductor will cost about 18 GBP

2. Original design with external Grayhill switches will cost about 45GBP

3. 3 band design with two inductors and three Grayhill switches on a single PCB will cost about 120GBP. About half this cost is for the two inductors and the third Grayhill  switch.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: atticmike on October 09, 2012, 09:52:04 PM

Alright.

Got a couple of questions left:

1. this one can by tube gain staged like the manley right?

Yes it can. I have designed a poor man's tube gain make up stage for this project.

http://www.groupdiy.com/index.php?topic=43973.0 (http://www.groupdiy.com/index.php?topic=43973.0)

Quote

2. which transformers would I have to get in order to be the closest to the manley as possible?

The Manley only has one transformer - at the input. I know David Manley prefers Lundhall transformers so I suggest you use one of their 10K:10K input transformers at the input.

Quote
3. what will I end up spending for a single channel unit?
4. can i use specific greyhill instead of those mouser plastic towers?

Yes, you can use Grayhill switches if you wish but they will not fit the PCBs. If you want to use Grayhill switches then you will probably be better off using the PCB I designed for them. This PCB has the advantages that it simplifies a lot of the wiring, includes space for an HF inductor so you get the same bell response as the original, and it also includes a mid boost/cut section which is based on the Pultec MEQ5.

Excluding the variable items like enclosure, gain make up amp, transformer and power supply, the approximate costs per channel are:

1. Original design with low cost switches and no inductor will cost about 18 GBP

2. Original design with external Grayhill switches will cost about 45GBP

3. 3 band design with two inductors and three Grayhill switches on a single PCB will cost about 120GBP. About half this cost is for the two inductors and the third Grayhill  switch.

Cheers

Ian

great, who is offering all the boards for the project?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kante1603 on October 10, 2012, 01:42:33 AM
Hello Mike,

Ian himself offers them in the white market:

http://www.groupdiy.com/index.php?topic=48986.0

Udo ;)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: atticmike on October 10, 2012, 07:14:01 AM
Hello Mike,

Ian himself offers them in the white market:

http://www.groupdiy.com/index.php?topic=48986.0

Udo ;)

ah great,

also found some great guts pics of the manley pultec:

(http://dl.dropbox.com/u/70609905/manley-labs-pultec-eqp-1a-413231.jpg)

(http://dl.dropbox.com/u/70609905/manley-labs-pultec-eqp-1a-413232.jpg)

(http://dl.dropbox.com/u/70609905/manley-labs-pultec-eqp-1a-413233.jpg)

looks like the manley has also tube make up gain and not DOA.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: atticmike on October 10, 2012, 02:47:11 PM
that build looks quite close to the manley:

http://www.groupdiy.com/index.php?topic=32973.0

do you offer all the boards for that?

since he also has those separate boards he connects the pots to instead of having them hanging on the pot.

(http://img147.imageshack.us/img147/7647/img1886c.jpg)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 10, 2012, 03:42:07 PM
that build looks quite close to the manley:

http://www.groupdiy.com/index.php?topic=32973.0

do you offer all the boards for that?


That's a completely different project. It is pretty much a clone of the EQP1A. I am not sure where you would get the PCBs.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: atticmike on October 10, 2012, 04:08:53 PM
that build looks quite close to the manley:

http://www.groupdiy.com/index.php?topic=32973.0

do you offer all the boards for that?


That's a completely different project. It is pretty much a clone of the EQP1A. I am not sure where you would get the PCBs.

Cheers

Ian

Alright.

But that is actually what I was looking for and what you I supposed referred to as well? Having the caps sit on a separate board and connecting them to the pots so that I can use grey hills. The same way manley's done that?

Plus he's got the same bands used in the manley not like the EQP1.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 11, 2012, 11:52:47 AM
Alright.

But that is actually what I was looking for and what you I supposed referred to as well? Having the caps sit on a separate board and connecting them to the pots so that I can use grey hills. The same way manley's done that?

Plus he's got the same bands used in the Manley not like the EQP1.

The Poor Man's EQP1A is designed to be low cost. So it omits the inductor in the original design, uses cheap switches and, with simple op-amp input buffer and gain make up amps, it can be made very cheaply. This is all explained in the orignal thread here:

http://www.groupdiy.com/index.php?topic=43859.0 (http://www.groupdiy.com/index.php?topic=43859.0)

There are plenty of Pultec EQP1A clone projects but the poor man's EQP1A is not one of them.

In this thread I am happy to discuss building the poor man's EQP1A and how it can be modified to suit your needs and I have given you three options for this earlier.

If you want to talk about EQP1A clones then you need to ask in the appropriate threads.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: TimS on October 11, 2012, 06:22:34 PM
Since you seem to be so dead set on having something that is exactly like a Manley, I would strongly recommend that you just go ahead and get a Manley. Ian has been extremely generous in putting this project together and in freely lending his assistance to people who are interested in building it, and your constant barrage of questions on multiple threads on replicating a Manley in every minute detail is really quite annoying and not what this forum is about. There is a ton of useful info on this forum and some really great people who are incredibly generous with their knowledge, but it's not fair to abuse their willingness to help - especially when you do so in what quite frankly comes off as a rude and demanding manner.

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 11, 2012, 06:50:46 PM
and your constant barrage of questions on multiple threads on replicating a Manley in every minute detail is really quite annoying and not what this forum is about.

If that is what he wants to do then the sensible thing would be to start his own thread on that topic in The Lab.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnnyscotch on October 26, 2012, 09:50:44 PM
Ian/or Anyone

The BOM says 220uF 400v for the PS board, but the board itself is labeled 470uF.

Also, the BOM calls for 1N4007, but the board is labeled 1N5408.

Which is correct?
This is for a US build

cheers!
Eric
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on October 27, 2012, 12:41:50 AM
Hi Eric,
If you bought the PSU board from Ian, it's labelled with 470µF caps and 1N5408 diodes because the PSU board was originally manufactured for a different project that Ian made.
The layout and form factor of the board can be used for the PMEQP-1A. When you have boards made, there is an additional charge for new silkscreen tooling if you want to change something on the screen.

That being said, you want to use the values from the BOM (220µF, and 1N4007 diodes)

Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 27, 2012, 05:39:43 AM
Hi Eric,
If you bought the PSU board from Ian, it's labelled with 470µF caps and 1N5408 diodes because the PSU board was originally manufactured for a different project that Ian made.
The layout and form factor of the board can be used for the PMEQP-1A. When you have boards made, there is an additional charge for new silkscreen tooling if you want to change something on the screen.

That being said, you want to use the values from the BOM (220µF, and 1N4007 diodes)

Dave

Exactly right. With the bigger diodes and caps, this supply was used for a 6 into 2 mixer using 18 tubes drawing over 100mA. For a couple of poor man's tube gain make boards drawing about 10mA the 1N4007 and 220uF values are more than adequate.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnnyscotch on October 27, 2012, 05:32:32 PM
Understood, thanks gents!

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on November 19, 2012, 06:05:03 AM
Hi

I've been some time with my Poor man's pultec unused, lot of things happened lately... Well, I fired up the unit yesterday, and it was not working properly, I opened it today and noticed the tubes were not glowing as usual, so I turned the power off, took out the tubes and with power on measured voltages. HT read 344V DC, and between H1 & H2 I had 7V AC. With the tubes on their place it's the same, also disconnecting the wires going to the Tube Make up Gain pcb.

I think 344V is too much for HT, IIRC that should be around 250V, right?

In the transformer secondaries I got 250V AC, as expected, but at the cathode of the diode before the first 1K resistor I got 344V DC. The resistors looks and measure ok, the PSU is properly grounded, any of the caps looks bad, and anything smell bad when I turn it on.

Any ideas on what to look for?

Thanks in advance
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on November 19, 2012, 12:35:49 PM
I replaced the diodes and the 100nF cap in the PSU and now have 315V in HT.

I plugged it on and tested the sound, without the output transformers, the first channel doesn't sound, anything, on the second channel I got sound both  with the EQ In & Out, but with EVERY switch I turn I got a loud POP, this didn't happen before...

Will check the wiring and all the usual, this little is giving me a lot of headaches...

EDIT: Also tried swapping the tubes, and the same channel doesn't sound.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 19, 2012, 12:47:10 PM
First you need to get the tubes glowing. If they are not glowing they do not draw HT current and the HT will go up to about 344V. I suggest you carefully check your heater wiring first.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: adeptusmajor on December 27, 2012, 02:48:21 PM
Hey guys, just wanted to share my (almost) completed 2 channel Poshman build. I picked up a broken Altec 1606B as a donor chassis and a handful of knobs for free at a hamfest last year, around the same time I purchased the boards from Ian. I was determined to make these work for this project, so the layout is pretty much based around the space constraints of the super shallow folding chassis and the front panel real estate of the control knobs. Backwards as hell, I know, but I saw it as a fun challenge to just work with what I acquired. It's tight and the front panel is a bit crazy but it works, kind of.

I went with a low-mid and high-mid control, with Chrion's inductors. I didn't even use the mounting holes for Chrion's daughter boards, just let the wiring kind of hold them in place naturally, seems totally secure that way. Sowter transformers, Amperex tubes, caps are mostly Wimas, values recalculated for US pot values. The wiring on the front panel is kind of messy. I just laced the wires around each other as I started wiring it up, it was looking nice at first but started to get out of control as more wires were added. It doesn't seem to be adding any noise so I may or may not clean it up later.

The EQ sounds great, it's nice and quiet and the low and mid controls sound particularly huge on everything I have tried thus far. I haven't had a chance to use it in a mix yet, but looking forward to it. At some point I'll do some tests and see how close the frequencies are. But my ears are telling me that they are pretty accurate.

I'm a bit embarrassed by the current state of the front panel, but I took a picture anyway. I printed out a design from front panel designer and used it to cover the Altec panel and provide a rough drilling template so I could test fit and get this thing up and running. You can't really see it because my printer is low on ink, but the controls are all color coded to make a little more sense out of the somewhat obscure layout. The design has been cleaned and prettied up quite a bit from what you see here and I'm ready to get a panel made when funds allow.

And on that note - I love the quality and look of panels from Front Panel Express, but pricing this one out on their software is getting up towards $300 at this point, which is a bit ridiculous. I would appreciate it if someone could recommend a place that could produce similar results as FPE with more reasonable pricing, if that exists. I would love to finish this thing up and give it the look that it deserves.

Anyway, thanks to Ian for the great project and to Chrion for offering the inductors which work flawlessly and beautifully. This one is definitely a fun and useful addition to the toolbox. Not to mention I learned quite a bit on this build.

(http://www.groupdiy.com/gallery/0/thumb_38684-271212130421.jpeg) (http://www.groupdiy.com/index.php?action=gallery;sa=view;id=139)

(http://www.groupdiy.com/gallery/0/thumb_38684-271212130657.jpeg) (http://www.groupdiy.com/index.php?action=gallery;sa=view;id=140)

(http://www.groupdiy.com/gallery/0/thumb_38684-271212130935.jpeg) (http://www.groupdiy.com/index.php?action=gallery;sa=view;id=141)

 
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 28, 2012, 06:14:44 PM
Well, done. It is really pleasing to see the finished results of your designs. Post another pic when the front panel is done.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: lymix on January 05, 2013, 11:20:57 AM
hi,
i built an EQ inspired by the Poorman and DIYgallery.de's EQP-1A, with a few customization
I added semi-parametric middle range correction, switchable into a notch, and with 12 selectable frequencies from 240 to 10kHz.
Each of the 5 bands are switchable, and there is a main bypass
I used bourns inductors for the mid section, and panasonic caps. Resistors are 1% vishay
The output amps is from the EQP-1a, i just changed the resistors to have 0dB gain but a highr max level input (+22dBu) now
I plan to add transformers for in and outs, probably an engraved front panel

(THANKS A LOT to the developpers of the initials projects, and to the forum for the many help/infos i got)

(http://s8.postimage.org/4cg9gsdtx/XPQ1_front.jpg)


 it's quite messy inside, i have to study connectors and strips for next project... it's the second one

no pcb inside, all components wired
(http://s8.postimage.org/4zjrk203p/XPQ1_inside_view.jpg)






Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on January 13, 2013, 12:33:51 PM
I'm almost finished gathering parts for this awesome project! Thanks for all of your hard work Ian!
Could someone more knowledgable let me know if these transformers would be a good fit for this?
Lundahl LL1521 (high impedance input, 1+1:2,28)
Lundahl LL1524 (bal output, 1+1:1+1)

Cheers.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 13, 2013, 04:01:46 PM
I'm almost finished gathering parts for this awesome project! Thanks for all of your hard work Ian!
Could someone more knowledgable let me know if these transformers would be a good fit for this?
Lundahl LL1521 (high impedance input, 1+1:2,28)
Lundahl LL1524 (bal output, 1+1:1+1)

Cheers.

You will probably get away with using the LL1521 at the input. You will need to reduce the gain make up to compensate for the transformer gain but that is not a problem. It does mean the input impedance of the EQ will look like 2500 ohms rather than the 10K is should. If your gear is happy driving that then it should be OK.

The LL1524 is not really suitable at the input  - its impedance is too low. As an output transformer it is intended to be driven by negative impedance semiconductor circuit so if you intend using a DOA or op amp gain make up stage it should be OK but it is not suitable for use with my  tube gain make up stage.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on January 13, 2013, 11:22:29 PM
Thanks Ian. I'll just order some Sowter's, like you designed this for. No reason to save a few pennies and cause a headache.
Cheers!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ricothetroll on January 14, 2013, 05:14:34 AM
Hi,

It seems to me that according to this schem...
http://www.ianbell.ukfsn.org/pics/PMEQP1-AMKII.png
...the worst case scenario is Zin ~ 50k (domined by hi boost pot + hi cut pot, with lo boost pot = 0) for freqs not affected by the EQ. Where does the 10k come from ?

Best regards.

Eric
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 14, 2013, 06:45:42 AM
Hi,

It seems to me that according to this schem...
http://www.ianbell.ukfsn.org/pics/PMEQP1-AMKII.png
...the worst case scenario is Zin ~ 50k (dominated by hi boost pot + hi cut pot, with lo boost pot = 0) for freqs not affected by the EQ. Where does the 10k come from ?

Best regards.

Eric

The input impedance varies with frequency.  The worst case is when hi boost  and cut pots are both at max then at some high frequency the caps are very low impedance so the effective  input impedance  is little more than the 4K7 resistor in series with the 470 ohm resistor. You are right that at unboosted frequencies it is closer to 50K.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: MatthisD on January 14, 2013, 07:01:49 AM
I'm almost finished gathering parts for this awesome project! Thanks for all of your hard work Ian!
Could someone more knowledgable let me know if these transformers would be a good fit for this?
Lundahl LL1521 (high impedance input, 1+1:2,28)
Lundahl LL1524 (bal output, 1+1:1+1)

Cheers.

The LL1521 works fine with the Poorman EQ. With the primaries and secondaries in series the ratio is 1:1.14 so primary impedance with a 10K load on the secondary is 7.7K and approx. 1dB of gain minus losses.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on April 21, 2013, 12:05:00 AM
I've finished my eqn pair, and when I get some more free time, i'll be ready to focus on wiring up these gems. I'm doing a poshman dual mid version, with Crion's inductors, and Sowter transformers. When connecting mid boards, do both lo mid and hi mid bands connect at the same place as stated in the schematics for the one midband?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 21, 2013, 05:28:36 AM
I've finished my eqn pair, and when I get some more free time, i'll be ready to focus on wiring up these gems. I'm doing a poshman dual mid version, with Crion's inductors, and Sowter transformers. When connecting mid boards, do both lo mid and hi mid bands connect at the same place as stated in the schematics for the one midband?

Yes, they do. You just have to make sure the frequency selections in each band do not overlap.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on July 24, 2013, 05:11:48 PM
I think troubleshooting my pm670 has made my brain into mush. I can't seem to wrap my head around how to hook up ChrioN's inductors to the Modified mid board fix. Can someone shed some light or draw connections to this image?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 24, 2013, 07:08:06 PM
I think troubleshooting my pm670 has made my brain into mush. I can't seem to wrap my head around how to hook up ChrioN's inductors to the Modified mid board fix. Can someone shed some light or draw connections to this image?
#

I would offer to help myself but I have not used one of Chrion's inductors yet. I am sure there are others here who have though.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on July 24, 2013, 07:32:21 PM
Thanks Ian.
I think I understand where the pins for Chrion's inductors are.
Red dot is zero and clockwise is tap 1,2,3, etc with the ground pins on the outside.

I'm confused at the pcb fix. I understand that I don't need to cut any traces. I think I do not need to connect the little corresponding numbers with a jumper.
Am I correct that the letters "S,B,D,E,...on the boards" would have originally mated with "Tap 0,1,2,3..."
If so then the inductor connections 0,1,2,3,... goes to the little numbers in the "fix photo", except 0 =screen, correct? And would it be best to use the number outside of the caps?

The new Screen pad appears to goes to cut/ boost switch.

 So....where would the newly labeled "ind" go to?


 I hope you can follow all of this, as I'm getting confused just reading it back ???


edit: Chrion discontinued his pcbs so I'll just be soldering wire direct to the pins.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 25, 2013, 05:59:23 PM
I'll get a board out tomorrow and have a look. It should just be a case of hand wiring it to the right holes on the PCB.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: adeptusmajor on July 25, 2013, 07:06:06 PM
I used Chrion's inductors, I do remember having a bit of a kludge to make it work. I remember having to fly some cap leads due to more frequencies being connected to a given tap than what the pcb had allowed. I just followed the schematic and used or reallocated the pcb traces where possible. I'll try to get it out and have a look again sometime, I need to troubleshoot some ground/hum issues that have surfaced anyway.

Chrion's inductors sound awesome in this circuit, BTW.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on July 27, 2013, 04:23:47 AM
Hi from Spain
I'm a newbie and I'm trying to build a stereo poor man's Pultec, basic version: no mids, no psu, no make-up. Just low and high 100% passive.

I have a couple of doubts. I'm doing some researches here, and reading a lot, but it's 20 pages and it's not easy to find what I'm looking for.

Firstly, I built the 4 pcb's and I don't know if I have to do something with the L1 position. Have I make a bridge, or leave it free?

Secondly, I took a wiring's guide from the info page and customize to my purposes. I've been comparing it with the schematic and have a doubt about the ground.
Attached is my wiring guide and the schematic.
(http://www.audiopeludo.com/mkportal/blog/images/740wiringwarripultec2.jpg)
(http://www.audiopeludo.com/mkportal/blog/images/741wiring2.jpg)

Have I put a wire from the low boost to the ground? (light green wire)

As I said, I'm a newbie, so take it into consideration.

Thanks in advance.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on July 27, 2013, 04:33:55 AM
Here is a snap of the Hi (left) and Lo (right) switch assemblies complete. What appear to be resistors on the Lo PCB are zero ohm resistors for the links.

Cheers

Ian
http://www.groupdiy.com/index.php?action=dlattach;topic=44213.0;attach=7417;image

???
I was thinking the resistors 1 & 2 was only in the HI pcb leaving the R3 free, while in the LO pcb I must put only the R3 and not the R1 & R2, according to what Ian said in another moment:
"The two resistors, R1 and R1 are only needed for the hi boost and cut and can be wire links or zero ohm resistors for the lo boost/cut. The terminals (pads really) T1 thru' T4 are the only external connections necessary. The only other component not on the PCB right now is the 56K resistor needed for the lo boost/cut."
Have I put a link in R1 and R2 in the low pcb? Have I put a link wire in R3 in the High pcb?
And what's about the L1? Have I put a resistor on it? A link?

Sorry, I'm sure this must had been discussed before. And remember...I'm a newbie.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 27, 2013, 04:54:59 AM
Hi from Spain
I'm a newbie and I'm trying to build a stereo poor man's Pultec, basic version: no mids, no psu, no make-up. Just low and high 100% passive.

I have a couple of doubts. I'm doing some researches here, and reading a lot, but it's 20 pages and it's not easy to find what I'm looking for.

Firstly, I built the 4 pcb's and I don't know if I have to do something with the L1 position. Have I make a bridge, or leave it free?

Secondly, I took a wiring's guide from the info page and customize to my purposes. I've been comparing it with the schematic and have a doubt about the ground.

Hi,

L1 was a late addition for some people who wanted a possibility of a peaking response at one frequency. For the normal PMEQP1A you need to replace it with a wire link.

Your grounding scheme is OK for unbalanced operation.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 27, 2013, 04:58:12 AM
???
I was thinking the resistors 1 & 2 was only in the HI pcb leaving the R3 free, while in the LO pcb I must put only the R3 and not the R1 & R2. Now I'm very very confused.
And what's about the L1? Have I put a resistor on it? Wich value, please?

You fir R1 and R2 only to the HI board. One the low board you need to fit a wire link. I have some zero ohm resistors I use for this so it looks as though I have resistors fitted but they are really short circuits.

For the regular PMEQP1A, L1 needs to be replaced by a wire link.

Hope that helps.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on July 27, 2013, 05:02:32 AM
thaks a lot, Ian  ;)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on July 29, 2013, 03:11:33 AM
Ian... I'm looking for the stuff to build the make up...
I just don't know wich preset pots I need for the VR1 and VR2.
would you give me an example, please?

Is something like this?
http://es.farnell.com/vishay-sfernice/t7ya102mb40/trimmer-pot-1k-1turn-thd/dp/1141645

http://es.farnell.com/vishay-sfernice/t63xb102kt20/trimmer-pot-1k-15turn-thd/dp/1141431

http://es.farnell.com/vishay-sfernice/t7yb474mb40/trimmer-470k/dp/1141671?whydiditmatch=rel_default&matchedProduct=preset+pot+470k&matchedProduct=preset+pot+470k&whydiditmatch=rel_default

http://es.farnell.com/te-connectivity-citec/cb10lv474m/trimmer-top-adjust-470k/dp/1227545


Thanks in advance
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on July 29, 2013, 09:50:22 AM
Ian... I am trying to avoid the makeup stage. The in/out transformers are 350 euro, plus the psu and so on. I think is very expensive.

My best option is making the Eq 100% passive and going from the output to a couple of instrument inputs of a mic preamp. You said I need at least 200k of input impedance. This is very affordable, since there are very low price IC based preamps.

I found another cheap option, but I'd like you to confirm that it's gonna work...
I can get a Behringer active DI like this
http://www.behringer.com/EN/Products/DI4000.aspx
(http://www.behringer.com/assets/DI4000_P0075_Front_XXL.png)

The input impedance is 220k, and the output impedance is 600 ohms. In this device there is a option of adding 20dB to the input signal, that is just what I'm looking for.
Am I wrong, or the Ultra DI is ok for my purposes?
Wich option do you think is better... the preamp through the DI Inpunts, the DI box or building the makeup stage (although is 10 times more expensive) ?

Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 29, 2013, 05:26:55 PM
Thanks Ian.
I think I understand where the pins for Chrion's inductors are.
Red dot is zero and clockwise is tap 1,2,3, etc with the ground pins on the outside.

I'm confused at the pcb fix. I understand that I don't need to cut any traces. I think I do not need to connect the little corresponding numbers with a jumper.
Am I correct that the letters "S,B,D,E,...on the boards" would have originally mated with "Tap 0,1,2,3..."
If so then the inductor connections 0,1,2,3,... goes to the little numbers in the "fix photo", except 0 =screen, correct? And would it be best to use the number outside of the caps?

The new Screen pad appears to goes to cut/ boost switch.

 So....where would the newly labeled "ind" go to?


 I hope you can follow all of this, as I'm getting confused just reading it back ???


edit: Chrion discontinued his pcbs so I'll just be soldering wire direct to the pins.

OK, I have had a look at this. Assuming Chrion's inductors start at 0 and the first tap is at 1, the second at 2 and so on, then you need to wire Chrion's inductor as shown in this picture:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/midbottomchrion.jpg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/midbottomchrion.jpg)

The pin labelled 'screen' is for the connection from the metal clips of Chrion's inductors.

Apart from that, all the connections on the PCB retain the exact function as intended in the original design.

Hope that helps.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 29, 2013, 05:36:34 PM
Ian... I am trying to avoid the makeup stage. The in/out transformers are 350 euro, plus the psu and so on. I think is very expensive.

My best option is making the Eq 100% passive and going from the output to a couple of instrument inputs of a mic preamp. You said I need at least 200k of input impedance. This is very affordable, since there are very low price IC based preamps.

I found another cheap option, but I'd like you to confirm that it's gonna work...
I can get a Behringer active DI like this
http://www.behringer.com/EN/Products/DI4000.aspx
(http://www.behringer.com/assets/DI4000_P0075_Front_XXL.png)

The input impedance is 220k, and the output impedance is 600 ohms. In this device there is a option of adding 20dB to the input signal, that is just what I'm looking for.
Am I wrong, or the Ultra DI is ok for my purposes?
Wich option do you think is better... the preamp through the DI Inpunts, the DI box or building the makeup stage (although is 10 times more expensive) ?

Thanks

You do need a gain make up stage but it does not have to be my tube design or use the expensive transformers. Many people have built versions with op amp input buffers and op amp balanced output drivers that are much cheaper that the tube plus transformers option. I think someone here even offered a PCB for this or there are several commercial PCBs you could use.

You can use an external amplifier provided it has a high enough input impedance and you use short screened cables from the EQ output to the make up amp input. Either the DI inputs of a preamp or the Behringer should work fine.

The best option is to have the make up with the EQ and you should be able to do this cheaply with op amps.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 29, 2013, 05:41:56 PM
Ian... I'm looking for the stuff to build the make up...
I just don't know wich preset pots I need for the VR1 and VR2.
would you give me an example, please?

Is something like this?
http://es.farnell.com/vishay-sfernice/t7ya102mb40/trimmer-pot-1k-1turn-thd/dp/1141645

http://es.farnell.com/vishay-sfernice/t63xb102kt20/trimmer-pot-1k-15turn-thd/dp/1141431

http://es.farnell.com/vishay-sfernice/t7yb474mb40/trimmer-470k/dp/1141671?whydiditmatch=rel_default&matchedProduct=preset+pot+470k&matchedProduct=preset+pot+470k&whydiditmatch=rel_default

http://es.farnell.com/te-connectivity-citec/cb10lv474m/trimmer-top-adjust-470k/dp/1227545


Thanks in advance

Any one of the first three pots will be fine but I would go for the second one because it is a multi-turn pot and it will allow you to make more accurate adjustments. The last one appears to be too large to fit the PCB.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on July 29, 2013, 06:16:06 PM
Thanks Ian.
I think I understand where the pins for Chrion's inductors are.
Red dot is zero and clockwise is tap 1,2,3, etc with the ground pins on the outside.

I'm confused at the pcb fix. I understand that I don't need to cut any traces. I think I do not need to connect the little corresponding numbers with a jumper.
Am I correct that the letters "S,B,D,E,...on the boards" would have originally mated with "Tap 0,1,2,3..."
If so then the inductor connections 0,1,2,3,... goes to the little numbers in the "fix photo", except 0 =screen, correct? And would it be best to use the number outside of the caps?

The new Screen pad appears to goes to cut/ boost switch.

 So....where would the newly labeled "ind" go to?


 I hope you can follow all of this, as I'm getting confused just reading it back ???


edit: Chrion discontinued his pcbs so I'll just be soldering wire direct to the pins.

OK, I have had a look at this. Assuming Chrion's inductors start at 0 and the first tap is at 1, the second at 2 and so on, then you need to wire Chrion's inductor as shown in this picture:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/midbottomchrion.jpg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/midbottomchrion.jpg)

The pin labelled 'screen' is for the connection from the metal clips of Chrion's inductors.

Apart from that, all the connections on the PCB retain the exact function as intended in the original design.

Hope that helps.

Cheers

Ian

Thanks for looking at it Ian.
I've included the pinout that Chrion has posted in his thread, for visual reference.
I think I understand it know.
1) S (screen) on the pm mid boards, go to the ground pins on Chrion's boards in his drawing.
2) IND on your boards goes to the cut/ boost switches.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 30, 2013, 05:47:58 AM
That looks right to me.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on August 06, 2013, 05:11:19 AM
I've just finished my two Pultecs, and they're working perfectly!!

I've taken some graphs.
Ian, this thing is AMAZING!!

Signal passing through the circuit:
(http://www.audiopeludo.com/mkportal/blog/images/756sinajustes.jpg)

Low 20hz
(http://www.audiopeludo.com/mkportal/blog/images/74820hzboost.jpg)
(http://www.audiopeludo.com/mkportal/blog/images/74920hzcut.jpg)
(http://www.audiopeludo.com/mkportal/blog/images/74720hzboostcut.jpg)

High 3khz
(http://www.audiopeludo.com/mkportal/blog/images/7433kcut.jpg)
(http://www.audiopeludo.com/mkportal/blog/images/7423kboost.jpg)

Hi 16k
(http://www.audiopeludo.com/mkportal/blog/images/74516kboost.jpg)
(http://www.audiopeludo.com/mkportal/blog/images/74616kcut.jpg)
(http://www.audiopeludo.com/mkportal/blog/images/74416kboostcut.jpg)

The signal falls over 10dB, so I really think makeup is not needed when coming from the daw at line level
(http://www.audiopeludo.com/mkportal/blog/images/751diferencianivelinyoutsobre10dB.jpg)

I bought the Behringer DI and works perfect. Just adds a few low level harmonics, being the third one the greater. In this pic I sent a 1khz sine through the Eq. At the right side of the sine you'll see the harmonic distortion added by the makeup.
(http://www.audiopeludo.com/mkportal/blog/images/753distor.jpg)


The only thing that I'm worried about is some noise in the low field (50hz) that comes from the circuit.
This graph shows the noise. In this plot there is not any makeup in the signal, just the Eq.
(http://www.audiopeludo.com/mkportal/blog/images/754ruidoEqsinmakeup.jpg)

Did I made something wrong, or this is normal?
I don't think this will be a problem. Some devices like the La2a or 1176 shows the same kind of low noise and this is not audible. Just wondering why it happens.

Great job, Ian. I think I'll build a few more Pultecs. It was only 92 euro for 2 channels + the enclosure. Ridiculous price for that amazing Eq.
In the next days I'll make a extensive review.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 06, 2013, 05:23:30 AM
Well done! That was a quick build.

You seem to have a 6dB loss at 20Hz when just passing signal. I am not sure what is causing this because with all the controls set to minimum there are just resistors in the circuit.

The noise you are seeing looks like 50Hz hum and its harmonics. The output of the EQ is relatively high impedance and hence is susceptible to picking up hum. However, if you mount the EQ in a metal enclosure and use a good quality screened cable at the output and input then there should be very little hum pick up.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on August 06, 2013, 05:28:33 AM
ah, ok. Yes, in this test I was using a 3m cable from the output to the AD converter. This may be causing the hum.
I have the same fall at 20hz in both channels, so maybe I did something wrong. I'm not worried about it. Some classic gear shows this kind of frequency response just passing the signal throug it.

Thanks man. I'll buy more pcb's soon!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on August 08, 2013, 04:52:58 AM
Look at this beauty
(http://www.audiopeludo.com/mkportal/blog/images/766IMG_9582.JPG)
(http://www.audiopeludo.com/mkportal/blog/images/765IMG_9581.JPG)

This was my first project ever, and I'm very satisfied.

Here is a step-by-step guide (in spanish)
http://www.audiopeludo.com/index.php?ind=blog&op=home&idu=3&singlepost=549
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 08, 2013, 05:44:12 AM
Excellent blog!! It loses something when Google translates it into English but otherwise it is a very good introduction for beginners. Well done.

I want to set up a gallery of pictures of my projects that have been built by other people. Could you send me some pics to my email address??

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on August 10, 2013, 03:58:59 AM
Ian, I did a deep test and I have some questions for you.

Firstly, the Low cut is very progressive and smooth in the first 3/4 of the pot. But once you reach the finals steps the cut becomes very hard, just like a HPF. Is this because the Lo cut pot is log? Wouldn't be better to put a linear pot on it?
(http://www.audiopeludo.com/mkportal/blog/images/778cut20hzal5.jpg)
(http://www.audiopeludo.com/mkportal/blog/images/779cut20hzal6.jpg)
(http://www.audiopeludo.com/mkportal/blog/images/780cut20hzal7.jpg)
(http://www.audiopeludo.com/mkportal/blog/images/781cut20hzal8.jpg)

The real frequencies never match with the references.
For instance, there is a cut in 20hz.
(http://www.audiopeludo.com/mkportal/blog/images/775cut20hzal5.jpg)
The cut comes until 800hz, that is a lot for a low cut, even at smooth settings.

When I did a boost in 20hz I've found a peak at 150hz.
(http://www.audiopeludo.com/mkportal/blog/images/774boost20hzal2.jpg)

Don't misundestand me... The Eq sounds great and I'm very happy with it. I'm just wondering why those results. The Highs are lower than expected, and the lows are higher than expected. If I set 10k I get 2k, if I set 20hz I get 150hz... I guess this is the Pultec style, correct me if I'm wrong.
Maybe I did something wrong in my building? I was very carefully. Some of you are getting similar results?
Cheers
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on August 10, 2013, 05:00:48 AM
ah, ok, I saw your freq response graphs and are similar to mine, so it's the natural response of the Eq and not a problem in my device.
Sorry  ;)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mylesgm on August 10, 2013, 05:37:43 AM
nice build pacorro!  I've got my pcbs set aside for a build next year, do you mid sharing the faceplate and where you got it made?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 10, 2013, 07:26:26 AM
ah, ok, I saw your freq response graphs and are similar to mine, so it's the natural response of the Eq and not a problem in my device.
Sorry  ;)

In a simple passive EQ like this one, the steepest rate of cut/boost is 6dB per octave which is the same as 20dB per decade. This means if you want 20dB of boost or cut at 10KHz then you have to start boosting/cutting close to a decade below which is why it starts at around 5KHz. The same arguments apply to the low boost cut which is why the 20Hz curt starts at around 150Hz. If you look on line you wll find curves for the original Pultec EQ and they are very similar.

Regarding the log pot for the bass cut, again this is the same as used by the Pultec. However, if you load the output of the EQ with anything less than about 470K you do get more cut at the 100% setting so the last 25% does seem rather crowded. The bass cut always flattens out eventually so it is not a true high pass filter. I think you are seeing the combination of the bass cut and the roll off already present in your circuit.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on August 10, 2013, 09:17:01 AM
do you mid sharing the faceplate and where you got it made?

Sure.
I've got it from Frank, at http://www.frontpanels.de
You can make your own design with a software called frontpanelexpress.
If you want mine, just give me an email and I'll send it to you.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on August 10, 2013, 09:46:32 AM
thanks Ian.

By the way... Do you think that my rolloff in 20hz is because the output impedance of my interface?
I'm using an Rme Multiface 2, wich is 100 ohm.
Is possible that entering to the Eq at this impedance can causes this rolloff?
Thanks for your patience
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 10, 2013, 10:15:14 AM
thanks Ian.

By the way... Do you think that my rolloff in 20hz is because the output impedance of my interface?
I'm using an Rme Multiface 2, wich is 100 ohm.
Is possible that entering to the Eq at this impedance can causes this rolloff?
Thanks for your patience

An output impedance of 100 ohms should be fine. With all the controls set to off, the EQ looks like a load of over 47K so a 100 ohms output should not have any roll off. It might be worth doing a loop  test without the EQ to check the response of the system before the EQ is added.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on August 10, 2013, 01:06:16 PM
I've found it.
The roll off is coming from the DI box.  :-[
I'm working now to add an opamp make-up.
Thanks, Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 10, 2013, 01:29:58 PM
I've found it.
The roll off is coming from the DI box.  :-[
I'm working now to add an opamp make-up.
Thanks, Ian

That's interesting. The Behringer specification says it has an incredibly flat response.

If you are going to add an op amp make up it is probably worth checking with some of the other builders on here who have already done that. I am sure they have circuits/PCBs etc you can use.

Cheers

Ian

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on August 14, 2013, 02:13:28 AM
I finished assembling my eq and it fired up with no black smoke! It passes signal and sounds clean. Dual mids and high bands boost nicely at apparent frequency settings. Low doesn't boost at all ??? NONE of the cuts seem to do anything either :( I've got something connected wrong. I will retrace the connections tomorrow and see if I can find something stupid. Ive used all Lorlin step switches.
What and where should the tube makeup gain trimmers be calibrated at?
Almost there!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 14, 2013, 04:50:17 AM
What and where should the tube makeup gain trimmers be calibrated at?
Almost there!

With the EQ in but all the controls off, adjust the VR1 pot on the tube gain make  up PCB for overall unity gain. So just feed in a 0dBu signal for example and adjust the pot for 0dBu out.

