Poor Man's Pultec EQP1-A Build Support Thread

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,940
Location
Norfolk - UK
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

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

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

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

Here is the PCB layout showing the component positions:

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

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

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

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

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/DavesPoor%20Mid%20Hookup.pdf

Thanks Dave.


Cheers

Ian
 

Attachments

  • PMEQP1Ahookup.pdf
    681.1 KB · Views: 590

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,940
Location
Norfolk - UK
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




Cheers

Ian
 

ej_whyte

Well-known member
Joined
Nov 12, 2010
Messages
263
Location
Cambridge, UK
Here are my stepped pot calcs, might be useful to have them in here.

Cheers
 

Attachments

  • Screen shot 2011-05-06 at 21.25.29.png
    Screen shot 2011-05-06 at 21.25.29.png
    78.2 KB · Views: 449

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,940
Location
Norfolk - UK
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
 

Attachments

  • PMEQP1Assy.jpg
    PMEQP1Assy.jpg
    372.3 KB · Views: 1,170

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,940
Location
Norfolk - UK
ej_whyte said:
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
 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,940
Location
Norfolk - UK
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


wiringsm.jpeg

 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,940
Location
Norfolk - UK
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
 

Attachments

  • hookupsm.jpg
    hookupsm.jpg
    371.7 KB · Views: 543

baadc0de

Well-known member
Joined
Jul 9, 2009
Messages
797
Location
Europe
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
 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,940
Location
Norfolk - UK
baadc0de said:
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

you will see what I said about possible inductor values.

Cheers

Ian
 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,940
Location
Norfolk - UK
3nity said:
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

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

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

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

Cheers

Ian






 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,940
Location
Norfolk - UK
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
 

Attachments

  • PMEQP1Aprotosm.jpg
    PMEQP1Aprotosm.jpg
    382.6 KB · Views: 850

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,940
Location
Norfolk - UK
gemini86 said:
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

Cheers

Ian
 

baadc0de

Well-known member
Joined
Jul 9, 2009
Messages
797
Location
Europe
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?
 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,940
Location
Norfolk - UK
baadc0de said:
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
 
Top