Next switch the EQ out and adjust the VR2 pot for unity gain. All this pot does is set the bypass attenuation to be the same as the EQ attenuation.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on August 14, 2013, 01:29:53 PM
Thanks Ian, that adjustment makes perfect sense.
Looking back through the thread, I think I may have connected my caps 1-6 boost values, and 7-12 cut values. I will have to confirm when I get back to my unit to look.
I tried to remember your comment on the first page, but think that since the capacitor calculations chart has boost listed first, I may have went ahead and did it with boost first. I suppose I will just need to swap the t1 to t3 and t2 to t4. I'll report back....
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 15, 2013, 08:17:20 AM
Thanks Ian, that adjustment makes perfect sense.
Looking back through the thread, I think I may have connected my caps 1-6 boost values, and 7-12 cut values. I will have to confirm when I get back to my unit to look.
I tried to remember your comment on the first page, but think that since the capacitor calculations chart has boost listed first, I may have went ahead and did it with boost first. I suppose I will just need to swap the t1 to t3 and t2 to t4. I'll report back....

It's an easy mistake to make. A few posts down from the top I posted a schematic for how to connect up the boards if you make this mistake. I have a strong suspicion that most people build it this way anyway.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on August 15, 2013, 01:55:52 PM
So... it looks like I have my cut caps installed first, on T1 and T2, and boost caps installed second, on the T3 and T4 sides. I did have my low boost pots (stepped switches) wired on the wrong side. However, I'm still not getting any of the cuts or low boosts controls working after correcting this.

I have modified and attached Dave's wiring diagram to SHOW HOW MINE IS CONNECTED. please let me know if you can see any errors.

1. I don't have the red wire (on Dave's modified drawing that is attached) from the low boost to the "G" on the mid boards. I didn't see this connection in your schematics. Is this needed? If so, after all the shuffling of the labeling of the mid boards, where should it attach to? to the screen pad ("S")?
2. I would only need 1 set of the 4k7 and 1k resistors (like in the drawing as well) for both mid connections, correct?
3. Is the 12k (in the drawing) that is between the white and yellow wire of the input transformer needed? I don't see it in any of the schematics.
4. The necessary jumper on the low boards (I still can't find this documented anywhere, except the question on post #4, pg, 1by EJ Whyte) is this supposed to be a jumper from 1 leg of r3 to 1 leg of r2?

I have ChrioN's Inductors hooked up as following:
Hi Mids 9042: Ground Clip to "S"
                      tap 0 to "ind"
                      tap 1 to "D"
                      tap 2 to "E"
                      tap 2 to "F"
                      tap 3 to "G"
                      tap 4 to "H"
Lo Mids 9047: Ground Clip to "S"
                      tap 0 to "ind"
                      tap 1 to "E"
                      tap 2 to "F"
                      tap 2 to "G"
                      tap 3 to "H"

Thanks for any insight!
                   
Edit: revised image mid board labeling and related questions
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 16, 2013, 03:59:43 PM
@Duantro,

Swa[[ing T1 theu T4 as you have done should do the trick but you will need to swap the values of R1 and R3 on this board as well. On the lo PCB you need to have shorting links in place of R1 and R2. You also need to fit R3 = 56K and a shorting link where the little vertical dotted line is at the bottom right hand corner of the PCB.

Don't forget on both PCBs to put a shorting link in place of L1.

Hope that helps.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 17, 2013, 08:57:05 AM
Then, If my low boost caps are C1-C6 I should have R3 as 56K or R1?

I'm building another one of this and my low cut pot acts strange, it reduces the overall volume and the cut goes really up, tuned to 20Hz, at max cut I have almost no sound and filtered up to 1khz, could it be related? or it's just a wiring mistake? I've checked it and looks fine, but I'll recheck it
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 17, 2013, 06:36:43 PM
Then, If my low boost caps are C1-C6 I should have R3 as 56K or R1?

It is always R3. R3 connects between the wipers of the two halves of the switch so uit does not matter which is boost and which is cut.

Quote
I'm building another one of this and my low cut pot acts strange, it reduces the overall volume and the cut goes really up, tuned to 20Hz, at max cut I have almost no sound and filtered up to 1khz, could it be related? or it's just a wiring mistake? I've checked it and looks fine, but I'll recheck it

Two possibilities. The first is that you are not feeding the EQ output into a high impedance input. Feeding into too low an impedance makes a big increase in lo cut.

If that aspect is OK then it is most likely a wiring error.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 18, 2013, 02:41:44 AM

Two possibilities. The first is that you are not feeding the EQ output into a high impedance input. Feeding into too low an impedance makes a big increase in lo cut.

If that aspect is OK then it is most likely a wiring error.

Cheers

Ian

I'm feeding the EQ out to the Tube make up gain stage, so I think it's ok, and the wiring looks fine (Actually I redid it for one channel), I should be misunderstanding something... I'll check it again, and see how it works right now (If I remember right, the low boost pot doesn't boost as expected and the low cut cuts up to 1khz and acts like a master volume)

EDIT: Cheking everything can't find nothing wrong in the wiring, and as I said, I'm using your tube gain stage, and it's output straight to xlr, maybe that's the issue? I'm not sure, because in bypass everything works fine, but maybe when I turn up the low cut pot the impedance goes up or something? I was thinking in build some simple opamp circuit for input unbalancing and output balancing, based in 5532's, but I have a 600:600 transformer at hand for trying
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 18, 2013, 06:02:45 AM
@dirtyhanfri

OK, if you are using my tube gain make up stage then the input impedance should be OK. Just to be sure can you measure VR1 to make sure it is 470K and also that the 1Meg resistor from its wiper to ground is 1Meg. Does the lo boost work OK?

Note: this is a simple passive EQ with a slope of 20dB per decade. So to get 20dB cut at 20Hz you have to start cutting at around 200Hz. In fact, on the 20Hz setting, the response is about 3dB down at 200Hz. Check out the curves I measured here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/LFresponse.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/LFresponse.pdf)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 18, 2013, 06:55:59 AM
Yes, I understand the slopes, but the cuts seems to be much wider than expected, the -3db point is around 1200Hz when tuned to 20Hz, it doesn't look fine, actually I was looking your response curves for reference.

Also, boost is not working properly, it doesn't give me more than 3 or 6 dbs.

I reworked the grounding, just forgot to route the pin 1 of xlr's to star ground, now it's done, all the rest remains the same, and now, the low cut pot acts as a master fader, no cut, just lows the volume of the whole signal.

My components looks fine, actually VR1 it's adjusted to it's minium, and anyway I can't get the same level with the eq in than in bypass.

I have jumpers for R1 & R2 in the lo board, R3 is 56K, The inductor and the little dotted line under R3 are jumpered, In Hi boards, I have R1 & R2 with their correct values, no jumper in R3, no jumper in dotted line and L1 jumpered. The wiring scheme, as far as I know looks fine, cap values are ok, the pots value also are ok

My ground (and general wiring) is according to dave's wiring diagram omitting the transformers, but I can't get it working propperly

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on August 18, 2013, 01:18:05 PM
@Duantro,

Swa[[ing T1 theu T4 as you have done should do the trick but you will need to swap the values of R1 and R3 on this board as well. On the lo PCB you need to have shorting links in place of R1 and R2. You also need to fit R3 = 56K and a shorting link where the little vertical dotted line is at the bottom right hand corner of the PCB.

Don't forget on both PCBs to put a shorting link in place of L1.

Hope that helps.

Cheers
Ian

I should clarify, I didn't actually swap T1 thru T4 on the boards, just swapped the wires coming off of T1-T4 to go to the correct cut boost pot switches. Thus I'm assuming that I don't need to swap any of the r1,r2, etc.
I didn't have the dotted line jumpered, but still have the same problem ( no Low boost and none of the cuts, except lows work) after applying this jumper.
I have all L1's, and r1 and r2 on the low boards jumpered.
I also have connect the red wire in question, in my updated Dave's drawing, that goes from the Low boost to the ground clips of the inductors of the mid boards and see if that would fix anything, but it didn't solve my problem.
Thanks for the help.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 18, 2013, 04:35:03 PM
There is clearly something basically wrong here. I would suggest simplifying first. Disconnect the two mid EQ boards by disconnecting the wires from the point labelled 'pot' on each mid board. Then check if the hi and lo EQ works ok or not on its own.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on August 19, 2013, 02:38:43 AM
There is clearly something basically wrong here. I would suggest simplifying first. Disconnect the two mid EQ boards by disconnecting the wires from the point labelled 'pot' on each mid board. Then check if the hi and lo EQ works ok or not on its own.

Cheers

Ian
I tried disconnecting the mid boards as you described, and it still is malfunctioning in the same manner. I've triple checked my wiring to my updated Daves dual mid guide, and everything is as listed. I am using stepped Lorlin switches instead of pots. Man this thing is kicking my butt! I will try again tomorrow.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 19, 2013, 05:56:24 AM
I tried disconnecting the mid boards as you described, and it still is malfunctioning in the same manner. I've triple checked my wiring to my updated Daves dual mid guide, and everything is as listed. I am using stepped Lorlin switches instead of pots. Man this thing is kicking my butt! I will try again tomorrow.

OK, keeping the mid disconnected, set all the controls to off. Feed a 0dBu signal in, and with the VR1 fully clockwise, measure the output level, Let me know the result.

Can you post the schematics of your switched pots?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on August 19, 2013, 12:08:12 PM
I tried disconnecting the mid boards as you described, and it still is malfunctioning in the same manner. I've triple checked my wiring to my updated Daves dual mid guide, and everything is as listed. I am using stepped Lorlin switches instead of pots. Man this thing is kicking my butt! I will try again tomorrow.

OK, keeping the mid disconnected, set all the controls to off. Feed a 0dBu signal in, and with the VR1 fully clockwise, measure the output level, Let me know the result.

Can you post the schematics of your switched pots?

Cheers
Ian

I will try to check signal voltage tonight. Here is an updated modified dave's wiring diagram, again, AS MINE IS HOOKED UP, with direction, resistance, and type of stepped switches labeled.

Edit: corrected typo on high cuts to 4k7
Edit: corrected labeling of high board connections on v1.3
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 19, 2013, 12:48:05 PM
Hi cut should be 4.7K lin not 47K.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mikeyB on August 19, 2013, 08:35:25 PM
Hi Ian,
You may have seen some of the other pultecs on this forum that have the lo band frequency select switches seperated.
I am thinking of trying this to enable more (12)frequencies for both boost and cut.
i understand that the cut frequencies are an octave above the boost frequencies and this spacing is maintained with the standard 2x6 way switching.
Would i encounter any loading problems if i seperate the switches.
I'm guessing that if the 2 actual frequencies get close to one another, they will just cancel out.
Would there be any loading problems when they are far apart (eg boost set at 30Hz and cut set at 200Hz(400Hz actually))?
I would incorporate this arrangement for the hi end also.

Once again - thanks for this great project :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on August 19, 2013, 11:55:17 PM
Hi cut should be 4.7K lin not 47K.

Cheers

Ian
My high cuts are 4k7 Lin. My mistake, it was a typo from being in a hurry. I have corrected previous image to version 1.3.
 When fed a 0dbu (0.755V) 1khz signal, measured at the input xlr jack at pin 2 and 3, the results are about 240mV on output xlr jacks. This is done with vr1 fully clockwise.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 20, 2013, 06:03:15 AM
My high cuts are 4k7 Lin. My mistake, it was a typo from being in a hurry. I have corrected previous image to version 1.2.
 When fed a 0dbu (0.755V) 1khz signal, measured at the input xlr jack at pin 2 and 3, the results are about 240mV on output xlr jacks. This is done with vr1 fully clockwise.

The EQ has a nominal loss of 20dB and the tube gain make up has a gain of close to 26dB so with all the EQ controls off and VR1 fully clockwise you should measure a gain of about 6dB which means the output should have been  about 1.5V. The fact you get only 240mV means there is an additional loss of about 14dB somewhere.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 20, 2013, 06:30:19 AM
Hi Ian,
You may have seen some of the other pultecs on this forum that have the lo band frequency select switches seperated.
I am thinking of trying this to enable more (12)frequencies for both boost and cut.
i understand that the cut frequencies are an octave above the boost frequencies and this spacing is maintained with the standard 2x6 way switching.
Would i encounter any loading problems if i seperate the switches.
I'm guessing that if the 2 actual frequencies get close to one another, they will just cancel out.
Would there be any loading problems when they are far apart (eg boost set at 30Hz and cut set at 200Hz(400Hz actually))?
I would incorporate this arrangement for the hi end also.

Once again - thanks for this great project :)

There should be no loading problems when using this technique for the lo boost/cut because in both cases the boost is achieved by increasing an impedance so loading is if anything reduced. However, the interaction of the lo boost and cut is modified by the 56K resistor. With no lo boost, this resistor is connected to ground (by the boost pot) and, in conjunction with the 470K pot, determines the amount of lo cut that can be achieved. As the lo boost is increased, this 56K becomes increasingly disconnected from ground and more connected across the 570L low cut pot. This has the effect of changing both reducing the amount of cut and the frequency at which it occurs. The result is the well known Pultec 'bump' where you get an initial cut of about 6dB then as the frequency reduces further this cut is replace by a boost at a lower frequency. The turnover frequencies being an octave apart are also instrumental in achieving the bump. So, if you separate the lo boost and cut frequencies you will alter this interaction so, even if the two frequencies are the same, they may not cancel out. If you remove the 56K resistor then the lo boost and cut are independent and should act as you would expect.

The hi boost and cut work by reducing impedance so when you apply both, the loading on the input transformer increases. This is mitigated a bit by the frequencies being an octave apart in the original design. If you make them identical then maximum loading will occur at the highest frequencies. The loading is limited by the 4K7 and 470 ohm series resistors connected to the wipers of these pots. In the worst case the loading should be no less than 5K which is simply reflected by the input transformer to the input of the EQ. As long as your source is happy driving 5K it should not be a problem.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 24, 2013, 03:49:57 AM
Mine is working nicely.

The issue was VR1, was 4k7 instead 470k. Now it works as expected. I've been making sweep tests and he curves looks juat similar to the ones in your graphics.

Also noise is so low, -103dbfs in one channel, didn't measured the other
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 24, 2013, 07:44:43 AM
Mine is working nicely.

The issue was VR1, was 4k7 instead 470k. Now it works as expected. I've been making sweep tests and he curves looks just similar to the ones in your graphics.

Also noise is so low, -103dbfs in one channel, didn't measured the other

Is that noise measurement using my tube gain make up stage?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 24, 2013, 08:29:56 AM
Yes, @100 Hz. But measured with the input and output connected to the converters using voxengo Span. It was quieter @50 Hz. Maybe it's not the most accurate measurement.

I forgot to say Thanks again for this great project Ian.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mus1k_freak on August 25, 2013, 12:07:09 PM
Heres my work in progress a poor mans pultec....pedal  8)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on August 26, 2013, 02:13:51 AM
My high cuts are 4k7 Lin. My mistake, it was a typo from being in a hurry. I have corrected previous image to version 1.2.
 When fed a 0dbu (0.755V) 1khz signal, measured at the input xlr jack at pin 2 and 3, the results are about 240mV on output xlr jacks. This is done with vr1 fully clockwise.

The EQ has a nominal loss of 20dB and the tube gain make up has a gain of close to 26dB so with all the EQ controls off and VR1 fully clockwise you should measure a gain of about 6dB which means the output should have been  about 1.5V. The fact you get only 240mV means there is an additional loss of about 14dB somewhere.

Cheers

Ian

I have found that I have missed the brown wire , on the hook up guide, that connects the High cut ccw and Low boost cw pins. After connecting it I'm getting around .650V on output. I'm not quite up to the correct output level here, and my Low boost and the rest of the cuts still don't work. It's got to be something on my Low boost or High cut boards or connections that are incorrect. I've been tracing the .755V thru the circuit and can't decipher where the signal should show up on these sections (Low boost and High cuts). any suggestions as to where I could check for this?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 26, 2013, 07:03:17 AM
Here is my finished unit, It needs the front pannel, but I'm deciding on what to do, I'd like to engrave it

(http://imageshack.us/a/img208/3549/jbuc.jpg)

(http://imageshack.us/a/img849/9577/i511.jpg)

(http://imageshack.us/a/img189/2719/88rz.jpg)

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on August 26, 2013, 12:38:06 PM
I'm assuming that this switch diagram is the current one? I found it in the drawing board thread.
I'm getting signal to the High boost side (T1 and T2 side), but nothing on the High cut side (T3 and T4).
Where should the signal be arriving to the High cut side from the High boost side?
I have R1 as 4k7, R2 as 430r, nothing on R3, L1 jumpered, and no dotted line jumper.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: wave on August 26, 2013, 01:59:08 PM
Here is my finished unit, It needs the front pannel, but I'm deciding on what to do, I'd like to engrave it

Looks great Hanfri! Hey did you etch your PSU PCB from the file that I drew up? How is it working for you? Can you post a complete shot of it?

Thanks!
Dave
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on August 26, 2013, 05:42:28 PM
Looks great Hanfri! Hey did you etch your PSU PCB from the file that I drew up? How is it working for you? Can you post a complete shot of it?

Thanks!
Dave

Yes, I use your layout, thanks!

I'll take some closer pics tomorrow.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: adeptusmajor on August 26, 2013, 07:07:22 PM
Heres my work in progress a poor mans pultec....pedal  8)

That's awesome, but I would probably stomp that tube into oblivion before I got halfway through a set in a dark club.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 27, 2013, 11:57:19 AM
I'm assuming that this switch diagram is the current one? I found it in the drawing board thread.
I'm getting signal to the High boost side (T1 and T2 side), but nothing on the High cut side (T3 and T4).
Where should the signal be arriving to the High cut side from the High boost side?
I have R1 as 4k7, R2 as 430r, nothing on R3, L1 jumpered, and no dotted line jumper.

This is the diagram that shows how the hi and lo boards are wired together:

(http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/hookupsm.jpg)

As you can see the input signal goes to T1 on the hi PCB (boost) and to the hi boost pot. This pot forms a pot divider with the low cut pot so the signal at the junction if the hi boost and hi cut pots should be about 20dB down at high frequencies because one is a 47K pot and the other is a 4K7 pot. The low boost pot and the lo boost caps are also in series with the lo cut pot BUT at high frequencies these caps are short circuits so the low boost pot does not affect the high frequencies.

As you turn up the hi boost, the caps between T1 and T2 start to short out the hi boost pot so the attenuation is reduced. At very high frequencies the caps are a short circuit so the 47K pot has the 4K7 R1 in parallel with it. This with the 4K7 of the hi cut leads to a 6dB loss instead of the nominal 20dB so this gives a 14dB boost. As you turn up the hi cut, the caps between T3 and T4 start to short out the hi cut pot thus increasing the attenuation. At very high frequencies these caps are short circuits so the 4Ky hi cut pot now as the 470R R2 in parallel with it so the total attenuation is nearly 40dB making a cut of 20dB relative to the nominal 20dB loss. If you turn the lo boost and cut pots fully anti clockwise you should be able to see the above effects happening.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on September 01, 2013, 09:58:18 AM
Hi Guys,  I'm starting to acquire parts to build a couple of these, so now might be as good a time as any to start with the noob questions.  Apologies if these have been covered already and I missed it in my reading.

1)  The BOM lists R1 as being a fixed resistor with a linear taper.   Is this a typo or an animal I'm not familiar with?

2)  My tube makeup PCBs are in the mail right now, but I'd like to get the tube sockets ordered ahead of time.  Will any 9-pin miniature PC mount socket fit?

Thanks in advance for any help.

John

EDIT:  Never mind on both counts.  Found the answers earlier in the thread.

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 02, 2013, 04:00:16 PM
Thanks for the description Ian. I've sent .775V 1k signal in, that measures .680V at bypass switch and on CCW of High boost pot/switch. At CW pin of High boost switch (the divider between the High boost and cut that should be -20db lower) my signal is 26mv. Am I correct that this isn't what I should be seeing? I apologize, I'm a horrible trouble shooter.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 02, 2013, 04:39:14 PM
Thanks for the description Ian. I've sent .775V 1k signal in, that measures .680V at bypass switch and on CCW of High boost pot/switch. At CW pin of High boost switch (the divider between the High boost and cut that should be -20db lower) my signal is 26mv. Am I correct that this isn't what I should be seeing? I apologize, I'm a horrible trouble shooter.

You are correct, that is not the right level. You should see something in the region of 75mV at that point but make sure you have the high cut turned fully off as well. I suspect there is something funny happening with you extra mid sections which are also connected between this point and ground. I would advise disconnecting the mid completely and just concentrate initially on the hi and lo boost/cut. Get that working first and then add in the mid circuits one at a time. it's a bit laborious but it is the only sure where to eliminate things.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 02, 2013, 05:42:05 PM
Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 03, 2013, 05:50:38 AM
Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.

OK then you need to trace and  check the circuit you have in detail. Try disconnecting the gain make up and the EQ bypass circuit and measure again. Something somewhere is pulling down that signal.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on September 04, 2013, 11:46:57 AM
Am I correct in assuming that the DPDT switch for the EQ bypass switch should be ON-ON, not ON-OFF-ON?  Sorry if this has been covered.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 04, 2013, 04:33:56 PM
Am I correct in assuming that the DPDT switch for the EQ bypass switch should be ON-ON, not ON-OFF-ON?  Sorry if this has been covered.

That is correct. Also, if you are using the mid section add on, the SPDT switch to select mid boost/off/cut should be an 0n-off-0n type.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on September 05, 2013, 11:10:30 AM
Thank you!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on September 08, 2013, 05:36:59 AM
Ian... I need to know the input impedance of the Poor man's Pultec for calculating one cap in the unbalancing stage. Can you tell me what impedance is at the input of the circuit?
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on September 08, 2013, 11:18:58 AM
I measured the impedance in my unit.
Input impedance is over 50k in both channels. Output impedance is also over 50k, though I expected over 10k as you told me, Ian.
Is this normal?  ???
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 08, 2013, 03:39:20 PM
I measured the impedance in my unit.
Input impedance is over 50k in both channels. Output impedance is also over 50k, though I expected over 10k as you told me, Ian.
Is this normal?  ???

How did younmeasure the input and output impedance?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on September 08, 2013, 03:51:51 PM
With a multimeter, red on hot at T2 and black at the ground in pin 3 for the input.
At the output with red on xlr pin 2 and black on ground at xlr pin 3.
One channel is 49,4 k input and 51,6 k output. The other is similar, 50k input and 51k output.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kante1603 on September 08, 2013, 04:04:43 PM
That is dcr,not the impedance.

Udo ;)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on September 08, 2013, 04:39:14 PM
Sorry, but... What is dcr?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kante1603 on September 08, 2013, 04:43:51 PM
Sorry, but... What is dcr?
DCR=Direct Current Resistance.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: pacorro on September 08, 2013, 04:46:24 PM
Thanks. How can I measure the input impedance in my device?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 09, 2013, 04:51:51 AM
With a multimeter, red on hot at T2 and black at the ground in pin 3 for the input.
At the output with red on xlr pin 2 and black on ground at xlr pin 3.
One channel is 49,4 k input and 51,6 k output. The other is similar, 50k input and 51k output.

I am confused about the putput XLR - is this directly out of the EQ or after a gain make up amp? What positions were the pots when you made this measurement?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 13, 2013, 12:44:21 PM
Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.

OK then you need to trace and  check the circuit you have in detail. Try disconnecting the gain make up and the EQ bypass circuit and measure again. Something somewhere is pulling down that signal.

Cheers

Ian

Upon disconnecting the output amp at the center pin of the bypass switch, I go from 12v to 58v, at this connection.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 13, 2013, 04:45:55 PM
Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.

OK then you need to trace and  check the circuit you have in detail. Try disconnecting the gain make up and the EQ bypass circuit and measure again. Something somewhere is pulling down that signal.

Cheers

Ian

Upon disconnecting the output amp at the center pin of the bypass switch, I go from 12v to 58v, at this connection.

Is that dc volts or signal?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 13, 2013, 04:53:51 PM
Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.

OK then you need to trace and  check the circuit you have in detail. Try disconnecting the gain make up and the EQ bypass circuit and measure again. Something somewhere is pulling down that signal.

Cheers

Ian

Upon disconnecting the output amp at the center pin of the bypass switch, I go from 12v to 58v, at this connection.

Is that dc volts or signal?

Cheers

Ian

AC signal from 775mv input signal generator
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 13, 2013, 06:28:32 PM
Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.

OK then you need to trace and  check the circuit you have in detail. Try disconnecting the gain make up and the EQ bypass circuit and measure again. Something somewhere is pulling down that signal.

Cheers

Ian

Upon disconnecting the output amp at the center pin of the bypass switch, I go from 12v to 58v, at this connection.

Is that dc volts or signal?

Cheers

Ian

AC signal from 775mv input signal generator

I don't understand this. With less than one volt input and no gain make up amp, how can you get a gibber output than the input. Or did you mean 'goes from 12mV to 58mV which would be about right.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 13, 2013, 07:18:41 PM
Sorry Ian. Yes I meant 12mv when output is connected and 58mv when disconnected.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 14, 2013, 05:50:38 AM
Sorry Ian. Yes I meant 12mv when output is connected and 58mv when disconnected.

OK, 58mV is close to what I would expect. So it seems something in your gain make up amp is pulling down the output.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 17, 2013, 01:12:34 AM
Sorry Ian. Yes I meant 12mv when output is connected and 58mv when disconnected.

OK, 58mV is close to what I would expect. So it seems something in your gain make up amp is pulling down the output.

Cheers

Ian


YEEEES! I found it! It was VR1 and VR2 were in the opposite spots. I started thinking when reading Dirtyhanfri's comment about the low cut being really wide bandwidth and like a volume control. Thanks for all of your help Ian. I thought for sure I botched the switch hookups and never thought of the simple makeup gain boards. I'l post pictures after I get it all buttoned up in a few days.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 17, 2013, 04:59:48 AM
YEEEES! I found it! It was VR1 and VR2 were in the opposite spots.

Wooohoooo!

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 17, 2013, 02:55:58 PM
I took it to the studio and it sounds great! Mid cuts are subtle as noted in the thread previously.
So glad I finally finished this thing. I had many hurdles to jump, all due to lack of knowledge on my part. However, I am learning so much! Thanks again Ian!

Hurdle #1- I used my FPexpress file from my PM670 as a template to start. Unfortunately the enclosure had different width spacing for front panel mounting, i.e. die grinder to elongate mounting holes. This really bummed me out, since Don-Audio did a killer job on the front panel!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 17, 2013, 03:02:08 PM
Here's a blurry guts shot.
Hurdle#2- When I made my fpexpress file I had the frequency pcb's 1/8" too close to the bottom of the case. So I had to flip some switch pcb's on their side and extend the others to fit. It was real tricky, even with a hakko 808, to desolder the switches that I needed to extend. This was also real fun while trouble shooting... Ha!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mikeyB on September 18, 2013, 09:10:53 PM
I took it to the studio and it sounds great! Mid cuts are subtle as noted in the thread previously.
So glad I finally finished this thing. I had many hurdles to jump, all due to lack of knowledge on my part. However, I am learning so much! Thanks again Ian!

Hurdle #1- I used my FPexpress file from my PM670 as a template to start. Unfortunately the enclosure had different width spacing for front panel mounting, i.e. die grinder to elongate mounting holes. This really bummed me out, since Don-Audio did a killer job on the front panel!

Hi Duantro - what is the function of the "SHIFT 1/2" switch?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 18, 2013, 09:32:29 PM
I took it to the studio and it sounds great! Mid cuts are subtle as noted in the thread previously.
So glad I finally finished this thing. I had many hurdles to jump, all due to lack of knowledge on my part. However, I am learning so much! Thanks again Ian!

Hurdle #1- I used my FPexpress file from my PM670 as a template to start. Unfortunately the enclosure had different width spacing for front panel mounting, i.e. die grinder to elongate mounting holes. This really bummed me out, since Don-Audio did a killer job on the front panel!

Hi Duantro - what is the function of the "SHIFT 1/2" switch?
It's the mod that Surfkat suggested back 10 pages or so. Adds a cap to shift the frequency of low cut and high boost. Seems to widen the cue some, when cutting and boosting. 
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mikeyB on September 19, 2013, 09:23:45 AM
Thanks - i'll read through it. :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on September 19, 2013, 04:35:48 PM
I know this has been discussed a lot, but I just want to double check.  Thanks for your patience.

I'm wiring up my pots (getting close - very exciting) and I wonder if someone can just verify for me that I'm making a correct translation from Dave's wiring diagram of normal boost/cut pots to my 12-position Lorlin stepped pots.  By my measurement, I think that pin 12 should be in the place of the right lug (looking from the rear), pin 1 should be in place of the left lug, and the center pin of the switch should go in place of the center lug of the normal pot.

For reference, turning the switch all the way ccw gives me the max resistance between pin 12 and the center pin of the switch.  Hope that's right or I've got a LOT of soldering to undo.  :)

Thanks in advance for any help.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 19, 2013, 10:57:16 PM
I know this has been discussed a lot, but I just want to double check.  Thanks for your patience.

I'm wiring up my pots (getting close - very exciting) and I wonder if someone can just verify for me that I'm making a correct translation from Dave's wiring diagram of normal boost/cut pots to my 12-position Lorlin stepped pots.  By my measurement, I think that pin 12 should be in the place of the right lug (looking from the rear), pin 1 should be in place of the left lug, and the center pin of the switch should go in place of the center lug of the normal pot.

For reference, turning the switch all the way ccw gives me the max resistance between pin 12 and the center pin of the switch.  Hope that's right or I've got a LOT of soldering to undo.  :)

Thanks in advance for any help.
Hey JohnWatkins,
I believe I have my Lorlin's wired up as CCW = 0r, and connected as the left lug of the pot, in the image (from the rear), of Dave's diagram. Conversely, CW = max resistance and connected as the right lug of the pot in Dave's diagram.
Hope this helps.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 19, 2013, 11:01:18 PM
Gentlemen,
I have created a diagram for my stepped switches (I need these visual aids) and I'm wondering if you can give it a look and make sure that I'm going to do this right.
The switch is viewed from the front (shaft) side and I have labeled the connections as Pin 1 Anti CW...etc.

(http://farm8.staticflickr.com/7278/7565169540_3e334d7495.jpg) (http://www.flickr.com/photos/wavedealer/7565169540/)

So if looking at my diagram, if I were using this switch as the Hi Boost Lin pot (switch) then Pin1 would be connected to T1 of the High PCB.
Pin 2 would be connected to T2 of the High PCB. Pin 3 would be connected to Pin3 of the Hi Cut switch, correct?

Conversely, if this were the Lo Boost Log pot (switch), Pin 1 would be connected to T1 of the Lo PCB while Pin 2 would be jumpered to Pin 3 and Pin 3 would be connected to T2 of the Lo PCB as well as Pin 1 of the Hi Cut pot (switch).

Does this sound right? Basically I'm trying to make sure I'm connecting the wires correctly to the switch (pot).

Thanks
Dave
JohnWatkins-I used this as a reference post #308
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 20, 2013, 06:12:49 AM
I took it to the studio and it sounds great! Mid cuts are subtle as noted in the thread previously.
So glad I finally finished this thing. I had many hurdles to jump, all due to lack of knowledge on my part. However, I am learning so much! Thanks again Ian!

I am really pleased we finally got that sorted out. At least it turned out to be something simple in the end.

Do you think you could email me some pictures to add to my projects gallery?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on September 20, 2013, 09:21:40 AM
Thanks Duantro.  I'm pretty confident now that I'm thinking of it correctly.  Time will tell, right? 
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 20, 2013, 07:28:50 PM
Ian- Photo's are headed your way! Thanks for helping me thru this stupid mistake. It truly sounds great and so smooth! I'm getting a small buzz from the right channel. I think it may be from the AC power switch being so close to the High frequency pcb and wiring. I may have to make a tube shield like forum member Kingston has done with his (p)m670.

JohnWatkins- look over these diagrams again. It sounds like you may have the Lorlin's resistors strung around the wrong way. In the switch diagram, from post #308, when flipped horizontally and viewed from the back, pin 1(on the right bottom) to center wiper pin should = 0 r. Daves switch diagram that I posted above, from post #308, is pictured as viewed from the front.
IF you are using Dave's hookup diagram, then 0r is on the left lug of pots.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on September 21, 2013, 07:13:21 AM
Duantro, thanks for double-checking.  I think we're maybe talking about the same thing only viewed a different way.  You're saying pin 1 should go to the left lug on the diagram and I'm saying pin 12 should go to the right.  Same thing, no? 

Unless I'm thinking of it incorrectly, the pins on the switch that represent minimum and maximum resistance are determined by the construction of the switch and the resistors can only be wired to it in one way (for a linear pot).

Am I confused?  Ian?  Dave?   
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on September 21, 2013, 07:39:15 AM
I measured a regular pot and all of the resistance is on the right (viewed from the rear) when fully ccw.   When measuring the stepped switch, all the resistance is at pin 12 when fully ccw.   That's how I came up with my earlier determination.  Please let me know if I'm wrong.  Thanks.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 21, 2013, 11:37:22 AM
I measured a regular pot and all of the resistance is on the right (viewed from the rear) when fully ccw.   When measuring the stepped switch, all the resistance is at pin 12 when fully ccw.   That's how I came up with my earlier determination.  Please let me know if I'm wrong.  Thanks.
Ok yes you are correct. In daves hookup drawing, 0r is on the left lug of pot. I was referring to the switch diagram, if it was flipped horrizontally, and viewed from the back, when i said on the right. This is what confused me on many things- too many different diagrams that aren't viewed the same way or are for different wiring.
So you should be good, and sorry for the confusion!
I edited my previous post, so it clarifies which diagram I was referring to, in hopes to clear up any further confusion here.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 27, 2013, 04:32:00 AM
@Duantro,

I got the pictures OK this time. Looking good.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on September 27, 2013, 05:59:20 AM
Hi,

Can i use 50K,5K,500K instead of 47K,4.7K,470K?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on September 27, 2013, 09:58:30 AM
Thanks Ian!

Forthmonkey- short answer is yes. Read post #17 on the first page.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on September 30, 2013, 07:47:05 AM
I've just paid. ;D

But i have questions.

What will happen if i use all pots linear? Cause there is no log pot in here. I know i will get different values with linear pots.Is there anyone use all pots linear?

Or can convert like this?

(http://www.learnabout-electronics.org/images/lin_to_log_pot.gif)

Thanks.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 30, 2013, 01:34:24 PM
If you use a linear pot instead of a log pot then the response is likely to be cramped towards one end of the scale. The law of the pots in an EQ is a compromise anyway because you do not want an exactly log or exactly linear response. Slugging a linear pot with a resistor does not work in an EQ because it makes the maximum value wrong. If I were you I would just try linear pots throughout and see what you get.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on September 30, 2013, 01:46:57 PM
If you use a linear pot instead of a log pot then the response is likely to be cramped towards one end of the scale. The law of the pots in an EQ is a compromise anyway because you do not want an exactly log or exactly linear response. Slugging a linear pot with a resistor does not work in an EQ because it makes the maximum value wrong. If I were you I would just try linear pots throughout and see what you get.

Cheers

Ian

Thanks Ian.

I will try with breadboard when i wait pcbs.

EDIT

I tried with linear pot.Now i'm looking for log-pot. >:(
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 07, 2013, 05:06:59 PM
Ok, I've finally got mine put together and fired up.  Let the troubleshooting begin!  :)   The good news is that all four (I built 2 stereo units) have the exact same behavior, so I'm pretty sure I misread some diagrams or something.

The symptoms are a) no signal in eq bypass mode, and b) no mid control at all.

I've got some suspicions about where I went wrong, so maybe someone can answer a couple of questions for me.  Thanks in advance for any help.

1)  Should the shield on the Pout cable (connected to "PG") be connected to ground, or cut and left unconnected at the switch end?  I did the latter.  If that's correct, then why else might I have zero signal in bypass mode?

2)  I've got pin "G" on the mid board going to both the low boost pot and pin 5 of Chrion's inductor.  I've also got the middle terminal of the mid boost/cut switch going to "screen" on the mid board, which as far as I can tell only connects to the metal brackets on the inductor.  Is this possibly because Dave's mid board hookup diagram was intended to be used for Carnhill inductors in conjunction with Ian's fix pdf?  If I've got it wrong, where should wires be connected?

Thanks guys.  Almost there.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 07, 2013, 05:41:51 PM
Hi John,

Pout cable screen should be left unconnected at the switch end. have you fitted the pad components on the PMTGMU PCB? If you have where is the setting of the 1K lin preset pot?

I think you are right about Dave's hook up diagram. If you are using CHrion inductors the 'screen'  pin on the PCB goes to 0V (which is the left hand tag of the low boost pot looking from behind), the 'pot' pin goes to the pot and the 'Ind' pin goes to the boost/off/cut switch.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 07, 2013, 06:10:46 PM

have you fitted the pad components on the PMTGMU PCB? If you have where is the setting of the 1K lin preset pot?

That was the first thing I thought of, but alas, it's at its mid-point.  Rotating it to its full extent in both directions had no effect.

Quote

I think you are right about Dave's hook up diagram. If you are using CHrion inductors the 'screen'  pin on the PCB goes to 0V (which is the left hand tag of the low boost pot looking from behind), the 'pot' pin goes to the pot and the 'Ind' pin goes to the boost/off/cut switch.


Thanks.  I'll make the changes and report back.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 08, 2013, 04:30:49 PM
Ok, the mid is fixed and sounds great!  Thanks for the tips, Ian.  Still not getting anything in bypass mode and everything seems to be hooked up according to the schematic. 

I've also noticed now that low boost does not work, but low cut is really pronounced.  I'll noodle around with that and make sure I didn't overlook something.

Once I get everything functioning, I'll hook it up to some sort of analyzer software and see what kind of curves I'm getting, make sure I don't have any dead positions on the stepped attenuators.  I assume there is a software that is every DIYers favorite for that sort of thing?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 08, 2013, 05:16:23 PM
Spoke too soon.  Mid "boost" works great.  I've got no response on Mid "cut".   :-[
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on October 08, 2013, 06:26:06 PM
Spoke too soon.  Mid "boost" works great.  I've got no response on Mid "cut".   :-[
Sounds like the same problem I was having with the trimmers in the wrong spots. Double check you trimmer placements.

Edit: I'd double check your wiring on your bypass switch as well.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 09, 2013, 06:26:49 AM
Ok, the mid is fixed and sounds great!  Thanks for the tips, Ian.  Still not getting anything in bypass mode and everything seems to be hooked up according to the schematic. 

I've also noticed now that low boost does not work, but low cut is really pronounced.  I'll noodle around with that and make sure I didn't overlook something.

Pronounced low cut and no mid cut is symptomatic of loading the EQ output with too low an impedance - maybe you have the wrong value for the 470K preset on the PMTGMU?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 09, 2013, 08:53:17 AM
Thanks, guys.  I've double-checked all of the wiring against Dave's diagram and the schematic and it seems correct.  I'll check the pots on the tube makeup.  I don't suppose I can measure the values without pulling them, can I?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 09, 2013, 03:31:35 PM
Yep, sure enough;  VR1 and VR2 are in each other's spots.  I think I must have glanced at the part list and assumed that the first one was VR1, when in fact VR2 is listed first.  That'll teach me to be in a hurry.   Re-working them all now.  Hopefully this fixes everything.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: erikb1971 on October 09, 2013, 03:34:26 PM
we all have been there... most of us more than once!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on October 09, 2013, 04:04:19 PM
Yes, that's what I did. I was so confused on the inductors and switches I didn't think to look at these trimmers. Glad you found it.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 09, 2013, 05:10:37 PM
Still having some issues and now going back to square one to understand the theory.  Asking "where do I put this wire" isn't helping me learn or get this thing working.

Please bear with me, as this is all new to me;

As I (barely) understand it, on the mid pcb, "inductor" is meant to be the input to the pin 0 of the inductor from either the bass boost or treble boost pot depending on the switch position.  Then the inductor feeds varying levels of inductance and subsequently varying levels of capacitance through the switch depending on it's position to the "pot" terminal which is meant to go to the center of the mid boost/cut potentiometer?  That then feeds the side of the treble boost pot opposite the side that fed the mid boost switch?

What is the 'screen' terminal's job.  Anything other than just a literal screen for hum cancelling?

Thanks for your help and patience.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 10, 2013, 05:46:19 AM
@John

The EQ is basically a pot divider consisting of the treble boost pot (47K) and the treble cut pot (4K7) giving a nominal 20dB loss. (Ignore the bas boost pot for now and assume it is off i.e. short circuited. Boost is achieved by frequency selectively shorting out the treble boost pot. For the mid boost that is done by connecting the pot L, C and and R in series across it.

Cut is achieved by frequency selectively shorting out the treble pot. Changing the mid switch does this by connecting one end of the RLC to ground.  Hopefully this is clear if you look at this schematic.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/PMEQMIDv1.1.png (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/PMEQMIDv1.1.png)

The 'screen' connection is there to allow the metal clasp that holds the inductor together to be connected to 0V.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 10, 2013, 09:05:07 AM
So with the treble boost pot fully counter-clockwise (off) the resistance is equal across all frequencies, but the makeup amp is providing gain equal to that resistance, so nothing happens, and when you turn it up you're providing a path of less/least resistance for the signal at whatever frequency the switch is set to?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 10, 2013, 11:16:18 AM
So with the treble boost pot fully counter-clockwise (off) the resistance is equal across all frequencies, but the makeup amp is providing gain equal to that resistance, so nothing happens, and when you turn it up you're providing a path of less/least resistance for the signal at whatever frequency the switch is set to?

Exactly. All passive EQ works in the same way; some of them are just drawn so badly it is impossible to see it but the bottom line is you can redraw them all to look like this.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 10, 2013, 11:47:20 AM
Ok.  Thanks so much for the help.  Sorry I'm having to be spoon-fed.  :)   
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 11, 2013, 09:54:58 AM
Eureka!  Several bone-headed mistakes fixed, and I now have bass boost.  The only problem that now remains is with the mids.  I have no cut control.  Everything else works perfectly at this point.  Any ideas as to what would cause the boost to function, but not the cut?  Thanks again.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 11, 2013, 10:40:24 AM
Ian, looking at the midbottomchrion.jpg, I assume that the pointer for pin 5 should actually go to the terminal just to the right since it's currently pointing to one of the switch terminals?  That's the only thing I can find that I did differently.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 11, 2013, 11:12:36 AM
The saga continues;  I realized that I had connected the 'screen' to the right-hand lug of the bass boost pot instead of the 0v, left lug.  However, after moving it, I have no mid boost or cut at all.  Honestly, I don't get how it can have so much impact on the circuit when it's only connected to the metal clips on the side of the inductor.  Clearly, I'm still not understanding something.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on October 11, 2013, 01:25:25 PM

I have ChrioN's Inductors hooked up as following:
Hi Mids 9042: Ground Clip to "S"
                      tap 0 to "ind"
                      tap 1 to "D"
                      tap 2 to "E"
                      tap 2 to "F"
                      tap 3 to "G"
                      tap 4 to "H"
Lo Mids 9047: Ground Clip to "S"
                      tap 0 to "ind"
                      tap 1 to "E"
                      tap 2 to "F"
                      tap 2 to "G"
                      tap 3 to "H"


Hey JohnWatkins there are a lot of confusing elements to decipher in this.
This quote is from my earlier post as to how I hooked up Chrion's inductors.

First- I'd double check how you have your Cut and Boost caps (on high and low boards) arranged on the pcb's-i.e: cut caps first and boost caps second, or vice versa. Then confirm that you are using the correct wiring diagram. Between this and the opposite direction of Chrion's inductor wiring pattern, I nearly had to put earplugs in to keep my brain from leaking out of my head!

Second- go over wiring and confirm everything else is connected correctly. I believe you are using mid boards, so my merged Daves wiring hookup should work, PROVIDED your cut boost caps are arranged as mine are on high and low boards.

When my mids would boost and not cut, It was do to my trimmers being reversed, which I think was messing with the impedance.

So if everything else is hooked up correctly, run a test signal thru it and measure to see if it drops down somewhere.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 12, 2013, 02:12:46 AM
Ian, looking at the midbottomchrion.jpg, I assume that the pointer for pin 5 should actually go to the terminal just to the right since it's currently pointing to one of the switch terminals?  That's the only thing I can find that I did differently.

Yes you are right, it ahould be the terminal to the right. I will update the picture.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 12, 2013, 04:39:08 AM
The saga continues;  I realized that I had connected the 'screen' to the right-hand lug of the bass boost pot instead of the 0v, left lug.  However, after moving it, I have no mid boost or cut at all.  Honestly, I don't get how it can have so much impact on the circuit when it's only connected to the metal clips on the side of the inductor.  Clearly, I'm still not understanding something.

You are right, it should make no difference which seems to imply that maybe it's not connected to the metal parts of the inductor or that the metal parts are also connected to something else. The screen connection is not essential so if I were you I would just delete it for now.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 12, 2013, 08:48:58 AM
Ok, I found one more incorrectly wired terminal and now I REALLY think I've got everything hooked up correctly in terms of wiring.  Everything now works as expected except the mid cut.  The mid boost seems a little pronounce (almost harsh), but I can't tell if that's a problem or expected behavior. 

I have run a 0db signal through it (skewed by using my DAW instead of a proper signal generator) and the results, with the tube makeup gain fully cw, are as follows;

Input voltage  - 1.71v
Bypassed output - 1.54v
EQ in, mid in the cut position - 2.01v
EQ in, mid in the boost position - 3.5v

Can any conclusions be drawn from this?

Also, should C12 on the mid-board be jumpered?  I'm having trouble reading the traces with everything connected, but it seems like I've got an orphaned inductor lead because there is no cap in that spot.  Thanks,  John



Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 12, 2013, 09:28:48 AM
I've taken the mid board out of one of the EQs and connected the leads that fed it to one another.  (the center of the mid pot and the center of the mid boost/cut switch)

The voltage result are now;

input    - 1.74v
bypassed output    -  2.03v
EQ in with mid cut enabled   -   2.07v
EQ in with mid boost enabled   -   3.91v

What could be causing that big jump?  All knobs are at fully ccw.  Thoughts?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 12, 2013, 09:54:12 AM
Trying to find where exactly it makes that jump in voltage.  So far I'm tracing from the inputs and after the input transformer it's 1.5v everywhere until it hits the other side of any of the pots where it drops to about 200 millivolts.  I'll try from the output side backwards now.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 12, 2013, 12:08:33 PM
Trying to find where exactly it makes that jump in voltage.  So far I'm tracing from the inputs and after the input transformer it's 1.5v everywhere until it hits the other side of any of the pots where it drops to about 200 millivolts.  I'll try from the output side backwards now.

If you are doing this at 1KHz then that is about right. The basic pot divider consists of the treble boost and treble cut pots which together should give an insertion loss of about 20dB so you would expect a 1.5V input to drop to 150mV or so at the junction of these two.

Regarding C12, the 'standard' poor man's mid has all 12 capacitors defined so you will probably be missing the 15KHz setting.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 12, 2013, 01:47:38 PM
Fixed and sounding fantastic!   Thanks so much to everyone who helped me.  The biggest obstacle was my own arrogance.  I kept looking for inconsistencies in the diagrams as clues to what was wrong when ALL of my problems were basic oversights on my part.  Live and (hopefully) learn.  I'll post pics as soon as I get them buttoned up.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 12, 2013, 03:06:16 PM
Here are a couple of pics as promised.

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 12, 2013, 03:07:03 PM
And the obligatory gut shot.

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on October 12, 2013, 07:29:30 PM
A simple question.
Make up gain related, is there a chance i could use an IC make up gain? or the 325 style
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: duantro on October 12, 2013, 09:02:53 PM
Congrats JohnWatkins! Looks pretty sweet!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 13, 2013, 06:23:07 AM
Well done John! It just confirms my theory that there is no such thing as a subtle fault - they are all pretty obvious once you find them.

Can you email me the pics for my gallery?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on October 13, 2013, 07:56:06 AM
Absolutely Ian.  I'm going to take some proper pics once they are racked, but I'll send you copies of these for now.  Thanks so much for making your designs and expertise available to the rest of us.  Your generosity with your time is very much appreciated.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on October 14, 2013, 06:00:57 AM
A simple question.
Make up gain related, is there a chance i could use an IC make up gain? or the 325 style

And i think like you,too.I'm planning use JFP gain module.I think it's possible.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on October 14, 2013, 10:12:10 AM
Yeah sounds good.
I think i have 2 options since i have parts for Neve outputs and Api.
Thanks.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mitsos on October 14, 2013, 10:28:38 AM
Trinity, for solid state gain makeup:

http://groupdiy.com/index.php?topic=48328.msg612931#msg612931

If using an IC, either get one that is 600 capable, to ensure it can drive the trafo sufficiently, or put a BD139/140 output stage after it.  I think there is a schematic in the original(not the updated one, because we stopped making those adapter PCBs) EQP-1S5 build document, at the beginning of the thread.  Works very nicely with an OPA604, but I'd like to try one of the LME ICs as well.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 15, 2013, 06:47:16 AM
A simple question.
Make up gain related, is there a chance i could use an IC make up gain? or the 325 style

You can use an IC based gain make up for the poor man's pultec BUT you need to make sure it has a high enough input impedance. The poor man's Pultec prefers to be loaded with not less than 470K bot you can get away with as little as 220K. Any less than that and the bass boost loses range and the bass cut becomes more severe.

An FET input op amp is ideal. I think several people used an IC gain make up in the original thread.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 03, 2013, 05:29:23 PM
Hi all,
   I think i've read most the thread and i did not find anything that looks like the problem i have...I'm using the P3band pcb with carnhill inductors. What happens is when i choose low cut with the toggle switch everything drops of about 5db....I have a two position switch either dip or boost no bypass...The cut seems a bit thinner then the boost but if i understand correctly is normal.
  If i look at the schematic i see a 1k resistor to ground but on the pcb i see a 470 so i tried changing that but it's not the cause... 

 If anyone has any idea of how i could solve this...

Big thanks in advance!

Pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 04, 2013, 05:19:54 AM
Hi Pierre,

If you lose 5dB when you switch in the mid, the first thing that comes to mind is that perhaps the mid pot is the wrong value. It should be 47K or 50K. Maybe you fitted a 4K7 or 5K?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 04, 2013, 09:28:01 AM
Good day Ian,
     I had a 50k log. Now i have a 50k lin and the response is more progressive but in both case i get the 5db loss...
Thanks again for your help!

Regards,

Pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 04, 2013, 10:48:40 AM
Good day Ian,
     I had a 50k log. Now i have a 50k lin and the response is more progressive but in both case i get the 5db loss...
Thanks again for your help!

Regards,

Pierre

Is the 5dB loss right across the spectrum?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 04, 2013, 11:08:07 AM
yes across the spectrum!

Regards!

Pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 04, 2013, 11:43:53 AM
yes across the spectrum!

Regards!

Pierre



Mmmmmm. Odd. The only other thing I can think of is perhaps one of the capacitors is faulty or there is a solder bridge some where. Does it work OK on boost?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 04, 2013, 12:16:04 PM
On boost it's ok, could it be a wrong value cap because i have the same problem  on all 4 channels so it is less likely to have a solder bridge.
If it was a wrong value cap would'nt the problem only be on that certain frequency?
Think of it it's hard to say if it's a 5db loss on the mid cut or a 5 db boost on low boost...

Regards,

Pierre



Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 04, 2013, 01:01:23 PM
On boost it's ok, could it be a wrong value cap because i have the same problem  on all 4 channels so it is less likely to have a solder bridge.
If it was a wrong value cap would'nt the problem only be on that certain frequency?
Think of it it's hard to say if it's a 5db loss on the mid cut or a 5 db boost on low boost...

Regards,

Pierre

I was thinking more of a faulty cap than a wrong value. If one of them was short circuit for example that might explain why the 5dB drop occurs right across the audio spectrum. But if you have the same effect on four boards that's still rather odd.

I am not sure about your last comment. Are you saying the 5dB cut is not the same across the audio band?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 04, 2013, 01:27:40 PM
yes it across the audio band. but if the pad was adjusted at unision with the switch in the cut position it would a 5 db boost.

regards!

pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 04, 2013, 04:38:03 PM
yes it across the audio band. but if the pad was adjusted at unision with the switch in the cut position it would a 5 db boost.

regards!

pierre

OK. Have you got the cut/off/boost switch wired correctly?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 04, 2013, 04:55:37 PM
yes it across the audio band. but if the pad was adjusted at unision with the switch in the cut position it would a 5 db boost.

regards!

pierre

OK. Have you got the cut/off/boost switch wired correctly?

Cheers

Ian


It's wired like this

Salutations,

Pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 04, 2013, 04:59:07 PM


It's wired like this

Salutations,

Pierre
[/quote]

OK, thewiring looks OK. The  picture shows a SPDT switch - you are using a centre off type yes?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 04, 2013, 05:03:59 PM
I'm not using a center off type, is it important?

Pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 04, 2013, 05:08:34 PM
the one i use is the on-on type.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 04, 2013, 05:27:48 PM
the one i use is the on-on type.

OK, that is the wrong type. You need the type with a centre off position optherwise you cannot turn off the mid boost/cut. The compromise that had to be made to get a simple mid boost/cut was that even with the pot at its maximum there would be a small resifual mid boost or cut. So the centre off switch allows the mid to be disconnected.

However, this does not explain your problem so it is something you need to do but I do not think it is the solution to the problem. Are you sure you have a 5K pot for the hi cut?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 04, 2013, 05:37:41 PM
Yes Ian Hi cut is 5k lin..

Cheers

Pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 04, 2013, 06:06:27 PM
Yes Ian Hi cut is 5k lin..

Cheers

Pierre

I am running out of ideas now and it's 11pm here. I'll sleep on it. Is it the same at all frequency settings?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 04, 2013, 08:35:59 PM
Yes Ian Hi cut is 5k lin..

Cheers

Pierre

I am running out of ideas now and it's 11pm here. I'll sleep on it. Is it the same at all frequency settings?

Cheers

Ian

Thanks a lot Ian, i'm sure we will find a solution in time! No rush!

Regards!

Pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 05, 2013, 04:22:01 AM
Good morning Pierre. I think it is time to check basics. Can you confirm the hi boost pot is 47K. With all the pots fully anti-clockwise, can you measure the dc resistance from the top of the hi cut pot to 0V and also from the top of the hi cut pot to the input.

Are you using Chrion's inductors?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 05, 2013, 11:28:59 AM
Good morning Pierre. I think it is time to check basics. Can you confirm the hi boost pot is 47K. With all the pots fully anti-clockwise, can you measure the dc resistance from the top of the hi cut pot to 0V and also from the top of the hi cut pot to the input.

Are you using Chrion's inductors?

Cheers

Ian

Good morning to you Ian,
    I get 14.6k from the top of the hi cut and pot 0V and to the input, with all the pot's fully anticlockwise. The same left over pot outside circuit does measure 45k on my meter. With all the pots clockwise i get  29.2k with the post fully clockwise and just bass boost really matters.

I'm using the carnhill inductors. I'm also using the caps value that were for the europe pots and not the north american values. I was under the impression that this would only alter the fréquence response?

Thanks Ian,

Pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on November 05, 2013, 12:08:48 PM
Hi Ian on another subject.
Im revising my build prior to hook up gain stage.
However im a bit confused following this page: http://www.ianbell.ukfsn.org/pics/alteq/hookupsm.jpg (http://www.ianbell.ukfsn.org/pics/alteq/hookupsm.jpg)
Hi-boost counter clockwise is connected at T1 but with this scheme: http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/DavesPMEQP-1A%20Hookup%20Diagram.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/DavesPMEQP-1A%20Hookup%20Diagram.pdf)
Clock wise side is connected at T1.

Can you clear that for me please!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 05, 2013, 06:55:23 PM
Hi Ian on another subject.
Im revising my build prior to hook up gain stage.
However im a bit confused following this page: http://www.ianbell.ukfsn.org/pics/alteq/hookupsm.jpg (http://www.ianbell.ukfsn.org/pics/alteq/hookupsm.jpg)
Hi-boost counter clockwise is connected at T1 but with this scheme: http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/DavesPMEQP-1A%20Hookup%20Diagram.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/DavesPMEQP-1A%20Hookup%20Diagram.pdf)
Clock wise side is connected at T1.

Can you clear that for me please!

They are the same. The second one is with the pots viewed from the rear.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 05, 2013, 07:03:35 PM

Good morning to you Ian,
    I get 14.6k from the top of the hi cut and pot 0V and to the input, with all the pot's fully anticlockwise.

That is not right. With all pots anti-clockwise you should get about 5K from the top of the hi cut pot to ground. If it is 14.6K then that would explain why the mid cut drops the level so much. Check the value of the hi cut pot.

Carnhill transformers is good. You are correct about using the US value pots only changes the frequency a little - not enough to worry about.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on November 13, 2013, 12:00:58 PM
I finished eq section.It's working perfectly!I need some advice.

Can i use 600:600 transformer for input? Cause i have lots of transformer like this and i want to use them.And JPF gain module is fit fot this?

Thanks!


For now it's like this. ;D I'm working on rack.

Pics.

http://n1311.hizliresim.com/1h/f/uhtkg.jpg (http://n1311.hizliresim.com/1h/f/uhtkg.jpg)
http://j1311.hizliresim.com/1h/f/uhtl8.jpg (http://j1311.hizliresim.com/1h/f/uhtl8.jpg)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 13, 2013, 06:40:07 PM
I finished eq section.It's working perfectly!I need some advice.

Can i use 600:600 transformer for input? Cause i have lots of transformer like this and i want to use them.And JPF gain module is fit fot this?

Thanks!

Yes, you can use a 600:600 transformer at the input; you just need to make sure that whatever feeds it is capable of driving  a 600 ohm load.

I am not familiar with the JPF gain module. Can you post a link or a schematic?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on November 13, 2013, 06:53:02 PM
I finished eq section.It's working perfectly!I need some advice.

Can i use 600:600 transformer for input? Cause i have lots of transformer like this and i want to use them.And JPF gain module is fit fot this?

Thanks!

Yes, you can use a 600:600 transformer at the input; you just need to make sure that whatever feeds it is capable of driving  a 600 ohm load.

I am not familiar with the JPF gain module. Can you post a link or a schematic?

Cheers

Ian

Thanks for reply.

Ops! My bad...Actually it's JFP.

http://www.diyrecordingequipment.com/wp-content/uploads/2011/02/hamptone_fet_scan.jpg (http://www.diyrecordingequipment.com/wp-content/uploads/2011/02/hamptone_fet_scan.jpg)

If it's not good,can you recommend easy to build gain stage?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 14, 2013, 06:05:37 AM

Thanks for reply.

Ops! My bad...Actually it's JFP.



If it's not good,can you recommend easy to build gain stage?

Thanks for the link. That JFP amp will be fine for a gain make up amp. It has the necessary high input impedance. Just make sure the input resistor is at least 470K and you should be fine.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on November 16, 2013, 03:09:22 PM
Hey Guys, what do you make of this?  I finally got around to doing some tests on my builds and this is the response I get with the EQ bypassed.  So, this should be the freq response of just the tube makeup, right?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 17, 2013, 07:09:48 AM
Hey Guys, what do you make of this?  I finally got around to doing some tests on my builds and this is the response I get with the EQ bypassed.  So, this should be the freq response of just the tube makeup, right?

Do you have transformers at the input and output?

The peak at 20Hz looks like it might possibly be the resonance of the output capacitor with the primary inductance of the transformer. The HF loss I do not understand. The tube make up board should be flat out to 150KHz with the HF once again limited by the transformers.

Either that or your bypass isn't bypassing. Were the EQ controls flat when you did this test?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on November 17, 2013, 07:23:04 AM
Yes, using the Sowter input and output transformers.  Yes, the EQ was flat.  The weird thing is, it doesn't sound like there's a big HF dropoff when I patch it in.  Maybe I'm not testing properly. 
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on November 17, 2013, 07:35:45 AM
I checked the other EQ in the same way and got the same result, but much less pronounced. 

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on November 19, 2013, 08:42:12 PM
Hi guys.
How do you guys test your eqs ? i dont have a mixer and my rig its not hooked at all.
Also heres a picture if you guys see something wrong.
On the Make up its all good it goes straight to the + side of the op-amp.

Thanks.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 19, 2013, 10:46:23 PM
How about comparing your curves with the ones Ian made available...

Regards.

Pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on November 19, 2013, 11:30:04 PM
what are you using for the curves?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on November 19, 2013, 11:44:35 PM
I use logic, i route a pink noise to the eq input using the test oscillator. I route the eq ouput back into logic were i insert a multimeter in analyser mode.
Ian has the curves in the folder were all the information for the eq is...
Maybe there is a better way to do this, other might shime in....thats how i do it anyhow.

I think most daws will have similar functions, if not i could bounce a pink noise for you.

Regards,

Pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 20, 2013, 10:54:32 AM
I use an audio test set made by Lindos in the UK.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on November 20, 2013, 05:33:17 PM
Ill drop the sweep curves im an idiot.

Now the Hi boost seems to work weird .
Complete CCW it boosts, complete Cw it boost...middle position it fades out...



Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 20, 2013, 07:05:48 PM
Ill drop the sweep curves im an idiot.

Now the Hi boost seems to work weird .
Complete CCW it boosts, complete Cw it boost...middle position it fades out...

Most of the problems that have been reported so far have been due to one of three things:

1. Incorrect pot values (including on the tube gain make up PCB if used)
2. Incorrect hook up
3. Too low a load on the output (should be 470K or higher).

If you get these three right then it usually works as advertised.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on November 20, 2013, 09:24:58 PM
Thanks Ian.
Im really impressed by the sound of this project.

Just tried a female vocal track and it just shines!

however tried a BYPASS switch and it really needs a PAD.

One more question do you think its a good idea to make the Hi section or Low section switchable??
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on November 20, 2013, 09:44:43 PM
heres my schematic for make up.
instead of 100k i installed 470K i havent installed the parallel cap as im not sure yet what value that is! any one?

(http://www.jlmaudio.com/EQP-1A3Schematic%20mod%20for%20most%20opamps.jpg)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 21, 2013, 05:46:18 AM
Thanks Ian.
Im really impressed by the sound of this project.

Just tried a female vocal track and it just shines!

however tried a BYPASS switch and it really needs a PAD.

One more question do you think its a good idea to make the Hi section or Low section switchable??

Here's a pic of the recommended way of doing a bypass, including the required pad.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/EQSystem.png (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/EQSystem.png)

The 470K pot is just one way of setting the overall gain to unity. You can change the gain of the make up amp. In your schematic you asked about the cap across the 470K. You don't need one.

Can you clarify what you mean by making the hi or lo section switchable? Do you mean changing the pots for switch pots or do you want to switch the hi or lo section in or out?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on November 21, 2013, 09:54:44 AM
no i meant just to be able to bypass the low section or the hi section?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on November 21, 2013, 12:40:16 PM
Quote
The peak at 20Hz looks like it might possibly be the resonance of the output capacitor with the primary inductance of the transformer

I'll have some time this afternoon to work on this.  Is there a recommended remedy?

Thanks, John
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 22, 2013, 06:39:37 AM
Quote
The peak at 20Hz looks like it might possibly be the resonance of the output capacitor with the primary inductance of the transformer

I'll have some time this afternoon to work on this.  Is there a recommended remedy?

Thanks, John

Depends on the transformer but you either try to move the peak below the audio band  by increasing the outout capacitor or make the peak smaller by lowering the Q of the resonance by adding a series resistor. Which transformer are you using?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on November 23, 2013, 08:51:04 AM
The transformer is an Antek AS-05T240.  I believe Dave Wheeler used the same one.  I wonder if he's had this issue.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 24, 2013, 05:38:23 AM
The transformer is an Antek AS-05T240.  I believe Dave Wheeler used the same one.  I wonder if he's had this issue.

Sorry, I meant the output transformer not the power transformer.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on November 25, 2013, 07:45:07 AM
Oh, sorry.  It's the Sowter that was recommended.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 25, 2013, 02:32:44 PM
Oh, sorry.  It's the Sowter that was recommended.

No problem. That probably explains the 3dB bump around 20Hz. If you are using both the 4.7uF output caps and the transformer primary inductance is about 10 Henries then the resonance is around 16Hz. The simplest solution is to increase the output cap to say 47uF. Try a 47uF 400V electolytic. That will move the resonance well below 10Hz by which time the amplifier output will be falling off rapidly anyway. Another solution is to use a 10K:10K transformer instead which will raise the inductance and lower the resonance. A third alternative is to use the output unbalanced.

To be honest, this amplifier stage was never designed to drive a transformer which is why I have always said not to load it with less than 10K.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on November 25, 2013, 03:09:16 PM
Got it.  Thanks for the tips and explanation.  I've got it racked up for a project now, but I'll try those solutions at the next opportunity. 
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 26, 2013, 05:05:01 AM
Got it.  Thanks for the tips and explanation.  I've got it racked up for a project now, but I'll try those solutions at the next opportunity.

I still don't know what is causing the apparent HF drop off.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: JohnWatkins on November 26, 2013, 06:32:13 AM
I decided to live with it and just compensate by giving it a little bump all the time in that range.  It's only a db and a half and goodness knows I'm not going to run out of boost capability.  Trying to strike a balance between learning as much as I can as I go and not spending a year on one project.  Gotta move on at some point. 

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on December 20, 2013, 12:18:43 PM
Is this possible to use something like this for gain stage?

http://www.ebay.com/itm/Tube-6N3-Buffer-Audio-Preamplifier-kit-Pre-AMP-AMP-kit-DIY-/130814272291?pt=US_Amplifier_Parts_Components&hash=item1e75236323 (http://www.ebay.com/itm/Tube-6N3-Buffer-Audio-Preamplifier-kit-Pre-AMP-AMP-kit-DIY-/130814272291?pt=US_Amplifier_Parts_Components&hash=item1e75236323)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 21, 2013, 06:51:31 AM
Is this possible to use something like this for gain stage?

http://www.ebay.com/itm/Tube-6N3-Buffer-Audio-Preamplifier-kit-Pre-AMP-AMP-kit-DIY-/130814272291?pt=US_Amplifier_Parts_Components&hash=item1e75236323 (http://www.ebay.com/itm/Tube-6N3-Buffer-Audio-Preamplifier-kit-Pre-AMP-AMP-kit-DIY-/130814272291?pt=US_Amplifier_Parts_Components&hash=item1e75236323)

Unfortunately this will not work. It is a simple stereo cathode follower so it has unity gain and we need a good 20dB of gain for the EQ.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on December 21, 2013, 02:10:00 PM
Is this possible to use something like this for gain stage?

http://www.ebay.com/itm/Tube-6N3-Buffer-Audio-Preamplifier-kit-Pre-AMP-AMP-kit-DIY-/130814272291?pt=US_Amplifier_Parts_Components&hash=item1e75236323 (http://www.ebay.com/itm/Tube-6N3-Buffer-Audio-Preamplifier-kit-Pre-AMP-AMP-kit-DIY-/130814272291?pt=US_Amplifier_Parts_Components&hash=item1e75236323)

Unfortunately this will not work. It is a simple stereo cathode follower so it has unity gain and we need a good 20dB of gain for the EQ.

Cheers

Ian

Thank for reply.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on December 23, 2013, 03:52:52 AM
Hi

I´d like to add 2 mid bands to my first Poor man´s build, my holidays gift, and when searched for the Chrion´s thread selling the Inductors It´s just gone!

Where can I get inductors suitable for this project?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 23, 2013, 09:34:46 AM
Hi

I´d like to add 2 mid bands to my first Poor man´s build, my holidays gift, and when searched for the Chrion´s thread selling the Inductors It´s just gone!

Where can I get inductors suitable for this project?

I have no idea what has happened to Chrion. Anybody?

The poor man's mid was designed to use Carnhill inductors. There is an error on the PCB that means some tracks need to be cut and links added for them to work. The document describing the frequencies you can get with each inductor type is here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/PMmidfeb12.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/PMmidfeb12.pdf)

and the document describing how to do the inductor fix is here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/MIDPCBfixv2.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/MIDPCBfixv2.pdf)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: dirtyhanfri on December 23, 2013, 12:32:54 PM
Great! Thanks for the answer, I'll start looking them
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on December 28, 2013, 10:12:07 AM
Hi
I'm working on  a P2P Redd47 and I want to ad a poor man's mid in same case as a Channel strip.
Which transformer can I use between Redd 47 out and poor man's mid in?
I can insert the eq at some point of the channel, rather than later?
THANKS!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 28, 2013, 11:22:13 AM
Hi
I'm working on  a P2P Redd47 and I want to ad a poor man's mid in same case as a Channel strip.
Which transformer can I use between Redd 47 out and poor man's mid in?
I can insert the eq at some point of the channel, rather than later?
THANKS!!!

The short answer is yes you can insert it in part of the chain but you need to add another stage of amplification. This was discussed in detail on one of the REDD 47 threads but I cannot remember which one.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mikeyB on January 16, 2014, 04:02:59 PM
Hi Ian - can the poorman make up amp be used with a standard pultec filter network - ie 600ohm.
someone is asking me if i can convert a diy chip amp to a tube output, but want to leave the filter circuit (based on the original) intact.
Wil the tube makeup circuit work ok with the original filter impedance?

Thanks in advance :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 17, 2014, 05:35:22 AM
Hi Ian - can the poorman make up amp be used with a standard pultec filter network - ie 600ohm.
someone is asking me if i can convert a diy chip amp to a tube output, but want to leave the filter circuit (based on the original) intact.
Will the tube makeup circuit work ok with the original filter impedance?

Thanks in advance :)

Yes, this should be possible. The poor man's tube gain make up (PMTGMU) has a very high input impedance so it will not load the filter. Does the chip amp circuit include the interstage transformer in the original EQP1A or not? Do you have a schematic available?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mikeyB on January 17, 2014, 09:13:08 PM
Hi Ian - the circuit does NOT have the interstage transformer - it's built from the diy gyraf filter and the nrgrecording amp stage, and is mounted in the tat purusha case. Output amp is just a 5532 chip but the bottom end doesn't sound right! - a bit thin at extreme settings - i think the opamp isn't up to it!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 18, 2014, 05:53:48 AM
Hi Ian - the circuit does NOT have the interstage transformer - it's built from the diy gyraf filter and the nrgrecording amp stage, and is mounted in the tat purusha case. Output amp is just a 5532 chip but the bottom end doesn't sound right! - a bit thin at extreme settings - i think the opamp isn't up to it!

OK, understood. The usual reason for poor low end performance is too low an input impedance . Can you post a link to the nrgrecording amp schematic?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: creal on February 19, 2014, 10:04:38 AM
I finished to modify my "poor man" EQP1.
My version include the API 325 as gain stage and a mid boost/cut add-on.
The mid add-on use old inductors from old midas PR03 chanelstrips with appropriate caps.
I advise to all poor man EQP1 builder to add this add-on.
Thank Ian for this project, it sound very nice.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on March 16, 2014, 11:33:43 AM
I finished my eq with JFet output stage.But it's unbalanced.I want to make it balanced with in&out transformers.What should i use? Input&output impedances?

Or can get balanced input and output circuit/pcb with NE5532/NE5534? Ebay or...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 16, 2014, 02:20:47 PM
I finished my eq with JFet output stage.But it's unbalanced.I want to make it balanced with in&out transformers.What should i use? Input&output impedances?

Or can get balanced input and output circuit/pcb with NE5532/NE5534? Ebay or...

For the input transformer you should use a 10K:10K type. The output transformer will depend on the circuit you used for the gain make up. Hard to say without a schematic.

Yes, you can use NE5532/4 for unbalancing and balancing. I think several people have already done this. Alternatively the Dingo Pup PCB made by JLM audio will provide a ready made PCB for just this purpose.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on March 16, 2014, 03:12:52 PM
I finished my eq with JFet output stage.But it's unbalanced.I want to make it balanced with in&out transformers.What should i use? Input&output impedances?

Or can get balanced input and output circuit/pcb with NE5532/NE5534? Ebay or...

For the input transformer you should use a 10K:10K type. The output transformer will depend on the circuit you used for the gain make up. Hard to say without a schematic.

Yes, you can use NE5532/4 for unbalancing and balancing. I think several people have already done this. Alternatively the Dingo Pup PCB made by JLM audio will provide a ready made PCB for just this purpose.

Cheers

Ian

Thanks for response! Dingo pup is great! It's one section for in & out right?

BTW i used this gain module.

http://www.diyrecordingequipment.com/wp-content/uploads/2011/02/hamptone_fet_scan.jpg (http://www.diyrecordingequipment.com/wp-content/uploads/2011/02/hamptone_fet_scan.jpg)

Gain about 26dB.Is it ok?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 17, 2014, 06:05:52 AM
Thanks for response! Dingo pup is great! It's one section for in & out right?


As far as I remember the Dingo Pup will do you a balanced to unbalanced at the input amd am unbalanced to balanced at the output.
BTW i used this gain module.
Quote
http://www.diyrecordingequipment.com/wp-content/uploads/2011/02/hamptone_fet_scan.jpg (http://www.diyrecordingequipment.com/wp-content/uploads/2011/02/hamptone_fet_scan.jpg)

Gain about 26dB.Is it ok?

Yes, 26dB is fine. You need an input trimmer to set the gain equal to the loss in the EQ but other than that it should be fine.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on March 17, 2014, 03:13:37 PM
Thanks for response! Dingo pup is great! It's one section for in & out right?


As far as I remember the Dingo Pup will do you a balanced to unbalanced at the input amd am unbalanced to balanced at the output.
BTW i used this gain module.
Quote
http://www.diyrecordingequipment.com/wp-content/uploads/2011/02/hamptone_fet_scan.jpg (http://www.diyrecordingequipment.com/wp-content/uploads/2011/02/hamptone_fet_scan.jpg)

Gain about 26dB.Is it ok?

Yes, 26dB is fine. You need an input trimmer to set the gain equal to the loss in the EQ but other than that it should be fine.

Cheers

Ian

Thanks.I want to add out control.

It's my front panel like Mercury EQH-1

(http://i.hizliresim.com/wLLQpZ.png) (http://hizliresim.com/wLLQpZ)

And compact.

(http://i.hizliresim.com/wvqaPR.png) (http://hizliresim.com/wvqaPR)

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 18, 2014, 06:08:51 AM

Thanks.I want to add out control.


Do you mean an output level control?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on March 18, 2014, 01:43:37 PM

Thanks.I want to add out control.


Do you mean an output level control?

Cheers

Ian

I was thinking like this but i won't add output level control.Just fixed input trim to gettin normal level.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on March 20, 2014, 02:35:32 PM
BTW why i'm gettin hum noise when i cut low?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 20, 2014, 03:17:59 PM
BTW why i'm gettin hum noise when i cut low?

There is no reason why you should provided you screen the signal cables as shown in the documentation. Could you post a picture of your wiring?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on March 20, 2014, 03:39:13 PM
BTW why i'm gettin hum noise when i cut low?

There is no reason why you should provided you screen the signal cables as shown in the documentation. Could you post a picture of your wiring?

Cheers

Ian

I built it.

(http://i.hizliresim.com/xJmB9W.jpg) (http://hizliresim.com/xJmB9W)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 21, 2014, 07:16:49 AM
@ForthMonkey,

What do you connect the output to?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on March 22, 2014, 10:35:30 AM
@ForthMonkey,

What do you connect the output to?

Cheers

Ian

First i connect output to XLR without any circuit like gain stage before building gain stage.Then i connect to gain module but still i'm getting hum noise.

Now i will re-build with new pots.And i think i have to screen low pots like this and connect to case,right?

http://hizliresim.com/emBJ14 (http://hizliresim.com/emBJ14)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 22, 2014, 11:50:54 AM
@ForthMonkey.

The connections to each XLR need to be done with screened cables. Connect the cable screen to pin 3 of the XLR. On the input XLR the screen at the other end of the cable should be left unconnected. On the output XLR the screen should replace the blue wire you have going from the low boost pot to pins 1 and 3 of the XLR. The way you have it wired now you are relyiong on the metal chassis to connect the 0V of the input to the 0V of the output. If you want to run it unbalanced like this then you need to add a wire from pin3 of one XLR to pin 3 of the other XLR.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on March 22, 2014, 12:43:42 PM
@ForthMonkey.

The connections to each XLR need to be done with screened cables. Connect the cable screen to pin 3 of the XLR. On the input XLR the screen at the other end of the cable should be left unconnected. On the output XLR the screen should replace the blue wire you have going from the low boost pot to pins 1 and 3 of the XLR. The way you have it wired now you are relyiong on the metal chassis to connect the 0V of the input to the 0V of the output. If you want to run it unbalanced like this then you need to add a wire from pin3 of one XLR to pin 3 of the other XLR.

Cheers

Ian

Thanks! Now i understood.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on May 08, 2014, 02:15:51 PM
Does this design cause noise? Placement is ok?

(http://i.hizliresim.com/7mqkDW.jpg) (http://hizliresim.com/7mqkDW)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 09, 2014, 06:33:58 AM
That will probably be OK. The mains inlet is a bit close to the gain make up amp so you must make sure the mains inlet connections are properly insulated. Other than that I think it should be fine.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on May 12, 2014, 07:00:32 AM
That will probably be OK. The mains inlet is a bit close to the gain make up amp so you must make sure the mains inlet connections are properly insulated. Other than that I think it should be fine.

Cheers

Ian

Thanks Ian.

I will build.Then i can see what happens...
Title: SUCCESS!!!
Post by: johnnyscotch on July 28, 2014, 01:32:10 AM
Hey all,

I just plugged in my Poor Man's Pultec for the first time. I calibrated it to Ian's (thanks Ian!!) instructions, and it worked brilliantly the first time!!

It so smooth and silky on the low and high freq ranges, it sounds like a real piece of gear! LOL. I think I'm going to build another one. I've only run some drum tracks through it to test out, and the boost and cut trick works great. It's also got nice gain to it when really pushing everything.
Another thing I was very surprised about is the noise floor. This is the most complicated wiring job I've ever done from scratch and I was a little bit worried, but the noise floor at it's loudest is -95db at 50hz, and virtually non-existent everywhere else (at least with BlueCat in my DAW, which is what I base everything off of anyway).

I would like to thank Ian and everyone here who helped me out with this, it's a wonderful EQ and a great project!!! Thanks guys!!

Now for a concern: the only problem I have encountered so far is with calibrating VR1 on my channel 2. On channel one, I got in and out set to 0dBu no problem. When I set channel 2, I couldn't get it to go past about -2dBu, so I just calibrated channel 1 and 2 the same. Not a huge deal, I'm losing 2db when I patch into it, but in and out are equal, I can work around that, however, I would eventually like to be able to set them both properly at 0dBu. Anyone have any thoughts? I'm so pumped right now, if it entails taking out board components, I might live with it for a while, LOL.

Now for pics!!
I made the front panel myself, using our laser engraver at the shop. Just a few coats of gloss white over primer, then a couple coats of satin blue. Cut through to the white and clear coat over that.

(hadn't installed pilot lamp yet)
(http://i169.photobucket.com/albums/u216/ericrickey/BA693BF5-C1B9-4A95-92D9-0D83B44C0E14_zpslelw4qzs.jpg) (http://s169.photobucket.com/user/ericrickey/media/BA693BF5-C1B9-4A95-92D9-0D83B44C0E14_zpslelw4qzs.jpg.html)

(http://i169.photobucket.com/albums/u216/ericrickey/B41C40B1-9DA5-4334-9545-5C8043D6A08F_zps9igz3rgu.jpg) (http://s169.photobucket.com/user/ericrickey/media/B41C40B1-9DA5-4334-9545-5C8043D6A08F_zps9igz3rgu.jpg.html)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 28, 2014, 05:56:12 AM
Lovely pictures. If you email them to me I can have Pierre add them to his project gallery.

It is unusual not to have enough gain in the gain make up amp not to be able to achieve unity gain overall. Possible reasons for insufficient gain are a low gain tube or a missing or faulty cathode bypass capacitor. It would be worth swapping the tubes to see if the gain change follows the tube. If it does then you most likely have a faulty tube. If it does not then check the cathode bypass capacitors.

I am assuming you are using the regular mu follower with 6CG7 tubes.

The only other possibility is odd potentiometer values in the EQ. The basic attenuation of the the poor man's Pultec is formed by the 47K pot of the hi boost circuit and the 4.7K pot of the hi cut which together give a nominal attenuation of nearly 21dB. (Some people use a 50K and 5K pot but the result is the same). The 6CG7 mu follower should give close to 26dB gain so there should be a few dB in hand. However, pots usually have a 20% tolerance, so worst case, one could be 20% high and the other 20% low which with 50K and 5K pots will give  you an attenuator with 60K in one arm and 4K in the other which would attenuate by 24dB. Even then there is still a couple of dB extra gain in the 6CG7 mu follower so it ought to work. The only way to find out is to disconnect the pots and measure them.

The only other possibility I can think of is that you have the wrong value for the 470K preset pot in one amp. In the past, someone accidentally got the two preset pots in the wrong positions on the PCB so that is worth checking.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnnyscotch on July 30, 2014, 06:15:25 AM
Thanks Ian, I'll try a couple things

those pics are attached in the previous email I sent you, let me know if I need to resend them


cheers
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 30, 2014, 07:08:04 AM
Thanks Ian, I'll try a couple things

those pics are attached in the previous email I sent you, let me know if I need to resend them


cheers

The ones you emailed will be fine. If you are happy for them to be included in the gallery then I will forward them to Pierre.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on July 30, 2014, 07:18:19 AM
Beautifull built! The pictures will make a nice addition to the gallery!

Regards,

Pierre
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnnyscotch on July 31, 2014, 08:42:50 PM
Let me know if you guys want something different, I have the pilot light in now.
I could probably take some fancier pics, it just might be a few days
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 01, 2014, 06:02:23 AM
Let me know if you guys want something different, I have the pilot light in now.
I could probably take some fancier pics, it just might be a few days

Fancier pics are always good. I am on holiday for a week so there is no rush. Just email them to me or direct to Pierre if you like.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 01, 2014, 08:43:31 AM
Hi
can someone share  schematics for IC make up / poor man's pultec ( TL071 Based) ?
THANKS!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: creal on August 01, 2014, 09:09:26 AM
Hi
can someone share  schematics for IC make up / poor man's pultec ( TL071 Based) ?
THANKS!!!

Hi
For IC make up you can use the nice I/O board  from Pier Paolo, this io board works great.
http://groupdiy.com/index.php?topic=33576.0 (http://groupdiy.com/index.php?topic=33576.0)
You can also try something like the old Frank's pultec make up board. I used this one in past with the gyraf pultec with nice result.
I hope this will help
Cyril
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 01, 2014, 09:22:30 AM
Thanks Creal
It's possible to use PPA board balanced without transformer?
Do you know how?
Thanks!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: creal on August 01, 2014, 09:30:06 AM
Thanks Creal
It's possible to use PPA board balanced without transformer?
Do you know how?
Thanks!!!

Yes, you can use the board without transformers.
All the informations you need are on the IO board support thread
http://groupdiy.com/index.php?topic=46320.0 (http://groupdiy.com/index.php?topic=46320.0)

Cryil
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Deepdark on August 21, 2014, 11:46:08 AM
Quick one for you guys

About the interstage tranny, The filter section goes out to the pin 4 of the triad HS-29. Why not the pin 1? Is the pin 4 the "+" of the primary and pin 1 the " - " ???

The pin one, according to the schematic, goes directly to the ground?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 21, 2014, 12:50:50 PM
Quick one for you guys

About the interstage tranny, The filter section goes out to the pin 4 of the triad HS-29. Why not the pin 1? Is the pin 4 the "+" of the primary and pin 1 the " - " ???

The pin one, according to the schematic, goes directly to the ground?

I am confused. The poor man's EQP1A does not have an interstage transformer.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Deepdark on August 21, 2014, 01:07:32 PM
sorry wrong forum XD
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 21, 2014, 02:56:47 PM
Hi
Can someone help me with unbalanced wirings ?
I want to try it as a Insert on my console without using transformer...
drawing please....
THANKS!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 22, 2014, 04:17:47 AM
Hi
Can someone help me with unbalanced wirings ?
I want to try it as a Insert on my console without using transformer...
drawing please....
THANKS!!!

The input impedance to the EQ is around 10K so you can just delete the transformer and drive straight into it for an unbalanced version. You still need the gain make up so, if you use my tube version you can just forget the output transformer.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 22, 2014, 04:24:05 AM
I've tried this ,but  I've too much noise..
Pin 3 of xlr must be link to pin 1 and after goes to ground?
Thanks!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 23, 2014, 06:17:41 AM
I've tried this ,but  I've too much noise..
Pin 3 of xlr must be link to pin 1 and after goes to ground?
Thanks!!!

I am a little condfused. Why are you using XLR connectors? Are you connecting it to balanced gear?


Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ctechdx on August 23, 2014, 09:09:10 AM
Hello my friends...

Congratulations for this project... seems to be very nice!

I would like to build a dual EQP1A and a dual MEQ-5 for mastering purposes.

The original project on the first post is a mono unity, right? I would like to know more about the dual possibilities. Any changes on energy transformers to feed up two channels?

I also see on posts some ideas adding the mid range on EQP1A... the PCB says "EQP1/MEQ-5" I would like to know more about that possibility to build a low, mid and high eq in a single unity.

Thanks,
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 23, 2014, 06:59:59 PM
I've tried this ,but  I've too much noise..
Pin 3 of xlr must be link to pin 1 and after goes to ground?
Thanks!!!

I am a little condfused. Why are you using XLR connectors? Are you connecting it to balanced gear?


Cheers

Ian
Hi Ian you are right, but, I've just mounted the xlr, and after I've decided to change my project from balanced to unbalanced...
Now I want to use xlr but on unbalanced.
THANKS!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 24, 2014, 08:39:53 AM
I've tried this ,but  I've too much noise..
Pin 3 of xlr must be link to pin 1 and after goes to ground?
Thanks!!!

I am a little condfused. Why are you using XLR connectors? Are you connecting it to balanced gear?


Cheers

Ian
Hi Ian you are right, but, I've just mounted the xlr, and after I've decided to change my project from balanced to unbalanced...
Now I want to use xlr but on unbalanced.
THANKS!!!

OK, in which case just tie pins 1 and 3 together at the connector. You just need to be careful about the balanced gear you drive it with. Some of them do not like having one of their outputs grounded.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 23, 2014, 03:31:39 PM
Hi
I'm building another Poor Man's pultec with IC's Make up gain
schematics attached
Can someone help me with a wirings?
I'm going crazy...
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 23, 2014, 03:32:27 PM
And this is the output
Thanks!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 23, 2014, 03:33:00 PM
Input Layout
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 23, 2014, 03:33:55 PM
output layout


All this documentation come from this forum
Thanks!!!

I've tried all the connections but It doesn't work :(
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 23, 2014, 06:11:53 PM
output layout


All this documentation come from this forum
Thanks!!!

I've tried all the connections but It doesn't work :(

You need to connect the output of your input circuit to the input of the EQ. Connect the output of the EQ to the input of your output amplifier. Don't forget the power supply.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 24, 2014, 05:02:39 AM
Thanks Ian
from the output of input circuit to EQ I must use a screen cable?
Same from the output of the eq to out circuit?
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 24, 2014, 03:03:27 PM
Thanks Ian
from the output of input circuit to EQ I must use a screen cable?
Same from the output of the eq to out circuit?
Thanks

Yes,

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on November 06, 2014, 07:22:20 AM
Hi Ian
now my new Poor man's pultec whith IC's I/O is working and sound very well ( is one of the cheapest project).
I've only one problem that don't understand:
when I touch the low bost and cut pot I've a hum coming in ( also when go to max with low boost).
I've checked all the connection to ground and seems all good...
Ideas?
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 06, 2014, 11:22:28 AM
Hi Ian
now my new Poor man's pultec whith IC's I/O is working and sound very well ( is one of the cheapest project).
I've only one problem that don't understand:
when I touch the low bost and cut pot I've a hum coming in ( also when go to max with low boost).
I've checked all the connection to ground and seems all good...
Ideas?
Thanks

Which part of the pots did you touch? Which type of pot are you using

The low cut pot is a rather high impedance so you need to make sure the signal cable from the output of the EQ to the gain make up is screened cable. Check out this hook up diagram for more info:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/2-wirescaled.jpeg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/2-wirescaled.jpeg)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on November 06, 2014, 12:02:46 PM
Thanks Ian
I've used screened cables...
Now i will try to change the type of cable.
I'm using omeg pot.
At very High level ,I listen that if I touch The front panel the hum go away, and also that if i go near the low frequency  pot The hum is very important
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 07, 2014, 04:39:26 AM
Thanks Ian
I've used screened cables...
Now i will try to change the type of cable.
I'm using omeg pot.
At very High level ,I listen that if I touch The front panel the hum go away, and also that if i go near the low frequency  pot The hum is very important
Thanks

Sounds like you have a grounding/screening problem. Check out this diagram agin:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/2-wirescaled.jpeg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/2-wirescaled.jpeg)

Notice that pin 1 of the input and output XLRs are connected directly to the chassis (enclosure) at the XLR. Also note how the mains safety earth is connected to the chassis at the mains inlet and that the power supply 0Vis connected to the chassis at the same point an nowhere else. Make sure the front panel is not insulated from the est of the chassis.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on December 22, 2014, 12:09:42 PM
Hi again!

I'm new about tube circuits because of high voltages.But i tried your gain make up circuit in spice with ECC86 (48V) and gain about 22.5 dB.

But i use 0.06V as input voltage because this eq has  24dB gain loss.Am i right?

Can you check my circuit? Can i use this circuit with your gain make up PCB? Only i will change power supply.

(http://i.hizliresim.com/A0gMl7.png)

EDIT:And with 12AX7 i'm getting about 36dB gain.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 22, 2014, 06:32:20 PM
Hi again!

I'm new about tube circuits because of high voltages.But i tried your gain make up circuit in spice with ECC86 (48V) and gain about 22.5 dB.

But i use 0.06V as input voltage because this eq has  24dB gain loss.Am i right?

Can you check my circuit? Can i use this circuit with your gain make up PCB? Only i will change power supply.

This is a very interesting tube. Snce you are using the original circuit values, it is probably running at rather too low a current. You will probably need to adjust R1, R2 and R3 to obtain a more suitable operating point.

One problem with a mu follower is that R2 drops a lot of HT voltage. When you only have 48V to start with this is probably not a good idea. I would suggest you change it to an SRPP (set R2  and R5 to zero ohms and leave out C2). This will leave about 24V across each tube. From tha data sheet, for 3mA of plate current at 24V you need a negative bias of -1.0V. This means R1 and R3 would need to be 300 ohms. Try those values and see what happens.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on December 23, 2014, 04:17:13 AM
Thanks Ian!

I researched about SRPP and Mu Follower.I'm really new about tube...

ECC86 and ECC88 almost same.I choose ECC88 for this circuit.It has higher gain.

Now with this circuit i'm getting about 26dB gain.Power supply is 24V.I showed voltage drops.

Is this circuit ok?

(http://i.hizliresim.com/7VP94N.png)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 23, 2014, 05:42:15 AM
I hear a lot of people who are just starting out on tubes say things like ECC88 and ECC86 are almost the same. In fact they are very different. For example the ECC88 has a typical mu of more than 30 but the ECC86 has a mu of 14. The other key factor is that the ECC86 is specifically designed to work off a car battery supply of around 12V but the ECC88 expects  a supply of at least 90v. It is very difficult to be certain of its performance with a 12V supply. You cannot simply use a different tube in a circuit and expect it to work properly without changing values.  You should spend some time studying the data sheets of both tubes until you are clear on this point.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on December 23, 2014, 08:05:49 AM
I hear a lot of people who are just starting out on tubes say things like ECC88 and ECC86 are almost the same. In fact they are very different. For example the ECC88 has a typical mu of more than 30 but the ECC86 has a mu of 14. The other key factor is that the ECC86 is specifically designed to work off a car battery supply of around 12V but the ECC88 expects  a supply of at least 90v. It is very difficult to be certain of its performance with a 12V supply. You cannot simply use a different tube in a circuit and expect it to work properly without changing values.  You should spend some time studying the data sheets of both tubes until you are clear on this point.

Cheers

Ian

Yes,you're right.I have to spend some time...But when i research about SRPP and Mu follower,i saw a circuit.I tried it with spice.

(http://i.hizliresim.com/Q4YXQr.png)

Input 0.06V and output 2V

I don't know where i saw but they were using this design.Can i try this with Poorman's Eq?Low voltage and good gain.I can learn something about Mu Follower and SRPP...

And which transformer do you suggest for this circuit? I want to use VTB2281 for output...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 23, 2014, 12:04:00 PM

I don't know where i saw but they were using this design.Can i try this with Poorman's Eq?Low voltage and good gain.I can learn something about Mu Follower and SRPP...

And which transformer do you suggest for this circuit? I want to use VTB2281 for output...

Which is the whole point. That design probably does work for the application it was designed for but I strongly suspect it was not designed to drive a transformer. You really need a supply voltage of about 200V and a standing current of 5mA to be able to drive a transformer acceptably. The VTB2281 is a good choice of transformer but not for an ECC88 working at 12V plate voltage.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on December 23, 2014, 03:10:59 PM

I don't know where i saw but they were using this design.Can i try this with Poorman's Eq?Low voltage and good gain.I can learn something about Mu Follower and SRPP...

And which transformer do you suggest for this circuit? I want to use VTB2281 for output...

Which is the whole point. That design probably does work for the application it was designed for but I strongly suspect it was not designed to drive a transformer. You really need a supply voltage of about 200V and a standing current of 5mA to be able to drive a transformer acceptably. The VTB2281 is a good choice of transformer but not for an ECC88 working at 12V plate voltage.

Cheers

Ian

I see...It can't drive transformer.

OK.I have last question.

Is this possible impedance balancing with this circuit?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 24, 2014, 11:05:26 AM

I see...It can't drive transformer.

Quote

A properly designed DRPP will drive a transformer but the circuit you posted with a 24V supply most likely will not.
Quote
OK.I have last question.

Is this possible impedance balancing with this circuit?

It should  possible be but to do this you first need to know the output impedance of the circuit.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on December 24, 2014, 01:37:04 PM
There is SRPP out impedance calculator.But i can't understand.

https://dl.dropboxusercontent.com/u/91809016/SRPP.xls (https://dl.dropboxusercontent.com/u/91809016/SRPP.xls)

In my circuit

Rk=300 ohm
RL=100K

I have no idea other values.

Or is there any way to calculate SRPP out impedance?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 25, 2014, 04:10:51 PM
Difficult to say anything about the spreadsheet without any accompanying explanation. Where did you find it?

What it does show is that output impedance gets lower as gm gets higher. Higher gm occurs at higher currents. Your circuit with its low HT inevitably results in low current which means a relatively high output impedance.

I know you have been using spice. Spice can be used to simulate output impedance by feeding an ac voltage source into the output and measuring the resulting current. The output impedance is the voltage divided by the current.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on December 25, 2014, 07:17:21 PM
Difficult to say anything about the spreadsheet without any accompanying explanation. Where did you find it?

What it does show is that output impedance gets lower as gm gets higher. Higher gm occurs at higher currents. Your circuit with its low HT inevitably results in low current which means a relatively high output impedance.

I know you have been using spice. Spice can be used to simulate output impedance by feeding an ac voltage source into the output and measuring the resulting current. The output impedance is the voltage divided by the current.

Cheers

Ian

I don't remember that where did i found it.

But...

I used a way to find output impedance.

"I'm estimating output impedance of nodes by attaching an AC 1A current source to the node of interest, and conducting a small signal AC analysis to see what voltage is produced.  By Ohm's law, the voltage at that node in V corresponds to the impedance in ohms."

There is a way.He says like this.

http://wombatamps.blogspot.com.tr/2011/11/on-output-impedence-of-cathodyne-phase.html (http://wombatamps.blogspot.com.tr/2011/11/on-output-impedence-of-cathodyne-phase.html)

When i try this,i'm getting this result.Output impedance is 2K...

http://i.hizliresim.com/BRDE2g.png (http://i.hizliresim.com/BRDE2g.png)

Did i do right?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 26, 2014, 06:27:17 AM
That looks good to me but R2 contributes 470 ohms of the output impedance so I would try it afain without R2.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on December 26, 2014, 06:47:39 AM
That looks good to me but R2 contributes 470 ohms of the output impedance so I would try it afain without R2.

Cheers

Ian

Thanks in advice!

I remove R2.Now result is 1.5K.Is this okay?Can i make impedance balancing?And how?Cause there is no series resistor to output.

But i think i need to add 1.5K resistor cold pin to ground.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 26, 2014, 12:09:04 PM

But i think i need to add 1.5K resistor cold pin to ground.

Correct.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on December 26, 2014, 12:10:00 PM

But i think i need to add 1.5K resistor cold pin to ground.

Correct.

Cheers

Ian

Big thanks!

Now i will use only 10K:10K input transformer. Or 600:600?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 26, 2014, 03:38:15 PM
X

Now i will use only 10K:10K input transformer. Or 600:600?

I recommend using a 10K:10K input transformer.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on January 06, 2015, 09:30:24 AM
By the way i'm building solid state gain stage like Lang PEQ-2.Actually it's different but it's based Lang.

You can check...

http://groupdiy.com/index.php?topic=58126.msg739932#msg739932 (http://groupdiy.com/index.php?topic=58126.msg739932#msg739932)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: G-Sun on January 21, 2015, 02:37:11 PM
Could I easy combine the EzTubeMixer preampsection with the PMEQP1A with the mid boost/cut in one unit?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 21, 2015, 06:48:20 PM
Could I easy combine the EzTubeMixer preampsection with the PMEQP1A with the mid boost/cut in one unit?

Yes. The 3 band Pultec PCB is pretty much exactly the PMEQP1A with a mid band on one PCB (with different switches) and is designed to be used with the EZTubeMixer preamps.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: G-Sun on January 22, 2015, 09:49:57 AM

Yes. The 3 band Pultec PCB is pretty much exactly the PMEQP1A with a mid band on one PCB (with different switches) and is designed to be used with the EZTubeMixer preamps.

Thanks! How would I typical mount the pcbs in such a build?
The preamp vertical, the others on the case bottom (horizontal) in a 3U case for one channel?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 22, 2015, 12:25:33 PM

Yes. The 3 band Pultec PCB is pretty much exactly the PMEQP1A with a mid band on one PCB (with different switches) and is designed to be used with the EZTubeMixer preamps.

Thanks! How would I typical mount the pcbs in such a build?
The preamp vertical, the others on the case bottom (horizontal) in a 3U case for one channel?

Most of the rack mounted builds using the EZTubeMixer that I have seen have  the preamp have it mounted horizontally. Easier to trouble shoot that way but there is reason you cannot mount it vertically in a 3U case.

The poor man's EQP1A and mid  board mount directly to the front panel via the  switches on them.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: G-Sun on January 22, 2015, 12:36:31 PM
Most of the rack mounted builds using the EZTubeMixer that I have seen have  the preamp have it mounted horizontally. Easier to trouble shoot that way but there is reason you cannot mount it vertically in a 3U case.

The poor man's EQP1A and mid  board mount directly to the front panel via the  switches on them.
Thanks! And then it's the makup-gain after the pulteq, right?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 22, 2015, 01:18:00 PM
Thanks! And then it's the makup-gain after the pulteq, right?

That's right and a 10k:10k transformer at the input.

If you are doing a pair of EQs in one box then you could use the twin line amp card for gain make up. It has two amps and positions on the PCB for two input transformers.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: G-Sun on January 22, 2015, 03:26:35 PM

That's right and a 10k:10k transformer at the input.

If you are doing a pair of EQs in one box then you could use the twin line amp card for gain make up. It has two amps and positions on the PCB for two input transformers.
Ok,  are (2ch) 2x preamp 2x PM Pulteq with mid doable in a 3U case?
And output-transformers are needed, right?

Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 22, 2015, 05:47:04 PM

That's right and a 10k:10k transformer at the input.

If you are doing a pair of EQs in one box then you could use the twin line amp card for gain make up. It has two amps and positions on the PCB for two input transformers.
Ok,  are (2ch) 2x preamp 2x PM Pulteq with mid doable in a 3U case?
And output-transformers are needed, right?

Thanks!

Yes they are.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on February 04, 2015, 02:13:38 PM
Hi
I need just some suggestion...
I've inserted the eq without make up gain and without transformers in Pro Tools track and all is ok ( I think).
My noise in pro tools with this configuration is -94db
Is this ok?
But, when I use makeup gain ( tube or ic's version) my noise go up to -65   ( no transformer) I want to use it on my amek m2000 ( unbalanced input)
I've cheked all the connection and tried all  but with no luck
It's normal this noise level?
THANKS!!!.... ???
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 06, 2015, 05:14:43 AM
Hi
I need just some suggestion...
I've inserted the eq without make up gain and without transformers in Pro Tools track and all is ok ( I think).
My noise in pro tools with this configuration is -94db
Is this ok?
But, when I use makeup gain ( tube or ic's version) my noise go up to -65   ( no transformer) I want to use it on my amek m2000 ( unbalanced input)
I've cheked all the connection and tried all  but with no luck
It's normal this noise level?
THANKS!!!.... ???

The PMEQP1A needs to be fed into a high impedance. Pro tools will probably load it with 10K which is far too low but does explain why the noise is low.

With a tube or semiconductor gain make up you should achieve an output noise level much better than -65dBu. The EQ needs to be built into a screened box and screened cabling needs to be used as indicated in the hook up diagrams in the documentation. If you do this the noise should be much lower.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on February 09, 2015, 05:31:36 AM
Thanks IAN
All the cable and the connections are  as indicated in the hook up diagrams...
Could be that I don't use audio transformers for in and out?
Thanks!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 10, 2015, 06:05:11 AM
Thanks IAN
All the cable and the connections are  as indicated in the hook up diagrams...
Could be that I don't use audio transformers for in and out?
Thanks!!!

It should not make a lot of difference. Thinking about your earlier post you said you got noise at -94dB when plugging straight into pro tools without any gain make up. Now, under those conditions, the EQ will have an insertion loss of about 20dB so the output level will typically be -20dB which means the signal to noise is about 74dB.

You then said with gain make up in place the noise became -65dB. The gain make up should bring the input signal back up to 0dB so the signal to noise is 65dB. So with gain make up it is actually only 10dB worse than without it. In practice the insertion loss is a little over 20dB so the difference is even smaller.

Having said all that, the actual figures are not very impressive. When you measured the noise, what did you have connected to the EQ input?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on February 10, 2015, 06:52:34 PM
Thanks
my connections:
pro tools out  ( digi 002) to eq in
eq out to pro tools in ( digi 002)...
Simply connected as insert on channel.

Now I'm trying to do a regulated 6.3v for see if something change.
Thanks

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 11, 2015, 06:31:47 AM
Were you able to look at the spectrum of the noise? Was there any hum evident?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on February 12, 2015, 08:21:17 AM
Hi Ian now with 6.3v regulated all the hum is gone but my noise level is always too hight...
Two info:
My HT loaded was 350v , I've changed 3 x1k resistor with 2.2k 5w but my tension is too hight 339v...
Could this create some problems (6CG7 tube)?

 Now I've insert in and out transformer and don't know why my noise with eq in go down to -80 (on pro tools) :)
It's good?

The only problem is that I have for the output only two Carnhill 600:600 and not 10k:10k....
Thanks !!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 12, 2015, 12:05:09 PM
The 6CG7 will be fine with 339V - each triode only has half this voltage across it so they are not stressed.heers

Ian

Noise at -80 is good!  Looks like you had a hum loop as well which the transformer has broken.

 600:600 transformer will be fine as long as it is a good quality one. Just make sure it only has a 10K load on it.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on February 12, 2015, 02:14:36 PM
"600:600 transformer will be fine as long as it is a good quality one. Just make sure it only has a 10K load on it."

what does it mean?
Thanks!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 12, 2015, 06:41:19 PM
"600:600 transformer will be fine as long as it is a good quality one. Just make sure it only has a 10K load on it."

what does it mean?
Thanks!!!

it means:

1. Use a transformer such as a Sowter 5069

2. Make sure what it is connected to has an input impedance of 10K ohms or more.(your pro tools inputs should be OK).

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on February 13, 2015, 07:07:10 AM
Hi this is my Poor Man's Pultec
Thanks Ian for great proyect!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on February 13, 2015, 07:07:59 AM
 :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on February 13, 2015, 02:06:37 PM
Well done. excellent build. Would it be OK if I ask Pierre to copy these pics to include in the gallery of projects of my designs?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on February 13, 2015, 06:51:06 PM
Of course , I am very pleased!!!
Thanks !
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: SteelyDan on March 08, 2015, 11:48:07 AM
Hi all.

I'm a complete novice and I'm building this project for as part of my Music Production degree.

Ian's been very generous with his advice but I thought maybe for the more trivial queries I have that I shouldn't be flooding his inbox  ;D

Anyway, thought I'd join in with this thread that I've been reading through. I've got a lot to learn and I've got a few books from the library on electronics and audio electronics but if anyone can recommend me any reading material then I'm all ears!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mike76 on March 16, 2015, 09:18:46 AM
Hello,

and at first thanks to all of your support.

I've got a newbie-question, so please be patient with me :-)

I am building an EPQ with NE 5532 gainstage similiar to Frank's Power PCB  http://groupdiy.com/index.php?action=dlattach;topic=44213.0;attach=29033 (http://groupdiy.com/index.php?action=dlattach;topic=44213.0;attach=29033) . Now I want to hookup an output transformer, the edcor xs1100. I searched and read a lot about transformers, but tbh, I can't get into it.

I am total confused about the connections of this tranny to the board. Is it true, that an 1:1 ratio is necessary? Would some give me a hint how to wire it correct to the output xlr?

Thanks a lot, pleased for every information.

Mike

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 16, 2015, 09:54:20 AM
You probably want to wire this as a 1:1 transformer. This means you need to connect the primaries in parallel and the secondaries in series. So wire pin 2 to pin 4 and pin 1 to pin 5. Input is between pins 1 and 2. On the secondary connect pin 8 to pin 9 and take the output between pins 7 and 10.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mike76 on March 16, 2015, 01:23:43 PM
Dear Ian,

Thanks a lot. I've read so much about this topic but I think I need to get in the fundamental stuff.

But I'm not sure what you mean with "between pin...and pin....". Does that mean any pin in that range oder that they have to be connected, too?

Sorry for the probably stupid question :)

Regards,

Mike
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 16, 2015, 02:00:30 PM
Dear Ian,

Thanks a lot. I've read so much about this topic but I think I need to get in the fundamental stuff.

But I'm not sure what you mean with "between pin...and pin....". Does that mean any pin in that range oder that they have to be connected, too?

Sorry for the probably stupid question :)

Regards,

Mike

For an input you need to make two connections, So when I say connect the input 'between' pins 1 and 2 I mean make one connection to pin1 and the other to pin 2. when I say connect the output 'between' pins 7 and 10 I mean make one connection to pin 7 and the other connection to pin 10. (Not obvious unless English is your mother tongue).

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mike76 on March 16, 2015, 02:53:38 PM
Okay, thanks, I got it ;)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mike76 on March 16, 2015, 03:01:37 PM
But, one last question :)

the two inputs and outputs are + and - I suppose?

What about the grounds? Xlr to chassis? What about the ground from the transformer?

Hell, it seems so complicated, but I think Im thinking to complicated :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 16, 2015, 03:13:26 PM
But, one last question :)

the two inputs and outputs are + and - I suppose?

What about the grounds? Xlr to chassis? What about the ground from the transformer?

Hell, it seems so complicated, but I think Im thinking to complicated :)

For the transformer primary, one connection goes to the NE5532 output and the other goes to 0V. For the secondary, one output goes to pin2 of the XLR and the other goes to pin 3. Pin 1 of your XLRs should be connected directly to chassis at the connector. Somewhere in your enclosure, 0V should be connected to the chassis. For more information of grounding in general I suggest you read this:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/SimpleMixer/grounding101v2.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/SimpleMixer/grounding101v2.pdf)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: mike76 on March 16, 2015, 03:33:24 PM
Okay, thanks for your patience. I appreciate this.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: buschfsu on April 16, 2015, 07:30:11 AM
hello all,

i'd like to make my two channel unit for mastering purposes.  i'd stick with dual mono but think that using stepped attenuators would be wise for the boost and cuts.  can someone show me how to figure out the resistor values to give 1db per step?  Last question is about the Q.  i remember ian mentioning dropping from 1 to 0.6 i think.  is it a huge effort to broaden the Q a bit more?

thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 16, 2015, 01:42:23 PM
hello all,

i'd like to make my two channel unit for mastering purposes.  i'd stick with dual mono but think that using stepped attenuators would be wise for the boost and cuts.  can someone show me how to figure out the resistor values to give 1db per step?  Last question is about the Q.  i remember ian mentioning dropping from 1 to 0.6 i think.  is it a huge effort to broaden the Q a bit more?

thanks

The poor man's EQP1A has no inductors in it so there is no Q to set. The add on mid boost/cut board does use an inductor so you can adjust the Q. The mid boost/cut circuit is something of a compromise because it alters boost/cut amount and Q together.

I have never plotted the pot positions versus boost or cut so I do not have figures for stepping in 1dB steps. The circuit is fairly easy to simulate if you want to do it yourself. You just manually adjust pot values in the circuit until you get the boost/cut you want and then repeat for the next 1dB increment/decrement. Tedious but it works.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: buschfsu on April 16, 2015, 06:53:29 PM
Thanks ian.

Sounds like we are already at a Q of .3 based on the drawing board thread so thats where i want to be. I will jump the inductor and be set.

Never done a circuit sim so this will be fun and should learn something. (All my time is spent in eagle pcb!)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 17, 2015, 04:41:29 AM
Thanks ian.

Sounds like we are already at a Q of .3 based on the drawing board thread so thats where i want to be. I will jump the inductor and be set.


Just to put this in context, the original poor man's Pultec design had no inductor - that was one of the expensive items I wanted to eliminate. However, lot' s of people asked it I could squeeze just one inductor on the board and I did find room for it. However, it only operates at one position of the switch i.e. at one frequency,  Because the other positions are RC based there is always a common resistor in series at every switch position. This is what limits the Q for the inductor position.

I am currently working on the Mark 2 version of the PMEQP1A. This still uses cheap Lorlin switches but does allow you to fit an optional inductor for the HI boost.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: snaper on May 12, 2015, 05:26:09 AM
Have somebody an FPD format, "classic-looking" front panel design for this?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Paradigm X on June 18, 2015, 07:32:13 AM
Hi there

I got my pcbs a few days ago, and im staring at them, trying to figure out if i can make a stereo pair with only 3 frequencies. Obviously have to manually wire everything, which is a shame, but with 4pole 3 way switches, i should be able to do this, i think (!)

If so, i think 30Hz, 60hz and 120Hz would be good frequencies, and

Ive got a pair of the MK2's to make a 'proper' racked EQ, but i was hoping/thinking about making a master EQ for my soundcraft desk.

I would greatly appreciate any comments.

Many thanks, cheers, Ben
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 19, 2015, 11:29:47 AM
With 4 pole 3 way switches there is no reason in principle why you cannot make a stereo EQ. Just populate fewer positions. You could even use s 2 pole 6 way switch for a stereo mid. For the hi boost don't forget that the new MK2 PCB uses an inductor for this function so you need to connect to the appropriate LC combinations for the frequencies you choose.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on June 23, 2015, 09:43:25 AM
Hi
I'm  start to build a Stereo version of EQP1/MEQ5 (IAN pcb)
I want to use lorlin for frequency selections,
Can someone tell me if there is a connector to use for Grayhill substitution on PCB?
Thanks!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 23, 2015, 09:48:12 AM
Hi
I'm  start to build a Stereo version of EQP1/MEQ5 (IAN pcb)
I want to use lorlin for frequency selections,
Can someone tell me if there is a connector to use for Grayhill substitution on PCB?
Thanks!!!

There is a separate PCB that implements the same EQ using Grayhill switches. It is called the 3band Pultec PCB.

Check out the Ruff Records PCB Emporium tab at my new web site:

https://sites.google.com/site/customtubeconsoles/ (https://sites.google.com/site/customtubeconsoles/)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on June 23, 2015, 10:55:54 AM
Hi Ian
yes I'm talking about that PCB, but I want to use Lorlin Switch instead Grayhill
but I'm searching a pin's connector that can insert  into Grayhill housing.
Thanks
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 23, 2015, 11:49:06 AM
Hi Ian
yes I'm talking about that PCB, but I want to use Lorlin Switch instead Grayhill
but I'm searching a pin's connector that can insert  into Grayhill housing.
Thanks

Ah, you want to use Lorlin switches on the Grayhill version of the PCB. I did do a Lorlin header board as a group buy a couple of years ago built I am afraid they all sold out (OK I have one left). That design managed to squeeze a pair of switches and headers into a PCB no bigger than 50mm by 39mm to keep the price really low. It meant the two switches were very close together and rather awkward to separate with a hack saw. I would be happy to create an updated PCB layout that was easier to use provided there was enough demand but it would be a larger and more expensive PCB.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Paradigm X on June 24, 2015, 11:07:56 AM
With 4 pole 3 way switches there is no reason in principle why you cannot make a stereo EQ. Just populate fewer positions. You could even use s 2 pole 6 way switch for a stereo mid. For the hi boost don't forget that the new MK2 PCB uses an inductor for this function so you need to connect to the appropriate LC combinations for the frequencies you choose.

Cheers

Ian

Many thanks. Sadly i think im going to be stuck for space, but nice to know it will work in principle.

Cheer,s Ben
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: troubleous on June 25, 2015, 03:13:24 AM
Hello everybody!

It seems the Antek AN-05T240 is currently out of stock - can't find it second hand either.

Can anyone recommend a equivalent trafo to be used with Ian's tube gain make up?

Cheers,
Jarkko
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 25, 2015, 05:18:45 AM
Hello everybody!

It seems the Antek AN-05T240 is currently out of stock - can't find it second hand either.

Can anyone recommend a equivalent trafo to be used with Ian's tube gain make up?

Cheers,
Jarkko

I might be worth asking Don-Audio about a custom transformer since the Antek seems to have been out of stock for a long time. The Antek is a bit of an overkill anyway even for a couple of poor man's tube gain make up amps.

To run two PMTGMU amps the transformer secondaries only need at the most:

240VAC @ 35mA
6.3VAC @ 1.2A

Which is little more than 20VA in total. Should be quite small and cheap.

Writing this it occurs to me that I never really documented the PMTGMU PCB. There's a schematic showing it used in the PMEQP1A using 6CG7 tubes but you can also use a 6922 instead and wire it as a mu follower or an SRPP depending on your drive requirements. I will put together a short descriptive document for this.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 27, 2015, 08:02:47 AM
As promised, I have put together a document describing the possible variants of the PMTGMU board you can build and the differences between them. You can find it in the PMEQP1A folder of the DIY section of my whizzy new web site:

https://sites.google.com/site/customtubeconsoles/diy (https://sites.google.com/site/customtubeconsoles/diy)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Rocinante on July 01, 2015, 12:49:42 PM
Good morning,
I have Pier's App IO boards and would like to use them for the PMEQP1A.  I am debating making a ic/DOA path switchable with the poor mans tube gain make up but for right now I need to get the IO board correct in my head. 
I do understand the PMTGMU but on the IO boards I have a few spots of confusion.
I will be using DOA/IC in but Carnhill transformer out.
I have modified Dave's diagram and am wondering where I would place where "Pin" would go since I am using the IO board.  Also is everything else correct?

Thanks
Dylan
(http://i.imgur.com/u4wqXK3l.jpg)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 01, 2015, 06:58:15 PM
All the DPDT switch does is connect a trimmable pad in in place of the EQ  in the EQ OUT position. You adjust it so its loss is the same as the EQ. This trimmable pad exists between Pin, Pout and PG on the PMTGMU board. If you are not using the PMTGMU solution then you need to build this trimmable pad somewhere. The eqsystem.jpeg drawing shows how to do this.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Rocinante on July 02, 2015, 12:54:14 AM
Ahh.. Thanks I see it now. I'll keep it just PMTGMU I guess. Thanks for the quick response.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on August 16, 2015, 03:59:04 AM
Do you think you could get away with using a SPDT switch instead? in other words, can you tie and output of the passive EQ and the output of the Pad together going to the makeup gain, and then just switch the input? Or the other way around?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 16, 2015, 05:43:22 AM
Do you think you could get away with using a SPDT switch instead? in other words, can you tie and output of the passive EQ and the output of the Pad together going to the makeup gain, and then just switch the input? Or the other way around?

You cannot tie together the output of the EQ to the output of the pad because the pad would load the output of the EQ and seriously distort its response. However, if you want to get away with a SPDT switch you could tie the inputs of the EQ and the pad together and switch the outputs. This will work but it is not ideal. Both the pad and the EQ are designed to provide a 10K load to the input transformer. If you connect the two inputs together the load becomes 5K. Provided whatever you drive the transformer with has a low output impedance then this will made little if any difference. If it does not then you could lose some bass response and, even with the EQ bypassed, its changing input impedance with frequency could alter the frequency response. I have never tried it but it will not do any harm so I suggest you give it a try.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on August 18, 2015, 03:59:36 AM
thanks ian. Very helpful.

i ended up positioning the IN/OUT switch on my panel in a bit of a tight spot and found I could only fit a SPDT toggle in.

I'll do some testing when peters inductors arrive. Worst case I use relay's.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on August 22, 2015, 06:00:42 AM
Hi Ian,

Another question.

I'm using this gain stage - https://dl.dropboxusercontent.com/u/91809016/MY_Circuit.pdf

What would you recommend for values for the input trim pot as I saw that your eq system guide shows 470k pot - http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/EQSystem.png

Should I replace the 10k pot with 470k pot - do I require any further input resistors?

Thanks for your time. Rob
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 22, 2015, 06:41:38 AM
Hi Rob,

The amp schematic you posted consists of a Darlington pair of input transistors as a gain stage followed by a regular totem pole output stage. As there is only one inversion (due to the Darlington) the NFB has to be applied at the amp input (dc NFB via the 1.5Meg and ac  NFB via the 220K). The gain is set by the ratio of the 200K divided by the value of the input  trim pot. Unfortunately, the input impedance is also determined by the value of the trim pot so it will never be more than 10K (the NFB makes the bas of the first transistor a virtual earth). 10K is far to low a load for the poor man's EQP1A. I am not 100% sure we can cajole this into working properly with the EQP1A.

We need about 20dB of gain make up. If we removed the 220K ac feedback resistor and replaced the trim pot with a 220K we might have a solution. The 1.5Meg now provides both the dc and ac feedback. The 47uF output cap is no no longer in the feedback path but I do not think this is important. If you feed the output into a 10K load, the response will be 3dB down at 0.33Hz.  The trim pot will end up at around 150K for 20dB of gain make up. This is a little on the low side but not enough to make the EQ unworkable.

Is this your own design?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on August 22, 2015, 07:59:38 AM
Hi ian,

Thanks for that explanation, I now have a much better understanding on how this particular gainstage is working and will have a play around with it.

Its not my design, you will find further details here -  http://groupdiy.com/index.php?topic=59222.0 - I've been playing around with it as an alternative to a 2520 gain amp I was planning on using so no big fuss if I run into some roadblocks.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 22, 2015, 08:30:25 AM
OK, understood. It did not want to criticize the design until I knew whose it was. That circuit, as it stands, is quite primitive as regards the way it biases the first stage. It is very hard to determine at what dc voltage the output will sit and it depends a lot on the gains of the transistors used. It was a common bias method in very early designs. If you look here:

http://s26.photobucket.com/user/rascalseven/media/PEQ-2Acircuit.jpg.html (http://s26.photobucket.com/user/rascalseven/media/PEQ-2Acircuit.jpg.html)

You will see the improved version that removes the dependence on transistor gain but it does require an extra transistor. It also disconnects the gain control form the input circuit so the input impedance is not changed as you change the gain. The input impedance is also a little higher. However, this circuit is still not ideal. First it uses a pot divider (1Meg and 47K) straight across the power supply to bias the first transistor. This gives it a nice 'stiff' bias voltage but any noise on the supply is injected directly into the base of the first transistor - not a good idea. I have not been able to find a later version that addresses these problems.

I guess the bottom line is that discrete transistor design is just as hard as tube design and there are plenty of designs out there that would better suit your purposes.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on August 23, 2015, 02:45:27 AM
Hi Ian,

Had a play around with this today and came up with a solution.

I have built an extra board using vero - it handles the IN/OUT relay's, the pad and pad trim, and also a jfet impedance buffer(not that there was anything wrong with your solution).  So before it gets to the gain stage the Poormans EQ gets the high impedance it wants/needs.  The circuit was simple enough, 1 transistor, a few caps + a few resistors. Best part is that I learned a lot today!

I tested with EQ without inductors installed and the low boost + cut works well and as expected - it was only tested by ear but a promising result nonetheless.

All and all a good day. Big thanks for your knowledge and wisdom and quick response - its always appreciated.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 23, 2015, 06:04:54 AM
For semiconductor gain make up for the PMEQP1A, a FET input is always the best solution. ell done.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on September 05, 2015, 06:24:13 AM
While I wait for peters inductors I thought some pictures of the front panel + knobs is in order.

I took these while doing testing of gainstage  + in/out. Its working very well. I can only test the low boost/cut and high cut, but these are working as expected so far, once the inductors arrive I can do the final test, but so far its looking very promising.

(http://www.thraxeh.com/Pics/pultec/progress/1.jpg)

(http://www.thraxeh.com/Pics/pultec/progress/2.jpg)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: anjing on September 05, 2015, 08:44:07 AM

Very nice looking front panel design!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on September 16, 2015, 01:53:53 PM
This is really great design.

About my gain stage,i understand what's wrong but it's fine with my pultec.I can't see any problem.But if we have to add impedance matching circuit(hi-z to low-z),we can use interstage transformer,too.Am i right?If we can use transformer,can you recommend any transformer or ratio?10K:600 or what?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 16, 2015, 07:35:17 PM
This is really great design.

About my gain stage,i understand what's wrong but it's fine with my pultec.I can't see any problem.But if we have to add impedance matching circuit(hi-z to low-z),we can use interstage transformer,too.Am i right?If we can use transformer,can you recommend any transformer or ratio?10K:600 or what?

A transformer might work if you used one of those intended for DI applications. However, the step down ratio means you need even more gain make up and this would probably   lead to noise problems so I would not recommend it. Way back in the early days of the design there was a lot of discussion of this topic and some interesting solutions were presented. I suggest you search through the original threads for them.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: troubleous on September 20, 2015, 06:39:15 AM
Hey fellow builders!

Anyone know a source for a power transformer for this project? I've got a dual channel build with Ian's EQP1A, PMMID and PMTGMU (+ HT Supply PCB) - been trying to hunt down a trafo, no luck by far :(

Any ideas very welcome!

Cheers,
Jarkko
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 20, 2015, 11:42:37 AM
Hey fellow builders!

Anyone know a source for a power transformer for this project? I've got a dual channel build with Ian's EQP1A, PMMID and PMTGMU (+ HT Supply PCB) - been trying to hunt down a trafo, no luck by far :(

Any ideas very welcome!

Cheers,
Jarkko

The power requirements of the two amplifiers are very modest and as far as I know there is not a transformer that exactly fits the bill. As a result, most people end up using a transformer that is a little bit of an overkill but nonetheless works well. I have heard that many people use an Antek  AS-05T240 - 50VA 240V transformer:

http://www.antekinc.com/as-05t240-50va-240v-transformer/ (http://www.antekinc.com/as-05t240-50va-240v-transformer/)

Don-Audio also makes one that you can use that was designed for the Mila project:

https://www.don-audio.com/Toroidal-Transformer-Mila-sec-250vct-63vct-48V (https://www.don-audio.com/Toroidal-Transformer-Mila-sec-250vct-63vct-48V)

Right now, Don-Audio is designing a custom mains toroid for me for the Classic Solo project which is basically a pair of PMTGMU circuits and a power supply on one board. THis transformer should therefore also be ideal for powering a couple of PMTGMU boards. The prototype board is due at the end of September.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: troubleous on September 20, 2015, 11:45:07 AM
Aaah, that Antec is back on stock - the last time I checked, it was out of stock. I will order that immediately.

Thanks Ian!

/Jarkko
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: troubleous on September 21, 2015, 03:55:44 AM
Another question for the wise:

What's would be the wisest way to hook up a pilot light - preferably led - when having dual channel build (Antec feeding two PMTGMU's from 6.3V)?

Cheers,
Jarkko
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 21, 2015, 05:27:19 AM
Another question for the wise:

What's would be the wisest way to hook up a pilot light - preferably led - when having dual channel build (Antec feeding two PMTGMU's from 6.3V)?

Cheers,
Jarkko

I would suggest you power it from the 6.3AC winding via a suitable current limiting resistor. As the supply is AC you should add a diode across the LED to limit the reverse voltage across the LED - a 1N41418 should do it. LEDs typically draw 10 mA so  series resistor in the region of 620 ohms should be about right.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on September 27, 2015, 08:55:17 AM
Hi,

Bought most of the parts for my build now and started preparing everything (building a stereo version with poor mans make up gain). I just wanted to make sure this power transformer would work ok? Specs show 2x6v secondaries 50va. I'm in the UK.

http://www.ebay.co.uk/itm/201257651358

Thanks
Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 28, 2015, 05:30:27 AM
Hi,

Bought most of the parts for my build now and started preparing everything (building a stereo version with poor mans make up gain). I just wanted to make sure this power transformer would work ok? Specs show 2x6v secondaries 50va. I'm in the UK.

http://www.ebay.co.uk/itm/201257651358

Thanks
Paul

That will do for the heaters but it is rather overkill. Even if you use 6CG7 tubes, the total heater current is only 1.2A which  is a power requirement of just just over 7.5 watts so a 10VA or 15VA  transformer would be more than enough. Don't forget you will also need a transformer for the HT voltage.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on September 28, 2015, 05:56:58 AM
Hi,

Bought most of the parts for my build now and started preparing everything (building a stereo version with poor mans make up gain). I just wanted to make sure this power transformer would work ok? Specs show 2x6v secondaries 50va. I'm in the UK.

http://www.ebay.co.uk/itm/201257651358

Thanks
Paul

That will do for the heaters but it is rather overkill. Even if you use 6CG7 tubes, the total heater current is only 1.2A which  is a power requirement of just just over 7.5 watts so a 10VA or 15VA  transformer would be more than enough. Don't forget you will also need a transformer for the HT voltage.

Cheers

ian

Thanks Ian I was hoping to wire my pair similar to Daveseqp-1ahookup.pdf on your dropbox documents. I went for the stereo pair of mk2 boards with x2 poor mans make up and psu board. I thought I only needed the 1 transformer to power it all. 

Stuffing the boards is giving me time to figure this part out so not rushing into it
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 28, 2015, 09:23:38 AM

Thanks Ian I was hoping to wire my pair similar to Daveseqp-1ahookup.pdf on your dropbox documents. I went for the stereo pair of mk2 boards with x2 poor mans make up and psu board. I thought I only needed the 1 transformer to power it all. 

Stuffing the boards is giving me time to figure this part out so not rushing into it

You can use one transformer but it needs to have two separate secondary windings; one for the heaters and one for the HT. Check out this post for recommended types:

http://groupdiy.com/index.php?topic=44213.msg766586#msg766586 (http://groupdiy.com/index.php?topic=44213.msg766586#msg766586)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on September 29, 2015, 07:11:49 PM
Ok last try at being cheap! What about this one? http://www.ampmaker.com/store/240V-6.3V-toroid-power-transformer.html

If not this im gonna have bite the bullet and go for the antec.

Cheers

Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 30, 2015, 04:54:09 AM
Ok last try at being cheap! What about this one? http://www.ampmaker.com/store/240V-6.3V-toroid-power-transformer.html

If not this im gonna have bite the bullet and go for the antec.

Cheers

Paul

That is absolutely perfect! I have a funny feeling we came across that one sometime earlier in the thread. I think it might be a good idea to create a list of suitable mains transformers and add it to the DIY section of my web site.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: p0ulp on October 03, 2015, 03:47:40 AM
For european , I think this one is also ok :)

http://www.ebay.de/itm/Ringkern-Roehren-Trafo-17-VA-240V-6-3V-Transformer-Roehre-Tube-Preamp-/291368326969?

sorry for the ebay link , if it's not ok I ll remove it, anyway I buy one and let you know if I can find info about the manufacturer and how does it looks like.

Sorry for UK product I m sure they are great quality but shipping is way more expensive to France :/, no need to say about US Antek ...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on October 03, 2015, 04:41:22 AM
hi ian,

this might be a silly question. I'm trying to understand the PAD for the EQ bypass.

As per the note, I used a 10K resistor + 1k trimmer for the pad and when I engage the pad I can only get the output to 2db less than the EQ, and if I turn the 1k trim the other way, I can get rid of the entire signal and it drops back to the noise floor.

I'm now a little bit confused as to why I can reduce the signal to nothing. It doesn't seem to behave has expected.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 03, 2015, 06:48:14 AM
hi ian,

this might be a silly question. I'm trying to understand the PAD for the EQ bypass.

As per the note, I used a 10K resistor + 1k trimmer for the pad and when I engage the pad I can only get the output to 2db less than the EQ, and if I turn the 1k trim the other way, I can get rid of the entire signal and it drops back to the noise floor.

I'm now a little bit confused as to why I can reduce the signal to nothing. It doesn't seem to behave has expected.

Looks like you have missed out the 470R resistor  between the bottom of the trim and 0V.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on October 03, 2015, 07:35:47 AM
you are right, I completely missed it, I just put it in place and its now sitting in proper range.

thank you!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Rocinante on October 11, 2015, 12:30:08 AM
Ooh lest I forget.  MY D-Pultec PM-EQP-2A.
Damn lovely.


THANKS IAN!!!!!!!




(http://s26.postimg.org/yfgxah3q1/2015_10_10_21_06_44.jpg)

(http://s26.postimg.org/655b6ulnd/2015_10_10_21_15_26.jpg)

(http://s26.postimg.org/ux4xe32u1/2015_10_10_21_18_52.jpg)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 11, 2015, 06:26:34 AM
Ooh lest I forget.  MY D-Pultec PM-EQP-2A.
Damn lovely.


THANKS IAN!!!!!!!


Cool! Would you like to email the pics to Pierre so he can add them to his gallery of my projects?

Cheers

ian


Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 11, 2015, 06:34:30 AM
While I remember,  I recently posted a note to my white market thread to announce the retirement of the HT350 PCB. It was originally intended for providing HT for a complete mixer so it was always a bit of an overkill for a couple of PMTGMU stages. I have now replaced it with the HT250 board. It uses smaller/cheaper 220uF caps, a low cost DIL recrtifier and the PCB is nearly half the size of the HT350. The new HT250 PCB cost just £4.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Rocinante on October 11, 2015, 07:20:47 AM
Ian,
I'd be happy to email some pics to you.  I also have finished the Classic Twin tube preamp (which the ht250 would've been perfect for as well) just need to take a couple of pics.
It'll also get its own thread.
Another great project sir. Thanks again.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnheath on November 03, 2015, 10:02:14 PM
Ian...

First of all I must say that you have a very interesting project here :)

Even though evereything is perfectly presented I still have a few questions:

Have you experienced any problems by having the output transformer inside the chassis together with the power transformer? If so how did you solve it? =)

The rotary switches are the shorting or not? And since I am a sucker for PTP and want to give it a try and I wonder if there are some rotary switches that you recommend specifically for this EQ?

And finally... The make up stage... Is your choice of tube critical or will anything close to it do?


Best regards

/John
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 04, 2015, 07:09:52 AM
Ian...

First of all I must say that you have a very interesting project here :)

Even though evereything is perfectly presented I still have a few questions:

Have you experienced any problems by having the output transformer inside the chassis together with the power transformer? If so how did you solve it? =)

Yes, but it depends on the transformer. The only ones I have had any slight hum problem with are the Carnhill ones. Sowter and Edcor have been fine. The solution is to keep them well apart and adjust their relative orientation for minimum hum. Having said this, the hum level level I have experienced has been down at -85dBu so I expect most people will jot have noticed it.

Quote
The rotary switches are the shorting or not? And since I am a sucker for PTP and want to give it a try and I wonder if there are some rotary switches that you recommend specifically for this EQ?

The switched are non shorting. The PMEQP1A PCB and the MK2 version are both designed to used low cost Lorlin rotary switches. The 3 band Pultec PCB is designed to use the (more expensive)  Grayhill 71 series switches.

Quote
And finally... The make up stage... Is your choice of tube critical or will anything close to it do?


Best regards

/John

The original PMTGMU stage was designed to use a 6CG7 tube mainly because it was a straight copy of one stage of one of my early mic pre designs. However, it does have limited drive capability which means it can only feed a 10K bridging load (not normally a problem). Later mic pre designs centred on the 6922 (E88CC) tube. This has a much lower plate resistance and hence a better drive capability. It produces more distortion than a 6CG7 but if run at a higher current it is nearly as distortion free as the 6CG7 and the higher current also improves its drive capability still further. More recently I have developed a third version using a 12AU7. The 12AU7 has nearly the drive capability of the 6922 but more distortion. Although not ideal, the 12AU7 version does at least provide the opportunity to operate from 12V heaters (which was why it was developed).

All the above is described in more detail on my web site. Under the DIY tab:

http://www.customtubeconsoles.com/diy (http://www.customtubeconsoles.com/diy)

 select the PMEQP1A folder and then the PMTGMU folder.



Did you have any particular tube in mind?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnheath on November 04, 2015, 12:06:42 PM
Hi Ian

Well, I can't really say that I had a specific tube in mind even though I have had good practice and experience with 12AU7 as driver tube in SRPP configuration. I am open to hear what people say about other tubes.

The 12V heater possibility is nice if you want it but have you had any problems with hum from the 6,3vac for heaters in this project... I guess it is a matter of proper layout with a touch o luck when designing the layout? :)


Best regards

/John
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 04, 2015, 12:34:45 PM
Hi Ian

Well, I can't really say that I had a specific tube in mind even though I have had good practice and experience with 12AU7 as driver tube in SRPP configuration. I am open to hear what people say about other tubes.

The 12AU7 is well known to have relatively high intrinsic distortion. An SRPP topology generally produces more distortion than a mu follower so a 12AU7 SRPP is definitely not a recipe for low distortion. That said, this is often a sound that people like. If you are happy with it then go for it.

Quote
The 12V heater possibility is nice if you want it but have you had any problems with hum from the 6,3vac for heaters in this project... I guess it is a matter of proper layout with a touch o luck when designing the layout? :)


Best regards

/John

Not had any problems with ac heaters on this design at 6V or 12V. With mu followers and SRPP you do need to use elevated heaters. This means the cathode of the lower triode is reverse biased relative to the heater so heater hum does not get coupled to the cathode. If you use NOS tubes with poor heater cathode insulation the elevated heaters will cause a lot of hum in the output - it is an excellent detector of dodgy NOS tubes.

The original EZTubeMixer designs used dc heaters because of my concerns about possible heater hum especially in sensitive mic pres. However, in the last few months I have  conducted a wide range of tests on them using ac heaters. I fully expected hum to be a problem and anticipated having to make considerable modifications to get them working with ac heaters.  However, I am pleased to report that they all work without modification  without any sign of heater hum.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnheath on November 04, 2015, 01:40:30 PM
Yes, I know about the heater elevation... been troubling with that before. But I thought that the 12AU7 was a good choice for SRPP but if you say it is not I might consider another tube for that  topology?

I also have been thinking about using ac for heaters since it is a low cost and low labour alternative to dc fixes... and as you say it is a concern about hum caused from this ac. I have ordered some cahssis to start testing myself and I am glad to hear that you don't have any trouble with it so far.

I use mostly sowter transformers and they are great I think (there might be better ones I don't know).

So... from your experience what would be a GREAT tube for SRPP final stage of a mic pre?

Best regards

/John
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 05, 2015, 02:24:31 AM

I use mostly sowter transformers and they are great I think (there might be better ones I don't know).

There are a number of transformer manufacturers in Sowters leaugue. Cinemag, Carnhill, , Jensen and Llundahl come to mind.

Quote
So... from your experience what would be a GREAT tube for SRPP final stage of a mic pre?

The output stage of my Eurochannel mic pre uses a 6922 configured as an SRPP principally for its output drive capability.  On its own this stage produces mostly second harmonic distortion which many people find pleasant. In the Eurochannel design its distortion is reduced by about 20dB of negative feedback.

Cheers

IAn
Best regards

/John
[/quote]
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on November 05, 2015, 01:24:41 PM
Hi
I'm working in a DOA make up stage.
If I use the schematics attached there are component  values to be changed?
Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 06, 2015, 02:27:57 AM
Hi
I'm working in a DOA make up stage.
If I use the schematics attached there are component  values to be changed?
Thanks!

This question was asked some time ago. I have added my recommended 2520 configuration in the PMTGMU folder of my web site.

https://drive.google.com/file/d/0B_n67A1hN3qtNzBHSGN5VkIxSFE/view?usp=sharing (https://drive.google.com/file/d/0B_n67A1hN3qtNzBHSGN5VkIxSFE/view?usp=sharing)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on November 06, 2015, 02:45:11 AM
Sorry and Thanks Ian!!!!
Just one question
only 3 resistor? no caps?
Thanks!!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on November 06, 2015, 04:07:46 AM
Sorry and Thanks Ian!!!!
Just one question
only 3 resistor? no caps?
Thanks!!!!

I created a DOA opamp gain stage and used Ian's recommended resistor vales(which will get you the correct input impedance + gain needed for PMPEQP1) + API's data sheets to help with capacitor values.

here is a copy of API's datasheets for 2520 - look at the line amplifier notes.

https://static.gearslutz.com/board/imgext.php?u=http%3A%2F%2Fwww.danalexanderaudio.com%2FApiInfo%2Fapi2520_02.jpg&h=219268859c89ebb165b98902767ad0c7

I will let someone confirm, but I think with a 10k feedback resistor, you will want to be around the 270pF value for a capacitor across the feedback resistor. This gives you a corner frequency of 59khz to help with potential oscillation issues.

Is this correct?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 06, 2015, 05:23:33 AM
My diagram was intended to show the resistor values you need to get an appropriate input impedance and gain range for the the  amplifier. You do need to also take into account the specific requirements for dc isolation and stability of the device you choose.  In general you should not need an input coupling capacitor. A capacitor inseries with the 2K2 pot is probably a good idea as it keeps bias current out of the pot and also ensures the op amp dc gain remains at unity so offset voltages are not amplified. I think 59KHz is a little on the low side for a 3dB point as this could lead to significant phase shift at 20KHz. I would try 100pF.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: theaterguy on November 06, 2015, 07:46:32 AM
Hi boost with RC or LC?
How do they compare soundwise? Now it seems that VTB9042 is going to be the most expensive item in my  eq. 
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 06, 2015, 11:19:59 AM
Hi boost with RC or LC?
How do they compare soundwise? Now it seems that VTB9042 is going to be the most expensive item in my  eq.

The RC high boost is a shelving type. This means just about all frequencies above a certain value are boosted more or less equally. Useful for adding overall clarity to the top end.The LC is a bell shape type which means a set band of frequencies only are boosted. This is handy if you need to pull a particular instrument out of the mix. I am sure you can find a free plug in somewhere that will allow you to compare the sound of the two. Only your ears can tell you which one you need/prefer.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: theaterguy on November 06, 2015, 03:58:48 PM
Thanks, it's very clear now!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on November 07, 2015, 05:20:45 PM
My diagram was intended to show the resistor values you need to get an appropriate input impedance and gain range for the the  amplifier. You do need to also take into account the specific requirements for dc isolation and stability of the device you choose.  In general you should not need an input coupling capacitor. A capacitor inseries with the 2K2 pot is probably a good idea as it keeps bias current out of the pot and also ensures the op amp dc gain remains at unity so offset voltages are not amplified. I think 59KHz is a little on the low side for a 3dB point as this could lead to significant phase shift at 20KHz. I would try 100pF.

Cheers

Ian
Thanks to all!!!
Now my unit it's working Thanks!!!

Just one info about a 2k2 series capacitor...
Little help for the right value?
THANKS!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 07, 2015, 06:06:44 PM
Just one info about a 2k2 series capacitor...
Little help for the right value?
THANKS!!!

Just calculate it for a subsonic -3dB point. For example 2K2 and 47uF has a -3dB point close to 1.5Hz.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on November 07, 2015, 06:45:19 PM
Thanks Ian
cap negative  to 2k2 pot?
Sorry for a stupid question...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on November 07, 2015, 07:58:24 PM
Hi boost with RC or LC?
How do they compare soundwise? Now it seems that VTB9042 is going to be the most expensive item in my  eq.

The RC high boost is a shelving type. This means just about all frequencies above a certain value are boosted more or less equally. Useful for adding overall clarity to the top end.The LC is a bell shape type which means a set band of frequencies only are boosted. This is handy if you need to pull a particular instrument out of the mix. I am sure you can find a free plug in somewhere that will allow you to compare the sound of the two. Only your ears can tell you which one you need/prefer.

Cheers

Ian

i was going to ask the same question but also had another question.

I've been using this calculator - http://www.calctool.org/CALC/eng/electronics/RLC_circuit

Very helpful for determining center frequency values - however I'm getting stuck on converting the results to Q.

They give the FWHP - which as I understand is the width between the half way points(halfway on each side of the bell curve). However, we actually want the value from the -3db point on each side instead so we can convert this to the Q value - is this correct?

So my question is, is there a simple(or at least a way) to convert the FWHP value they provide to Q?

Secondly - have I opened up a can of worms I shouldn't have opened?  ;D
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 08, 2015, 02:09:44 PM
It is very easy to calculate Q. It is just wL/R where w is the frequency in radians (2,pi,f), L is the inductance and R is the resistance.

The hard part is determining the value of R. Most passive EQs use a series resonant circuit. This means R is the sum of all series resistances in the series resonant circuit. These include the resistance of the inductor, the resistance of the Q pot if there is one and the resistance of the boost/cut control itself. You also have to consider what you mean by Q. If you set a resonant EQ circuit to give 2dB of boost, how would you measure the -3dB points? For this reason it is common to specify the Q at maximum boost or cut.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 08, 2015, 09:22:14 PM
Hi can anyone help me with the pad switch wiring for the new mk2 boards (with mid)? I see in Dave's wiring diagram some of the pots (and from T1 on the high board) are wired to the dpdt switch,  yet my board has no T1-4 connections, instead just 'in' and 'out'  as the pots are wired direct to there own 3 pin connectors on the board. Everything else is in order (pcb's complete, pots wired, power wired and ready to test) but just the wiring diagram is not making much sense as it for separated hi and low board which required manual wiring of the pots which mine does not seem to need. If I had the separated hi and low boards it would make perfect sense to wire it as per Dave's hook up diagram. If I wanted to I could wire the same way as Dave but using my mk2 boards but wont that defeat the object of the updated board with nice 3 pin connectors for the pots?

I'm wiring 2 mk2 boards up in 1 case for a stereo pair. Will this make any difference? Ive got 2 dpdt switches 1 for each channel.

Hope someone can help.

Thanks

Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 09, 2015, 02:34:47 AM
Dave's hook up diagram is intended for the original design. The MK2 aimed to simply construction by containing a lot of the wiring on the PCB and having standard pin outs for the pots and switch. You need to read the MK2 assembly guide which you can get here:

https://drive.google.com/file/d/0B_n67A1hN3qtbXNYWHc0STBlZGM/view?usp=sharing (https://drive.google.com/file/d/0B_n67A1hN3qtbXNYWHc0STBlZGM/view?usp=sharing)

It is also in the MK2 folder in the PMEQP1A folder of the DIY tab of my web site.

Cheers

IAn
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 09, 2015, 06:14:08 AM
Thanks Ian, I have read the guide over and over and I can see just looking at the board/components everything is built in for the switches. I dont see any mention of switch wiring in your guide. Ive never wired a pad switch before.  Am I meant to wire 1 side of the dpdt switch to the in/out of the pots and the other to the in/out of the pad? it seems to me that would bypass the gain stage. Im just learning here and feel so confused. So sorry to ask these stupid questions but I need to understand.

Im trying to wire 2x of your mk2 board to 2x your tube gain stages. This is the part Im finding most difficult.

Cheers
Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 09, 2015, 08:51:15 AM
Maybe I should just follow the in/out for the eq on the 2 wire digram? Would that work ok?

https://drive.google.com/folderview?id=0B_n67A1hN3qtfkNFTjdqVUtDeUM0YlNzWHZUQ1BKUHpPTkt4TnB3aV8xREtIVmo4Z0xPVlU&usp=drive_web

Thanks again
Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 09, 2015, 10:07:50 AM
Maybe I should just follow the in/out for the eq on the 2 wire digram? Would that work ok?

https://drive.google.com/folderview?id=0B_n67A1hN3qtfkNFTjdqVUtDeUM0YlNzWHZUQ1BKUHpPTkt4TnB3aV8xREtIVmo4Z0xPVlU&usp=drive_web

Thanks again
Paul

Apologies, I had not noticed you were talking about the EQ bypass switch. Yes, you wire that up like any passive EQ as shown in the 2-wire diagram.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 09, 2015, 10:10:21 AM

They give the FWHP - which as I understand is the width between the half way points(halfway on each side of the bell curve). However, we actually want the value from the -3db point on each side instead so we can convert this to the Q value - is this correct?

So my question is, is there a simple(or at least a way) to convert the FWHP value they provide to Q?

I just realise the FWHP stand for full width half power which is the -3dB points. So just divide the centre frequency by FWHP to get Q.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 09, 2015, 11:04:03 AM
Maybe I should just follow the in/out for the eq on the 2 wire digram? Would that work ok?

https://drive.google.com/folderview?id=0B_n67A1hN3qtfkNFTjdqVUtDeUM0YlNzWHZUQ1BKUHpPTkt4TnB3aV8xREtIVmo4Z0xPVlU&usp=drive_web

Thanks again
Paul

Apologies, I had not noticed you were talking about the EQ bypass switch. Yes, you wire that up like any passive EQ as shown in the 2-wire diagram.

Cheers

ian

Thanks Ian at I think i'm on the right path, its making sense now.  Just to clarify on the 2 wire digram the eq board shows in and out being 1 wire with a 0v line ran from the transformer to the eq board and finally the output switch. I have 2 wires each side of my mk2 board for i/o. Do I simply measure the voltage to find out which pin is 0v and link them together at the switch? Also do I omit the 12k resistor on the input with my version being unbalanced (may add transformers for the next eq build, but keeping costs low for this one).

Ill get some pics up when I have the front panel sorted.

Thanks for all the help.

Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 09, 2015, 06:08:02 PM
Thanks Ian at I think i'm on the right path, its making sense now.  Just to clarify on the 2 wire digram the eq board shows in and out being 1 wire with a 0v line ran from the transformer to the eq board and finally the output switch. I have 2 wires each side of my mk2 board for i/o. Do I simply measure the voltage to find out which pin is 0v and link them together at the switch? Also do I omit the 12k resistor on the input with my version being unbalanced (may add transformers for the next eq build, but keeping costs low for this one).

Ill get some pics up when I have the front panel sorted.

Thanks for all the help.

Paul

Just take the 0V from the EQ input connector to the input. Use the 0V connection of the output for the screen of the output cable shown on the 2-wire. The 0V pin on both connectors is the one with the square pad which is the bottom one in both cases. You can omit the 12K resistor at the input.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 10, 2015, 01:11:08 PM
I have drawn and attached my own version of the 2 wire hook up diagram based on the power transformer I am using and the MK2 boards. Its is for unbalanced operation. I will be using this to power 2 gain stages so I'll be duplicating many of the power connections from one toroid/psu but decided just to keep it simple and show the one in the diagram. I hope it can help someone else in the future.  Re-drawing it myself really helped me to understand how and why it works.

Fingers crossed it might actually work.

Cheers
Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 10, 2015, 05:38:20 PM
Looks OK to me ap[art from the output socket is wired incorrectly. Right now the Out goes direct to chassis.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 10, 2015, 07:47:23 PM
Well spotted! Id originally done that on the input as well but id changed that and must have missed it on the output. Also the fuse should be on the brown live wire and not the neutral. Ill get it changed tomorrow and repost it.

Thanks again
Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 11, 2015, 02:25:13 AM
Well spotted! Id originally done that on the input as well but id changed that and must have missed it on the output. Also the fuse should be on the brown live wire and not the neutral. Ill get it changed tomorrow and repost it.

Thanks again
Paul

You might like to add screened cable from the EQ input to the switch and from the switch to the input connector.  Connect the screens together at the switch so there is a 0V connection all the way from the EQ in to the input connector. It is not strictly necessary as the input is likely to be relatively low impedance but  it is good practice.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 11, 2015, 08:28:36 PM
Well spotted! Id originally done that on the input as well but id changed that and must have missed it on the output. Also the fuse should be on the brown live wire and not the neutral. Ill get it changed tomorrow and repost it.

Thanks again
Paul

You might like to add screened cable from the EQ input to the switch and from the switch to the input connector.  Connect the screens together at the switch so there is a 0V connection all the way from the EQ in to the input connector. It is not strictly necessary as the input is likely to be relatively low impedance but  it is good practice.

Cheers

Ian

Ive updated my wiring diagram with a few more things and taken into consideration the input shield you mentioned. Hopefully this is better and will make a little more sense to people like me who are still learning.

Thanks again

Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 12, 2015, 02:28:48 AM
I just realaied you have pins 1 & 3 of  both input and output  XLRs strapped together and connected to chassis. You do not need to strap them together. Tie pin1 to chassis but not to pin 3. The signal 0V (pin3) gets connected to chassis via the power supply. You should also add a screened lead from the input XPR to the switch an connect its screen to the one going to the EQ input.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: troubleous on November 13, 2015, 05:06:59 AM
Hi Ian and everyone following!

I'm almost finished with my build but I have a peculiar problem with my mid board. Everything is working as expected, except when I turn the mid switch to 4K position, the sound cuts off completely.

I'm re-checking and re-checking the wiring (as per the Mid Hookup PDF), but I just can't figure out what the problem is. Probably something obvious that keeps missing my eye :)

I've also cut the traces from the mid board as instructed.

Is there anything obvious that comes to mind that could be wrong? Maybe someone has had the same problem before, no?

Cheers from Sweden!
/Jarkko
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 14, 2015, 02:42:43 AM
If all the other mid frequencies work OK then it suggests to me that there is a short across the 4K capacitor. SOlder splash or faulty cap maybe. Try removing the 4K cap and see if it goes away.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: troubleous on November 14, 2015, 03:29:43 AM
Hi Ian!

I'll try removing the capacitor - though the problem is the same on both channels (building 2xmono unit here), suggesting me it's some stupid wiring error on the mid boards.

I'll let you know.

Cheers,
Jarkko
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: troubleous on November 15, 2015, 06:40:16 AM
Hi!

Alright, no change after removing 4K (C7) cap from both mid boards - the sound still cuts off when mid frequency is set at 4K and boost/cut is full on (rotary switch at pos 12).  Staring at the schematics + wiring guide and trying to figure out what could be wrong...

Any ideas?

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 16, 2015, 05:54:30 AM
I just realaied you have pins 1 & 3 of  both input and output  XLRs strapped together and connected to chassis. You do not need to strap them together. Tie pin1 to chassis but not to pin 3. The signal 0V (pin3) gets connected to chassis via the power supply. You should also add a screened lead from the input XPR to the switch an connect its screen to the one going to the EQ input.

Cheers

Ian

Ok so I changed the xlr wiring and the screen like you said and I got the gain stages working but I have a few issues:

When bypassed all is well and sounds really nice and 'tubey' but when I engage the eq the mid band seems to have around a 2db boot or cut (depending on mid switch position) at the lowest pot setting (fully ccw). 

My high bands are not working properly. I get maybe 2db of cut when the pot is up fully cw but I dont get any boost at all. I'm not using a high inductor so your guide shows to short all the points where the inductor would gone and short the high Q. I've used hook up wire to short all the high inductor points together and Ive shorted the 3 high Q pins with some wire. Do I now hook these together with some more wire?

The last problem is that one of my channels looses the bass cut when it is connected to the pmgmu stage, if I remove the eq and connect to my d/a converters with a preamp the bass works fine. It's strange because I have both channels wired the exact same way yet just the 1 has this issue.

I've checked all cap values and they all match up to the schematic. I cant see any shorts.

I'm getting there, slowing but surely.

Cheers

Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 16, 2015, 06:00:46 AM
If you are using  a Carnhill inductor with the built in metal clamp, this can sometimes short against on of the switch pins.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 16, 2015, 06:31:29 AM

Ok so I changed the xlr wiring and the screen like you said and I got the gain stages working but I have a few issues:

When bypassed all is well and sounds really nice and 'tubey' but when I engage the eq the mid band seems to have around a 2db boot or cut (depending on mid switch position) at the lowest pot setting (fully ccw). 

The mid boost cut switch is supposed to be a three position centre off type. This is required because the simple design of the mid EQ means that this is the only way it can be fully off.
Quote
My high bands are not working properly. I get maybe 2db of cut when the pot is up fully cw but I dont get any boost at all. I'm not using a high inductor so your guide shows to short all the points where the inductor would gone and short the high Q. I've used hook up wire to short all the high inductor points together and Ive shorted the 3 high Q pins with some wire. Do I now hook these together with some more wire?
The boost and cut are separate circuits.For the hi boost you just short all the inductor pins together and also short the hi Q pins together. Don't forget to fit the Qmax resistor 4K7. Did you use the Cpoorboost capacitor values?

For the cut, the only thing I can think of is you have the wrong value resistor for the 430 ohms just above and to the right of the the hi switch.
Quote
The last problem is that one of my channels looses the bass cut when it is connected to the pmgmu stage, if I remove the eq and connect to my d/a converters with a preamp the bass works fine. It's strange because I have both channels wired the exact same way yet just the 1 has this issue.

I've checked all cap values and they all match up to the schematic. I cant see any shorts.

I'm getting there, slowing but surely.

Cheers

Paul

The loss of low cut is unusual. Most faults I have come across tend to increase the lo cut rather than reduce it. If the other EQ lo cut works OK on both PMTGMU boards then the fault is clearly in the EQ board, but I cannot think what the fault would be.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 16, 2015, 07:31:47 AM

Ok so I changed the xlr wiring and the screen like you said and I got the gain stages working but I have a few issues:

When bypassed all is well and sounds really nice and 'tubey' but when I engage the eq the mid band seems to have around a 2db boot or cut (depending on mid switch position) at the lowest pot setting (fully ccw). 

The mid boost cut switch is supposed to be a three position centre off type. This is required because the simple design of the mid EQ means that this is the only way it can be fully off.
Quote
My high bands are not working properly. I get maybe 2db of cut when the pot is up fully cw but I dont get any boost at all. I'm not using a high inductor so your guide shows to short all the points where the inductor would gone and short the high Q. I've used hook up wire to short all the high inductor points together and Ive shorted the 3 high Q pins with some wire. Do I now hook these together with some more wire?
The boost and cut are separate circuits.For the hi boost you just short all the inductor pins together and also short the hi Q pins together. Don't forget to fit the Qmax resistor 4K7. Did you use the Cpoorboost capacitor values?

For the cut, the only thing I can think of is you have the wrong value resistor for the 430 ohms just above and to the right of the the hi switch.
Quote
The last problem is that one of my channels looses the bass cut when it is connected to the pmgmu stage, if I remove the eq and connect to my d/a converters with a preamp the bass works fine. It's strange because I have both channels wired the exact same way yet just the 1 has this issue.

I've checked all cap values and they all match up to the schematic. I cant see any shorts.

I'm getting there, slowing but surely.

Cheers

Paul

The loss of low cut is unusual. Most faults I have come across tend to increase the lo cut rather than reduce it. If the other EQ lo cut works OK on both PMTGMU boards then the fault is clearly in the EQ board, but I cannot think what the fault would be.

Cheers

Ian

I will double check the resistor near the high is 430 ohms and will wire the 2 boards seporatley to the suspect tube gain section to double check. I'm glad I used molex connectors now! Ill check the wiring again while i'm there. Also i'm getting a little hum around -60db but I assume thats due to it being unbalanced and without a lid on the chassis.

All these problems aside, what I have heard sounds great and it punches well above its price range. Looking forward to getting rid of all these niggles and moving onto the next one (1176 rev A).

thanks for all the advice
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 17, 2015, 04:30:31 AM

Ok so I changed the xlr wiring and the screen like you said and I got the gain stages working but I have a few issues:

When bypassed all is well and sounds really nice and 'tubey' but when I engage the eq the mid band seems to have around a 2db boot or cut (depending on mid switch position) at the lowest pot setting (fully ccw). 

The mid boost cut switch is supposed to be a three position centre off type. This is required because the simple design of the mid EQ means that this is the only way it can be fully off.
Quote
My high bands are not working properly. I get maybe 2db of cut when the pot is up fully cw but I dont get any boost at all. I'm not using a high inductor so your guide shows to short all the points where the inductor would gone and short the high Q. I've used hook up wire to short all the high inductor points together and Ive shorted the 3 high Q pins with some wire. Do I now hook these together with some more wire?
The boost and cut are separate circuits.For the hi boost you just short all the inductor pins together and also short the hi Q pins together. Don't forget to fit the Qmax resistor 4K7. Did you use the Cpoorboost capacitor values?

For the cut, the only thing I can think of is you have the wrong value resistor for the 430 ohms just above and to the right of the the hi switch.
Quote
The last problem is that one of my channels looses the bass cut when it is connected to the pmgmu stage, if I remove the eq and connect to my d/a converters with a preamp the bass works fine. It's strange because I have both channels wired the exact same way yet just the 1 has this issue.

I've checked all cap values and they all match up to the schematic. I cant see any shorts.

I'm getting there, slowing but surely.

Cheers

Paul

The loss of low cut is unusual. Most faults I have come across tend to increase the lo cut rather than reduce it. If the other EQ lo cut works OK on both PMTGMU boards then the fault is clearly in the EQ board, but I cannot think what the fault would be.

Cheers

Ian

I will double check the resistor near the high is 430 ohms and will wire the 2 boards seporatley to the suspect tube gain section to double check. I'm glad I used molex connectors now! Ill check the wiring again while i'm there. Also i'm getting a little hum around -60db but I assume thats due to it being unbalanced and without a lid on the chassis.

All these problems aside, what I have heard sounds great and it punches well above its price range. Looking forward to getting rid of all these niggles and moving onto the next one (1176 rev A).

thanks for all the advice

I've checked the hi resistors and they are 100% 430 ohms.  I didn't get around to removing the inductors and checking for shorts but I did rewire the suspect tube gain channel using better wires and crimped connectors for the switches. This seems to have fixed the problem and now the low boost is working fine. So that's most of my problems solved I just need to check for the shorts underneath the inductors and Ill have her all working.

I'm expecting my front panel to arrive back today or tomorrow complete with powder coating. Next Ill need to figure out how to use this water slide decal paper to do the silk screening. Either that or I may have it engraved, not sure yet.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 18, 2015, 06:28:42 AM
Ive hit a wall with the high boost. I have joined all the pins where the high inductor would have been with wire links and shorted out the 3 high q pins together with a bit of wire. I get the high cut working fine now, however the high boost is not working properly. The pot I'm using is 47k(b) linear, yet it acts like a high pass filter. Im not sure what Ive done wrong as been over and checked the pot wiring, all cap values, resistors and everything appears to be correct. Ive removed the inductors (not an easy job) and added electrical tape (direct on clips) followed by card taped down again with electrical tape to stop the clips shorting out on the pins. Im getting close now but a little lost here about what I can do to solve the hi boost problem?

Also I still notice when I engage the mid switch from cut to boot it always seems to be slightly boosted by maybe 2db (pot at lowest point ccw). Is there anyway to stop that, or is it just the way the design is?

Thanks
Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 18, 2015, 06:40:19 AM
Ive hit a wall with the high boost. I have joined all the pins where the high inductor would have been with wire links and shorted out the 3 high q pins together with a bit of wire. I get the high cut working fine now, however the high boost is not working properly. The pot I'm using is 47k(b) linear, yet it acts like a high pass filter. Im not sure what Ive done wrong as been over and checked the pot wiring, all cap values, resistors and everything appears to be correct. Ive removed the inductors (not an easy job) and added electrical tape (direct on clips) followed by card taped down again with electrical tape to stop the clips shorting out on the pins. Im getting close now but a little lost here about what I can do to solve the hi boost problem?

 i just had a look at a bare PCB and I just realised there is one pin of the inductor you should not short to the others. This is the pin labelled G which would connect to the metal frame of the inductor. This pin is connected to 0V so it will seriously mess up your EQ if shorted to the other pins.
Quote
Also I still notice when I engage the mid switch from cut to boot it always seems to be slightly boosted by maybe 2db (pot at lowest point ccw). Is there anyway to stop that, or is it just the way the design is?

Thanks
Paul

That's the way the design is - it was a compromise. As I mentioned before, the mid boost/cut toggle switch should be a 3 position type with a centre off position so when the mid EQ is not needed it is really off.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: unklepablo on November 19, 2015, 06:25:19 AM
Ive hit a wall with the high boost. I have joined all the pins where the high inductor would have been with wire links and shorted out the 3 high q pins together with a bit of wire. I get the high cut working fine now, however the high boost is not working properly. The pot I'm using is 47k(b) linear, yet it acts like a high pass filter. Im not sure what Ive done wrong as been over and checked the pot wiring, all cap values, resistors and everything appears to be correct. Ive removed the inductors (not an easy job) and added electrical tape (direct on clips) followed by card taped down again with electrical tape to stop the clips shorting out on the pins. Im getting close now but a little lost here about what I can do to solve the hi boost problem?

 i just had a look at a bare PCB and I just realised there is one pin of the inductor you should not short to the others. This is the pin labelled G which would connect to the metal frame of the inductor. This pin is connected to 0V so it will seriously mess up your EQ if shorted to the other pins.
Quote
Also I still notice when I engage the mid switch from cut to boot it always seems to be slightly boosted by maybe 2db (pot at lowest point ccw). Is there anyway to stop that, or is it just the way the design is?

Thanks
Paul

That's the way the design is - it was a compromise. As I mentioned before, the mid boost/cut toggle switch should be a 3 position type with a centre off position so when the mid EQ is not needed it is really off.

Cheers

Ian

I removed the wire link to the G pin and it is all now working in full, it sounds great!

I'd missed where you said about the mid switch having a centre off position. That makes perfect sense now. I just used an spdt which is why I always get the mid bump. I will get one ordered soon as I can.

I did eventually finish my wiring diagram and used it to get the wiring right in the end. Ive attached it in case any one new to switch wiring (like me) can save some time.

1 tip I will give about the switch wiring is that I found it much easier to use crimped spade connectors and heat shrink make the connections solid. Soldering direct they would just snap off while I was working around them.

Thanks for all your help, Ive really enjoyed the whole process. It seemed much easier than my 1st build (GSSL). I think thats mostly down to your support here Ian:-)

Cheers
Paul
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnheath on November 29, 2015, 02:06:33 PM
Ian

Sorry if this has been asked before, but what are your opinion on ceramic capacitors in this project… compared to the film capacitors. I guess there would some space to save if using ceramics… and some money as well?

Best regards

/John
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 29, 2015, 03:05:24 PM
Ian

Sorry if this has been asked before, but what are your opinion on ceramic capacitors in this project… compared to the film capacitors. I guess there would some space to save if using ceramics… and some money as well?

Best regards

/John

Generally speaking I would not recommend ceramic capacitors in EQ circuits because they can be microphonic.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: johnheath on November 29, 2015, 04:30:24 PM
Thanks Ian

Straight forward answer is something I like =)

Best regards

/John
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: troubleous on December 08, 2015, 05:58:40 AM
Hi everyone!

Happy to report finally finishing my dual channel build. Extremely pleased with the sound and will definitely build another one asap :)

Many many extra thanks to Ian for answering my stupid questions and giving great advice along the way!

Attached a photo of the finished unit.

Cheers!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: theaterguy on December 08, 2015, 03:45:21 PM
Yeah, the front panel is indeed "finnished".  Jättebra.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: G-Sun on December 31, 2015, 06:20:24 AM
What's the LORLINPULTEC pcbs?
This: https://lh3.googleusercontent.com/MgRF-arOhdafAx1990s94h1LJKO0xf5li3Dt94gQtY6GvkHQamZHu_98judnki4Nz4eLuQ=w1157-h669
?
Does the "Classic Mic Pre V3" replace "Classic Solo v2"?
and work in e.g. a 2U chassis 2ch with the LORLINPULTEC?

Edit: Ok, the solo has onboard psu.

The "LORLIN" and "GRAYHILL": Are these for stepped pots? Can work for 3bandpulteq and Classic gain?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 31, 2015, 08:34:32 AM
LOLINPULTEC PCB is the old PMEQP1A plus the mid board all on one new PCB. Basically it is a V2 version of the PMEQP1A called the PMEQP1A MK2. original design thread is here:

http://groupdiy.com/index.php?topic=59065.msg750451#msg750451

You are right. Classic V3 is EZMixer standard Classic mic pre. Classic Solo is same thing with PSU on one board.

The LORLIN and GRAYHILL are to interface regular PCB mounting Grayhill and Lorlin switches to IDC connectors. Easier to assemble/dissemble than hard wired regular switches. Designed a LONG time ago. All the LORLIN's are gone. Lot's of Grayhills left. There was some talk about a new Lorlin version but not much interest.

Cheers

Ian

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: G-Sun on January 01, 2016, 03:16:56 PM
Would you say a 2ch pulteq is suitable for masterbus?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on January 01, 2016, 06:54:28 PM
Would you say a 2ch pulteq is suitable for masterbus?

Yes, I am pretty sure I have come across articles about people using them on the master bus and I have certainly been asked to include it in a custom design. Assuming you want identical EQ on both the left and the right it would probably best to use stepped pots for accuracy and repeatability.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: miszt on March 06, 2016, 07:51:18 AM
I'm looking at trying my hand at a point-to-point MEQ, but I'd like to start out with an opamp gain stage - and then possibly switch it out for a tube gain stage at a later date;

can someone point me in the direction of a schematic that would work for this idea? (ie so i can switch the opamp for tubes without having to change anything else)

(or even a FET gain stage maybe? but something fairly simple, i don't need gain control except via the filter section)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 06, 2016, 08:37:59 AM
I'm looking at trying my hand at a point-to-point MEQ, but I'd like to start out with an opamp gain stage - and then possibly switch it out for a tube gain stage at a later date;

can someone point me in the direction of a schematic that would work for this idea? (ie so i can switch the opamp for tubes without having to change anything else)

(or even a FET gain stage maybe? but something fairly simple, i don't need gain control except via the filter section)

The easiest solution is to using a FET op amp like the TL072. Here is a link to a simple op amp gain make up circuit. It uses a 2520 but half a TL072 will do fine:

https://drive.google.com/file/d/0B_n67A1hN3qtNzBHSGN5VkIxSFE/view?usp=sharing (https://drive.google.com/file/d/0B_n67A1hN3qtNzBHSGN5VkIxSFE/view?usp=sharing)

It has an unbalanced output but it is easy to convert it to balanced.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on March 06, 2016, 09:08:19 AM
Here is my finished Poorman's Pultec!

Big thanks to ruffrecords!

https://www.youtube.com/watch?v=VExQo2mWuXc&feature=youtu.be (https://www.youtube.com/watch?v=VExQo2mWuXc&feature=youtu.be)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on March 06, 2016, 02:20:53 PM
Here is my finished Poorman's Pultec!

Big thanks to ruffrecords!

https://www.youtube.com/watch?v=VExQo2mWuXc&feature=youtu.be (https://www.youtube.com/watch?v=VExQo2mWuXc&feature=youtu.be)

Cool video. Would you like to send me some pics of the finished unit so I can get Pierre to add them to his gallery of projects based on my desings?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ForthMonkey on March 07, 2016, 10:11:46 AM
Here is my finished Poorman's Pultec!

Big thanks to ruffrecords!

https://www.youtube.com/watch?v=VExQo2mWuXc&feature=youtu.be (https://www.youtube.com/watch?v=VExQo2mWuXc&feature=youtu.be)

Cool video. Would you like to send me some pics of the finished unit so I can get Pierre to add them to his gallery of projects based on my desings?

Cheers

Ian

Just sent!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: miszt on March 07, 2016, 01:16:58 PM
Would you say a 2ch pulteq is suitable for masterbus?

definitely, i'm using my PQD2 for mastering, and its doing an amazing job, client feedback has been positive all the way

took some effort to match all the components (i decided to go with 0.1% tolerance), but the results where worth the effort; was so impressed (and amazed that i'd actually built the thing lol) i'm now starting an MeQ to go along with it

(agree with the above, stepped controls are the way to go - I also switched out the TOKO inductors for don-audio inductors)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on May 20, 2016, 07:48:27 PM
finally getting my PM projects finished now I have the inductors.

Here is my mic pre/DI with Ian's Poor Man's Pultec EQP1-A

While Its use will be mainly be in the studio, its first job will be vocal duties during a jam sesh today going into an 80's Yamaha PA.

(http://www.thraxeh.com/Pics/pmeq.jpg)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 21, 2016, 06:59:20 AM
Lovely build. Do you also have pics of the guts?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fragletrollet on May 21, 2016, 10:34:50 AM
If I wanted to use a CAPI VP312 as makeup gain for the 3band pultec (afaik the same as this one but with included mid and greyhill switches footprints..?), how would I go about?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 21, 2016, 11:54:56 AM
If I wanted to use a CAPI VP312 as makeup gain for the 3band pultec (afaik the same as this one but with included mid and greyhill switches footprints..?), how would I go about?

All my passive Pultec EQ designs need a gain make up amplifier with a high input impedance (preferably at least 40K). They were not designed to feed a low impedance input device like the VP312, so if you want to use one you first need to buffer the output of the EQ with something like a FET follower.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fragletrollet on May 21, 2016, 12:22:26 PM
Ok. Somehow I imagined I could run the eq into a passive DI, then into the VP`s. Maybe you have a link to a schematic of some sorts? Don`t know what to look for  8)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 21, 2016, 03:25:24 PM
Ok. Somehow I imagined I could run the eq into a passive DI, then into the VP`s. Maybe you have a link to a schematic of some sorts? Don`t know what to look for  8)

Yes, you are quite right, you can use a DI. Once again, a high input impedance is preferable so and active type would be best. However, if you happen to already have a passive DI then it is certainly worth a try. The only problem with a passive DI is noise. The Pultec EQ already has an insertion loss of 20dB. A passive DI will have at least as much insertion loss again so you are looking at a total gain make up of over 40dB. Most mic pres will achieve a noise level below -80dBu at 40dB gain so in theory noise should be OK. The other thing with a passive DI is that the input impedance is not as high as the EQ would like. The effect is a reduction in the range of the bass boost control and an increase in the range of the bass cut control.

The simplest form of gain make up amplifier for my passive EQs is one based on a FET input op amp like the TL072. Attached are a couple of schematics for such a gain make up amp.  One is a split supply version and the other is a single supply version. I will also add the schematic to the documentation for the EQs.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fragletrollet on May 21, 2016, 03:51:38 PM
Thanks for all the help!  8)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on May 22, 2016, 03:06:08 AM
Lovely build. Do you also have pics of the guts?

Cheers

Ian

Here is one.

(http://www.thraxeh.com/Pics/pmeqin.jpg)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 22, 2016, 03:34:23 AM
Lovely build. Do you also have pics of the guts?

Cheers

Ian

Here is one.


Very nice. Would you like to email a couple of pics to me so I can get Pierre to put them in the gallery?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: skeeler87 on May 23, 2016, 07:48:33 PM
Ok. Somehow I imagined I could run the eq into a passive DI, then into the VP`s. Maybe you have a link to a schematic of some sorts? Don`t know what to look for  8)

Yes, you are quite right, you can use a DI. Once again, a high input impedance is preferable so and active type would be best. However, if you happen to already have a passive DI then it is certainly worth a try. The only problem with a passive DI is noise. The Pultec EQ already has an insertion loss of 20dB. A passive DI will have at least as much insertion loss again so you are looking at a total gain make up of over 40dB. Most mic pres will achieve a noise level below -80dBu at 40dB gain so in theory noise should be OK. The other thing with a passive DI is that the input impedance is not as high as the EQ would like. The effect is a reduction in the range of the bass boost control and an increase in the range of the bass cut control.

The simplest form of gain make up amplifier for my passive EQs is one based on a FET input op amp like the TL072. Attached are a couple of schematics for such a gain make up amp.  One is a split supply version and the other is a single supply version. I will also add the schematic to the documentation for the EQs.

Cheers

Ian

Is there any benefit from using a split supply version over a single supply version or vice versa?
Sorry for the extremely elementary question!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on May 24, 2016, 04:26:01 AM

Is there any benefit from using a split supply version over a single supply version or vice versa?
Sorry for the extremely elementary question!

None whatsoever; I just put them both in because I did not know what supplies people would have available. Also, following some help from others here on groupDIY, I have updated the schematic to include modern FET op amps that can drive a 600 ohm load or a transformer. Revised schematic attached,

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kambo on June 09, 2016, 09:18:08 PM
hey Ian,
been reading your tech documents and EQ documents!
hats off  8)
its almost a  free personal online tutor :)

before, i was doing some calc and experimentations etc... it was just so confusing; one thing u make better,
next u make the other parameter worst!

after reading and studying ur docs, i feel much better :)

thank you for the hard work and time you are putting in to DIY community, (also many others !)

BTW:
i understood why ur eq was called poormans EQ, after i added some  inductors to sowter chart  :o
OMG, almost 350 GBP for set of two mid eq inductors!



Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 10, 2016, 04:51:59 AM
Sowter inductors are rather expensive but they do have the advantage of being fully screened. If you use unscreened Carnhill inductors from http://www.audiomaintenance.com/ (http://www.audiomaintenance.com/)your inductor costs will drop dramatically.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: G-Sun on June 10, 2016, 08:01:08 AM
finally getting my PM projects finished now I have the inductors.

Here is my mic pre/DI with Ian's Poor Man's Pultec EQP1-A
Now this is a very cool layout and build.
Thanks for sharing pics.

How does it work for you?

I don't quite understand the psu-part.
I see only a single rail coming in. ?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fragletrollet on June 13, 2016, 07:09:11 PM
Can the 3-band pultec fit in a 500-series rack? I guess it would be a double width frontpanel to fit all the switches and pots, but does the pcb fit? I was thinking one could use one of these:

http://www.jlmaudio.com/shop/inx5-pcb.html

for the i/o & makeup gain?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 14, 2016, 04:52:14 AM
Can the 3-band pultec fit in a 500-series rack? I guess it would be a double width frontpanel to fit all the switches and pots, but does the pcb fit? I was thinking one could use one of these:

http://www.jlmaudio.com/shop/inx5-pcb.html

for the i/o & makeup gain?

The original 3 band Pultec that uses Grayhill switches has a PCB that is 123mm tall and 73mm deep and mounts at right angles to the fron panel. As long as it is not too tall for a 500 series module then I guess it should fit. The new Lolrlin version (MK2) uses a PCB that is 150mm tall and 50mm wide and mounts parallel to the front panel. I think the 150mm height makes it too big for a 500 series module.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fragletrollet on June 14, 2016, 04:58:39 AM
Cool, thanks for the input Ian. I`ll measure up some of my 500-series modules.

Not totally sure I got all the differences between the two right, but here goes:

PoorMansPultec: 2 pcb`s + mid extension pcb. Or only one pcb? Confused by the pics on your site, as the wiring diagram shows 3 pcb`s while there are pictures of a pcb fitting all switches (Lo, MID & High)  on one pcb.  Made for Lorlin switches.

3-band Pultec: Lo, Mid and High band all on one pcb, made for grayhills.

Both projects are available to build with inductor for High-band, both need external makeup-gain etc.

...am I getting it right?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fragletrollet on June 14, 2016, 12:29:14 PM
Also the mid-section is 1x boost / 1x cut, not 2x boost & (1x) cut as on the meq-5...?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on June 14, 2016, 03:51:02 PM
There are three implementations of my Pultec design:
1. Original poor man's consisting of separate PCBs for hi, mid and lo uising Lorlin switches. The hi boost is RC only
2. Grayhill 3 band Pultec with everything on a 124mm by 73mm PCB. The hi boost is RC or LC (as in the original)
3. The MK2 poor man's, using Lorlins but with all three bands on a 150mm by 50mm PCB. The hi boost is RC or LC (as in the original )

The MK2 is mean to replace the poor man's three boards with an easier to build version.

In all three versions the mid is a single set of frequencies and a switch selects between cut or boost.

I guess I ought to create a single document that explains/clarifies the three.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on July 10, 2016, 09:32:18 PM
After 3 years of having this completed i just tested....today..
using an 325 output like...

Now questions:
Bypassed EQ signal is just too loud..what was guys your solution^
DO i need the pad IAn sugested here: http://www.ianbell.ukfsn.org/pics/EQSystem.png

Now for calibration ..wheres the info?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 11, 2016, 06:23:29 AM
DO i need the pad IAn sugested here: http://www.ianbell.ukfsn.org/pics/EQSystem.png

Now for calibration ..wheres the info?

Yes, that is exactly what you need. The Pultec EQ has an insertion loss of about 20dB. The pad is designed to have the same loss when in circuit so the level stays the same. To calibrate set the EQ in and all the controls flat. Feed in a 1KHz signal and measure the output level. Switch the pad in (EQ out) and adjust the preset pot for the same output level.

That's all there is to it.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on July 21, 2016, 03:15:36 PM

Is there any benefit from using a split supply version over a single supply version or vice versa?
Sorry for the extremely elementary question!

None whatsoever; I just put them both in because I did not know what supplies people would have available. Also, following some help from others here on groupDIY, I have updated the schematic to include modern FET op amps that can drive a 600 ohm load or a transformer. Revised schematic attached,

Cheers

Ian


Hi Ian
have you the schematics ( Fet makeup for driving 600 ohm transformer) whit better resolution?
I can't read the components value...
Thanks!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 21, 2016, 05:54:51 PM


Hi Ian
have you the schematics ( Fet makeup for driving 600 ohm transformer) whit better resolution?
I can't read the components value...
Thanks!!!

Crikey, they are unreadable! I am surprised nobody mentioned it before. Here is a pdf version which should be much better.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on July 21, 2016, 08:04:27 PM
Thanks!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: jonasmaks on July 25, 2016, 10:16:30 AM
Hello,
Has anyone measured Ian's Pultec frequency responses beyond 20 kHz? I've just built 3 Band Pultec inductive version (EQWithGainMakeUp) and found that HiBoost starts to ring above 26kHz and MidBoost at 16-17kHz . What is the cause of such behaviour (damping?), is it possible to avoid it?
Measurements were done @96kHz rate with RME Fireface400 Mic input, 4dBu Line Out, Eq input unbalanced, loaded with 100 K resistor, output via Ian's TL072 buffer, loaded with 470 K resistor.
G-Pultec HiBoost @2K&16K with 100Hz LoCut LoBoost added for comparison.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 25, 2016, 01:20:39 PM
Interesting. I have not seen that before but I have not made extensive measurements above 20KHz. What setting was the Q control for the high boost? Which inductors are you using?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: jonasmaks on July 25, 2016, 03:40:51 PM
Q control was at maximum - here is a new plot with max and min Q values. I'm using Carnhill inductors - VTB9042 for HiBoost and VTB9050 for MidBoost. I've measured inductance before fitting them into PCB - all looked like OK. I've built 2 channels (for stereo unit) - one is fitted with tube gain stage already (VTB9071/ VTB2291) - same  response.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on July 25, 2016, 06:14:19 PM
Hi
I'm building the same 3 band Pultec  with inductors.
I want to use stepped pot instead regular pot.
How I can realize 1 db for step (lorlin switch 1 x 12)?
Suggestions?
Thanks!


Hi jonasmaks
have you some wiring plot?
Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 25, 2016, 07:30:32 PM
Q control was at maximum - here is a new plot with max and min Q values. I'm using Carnhill inductors - VTB9042 for HiBoost and VTB9050 for MidBoost. I've measured inductance before fitting them into PCB - all looked like OK. I've built 2 channels (for stereo unit) - one is fitted with tube gain stage already (VTB9071/ VTB2291) - same  response.

Thanks for that. it appears the Q control has no effect on the spurious response. I was thinking along the lines of stray capacitance inside the inductor causing a secondary resonance but that would have reduced as the Q control resistance increased. Your graphs show this is not the case. Is the 26K bump there with the controls flat?

Cheers

ian

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Humner on July 25, 2016, 09:15:28 PM
That's interesting as I have had similar ringing in the same spot - 16-17kHz - when testing an EQ(not ian's pultec, but a different style of inductor EQ) and I'm using an RME Multiface with a TL071 as the make up gain/output buffer and going straight to my RME unbalanced.

I wonder if the RME has caused some issue here.  I still haven't fully tested my poorman's pultecs since I received prescotts inductors, when I get some time I might do some similar tests and see if there any relation to the RME etc.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 26, 2016, 03:36:08 AM
Hi
I'm building the same 3 band Pultec  with inductors.
I want to use stepped pot instead regular pot.
How I can realize 1 db for step (lorlin switch 1 x 12)?
Suggestions?
Thanks!
You need to work out the resistor values for each step. You realise the Pultec can give as much as 20dB cut or boost but with a 12 position switch you will only be able to go from 0 to 11dB in 1dB steps. I can work out the values for you if you wish but it will take a little time.

[/quote]
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on July 26, 2016, 02:54:47 PM
Many Thanks Ruffrecords!!!
11 db for me it's perfect!!!
If you will help me I will wait...
THANKS!!!


there is somewhere a wiring istructions on forum? ( 3 band Pultec)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: jonasmaks on July 26, 2016, 04:37:14 PM
I wonder if the RME has caused some issue here.

Hi Humner - unfortunately no, it is not. I've made more measurements today with different interfaces - same result.

Is the 26K bump there with the controls flat?

Hi Ian. There is no bump from 26K with flat controls, flat response was included in first graph. Anyway, today I removed "WTF" 9042 from the PCB and installed stand alone 100 mH Toko inductor in S-A place.
Guess what? No ringing whatsoever. Graph with different Q values attached. Green & Violet - 100 mH Toko, Red & Blue - first winding of "A high performance, professional audio, multi-tapped inductor, intended for line level inductor based equalisation applications."

Could it be possible that whole inductor resonates at some frequency depending on elements around? In my case brake points are ~26K for 9042 and ~16K for 9050.

Ian, I've looked at your "3 Band Pultec Test Results" again. Maybe I've become paranoid about everything, but [email protected] (page 6) does not look very symetrical to me :(
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 26, 2016, 05:17:52 PM

Could it be possible that whole inductor resonates at some frequency depending on elements around? In my case brake points are ~26K for 9042 and ~16K for 9050.

Quite possible. We both already know that the 10K and 16K calculated capacitance for 100mH actually result in frequencies that are too low. I had put this down to a parasitic parallel capacitance in the inductor which appears to be about 320pF. The theoretical resonant frequency of 320pF with 100mH is, surprise, surprise, 28KHz. This may well simply be the self resonance of the inductor but why it is not simply swamped by the parallel 680pF capacitor I do not know. Very odd.
Quote
Ian, I've looked at your "3 Band Pultec Test Results" again. Maybe I've become paranoid about everything, but [email protected] (page 6) does not look very symmetrical to me :(

What makes you think it should be symmetrical?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: jonasmaks on July 27, 2016, 03:27:27 AM
What makes you think it should be symmetrical?

Graph in my previous message "100mH.png". Peaking with single inductor gives (at least shows) symmetrical bell shape frequency response, doesn't it? Peaking with VTB 9042 shows gausian rise but somehow exponentional decline because of new resonance nearby. Previous graph "HiBoostLoQ.png" shows that the closer new rise is - the  steeper the decline is.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 27, 2016, 04:43:24 AM
What makes you think it should be symmetrical?

Graph in my previous message "100mH.png". Peaking with single inductor gives (at least shows) symmetrical bell shape frequency response, doesn't it? Peaking with VTB 9042 shows gausian rise but somehow exponentional decline because of new resonance nearby. Previous graph "HiBoostLoQ.png" shows that the closer new rise is - the  steeper the decline is.

Ah, now I understand what you are getting at. Looking at the 100mH graph I take it the green and purple lines are the single 100mH at different boosts and the red and green ones are with the VTB9042. The more I look at this the more I become convinced there are two additional resonances. If you look at your original set of graphs for the high boost, in every case there is a dip somewhere between 20KHz and 30KHz followed by a peak at at 40 something KHz.

The dip implies either a parallel resonance in series with the wanted series resonance or a series resonance to ground, neither of which I can see an obvious mechanism for. The peak implies a parasitic series resonance which again is hard to visualise but both must have something to do with the construction of the inductor.

Can you do an experiment for me? Can you wire just the 100mH part of the VTB9042 into the circuit and repeat the measurements. I am just wondering if it is anything to do with parasitic resonance of the other windings in the inductor possibly via the capacitance across switch contacts.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: jonasmaks on July 27, 2016, 12:40:17 PM
Hi Ian,
Graph shows frequency response of VTB9042 (100 mH part) connected directly between QMAX resistor and filter input (via switch) with Max/Min Q value. Red curve represents frequency response of stand alone 100 mH inductor with 1nF condenser resonating @ ~15.9kHz. So no big strays around switch or leads or PCB…

Anyway, would be so great if someone who owns Pultec based on whose VTB 9042/9050 inductors could repeat measurements of HiBoost (and MidBoost if any) frequency response above 20K.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 27, 2016, 07:38:54 PM
Hi Ian,
Graph shows frequency response of VTB9042 (100 mH part) connected directly between QMAX resistor and filter input (via switch) with Max/Min Q value.

So just to be clear there is no capacitor in series with the VTB9042 so these are purely self resonances.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: jonasmaks on July 28, 2016, 05:06:27 AM
So just to be clear there is no capacitor in series with the VTB9042 so these are purely self resonances.

No capacitor. Switch and few centimeters of lead to inductor. I've updated graph with all taps measured. With growing inductance (resistance) quality gets lower. Black line represents VTB9050 self resonance (~18.7 kHz) with 100 mH tap connected same way.

Ian, I think you definitely should know Colin from Audio Maintenance? Maybe he could comment this? Something went wrong with particular batch of current inductors? Or this is determined by design?

I extended experiment connecting VTB9042 and 9050 directly between sound interface (FF400) mic input and output. Lines in magenta represent corresponding frequency responses in this configuration. Dips slightly moved to ~19.8 and ~30.9 kHz.

And probably I should stop looking what is wrong with whose Carnhill inductors - maybe they just not intended to work with such high (higher than, say 8-10 kHz) frequencies? As far in 1073 EQ VTB9050 works only up to 7.2 kHz?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 28, 2016, 07:20:40 PM
Yes, I know Colin very well.  I will get in touch with him.

Self resonance is a fact of life in inductors:

https://wiki.analog.com/university/courses/electronics/comms-lab-isr

but I had not expected it to occur so close to the audio band.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 31, 2016, 04:55:53 PM
Many Thanks Ruffrecords!!!
11 db for me it's perfect!!!
If you will help me I will wait...
THANKS!!!


there is somewhere a wiring istructions on forum? ( 3 band Pultec)

It has taken a while but I have finally managed to work out all the resistor values required to get up to 11dB boost and cut in 1dB steps. I was a bit concerned that it might not be possible with the mid boost/cut because this circuit was always a bit of a kludge but it turns out not to be so hard in the end. Attached is a document describing all you should need to know.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 01, 2016, 03:09:03 PM
THANKS IAN!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: jonasmaks on August 01, 2016, 05:18:52 PM
Hi Ian,
My MidBoost gain stays somehow high in 0dB position so I thought that adding 300 K resistor mentioned in SteppedPotsfor3BandPultec.pdf would solve this issue.
Frequency response with MidBoost enabled drops practically to flat when resistance is changed (yellow line in graph - flat is in green) - it was ~5 dB higer with 4.7K resistor (blue line) - but no boost occurs when resistors network is low (OK, I'm cheating and still using 50K pot). The way to get boost is shorten that 300 K resistor and pot (red line). How sensitive your design is for 5K/50K pots use instead of 4.7K/47K (in one post you wrote that not much, but still)? One more thing - I'm using 10K:10K Canhill input trafo with 12K load resistor instead of nominal 100K - am I right with this value? Output to tube is loaded with 470K.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 02, 2016, 01:30:55 PM
Hi Ian,
My MidBoost gain stays somehow high in 0dB position so I thought that adding 300 K resistor mentioned in SteppedPotsfor3BandPultec.pdf would solve this issue.

The mid boost/cut was always a compromise design. I could not find a way of modifying the original poor man's Pultec to include a proper mid section. But so many people wanted a simple to add mid section that I was forced to come up with this compromise design. One of the compromises is that using pots, the  minimum boost/cut is not zero - that's why there is a three way switch in series with the pot so it can be switched completely out. The only way to get zero boost/cut is with an open circuit. The boost pot + series resistor is in parallel with the 47K pot of the high boost, so in the nominal minimum boost position there is just under 6dB of boost. Changing the series resistor to 300K will reduce this to about dB.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: jonasmaks on August 02, 2016, 04:55:00 PM
Hi Ian, thank you for replay. I clearly understand that MidBoost is a compromise, I'm trying to figure out why Mid Boost stopped working (boosting) at all after changing resistor from 4.7K to 300K.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 03, 2016, 06:04:34 AM
Hi Ian, thank you for replay. I clearly understand that MidBoost is a compromise, I'm trying to figure out why Mid Boost stopped working (boosting) at all after changing resistor from 4.7K to 300K.

The nominal loss in the EQ is due to the 47K pot and the 4K7 pot and is  20.82dB. With 300K in parallel the 47K drops to 40.63K and the attenuatioin is reduced to  19.68dB which is a boost of 1.13dB. To get more boost the 300K needs to be reduced. Clearly my conclusion that the boost in 1dB steps to 11dB can be achieved using the 1dB cut values in sereis with 300K is completely wrong! I thought it was too good to be true! Back to the drawing board.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 03, 2016, 09:16:18 AM
I found the error in my spreadsheet that led me to belive you could use one set of resistor values for mid boost and cut. I have corrected this and it is now clear that the cut resistor values are approximately one tenth the value of the boost ones. So there is no single set of resistors you can use for boost and cut. Instead a two pole 12 way switch will have to be used with cut values fitted to one pole and boost values to the other. I have updated the document to reflect these changes. The file is called SteppedPotsfor3BandPultecv0.2.pdf and you can find it in the 3BandPultec folder of the DIY tab of my web site:

http://www.customtubeconsoles.com/diy (http://www.customtubeconsoles.com/diy)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 03, 2016, 10:25:29 AM
hey guys,
i need to step in here as well since i have a bunch of these exact inductors that i was just about to solder onto the pcb. im really not certain after reading about the high end problems. i can do some measurements as well - but they are not soldered in yet. i have 8 of them though so if you tell me what to do ill try my best to hepl sorting this out.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: jonasmaks on August 03, 2016, 11:57:23 AM
Hi salomonander,
If you would run your sound interface at regular 44.1K sampling rate you probably would not notice any HF problems (or at least they be minor). So you  should run tests on as high sampling frequency as you sound card allows (I've done at 96K).
I connected first tap of inductor (S-A) in series between my sound interface input and output and ran FuzzMeasure software sweeps.
You can get demo (with no much limitations) from http://supermegaultragroovy.com/products/fuzzmeasure/ or alternatively use http://audio.rightmark.org/products/rmaa.shtml if you are on PC. Now it depends on your sound interface impedance what type of curves you will get (like red in this page - https://wiki.analog.com/university/courses/electronics/comms-lab-isr if impedance is low (Mic IN) or blue if high (Instrument IN). Or just connect selected inductor to Ian's PCB on leads and run the sweeps. The place to start - http://supermegaultragroovy.com/products/fuzzmeasure/gs/

I've added primitive drawing of my test setup.
Looking forward for your results!!!!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 03, 2016, 12:29:07 PM
great thanks mate. ill do this tomorrow. i can run it as high as 192khz no prob. not certain about impedance. im running a burl mothership. i assume its low on the output and high impedance on the line ins.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 04, 2016, 04:59:35 AM
great thanks mate. ill do this tomorrow. i can run it as high as 192khz no prob. not certain about impedance. im running a burl mothership. i assume its low on the output and high impedance on the line ins.

If you add a 4K7 resistor across the input it will be reasonably close to the conditions in the EQ. It is beginning to look like this is a common property of inductors of this type of construction.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 04, 2016, 08:50:31 AM
hey Ian,
you mean between my hot and cold pins on the input xlrs?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 04, 2016, 01:28:49 PM
alright. so i did not have a 4k7 resistor handy. plus i could not get the rightmark to install on my system. so i just used some whitenoise and an analyzer. im haveing the exact same issues (9042). sorry for no graphs  - but they would look exactly the same. are these inductors faulty?

what are we going to do about this? any possible solution except using a different inductor? gosh i bought lots of them and most likely wont be able to return them :( i do work at 96k a lot so i cant just ignore this...

ps: on my redd eq - which uses a carnhill as well for the10k boost - everything works fine.

ps2: i just wrote an email to martin at carnhill pointing this out. ill let you know what he says.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 04, 2016, 03:09:01 PM
hey Ian,
you mean between my hot and cold pins on the input xlrs?

Hot and cold of the output XLR.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 04, 2016, 03:21:03 PM
alright. so i did not have a 4k7 resistor handy. plus i could not get the rightmark to install on my system. so i just used some whitenoise and an analyzer. im haveing the exact same issues (9042). sorry for no graphs  - but they would look exactly the same. are these inductors faulty?

It is beginning to look like it is systematic. All inductors have a self resonance but I had not expected it to occur so close to the audio band.
Quote
what are we going to do about this? any possible solution except using a different inductor? gosh i bought lots of them and most likely wont be able to return them :( i do work at 96k a lot so i cant just ignore this...

Do you really have any content above 20KHz?
Quote
ps: on my redd eq - which uses a carnhill as well for the10k boost - everything works fine.

The REDD EQ uses a VTB9044  which has a maximum inductance of 200mH compared with 1000mH of the VTB9042. This means there are less turns on the VTB9044 which means less self capacitance which means a higher self resonance which means no problem at 10K.

So the obvious way to fix it is to redesign it for a different inductor like the 9044 which is a pain for both you and me.
Quote
ps2: i just wrote an email to martin at carnhill pointing this out. ill let you know what he says.
I have written to Colin at Audio Maintenance and asked him also to contact Carnhill. I do wish manufacturers of inductive components, both inductors and transformers, would publish comprehensive specifications.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 04, 2016, 03:46:43 PM
hey Ian,

yes, its the same on all of my inductors. i did measure some other randome inductors i had lying around and they showed similar behaviour.
as you have said, the only proper way to fix this is most likely to re-calculate for another lower value  inductor. while a pain for all, i think it would be worth it.  if you dont have the time i might try myself but im horrible at math :) but building an eq that i intend to use for high end bossing  that has this behaviour is not an option for me.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 04, 2016, 03:50:28 PM
ps: im really no expert but it seems that the oscillation goes further down when using a higher tap. meaning that the issue might only occur at say 30k when boosting 12k&16k but seems to moves down to the audible band when using the higher taps.
this comes from a noob that tested the inductor outside of the circuit but measuring the inductor on itself it oscillated at 18k when using the highest tap.

but i cant really believe that so many people build this without anyone experiencing issues..  did people not measure their units? maybe some builders can help by measuring their finished units?

it also doesnt make sense that the toko inductor that jonas measured, did fine at 100mhz. otherwise id say that there is some misdesign happening (with all due respect) but if the other one works, we might simply have to find an inductor that does the job.
are we having the same issue on the mid band?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 04, 2016, 04:47:06 PM
Quote
what are we going to do about this? any possible solution except using a different inductor? gosh i bought lots of them and most likely wont be able to return them :( i do work at 96k a lot so i cant just ignore this...

Do you really have any content above 20KHz?
Quote

im afraid i do. otherwise no one would record 96k . plus my mastering engineer will ask me whats wrong  up there :) its no option. i do own around  50 analog eqs and none of them show any behaviour like this. this needs fixing asap. while it might be a minor issue to some, it is desaster to me.  i will try some axial single tap inductors tomorrow.  but how can the most built eq on this forum not even work properly? whats happening here?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: jonasmaks on August 04, 2016, 05:39:11 PM
Hi salomonander,

are we having the same issue on the mid band?

If you would look at the picture in my Reply #835 you see that we have even bigger problem on Mid Boost, because VTB9050 have lower self resonance than VTB9042.

but i cant really believe that so many people build this without anyone experiencing issues.  did people not measure their units? maybe some builders can help by measuring their finished units?

I think people judge by the ear as much as by numbers (measurements) - and it's hard to judge about those frequencies by just auditioning them - you should have at least descent equipment (and be quite young - I probably do not hear as much over 10K as I did 25 years ago). And maybe someone could find those filters artifacts pleasing - without knowing the math and looking at the graphs…

what are we going to do about this? any possible solution except using a different inductor? gosh i bought lots of them and most likely wont be able to return them :(

Yesterday I have wound my own multitap inductor to mimic VTB9042 - it exibits very similar low self resonance. I will try another core material/turns count during the weekend to see if we could achieve lower capacitance for same inductance.

it also doesnt make sense that the toko inductor that jonas measured, did fine at 100mhz.

I've measured 100 mH toko (or to be exact - murata R1900 series) inductor which did fine up to 40 kHz.
You can find measurements of G-Pultec based on those standalone inductors in my Reply #835.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 04, 2016, 05:45:59 PM
Hi salomonander,

are we having the same issue on the mid band?

If you would look at the picture in my Reply #835 you see that we have even bigger problem on Mid Boost, because VTB9050 have lower self resonance than VTB9042.

but i cant really believe that so many people build this without anyone experiencing issues.  did people not measure their units? maybe some builders can help by measuring their finished units?

I think people judge by the ear as much as by numbers (measurements) - and it's hard to judge about those frequencies by just auditioning them - you should have at least descent equipment (and be quite young - I probably do not hear as much over 10K as I did 25 years ago). And maybe someone could find those filters artifacts pleasing - without knowing the math and looking at the graphs…

what are we going to do about this? any possible solution except using a different inductor? gosh i bought lots of them and most likely wont be able to return them :(

Yesterday I have wound my own multitap inductor to mimic VTB9042 - it exibits very similar low self resonance. I will try another core material/turns count during the weekend to see if we could achieve lower capacitance for same inductance.

it also doesnt make sense that the toko inductor that jonas measured, did fine at 100mhz.

I've measured 100 mH toko (or to be exact - murata R1900 series) inductor which did fine up to 40 kHz.
You can find measurements of G-Pultec based on those standalone inductors in my Reply #835.

thanks jonas,

maybe the muratas are the solution then. the osciallation certainly is not.  its totally off. i will check my surplus dealer tomorrow lookng for some 100mhz inductors just to get an idea.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 04, 2016, 05:49:28 PM
just looking at the mid boost now '835. thats totally off and broken. its clearly in the measurable region even with the worst test equipment.  omg.  but the toko looks fine. the bell is even.  darn carnhills...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 05, 2016, 05:45:17 AM
hey Ian,

yes, its the same on all of my inductors. i did measure some other randome inductors i had lying around and they showed similar behaviour.
as you have said, the only proper way to fix this is most likely to re-calculate for another lower value  inductor. while a pain for all, i think it would be worth it.  if you dont have the time i might try myself but im horrible at math :) but building an eq that i intend to use for high end bossing  that has this behaviour is not an option for me.

If only it were as simple as recalculating for a different inductor. The problem, as I have explained privately to Jonas is one of sharpness (Q) and impedance. The sharpness (Q) of a series resonant circuit like the one used in this EQ is given by:

Q = w*L/R

where w(omega) is 2*pi*f where f is the frequency, L is the inductance and R the obverall circuit resistance. If we just make L smaller to raise the self resonant frequency, the Q is lowered (which probably explains why there are no vintage high Q EQs)

Rearranging the above formula you get:

L = Q*R/w which means for a given Q and frequency, L depends on the overall circuit impedance. The original Pultec is designed as a 600 ohm input and uses a 10K pot and a 1K pot to form its basic divider and it is these that determine the basic circuit resistance R. Today we use 10K inputs so when I designed the Poor Man's Pultec I raised the pot values by 5 times to 50K and 5K which means the circuit resistance is also 5 times higher so the inductor values need to be five times higher to get the same Q -a dn now we know what the hidden consequences of that are. The orignal Poor Man's Pultec had no inductors in it. After resisiting a lot of requests I finally relented and added  the mid section but it was always known to be a bit of a compromise. Later after many requests for a high boost like the original I came up with the 3band version. As as been said, many people have built this and are perfectly happy with it, quirks and all.

So, bottom line is, to lower the inductor value and maintain the original Q needs a complete redesign and will change the input impedance of the EQ.  The question is how low to go? The VTB9044 used in the REDD EQ I am told hs a much higher self resoance. The REDD EQ uses 22K and 5K1 resistors in its pot divider so its circuit resistance is about half that of the 3B Pultec. This combined with the inductance being about one fifth that of the Pultec means the Q of the REDD is about 2.5 times lower than the Pultec. So we could change the pot divider to 22K and 2K2 to maintain the range of the boost/cut, use the VTB9044 and accept a lower Q. To keep the Q as it is with the VTB9044 we would need to change the pot divider to 10K and 1K just like the orignal Pultec which means the input is now  more like 600 ohms and the inout trnaformer would need to be changed.

Another alternative is to keep the existing pot divider and change the inductors to use individual 100mH inductors (Toko, Murata etc). To make the 1H total of the VTB9042 will need 10 in series nd for the 2H of the VTB9050 will need 20. I think it would make sense to accept lower Q at the lower frequencies of both bands so that maximum inductance is halved in both cases so we just need just 5 inductors for the high boost and 10 for the low.

The only other thing worth thinking about is if there is some way to dampen the out of band peak (ascillation is not the right word) but doing this without affecting the the overall response may not be possibe.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 05, 2016, 11:17:25 AM
hey Ian,

thanks for the reply. i will need some time to understand everything properly :)
today i went to tghe surplus shop and bought some more inductors. it was difficult to find some values that resemble that of the carnhills but i found three that had a similar tap and were of the same type of construction.
one of them behaved exactly like the carnhills. meaning that the response resembled more of a tight notch. the other two measured rather different. i attached some pics. they are not the exact same value as the carnhills but very close. maybe this helps somehow.

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 05, 2016, 11:18:49 AM
 160mh carnhill
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 05, 2016, 11:19:25 AM
166mh siemens
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 05, 2016, 11:20:19 AM
220mh carnhill
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 05, 2016, 11:21:04 AM
250mh noname
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 05, 2016, 11:23:55 AM
as i have said - im really no expert. but the none carnhill inductors look so much more heathy and are almost the same value. say id find a multitap inductor that has the necessary values and behaves more like the ones i have found at the surplus - would my q change? aaron at don audio does some great custom inductors for fair prices. maybe his work better.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kambo on August 05, 2016, 12:09:50 PM

can you measure the resistances on same value inductors.... which changes the Q

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 05, 2016, 12:12:25 PM

can you measure the resistances on same value inductors.... which changes the Q

you mean simply measure resistance with a multimeter? sorry im a noob :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kambo on August 05, 2016, 12:13:16 PM
yeap, with simple multimeter


edit: Ian has a great documentation on his web btw... all the formulas, tip and tricks... 
easy to understand language too! not full of technical jargons unlike some books!


Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 05, 2016, 12:17:12 PM
as i have said - im really no expert. but the none carnhill inductors look so much more heathy and are almost the same value. say id find a multitap inductor that has the necessary values and behaves more like the ones i have found at the surplus - would my q change? aaron at don audio does some great custom inductors for fair prices. maybe his work better.

If the inductance values stay the same then then there are no other changes to make and the Q would remain the same. Although it is affected by the resistance of the inductor this is usually  swamped by the overall circuit resistance. It would be interesting to see what Don comes up with. I use him all the time for mains transformers and his work is excellent.

In the meantime I may have found a fix. I have been looking for a way to counteract the rise above 20KHz. The problem is to do it without affecting the flat response. I think I may have a possible solution. To try it all you need to is a 5mH inductor connected  in series with 390pF capacitor in series with a 1K resistor. Connect this combination between the junction of the high boost/high cut pots and 0V. It is a series resonant circuit at about 110KHz. Its effect is to tame the tail end of the 10KHz boost. I have only simulated this and only with the 10KHz boost so I don't know if it will have any effect at the other frequencies.


Edit: 15mH should have been 5mH

Cheers

Ian

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 05, 2016, 12:21:53 PM
as i have said - im really no expert. but the none carnhill inductors look so much more heathy and are almost the same value. say id find a multitap inductor that has the necessary values and behaves more like the ones i have found at the surplus - would my q change? aaron at don audio does some great custom inductors for fair prices. maybe his work better.

If the inductance values stay the same then then there are no other changes to make. It would be interesting to see what Don comes up with. I use him all the time for mains transformers and his work is excellent.

In the meantime I may have found a fix. I have been looking for a way to counteract the rise above 20KHz. The problem is to do it without affecting the flat response. I think I may have a possible solution. To try it all you need to is a 15mH inductor connected  in series with 390pF capacitor in series with a 1K resistor. Connect this combination between the junction of the high boost/high cut pots and 0V. It is a series resonant circuit at about 110KHz. Its effect is to tame the tail end of the 10KHz boost. I have only simulated this and only with the 10KHz boost so I don't know if it will have any effect at the other frequencies.

Cheers

Ian

thanks ian,

great to know that you are on it!  i do have one of dons multitap inductors that features a 12mh tap. but i dont have any finished pcbs here. can i test this with the inductor alone? otherwise we will have to wait until i built one of the units. or maybe jonas can try this with his unit?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 05, 2016, 12:22:45 PM
yeap, with simple multimeter


edit: Ian has a great documentation on his web btw... all the formulas, tip and tricks... 
easy to understand language too! not full of technical jargons unlike some books!

ill do this  and report back
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 05, 2016, 02:26:21 PM
thanks ian,

great to know that you are on it!  i do have one of dons multitap inductors that features a 12mh tap. but i dont have any finished pcbs here. can i test this with the inductor alone? otherwise we will have to wait until i built one of the units. or maybe jonas can try this with his unit?

I made a typo in the previous post ; the inductor value is 5mH not 15mH.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 05, 2016, 08:14:15 PM
no worries. i sthis something i can test with the inductor alone or will i need a finished unit in order to try?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 06, 2016, 03:49:04 AM
no worries. i sthis something i can test with the inductor alone or will i need a finished unit in order to try?

If you test the inductor into a 4K7 load and add the netwrok I desicribed across the 4K7 then you should  see the effect.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 06, 2016, 09:48:43 AM
alright,
did not have a 5mh inductor so i could oly measure the resistance on the coils. for some reason die induction measured differently today (slightly)

so the siemens 166mh measured perfect 160mh today. it has a resistance of 76,2Kohms compared to 29,8K on the carnhill winding
the noname 250 measured 240mh today and has a resistance of of 36k as opposed to 47k on the 220mh winding on the carnhill.
dont know why my inductance is different today. maybe i did not calibrate yesterday.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kambo on August 06, 2016, 01:04:06 PM

your resistance measurements seems extremely high to me!
i think they should be in "ohm" range not in "K" kilo_ohm range  ???



Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 06, 2016, 01:45:05 PM

your resistance measurements seems extremely high to me!
i think they should be in "ohm" range not in "K" kilo_ohm range  ???

maybe i have misread. ill double check. if anything i invented the k by accident
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 06, 2016, 02:25:54 PM
no. values are correct. at least thats what my lcr tells me. its a new one but i measured some resistors just now and they measured perfectly. so i assume my inductor resistances are correct. unless i somehow messed up the process. i simply measured the taps....


this was measured at 1khz. i can aslo measure at 120hz and get way lower resistances.... as ive said - im a noob :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 06, 2016, 02:54:16 PM
my reguar multimeter gives me way different results:

for the 160mh siemens its 5 Ohms
carnhill 160mh is 33,2 OHms

carnhill 220 measures 41,3 Ohms
noname 250 measures 3,6 Ohms

maybe i do really not understand the resistance reading on my lcr properly. these would make a whole lot more sense and point towards the carnhills having a very high resistance. sorry that im of no better help. just trying my best :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kambo on August 06, 2016, 03:05:19 PM
these measurements makes more sense.. even if u typed "K" by mistake they dont match with ur first measurements!

just curious... what "lcr" r u using ?

may be add a 1K  - 3k3 or something (measure it first) in series with ur inductor and re measure and deduct series resistor measured value from the reading... and compare to other multimeter readings....


Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 06, 2016, 03:10:56 PM
these measurements makes more sense.. even if u typed "K" by mistake they dont match with ur first measurements!

just curious... what "lcr" r u using ?

may be add a 1K  - 3k3 or something (measure it first) in series with ur inductor and re measure and deduct series resistor measured value from the reading... and compare to other multimeter readings....


i know.... i literally just swapped the probes to the other unit. my lcr is a bk precision 878b. akward thing is that it measured 5 resistors perfectly (and they were 1% ones). ill try around some more...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 06, 2016, 03:24:19 PM
alright .... im just swapping around now and values change slightly all over the place. but they are getting closer. i think im too dumb to read the lcr and the measurements done with the reguar multimeter are about right. not exact but about right. way more resistance in the carnhills.


 
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 06, 2016, 07:17:16 PM
alright .... im just swapping around now and values change slightly all over the place. but they are getting closer. i think im too dumb to read the lcr and the measurements done with the reguar multimeter are about right. not exact but about right. way more resistance in the carnhills.

Way more resistance than what? What exact values are you measuring.?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 07, 2016, 08:59:54 AM
ill try to sound less confudsing:

first i measured the taps resistance with my lcr meter which gave me the following readings (i measured the four coils i posted screenshots of. so one of each carnhill inductor compared to other inductors of similar value):

for the 160mh siemens its 76,2Kohms
carnhill 160mh is 29,8K

carnhill 220 measures 47k
noname 250 measures 36k

since kambo said that these look way too high i tried again with my regulat multimeter which gave me these readings:

for the 160mh siemens its 5 Ohms
carnhill 160mh is 33,2 OHms

carnhill 220 measures 41,3 Ohms
noname 250 measures 3,6 Ohms

so i assume that my lcr showed the "k" for no reason (or im too stupid to read it). if comparing these results, they are somewhat in the same ballpark (ignoring the "k") and when considering how low the resistance is it would also explain why my readings vary slightly each time i try (especially on my sh*tty multimeter). i hope this makes more sense. let me know if i still not made it clear. cheers
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 07, 2016, 09:24:22 AM
The second set of DCR readings seem about the same as I meaure for the Carnhills. I suspect there is something wrong with your LCR meter.

Cheers

In
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 07, 2016, 10:01:07 AM
The second set of DCR readings seem about the same as I meaure for the Carnhills. I suspect there is something wrong with your LCR meter.

Cheers

In

yeah i think so too. that aside is there anything you can tell from these tests? am i correct in assuming that we need as low of a resistance as possible for this circuit?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 07, 2016, 10:07:30 AM
The second set of DCR readings seem about the same as I meaure for the Carnhills. I suspect there is something wrong with your LCR meter.

Cheers

In

yeah i think so too. that aside is there anything you can tell from these tests? am i correct in assuming that we need as low of a resistance as possible for this circuit?

What you can tell is that the resistance of the Carnhills is OK.  It is not necessary for it to be as low as possible. As long as it is small compared to the overall circuit resistance which ti is.

Ceers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 07, 2016, 01:03:26 PM
hey Ian,
alright so you think that the carnhills do not give these issues due to higher resistance (compared to the other ones i have tested)?
just trying to get a better idea of what the problem really is before i go inductor hunting. don will make me two inductors the coming week for testing. one using his rm8 core, the other one the ad ef core.
i also looked at sowter but i think they are really too expensive.  their resistance seems to be extremely low though.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: kambo on August 08, 2016, 01:19:40 AM
hey Ian,
alright so you think that the carnhills do not give these issues due to higher resistance (compared to the other ones i have tested)?
just trying to get a better idea of what the problem really is before i go inductor hunting. don will make me two inductors the coming week for testing. one using his rm8 core, the other one the ad ef core.
i also looked at sowter but i think they are really too expensive.  their resistance seems to be extremely low though.

Cinemag make some too...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 08, 2016, 04:27:06 AM
hey Ian,
alright so you think that the carnhills do not give these issues due to higher resistance (compared to the other ones i have tested)?

Correct
Quote
just trying to get a better idea of what the problem really is before i go inductor hunting. don will make me two inductors the coming week for testing. one using his rm8 core, the other one the ad ef core.

The problem is due to stray capacitcance inside the inductor caused simply because the winding wires are close to eachother. All real inductors have this property. It forms a parallel parasitic resonant circuit nside the inductor. The frequency it resonates at is called the self resonant frequency. The more turns you have on an inductor the bigger the stray capacitance and the lower the self resonance.
Quote
i also looked at sowter but i think they are really too expensive.  their resistance seems to be extremely low though.
And none of the manufacturers quotes self resonance frequency so you have no idea if they would be any better. The only time I have seen self resonance quoted is for the little 100mH  inductors made by TOKO/Murata/Bourns.

Havr you tried the 5mH plus 390pF plus 1K modification I posted?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 08, 2016, 08:19:33 AM
hey Ian,

alright i see. i assume its down to luck then. the one "noname" inductor i tested was constructed just like the carnhills with multiple taps and did fine. so it has to be possible somehow i guess. i will try dons inductors and report back.
i have not tried you fix since i assume it will only adress the high frequency ringing not the asymmetric bell shapes. which im majorly concerned with honestly.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 08, 2016, 12:07:17 PM
hey Ian,

alright i see. i assume its down to luck then. the one "noname" inductor i tested was constructed just like the carnhills with multiple taps and did fine. so it has to be possible somehow i guess.
Depends. What were the inductance values on the no name inductor? I ask because the VTB9044 used in my REDD EQ does not have this problem but its maximum inductance is only 200mH. The inductors used in the Pultec have up to 10 times the inductance and hence more turns and more capacitcance and a lower self resonance.


Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 08, 2016, 02:00:32 PM
hey Ian,

alright i see. i assume its down to luck then. the one "noname" inductor i tested was constructed just like the carnhills with multiple taps and did fine. so it has to be possible somehow i guess.
Depends. What were the inductance values on the no name inductor? I ask because the VTB9044 used in my REDD EQ does not have this problem but its maximum inductance is only 200mH. The inductors used in the Pultec have up to 10 times the inductance and hence more turns and more capacitcance and a lower self resonance.


Cheers

Ian

hey ian,
the inductance values are in the screenshots names i posted. they were 160mh (on the carnhills); 166mh (on one noname) and 220mh (on the carnhill) and 250mh (on the noname). so rather similar values.  when i tested the carnhills they showed this weired resonance no matter which tap i tried.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 08, 2016, 03:31:14 PM

hey ian,
the inductance values are in the screenshots names i posted. they were 160mh (on the carnhills); 166mh (on one noname) and 220mh (on the carnhill) and 250mh (on the noname). so rather similar values.  when i tested the carnhills they showed this weired resonance no matter which tap i tried.

OK, understood. Does the no name have any other higher inductance taps like the Carnhill or does it just have the 166 and 250mH ones?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 08, 2016, 03:33:49 PM

hey ian,
the inductance values are in the screenshots names i posted. they were 160mh (on the carnhills); 166mh (on one noname) and 220mh (on the carnhill) and 250mh (on the noname). so rather similar values.  when i tested the carnhills they showed this weired resonance no matter which tap i tried.

OK, understood. Does the no name have any other higher inductance taps like the Carnhill or does it just have the 166 and 250mH ones?

Cheers

Ian

250 is the highest.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 08, 2016, 04:16:55 PM

hey ian,
the inductance values are in the screenshots names i posted. they were 160mh (on the carnhills); 166mh (on one noname) and 220mh (on the carnhill) and 250mh (on the noname). so rather similar values.  when i tested the carnhills they showed this weired resonance no matter which tap i tried.

OK, understood. Does the no name have any other higher inductance taps like the Carnhill or does it just have the 166 and 250mH ones?

Cheers

Ian

250 is the highest.

OK, so that is the difference. The Carnhills have extra windings which add to the stray capacitance. Other Carnhill inductors like VTB9044, which has a maximum inductance of 200mH, does not have the problem. So we conclude that as some point above 200mH, the stray capacitcance in an inductor means the self resonant frequency drops so low that ir can affect the EQ response. What I am not sure of is how much far over 200mH we can go.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 08, 2016, 05:17:38 PM

hey ian,
the inductance values are in the screenshots names i posted. they were 160mh (on the carnhills); 166mh (on one noname) and 220mh (on the carnhill) and 250mh (on the noname). so rather similar values.  when i tested the carnhills they showed this weired resonance no matter which tap i tried.

OK, understood. Does the no name have any other higher inductance taps like the Carnhill or does it just have the 166 and 250mH ones?

Cheers

Ian

250 is the highest.

OK, so that is the difference. The Carnhills have extra windings which add to the stray capacitance. Other Carnhill inductors like VTB9044, which has a maximum inductance of 200mH, does not have the problem. So we conclude that as some point above 200mH, the stray capacitcance in an inductor means the self resonant frequency drops so low that ir can affect the EQ response. What I am not sure of is how much far over 200mH we can go.

Cheers

ian


makes sense. we'll know for sure once i get dons inductors.  ill post my findings as soon as they arrived.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 10, 2016, 02:38:16 PM
Hi Ian
I'm building your 3 Band pultec but with Peter custom inductors ( finally rrived)
From your PDF

"To account for QMAX (470 ohms) and the average resistance of the VTB9042
inductor (40 ohms), you can subtract 510 ohms from the final 10K resistor making it
9490 ohms. This can be made from 9K1 resistor in series with a 390 ohm resistor."

It's ok also with this inductors?
THANKS!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 10, 2016, 06:34:57 PM
Hi Ian
I'm building your 3 Band pultec but with Peter custom inductors ( finally rrived)
From your PDF

"To account for QMAX (470 ohms) and the average resistance of the VTB9042
inductor (40 ohms), you can subtract 510 ohms from the final 10K resistor making it
9490 ohms. This can be made from 9K1 resistor in series with a 390 ohm resistor."

It's ok also with this inductors?
THANKS!!!

That pdf refers to the untested swtiched pot modification. That said, yes that should work also for theose inductors with those values.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 10, 2016, 08:58:40 PM
OK
THANKS!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 12, 2016, 12:27:55 PM
hey,
bad news. dons inductors measure just like the carnhills. i assume we either ignore the issues or ian has to design this around different inductor values. cheers
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 12, 2016, 07:02:05 PM
hey,
bad news. dons inductors measure just like the carnhills. i assume we either ignore the issues or ian has to design this around different inductor values. cheers

Which unfortunatey just shows  it is a property of that kind of mulit-tapped inductor. What surprises me is that nobody has noticed this before but I guess that is because people mostly just measure up to 20KHz. Most of the Helios clones use the VTB9042 inductor so I guess they must have this feature but just don'rt realise it. Even some classic Neve's use inductors of the same basic construction. Maybe its just part of what gives those vintage designs their 'sound'.

The out of band rise is the the problem you need fixing which is due to the top boost circuit. Fortunately this does not need a huge inductance so we could probably substitute a number Toko 100mH inductors or the equivqlent. Five of the frequencies need just three of these. The 6th is qite close to the fifth so we can probably get away with i=one more for this. So I am thinking maybe I can squeeze four Toko 100mH inductors on a small PXB that yo can wire in instead of the Carnhill. What do you think?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 13, 2016, 08:46:36 AM
hey,
bad news. dons inductors measure just like the carnhills. i assume we either ignore the issues or ian has to design this around different inductor values. cheers

Which unfortunatey just shows  it is a property of that kind of mulit-tapped inductor. What surprises me is that nobody has noticed this before but I guess that is because people mostly just measure up to 20KHz. Most of the Helios clones use the VTB9042 inductor so I guess they must have this feature but just don'rt realise it. Even some classic Neve's use inductors of the same basic construction. Maybe its just part of what gives those vintage designs their 'sound'.

The out of band rise is the the problem you need fixing which is due to the top boost circuit. Fortunately this does not need a huge inductance so we could probably substitute a number Toko 100mH inductors or the equivqlent. Five of the frequencies need just three of these. The 6th is qite close to the fifth so we can probably get away with i=one more for this. So I am thinking maybe I can squeeze four Toko 100mH inductors on a small PXB that yo can wire in instead of the Carnhill. What do you think?

Cheers

Ian

hey Ian,
yes im leaning towards the tokos as well. its most likely the best Methode. if you redesign around another inductor i assume all cap values and resistors - well everything would Change. ill try some single inductors. i guess it doesnt matter which manufacturer as Long as the values are not too high. do you think there will be a big Impact to the Sound of the unit? is it worth trying a few different manufacturers?

i also find it super akward that no one measured this before. the mid band seems to Show the issues well below 20k. remember - i have only tested the inductors outside of the unit. only jonas did the tests in a finished unit. i wonder if there is anyone else with a finished unit who could give  it another test drive. but i assume People who finished it dont lurk around the thread anymore.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on August 13, 2016, 09:17:27 AM
PS: alternatively - if we'd know how high we can go in inductance - we could ask don to wind us say 2x 0-300mh inductors in one housing. but we dont know how high we can go. the one i measured was 250mh. so that is most likely still fine...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 13, 2016, 01:41:06 PM
hey Ian,
yes im leaning towards the tokos as well. its most likely the best Methode. if you redesign around another inductor i assume all cap values and resistors - well everything would Change. ill try some single inductors. i guess it doesnt matter which manufacturer as Long as the values are not too high. do you think there will be a big Impact to the Sound of the unit? is it worth trying a few different manufacturers?

Difficult to tell how the sound will be affected. Certainly many of the characteristics of inductor based passive EQs are due to the particular inductors used. Both the Carnhill and the small Toko type inductors use ferrite as the core so at least in that respect they are similar but there are lots of different ferrites so the chance of them being the same is small. You will have noticed that the Carnhills are a lot bigger than the Toko. A bigger core means the ability to handle a bigger signal level so one possible concern about the Toko is whether the core will saturate under normal conditions. The worst case is at full boost when the full signal is right across the inductor. I have ordered some of these type of inductors and I will check them out before designing them in.

The other problem with the Tokos is they have now ceased production and I don't really want to design in an obsolete aherd to find component. However, there do seems to be manufacturers of very similar inductors (Bourns for example) which seem to be readily available. I have ordered a bunch from Mouser to try out.
Quote
i also find it super awkward that no one measured this before. the mid band seems to Show the issues well below 20k. remember - i have only tested the inductors outside of the unit. only jonas did the tests in a finished unit. i wonder if there is anyone else with a finished unit who could give  it another test drive. but i assume People who finished it don't lurk around the thread anymore.

Lot's of people have built and are building these EQs but I guess nobody has thought to measure above 20KHz because for the vast majority of people it is not important.  Everyone who has commented on the EQ said they like the way it sounds. As I mentioned before, I only added the mid band after numerous requests and even then I made it clear that the design was at best compromise.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 21, 2016, 06:08:57 AM
Hi Ian
sorry for a stupid question:
I've download the " SteppedPotsfor3BandPultecv0.2"
I don't understand if the series Mid boost resistor need to be 4k7 or 300k....
Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 21, 2016, 07:13:49 AM
Hi Ian
sorry for a stupid question:
I've download the " SteppedPotsfor3BandPultecv0.2"
I don't understand if the series Mid boost resistor need to be 4k7 or 300k....
Thanks!

It is 4K7 just as in the orignal 3bandpultec. When I first did the calculations I mistakenly thought you could use the same set of resistors for boost and cut but it was an error in my spreadsheet. Unfortunately this means you need separate sets of resistors for boost and cut  so you need to use a 2 pole switch.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 29, 2016, 01:09:56 PM
Hi Ian
thanks for your help!
I'm working on make up stage with PPA Doa
Could work fine like this?
Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 29, 2016, 03:48:04 PM
Hi Ian
thanks for your help!
I'm working on make up stage with PPA Doa
Could work fine like this?
Thanks!

That is basically right. If the DOA has split supplies then you should not need the 47uF cap but otherwise it looks OK.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 04, 2016, 08:14:37 AM
hey,
bad news. dons inductors measure just like the carnhills. i assume we either ignore the issues or ian has to design this around different inductor values. cheers

I have done a lot of work on this trying to find a workable solution. I think I have one at least for the Hi Boost. The current design uses the VTB9042 inductoe which has taps up to 1 Henry. The designonly uses the taps up to 0.6H. We can replace this inductor with four 100mH inductors. The top five frequenies only need 100mH, 200mH or 300mH so the capacitor values stay the same as the original. Only the 3K uses the 0.6H winding which will now be 400mH. The required capacitor to resonate at 3KHz is  7.1nF which you can make form a 6.8nF and a 330pF. Just fit these to C7 and C7A. The inductors could be fitted directly to the PCB. As this is just a boost, we a re less concerned about the series resistance of the inductors. So we can use axial leaded types. I recommend theEPCOS B82144A2107J type avialabke from Farnell part number 518300. You need to fit one between the S  pin and the one immediately to its left  (unlabelled). Then fit one between the unlabelled pin and the pin labelled B. Then one between the B pin and the D pin and lastly one between the D pin and the E pin. These inductors have a dc resistance of  420 ohms so we now longer need the Qmax resistor. The Q range will be corret for the 16K and 10K frequencies but the max will be slightly lower for the lower frequencies because of the added resistance of the extra inductors. If you want to avaoid this you need to go to radial leaded inductors (like the Toko) which have a sereis resistance of only 80 ohms and they will be more awkward to retrofit.

For the mid, the problem is more difficult because the lowest frequency is 200Hz and uses a 2H inductor. Even if we used 120mH inductors we would need 16 of them to reach 2H so this is not practical. I suggest we use 8 of them. With this many, the series resistance of the axial types is so high that the when switched to cut there would be no cut at all. With 8 of the Tokos the resistance ia about 640 ohms which is not too far away from the 470 series resistor normally fitted  with the Carnhills. This will give use 960mH total so the Q of the frequencies between 200Hz and 700Hz will be halved but I think this is no bad thing at low frequencies. Fitting 8 into the space of the existing inductor should just about be possible but it wll need an add-on PCB. My next task is to work out the new capacitor values and design the add-on PCB.

Cheers

Ian

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 04, 2016, 04:57:02 PM
I have now worked out the values for the mid.

F=200Hz, L=960mH, C=680nF, Fact=197
F=300Hz, L=960mH, C=270nF, Fact=313
F=500Hz, L=960mH, C=100nF, Fact=514
F=700Hz, L=960mH, C=47nF+6n8, Fact=700
F=1KHz, L=960mH, C=27nF, Fact=988
F=1K5Hz, L=960mH, C=12nF, Fact=1482
F=2KHz, L=480mH, C=12nF+1nF, Fact=2014
F=3KHz, L=480mH, C=4n7+1n2, Fact=2990
F=4KHz, L=240mH, C=6n8, Fact=3939
F=5KHz, L=240mH, C=4n3, Fact=4954
F=7KHz, L=120mH, C=4n3, Fact=7006

Where:

F is the desired frequency,
L is the inductance
C is the actual capacitance
Fact is the calculated actual resonant frequency.

When I get back from my holiday I will look into designing an adaptor PCB.

Cheeers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on September 04, 2016, 06:01:59 PM
hey Ian,
you are the man! thanks so much for not giving up on this. i hope you have a great vacation.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on October 02, 2016, 04:29:32 PM
hey Ian,
maybe you can elaborate on the output transformer when using a 2520 opamp. im not sure what to use. the origina pultec u. is used a 250:600 for the output. will we also need something in the 1:2 range, or will a 1:1 be fine as well?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 02, 2016, 04:38:30 PM
hey Ian,
maybe you can elaborate on the output transformer when using a 2520 opamp. im not sure what to use. the origina pultec u. is used a 250:600 for the output. will we also need something in the 1:2 range, or will a 1:1 be fine as well?

I am no expert on the 2520 (tubes are my thing) but if a 1:2 is normally used then a 1:1 will be fine. You will just have 6dB less headroom.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 04, 2016, 08:08:22 AM
Hi Ian
I'm at the end of 3 Band pultec
I must use 12k resistor on the input transformer as poor man's pultec?
Input transformer Sowter 3575.
Another question is the stepped mid connections:
DPDT on off on Switch
one side go to PCB Boost -off-Cut
other side ???
I don't understand how to select one or other set of resistor..
Thanks!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 04, 2016, 11:07:02 AM
Hi Ian
I'm at the end of 3 Band pultec
I must use 12k resistor on the input transformer as poor man's pultec?
Input transformer Sowter 3575.
No, the 12K is not required for the 3 band Pultec.
Quote
Another question is the stepped mid connections:
DPDT on off on Switch
one side go to PCB Boost -off-Cut
other side ???
This switch selects the mid band between boost, off and cut.  You can use a SPDT switch with a centre off position. If you use a DPDT type the other half is not used.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 04, 2016, 11:39:42 AM
Hi Ian
Thanks but
I'm building with your great help to switch stepped version and in your "SteppedPotsfor3BandPultecv0.2" you say to use a DPDT to select the row of different resistor for cut and boost.
I don't understand how select the different resistors whit the same switch.
Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: salomonander on October 04, 2016, 01:12:55 PM
Hi Ian
Thanks but
I'm building with your great help to switch stepped version and in your "SteppedPotsfor3BandPultecv0.2" you say to use a DPDT to select the row of different resistor for cut and boost.
I don't understand how select the different resistors whit the same switch.
Thanks!

if you have a doube switch it has two poles. so you can use each one individually.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 05, 2016, 01:11:52 PM
Hi Ian
Thanks but
I'm building with your great help to switch stepped version and in your "SteppedPotsfor3BandPultecv0.2" you say to use a DPDT to select the row of different resistor for cut and boost.
I don't understand how select the different resistors whit the same switch.
Thanks!

OK, now I understand! I have just reviewed the documentation and I think there is a more simple way to achieve what is needed. However, the original method is as follows:

The documentation says:

K is connected to 1&2
L is connected to 3

For the mid boost/cut you have a 2 pole 12 way switch instead of a single pole oneWhat you actually need to do is:

K is connected to 1&2 of both poles of the 12 way switch
L is connected to the wiper of the second half of the DPDT switch
The boost connection of the second half of the DPDT switch goes to the boost pole pin 3
The cut connection of the second half of the DPDT switch goes to the cut pole pin 3.

This is to accommodate the different resistor networks needed for boost and cut.

That is basically it.

However, as I mentioned above, there is a simpler way to do it using the original SPST switch. Simply wire the boost pole in series with the 1K resistor and the cut pole in series with the 4K7 resistor and short K and L. If you wanted you could even use seprate 1 pole 12 way switches, one for mid boost and one for mid cut which means all three bands have seprate boost and cut controls.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 06, 2016, 03:03:02 PM
THANKS IAN!!!
My 3 Band Pultec is Alive and it sound wonderfully!!!
I have only one problem:
when mid boost is on it add 1db of boost
when mid cut is on it cut 1 db cut
Tomorrow I will do some tests and after in Studio for more impressions.
I will post some Images and some info about the combo:
Ian 3 band Pultec
PPA Make up gain and DOA
Begis custom Toroidal
THANKS!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 07, 2016, 04:38:46 AM
I am really pleased you got it working. I don't understand why you get the 1dB mid boost/cut. If the  stepped pots are wired correctly then the boost/cut circuit should be completely disconnected at the 0dB setting. However, you are the first person to build this so we are breaking new ground.

It would be nice if you could email me some pics so I can send them to Pierre to include in his gallery of projects of my designs.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 07, 2016, 04:58:42 AM
Thanks Ian
Could be just When the inductor is in circuit also without resistor?
Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 07, 2016, 05:26:23 AM
Thanks Ian
Could be just When the inductor is in circuit also without resistor?
Thanks!

There would have to be some stray capacitance to complete the circuit but that would likely be very small which would alter the resonant frequency. Jus the inductor hanging off the main circuit but connected nowhere else should produce no effect at all. Does the 1dB bump change in frequency as you alter the mid frequency control?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 07, 2016, 05:41:59 AM
Yes on all mid frequencies.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 07, 2016, 09:38:59 AM
Yes on all mid frequencies.

What happens if you disconnect the wipers of the new  mid level switch?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 07, 2016, 10:19:25 AM
if I disconnect the wiper there is no boost or cut at all.
But I think it's one of my stupid error:
I've seen that i've started with resistor from R1 instead of open.
But I think it's not a big  problem because if If Mid come in it's for cut or boost something.
Ian Sorry for my stupid error.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 07, 2016, 10:38:15 AM
if I disconnect the wiper there is no boost or cut at all.
But I think it's one of my stupid error:
I've seen that i've started with resistor from R1 instead of open.
But I think it's not a big  problem because if If Mid come in it's for cut or boost something.
Ian Sorry for my stupid error.

No problem. We ALL make mistakes.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 07, 2016, 01:22:54 PM
2 crappy Images
next week I will do some good photos just the time to complete tests.
Thanks to
Ian for this great project and great help
PPA for great make up board and Doa
Begis for his great custom Toroidal transformer!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on October 07, 2016, 01:29:01 PM
 :)
PSU is out of the case...
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 08, 2016, 05:15:59 AM
Very nice build. Well done.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on November 25, 2016, 12:53:10 PM
Hi Ian!
I'm totally in love with your eq!!!
Now I want to build a guitar pedal...
what need to change for impedance matching for Input ( from guitar) and output ( to guitar amp) ?
I need a input buffer?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 25, 2016, 01:15:11 PM
Hi Ian!
I'm totally in love with your eq!!!
Now I want to build a guitar pedal...
what need to change for impedance matching for Input ( from guitar) and output ( to guitar amp) ?
I need a input buffer?

You do need an input buffer. A simple FET follower will probably be all you need. If the guitar amp has a high impedance input then you can feed the EQ output straight into it.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on November 25, 2016, 01:33:42 PM
Perfect Thanks!
But for output which Could be the best make up in this applicazions?
Thanks!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 25, 2016, 06:48:34 PM
Perfect Thanks!
But for output which Could be the best make up in this applicazions?
Thanks!!!

Keep it simple. You could use FET op amp like the TL072. Use one half for the input buffer and the  other for the gain make up.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on November 29, 2016, 06:18:27 PM
Hi Ian
finally today have do more tests to the 3 Band pultec:
The sound is marvelous!
2 things :
when mid on
in cut mode the Q is narrow
in boost mode is very wide ( too  wide) It's normal?

I have a little ( very little + 1 db) of narrow boost at 16KZ ( only with eq in, not on bypass mode)...
Thanks!!!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 29, 2016, 06:25:05 PM
Hi Ian
finally today have do more tests to the 3 Band pultec:
The sound is marvelous!
2 things :
when mid on
in cut mode the Q is narrow
in boost mode is very wide ( too  wide) It's normal?

Yes, this is normal. It is a consequence of the basic circuit design of the EQP1A.
Quote
I have a little ( very little + 1 db) of narrow boost at 16KZ ( only with eq in, not on bypass mode)...
Thanks!!!
Do you mean you can only get a maximum of +1dB of boost or you get 1dB of boost with the boost/cut pot turned off?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on November 30, 2016, 03:18:38 AM
with eq flat (no boost or cut) and with mid off there is  1db of boost at 16kz...


There is a way to have a mid boost more narrow?

Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on November 30, 2016, 03:24:18 AM
with eq flat (no boost or cut) and with mid off there is  1db of boost at 16kz...
Unfortunately that is a limitation of the design. Remember this started life as an add on to the original poor man's EQP1A so it was always a bit of a compromise. That's why I recommend using s a cut/boost switch with a centre off position to completely disconnect the mid section when it is not being used.
Quote
There is a way to have a mid boost more narrow?

Thanks!
Not really. The curves are designed to be similar to the shape of the MEQ5.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on November 30, 2016, 08:21:51 PM
Thanks Ian
It's not a  problem It's a great sounding EQ!!!
Thanks to share this great project!!! :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on December 09, 2016, 06:55:41 AM
Hi Ian just for info:
The bump at 16KZ come out only with mid on.
With eq in and mid out the responce is near flat...
Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on December 09, 2016, 11:13:31 AM
Hi Ian just for info:
The bump at 16KZ come out only with mid on.
With eq in and mid out the responce is near flat...
Thanks!

Yup, that's the way it should be!

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fazeka on July 03, 2017, 10:40:42 PM
Hi all,

Just completed my Pultec 3-band.

I am a little bummed out, I am getting some bad hum on channel 2, it gets worse when tweaking the low end. Certain frequencies make it worse. Even at its best, the hum/buzz is not acceptable. Thinking it's due to the high impedance of the EQ output being interfered with due to the proximity to the toroidal transformer? I tried rotating, moving wires around, no real help. Swapped out tubes, nothing. Channel 1 is fine. Beautifully quiet, in fact.

Read someplace else that two-channel Pultec-type builds are discouraged for this reason, but I didn't get the memo before starting this build...

Anyone have any pointers? Surely someone else must have built a two-channel Pultec-type build that is hum-free?

Cheers,
Chris

(http://i.imgur.com/PdaYM6V.jpg)

(http://i.imgur.com/zzrpxrD.jpg)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 04, 2017, 03:03:50 AM
A couple of things come to mind to try. First swap the gain make up amps around. If the hum swaps then it is getting into the makeup amp not the EQ. If it stays in the same channel it is getting into the EQ.

Second, I assume channel 2 is on the right. From the pics it looks like your mains cable run to the on/off switch runs right under the lo section of that channel's EQ board. Try taking out the switch and hanging the cable over the back of the unit.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fazeka on July 04, 2017, 03:44:31 AM
Hi Ian,

OK, I swapped the gain make up amps around.  Unfortunately, the hum stays with the channel.

Also pulled the switch and transformer primary wire away from the board, hanging off the back side. No dice. Still got the hum. =(

Cheers,
Chris
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Michael Tibes on July 04, 2017, 04:09:01 AM
I'd suspect the power transformer magnetically coupling into the filter coils. You could try turning it and see if that changes anything.

Michael
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fazeka on July 04, 2017, 04:18:00 AM
Unfortunately, I think you're right. FWIW, I did try rotating the transformer in various positions. No discernible improvement.

Is there some kind of mu-metal shield I can use?  :o
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Michael Tibes on July 04, 2017, 04:34:08 AM
Even if there is no improvement, does the sound of the hum change when you rotate the transformer? I'd expect a 'sweet spot' with less hum. I had the problem with a 1073 build (900 modules in a dual 19" case) and couldn't solve it completely, not even with an expensive 'high-end' power transformer and mu-metal sheets from don audio. In that case I had a mic pre and an eq module and in the end I swapped the mic pre with the eq module, so that the filter coil was further away from the power transformer. The mic transformer was shielded and didn't have a problem. You could put the power transformer into a separate case. I hate that, but I hate hum even more. Otherwise the mu metal wrapped around the transformer helped, it just didn't help enough in my particular case. Maybe it would be sufficient in your case.

I don't know if rotating the pcb with the coil is an option (mounting it at 90 degrees?), it might be worth a try as well.

I'm curious how you solve this, I'm about to start building 2 stereo units myself.

Michael
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 04, 2017, 04:53:55 AM
Hi Ian,

OK, I swapped the gain make up amps around.  Unfortunately, the hum stays with the channel.

Also pulled the switch and transformer primary wire away from the board, hanging off the back side. No dice. Still got the hum. =(

Cheers,
Chris

OK, so now we know the gain make up amps are innocent and it is not the mains lead. What happens if you short the input at the XLR (short pins 2&3)?

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fazeka on July 04, 2017, 04:57:07 AM
I was afraid you were going to say that.  :o

To be honest, I don't know if the sound of the hum changed. I didn't want to rotate the transformer with the unit on, so I would rotate, turn on, listen, turn off, rotate, turn on, listen, turn off, etc. I did this quite a bit of times, as much as I could given the length of the leads on the transformer would allow me. And all variations in between.

I don't know how I could rotate the PCB with the coil as it has to be in that position to allow the rotary switches to enter through the front panel. Unless I am misunderstanding?

Only thing I can think of at this point like you say is to put the mains transformer outside the unit... unless there's something else I'm overlooking/haven't thought of?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fazeka on July 04, 2017, 05:04:16 AM
Hi Ian,

Nothing. No effect. Hum is still there.

OK, so now we know the gain make up amps are innocent and it is not the mains lead. What happens if you short the input at the XLR (short pins 2&3)?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Michael Tibes on July 04, 2017, 08:08:39 AM
I didn't realize before that the switches are soldered to the pcb, this makes it hard to move them around. I'd just take out the power transformer, put 2m leads on it and see what happens if it is out of the picture. Should be easy to improvise, you don't need a proper switch and so on. Just add a power lead, make sure the connections are all safely isolated and you're ready to go. Simple but safe.

Michael
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fazeka on July 04, 2017, 05:54:20 PM
OK, I can move the transformer out... I have some diecast Hammond enclosures in my spares...

Question: how do I handle the grounding with moving the trafo out?

Do I:

1. Do not take the ground off the Classic Solo to the external case IEC with the power transformer?
2. Take the ground off the Classic Solo to the external case IEC with the power transformer?
3.  If #2, does that get connected to the external case chassis?

Cheers,
Chris
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 04, 2017, 06:01:00 PM
The puzzling thing for me is I don't thing this is H field (magnetic interference). The lo cut is purely RC based, no inductors involved. The resistor increases as the cut increases so it will be more susceptible to E field (electric field). There is an inductor in the hi boost circuit immediately before the low cut but if the inductor was picking up hum then increasing the lo cut should reduce not increase it.

The only other thing it could possibly be is a ground loop in channel 2.  Are there any differences at in the grounding schemes of the two channels?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 04, 2017, 06:06:45 PM
OK, I can move the transformer out... I have some diecast Hammond enclosures in my spares...

Question: how do I handle the grounding with moving the trafo out?

Mains in to Hammond transformer box. Safety earth connected directly to box. You need to continue the chassis/safety earth to the main box so you need a screened cable for the ac from the transformer to the main box. Cable screen connects to Hammond box at transformer end and to chassis at other end as close as you can to where it comes in.

Or are thinking of simply mounting ithe transformer on the outside of the rear panel of the main box and covering it with a hammond box?

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fazeka on July 04, 2017, 07:46:00 PM



Hi Ian,

The puzzling thing for me is I don't thing this is H field (magnetic interference). The lo cut is purely RC based, no inductors involved. The resistor increases as the cut increases so it will be more susceptible to E field (electric field). There is an inductor in the hi boost circuit immediately before the low cut but if the inductor was picking up hum then increasing the lo cut should reduce not increase it.

What you say makes sense, but yeah, I dunno...

The only other thing it could possibly be is a ground loop in channel 2.  Are there any differences at in the grounding schemes of the two channels?

I will check the grounding again/compare to channel 1.

Cheers,
Chris
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: fazeka on July 04, 2017, 07:51:03 PM
Or are thinking of simply mounting ithe transformer on the outside of the rear panel of the main box and covering it with a hammond box?

The Antek is too big to mount 90 degrees/sideways (if that is what you meant) to any part of the chassis including the rear panel (only 2RU). I wish I had that as an option.

If I can't find an issue in the grounding on channel 2 and I have to move the transformer out, it's kind of a pain in the a** to do all that work getting the transformer in it's own box and wired up to the mother ship... not too mention that my "Pultec" would then be in two pieces... :P

Cheers,
Chris
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 05, 2017, 03:03:28 AM
@Chris,

I think I have a spare 60mm diameter transformer from one of the early prototypes. Email me your postal address and I will ship it out to you. At least that will give you the freedom to fit it inside the box in any orientation.

Cheers

ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: krabbencutter on July 14, 2018, 06:01:33 PM
Hi everyone,

I'm currently trying to follow this poor man's pultec schematic (http://www.ianbell.ukfsn.org/pics/PMEQP1-AMKII.png) and set everything up on a breadboard with some fixed capacitors for 100Hz and 10k to just get the basics working. However I'm pretty new to this whole DIY Audio world. I've started from Scratch several times now but it seems I'm missing something (probably something very very basic  :-X ) because my pots are acting and interacting in very weird ways. I'm measuring the Circuit with my presonus Studio26, which Outputs a line Level Signal and the receiving Input is set to Hi-Z. I'm using DDMF Plugindoctor to look at the frequency Response.

Here's a Picture of my breadboard: https://1drv.ms/u/s!Aob75XFkRCIipvw-N1cpjKXE2UG-qw
and because that's Pretty messy to look at, I tried to create a hopefully-not-so-messy Version with fritzing:
https://1drv.ms/u/s!Aob75XFkRCIipvw9k4qelxmOOT15Ig
The pots/circuit setions from left to Right are Hi boost (47k lin, 4700pf, 4k7R), Hi cut (4k7 lin, 0.022uf, 470R)  Lo boost (47k log, 0.068uf) and Lo cut (470k log, 3300pf, 56kR).

After wiring everything up the volume is dropping by 20dB, as is expected. The Hi-Boost and -Cut knobs however are only increasing the whole signal and my low cut is doing nothing at all. The Low-Boost works correctly but only if the high cut is not zero.

Can somebody maybe point me in the right direction?  :) Let me know if I need to provide any additional information!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 14, 2018, 07:24:39 PM
On your frizting board you seem to have the RC for bot the hi boost and hi cut across the pot rather than form the top to the wiper.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: krabbencutter on July 15, 2018, 05:22:53 AM
(Oops) Thanks a lot, that did the trick! I also had to swap out my 470k pot. They only had one with an additional switch at my local electronics store and it seems that it doesn't play nice with a breadboard, because the switching pins are in the same row as the outer pins. Speaking of "trick", I've attached a screenshot of that famous pultec curve (and some 50Hz hum  ::) )

Now to get a line output level I'll simply add a TL071 in a non-inverting amplifier configuration and to compensate for the 20dB gain loss I need a ratio of 10, correct?
Regarding the input stage I'm still a bit confused about the bridging transformer, Impedance and load.  I have one of these lying around: http://www.produktinfo.conrad.com/datenblaetter/725000-749999/739643-da-01-en-UEBERTRAGER_1_55V_1500MH.pdf

Would that somehow work? It will probably not have a favorable impact on sound quality. But as I'm still trying to catch up with all the stuff from my physics class 10+ years ago, my main goal here is to get it working and to understand the concepts. I guess a transformer would also help eliminating the ground loop?
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on July 15, 2018, 07:20:44 AM
Here is a link to the recommended TL072 circuits for the PMEQP1A and all my other passive EQs:

https://drive.google.com/open?id=0B_n67A1hN3qtSkg5MW9wRDBWS1k (https://drive.google.com/open?id=0B_n67A1hN3qtSkg5MW9wRDBWS1k)

This and lots of other info is in the PMEQP1A folder in the DIY tab of my web site:

http://www.customtubeconsoles.com/diy (http://www.customtubeconsoles.com/diy)

Regarding the transformer you mentioned, looking at its datasheet I do not think it will be suitable. First it is a 5:1 step up transformer and secondly its inductance is far too low to have a decent bass response.  think this transformer is more likely designed for use in a power supply.

What you need is a 10K:10K audio transformer. These are generally not cheap. Good ones from Cinemag, Jensen, Sowter and Lundahl will cost around $75 or more. OEP do some relatively inexpensive ones that are still capable of good performance. Something like their Z21807C would be a good choice.

Alternatively you can use another op amp to unbalance the input.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: krabbencutter on August 01, 2018, 11:49:20 AM
Thanks a lot Ian,

I've built the EQ section today :) As this is my first project and I have a Eurorack formfactor in mind, I've chosen only two frequencies for each band (30, 100 / 10k, 16k). Instead of Switching potentiometers I'm using simple two-way stereo switches and have also linked the cut/boost frequency for each band. The passive EQ board is working pretty well (if you ignore the horrible ground hum  on the screenshot  ;D) and I will take a look at the input/output stages next.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 01, 2018, 01:35:05 PM
Looks like you are making good progress.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 26, 2018, 09:17:26 AM
Hi
Could this schematics work as makeup stage for poor man's pultec?
It's correct?
thanks!

I've a low frequency attenuation on output ( from 100hz go down)....
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 26, 2018, 03:34:33 PM
Loss of low frequency usually means the EQ is loaded too much. The circuit you posted should work OK. I assume the pot slide is meant to connect to the top of the 47uF.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 26, 2018, 04:31:26 PM
Thanks Ian
yes the pot slide is connected to the top of 47uf cap.
Sorry I'm not an expert :
"Loss of low frequency usually means the EQ is loaded too much" ?
Can you explain what could be?
I'm using a this circuit with Carnhill 2281...
Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 26, 2018, 06:18:30 PM
Thanks Ian
yes the pot slide is connected to the top of 47uf cap.
Sorry I'm not an expert :
"Loss of low frequency usually means the EQ is loaded too much" ?
Can you explain what could be?
I'm using a this circuit with Carnhill 2281...
Thanks!

The output of the EQ needs a gain make up amplifier. This needs to have a high impedance input;preferably at least 470K. If it is much lower than this it loads the output of the EQ too much which results in loss of bass response.

It is not deigned to be fed directly to a transformer, Check out the documentation in the PMEQP1A folder under the DIY tab of my web site:

http://www.customtubeconsoles.com/diy (http://www.customtubeconsoles.com/diy)

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: krabbencutter on August 29, 2018, 04:47:56 PM
Hi Ian,

after jumping through some more hoops and wiggling with some other stuff I'm ready to built your suggested amplifier stage.
As this will be part of my Eurorack, it will run from +/-12v and the input/output signal will be unbalanced.
- Do I need to take any special measures to separate signal & power ground?
- I guess the input signal should be buffered before hitting the EQ? If so I could just use the second opamp of the TL072.

Thanks :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: L´Andratté on August 29, 2018, 05:13:15 PM
Check ruffrecords folder posted above. There´s exactly the schematic you want in there!  :)
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: krabbencutter on August 29, 2018, 05:44:59 PM
Check ruffrecords folder posted above. There´s exactly the schematic you want in there!  :)

Thanks, my questions are regarding his schematic (the TL072 dual supply output stage).
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 29, 2018, 06:46:25 PM
Hi Ian,

after jumping through some more hoops and wiggling with some other stuff I'm ready to built your suggested amplifier stage.
As this will be part of my Eurorack, it will run from +/-12v and the input/output signal will be unbalanced.
- Do I need to take any special measures to separate signal & power ground?
- I guess the input signal should be buffered before hitting the EQ? If so I could just use the second opamp of the TL072.

Thanks :)
The input signal does not have to be buffered. The EQ input impedance is nominally 10K but varies as you vary the controls. As long as your driving source can work happily into a 5K load it should be fine to go in direct, especially as you are working unbalanced.

For advice on what to do with the various sorts of ground check out my Grouding 101 document in the Power folder under the DIY tab of my web site.

Cheers

Ian

Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on August 31, 2018, 08:12:02 AM
Hi Ian
I want to try your  TL072 make up stage.
It's possible to drive directly from output a 600 ohm transformer?
Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on August 31, 2018, 09:05:54 AM
Hi Ian
I want to try your  TL072 make up stage.
It's possible to drive directly from output a 600 ohm transformer?
Thanks!

The smallest load a TL072 will drive is 2K ohms. So you might be able to get it to drive a 600:600 transformer provided the transformer secondary is loaded with 2K or higher. I have not tried this so I cannot be sure.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ilfungo on September 09, 2018, 06:29:40 AM
Hi IAN!
The  TL072 make up sound good!!!
Just last info I'm using ll5402 transformer on input
I need 12k resistor on secondary?
If yes can you explain why?
Thanks!
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on September 09, 2018, 10:39:53 AM
Hi IAN!
The  TL072 make up sound good!!!
Just last info I'm using ll5402 transformer on input
I need 12k resistor on secondary?
If yes can you explain why?
Thanks!

According to its data sheet. the LL5402 is an output transformer designed for use in special feedback outputs. It is not really suitable for use as an input transformer.

With the controls set to flat. the input impedance of the poor man's EQP1A is about 55K. In order to ensure the 10K:10K input transformer sees a load close to 10K the 12K resistor is used. 12K//55K = 9K8.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: shot on September 26, 2018, 10:16:53 AM
I'm having issues with high frequency roll off similar to this post (https://groupdiy.com/index.php?topic=44213.msg692871#msg692871) on page 29.
But since I've built a different filter section, I've opened another thread for it.
Please chime in with some solution if you can!

:)

Luka
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: Alexwfm on April 23, 2019, 10:08:50 AM
Hello,

Was just looking for some PCB's to make a stereo version of the eq with tube make up, does anyone know how to possibly get hold of them?

I tried writing Ian an email but afraid I might have ended up in the junk!

Cheers,
Alex
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on April 26, 2019, 04:17:05 PM
Hello,

Was just looking for some PCB's to make a stereo version of the eq with tube make up, does anyone know how to possibly get hold of them?

I tried writing Ian an email but afraid I might have ended up in the junk!

Cheers,
Alex

I still have some boards left. My current email address is in my groupDIY profile and also on my web site. I checked my spam folder and you are not in there. Try emailing me a gain and I will look out for it.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: 3nity on October 12, 2019, 11:18:01 AM
Hi Ian.
If using a bA283 output style is there any changes that i would have to do?
Thanks in advance.
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 12, 2019, 04:30:20 PM
Hi Ian.
If using a bA283 output style is there any changes that i would have to do?
Thanks in advance.

Unfortunately the BA283 has a relatively low input impedance and this EQ prefers to work into an input impedance of at least 470K. So, if you want to use the BA283 then it would be a good idea to consider using a FET follower after the EQ and before the BA283.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: skal1 on October 18, 2019, 12:36:36 PM
Hi Ian,

just a quick ? about  TL072 circuits for the PMEQP1A and all my other passive EQs:

https://drive.google.com/open?id=0B_n67A1hN3qtSkg5MW9wRDBWS1k

can i use this to work with the  original pultec filter circuit , without any changes to your  TL072 circuit.

Regards

skal
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: ruffrecords on October 18, 2019, 03:38:51 PM
Yes you can.

Cheers

Ian
Title: Re: Poor Man's Pultec EQP1-A Build Support Thread
Post by: skal1 on October 18, 2019, 06:34:15 PM
Yes you can.

Cheers

Ian

cool

skal