Hank Dussen

Re: Poor Man's Pultec EQP1-A
« Reply #320 on: June 22, 2011, 03:03:26 AM »
If you look at the capacitor calculator spreadsheet you will see I have included 20KHz and 30KHz frequencies. Note that the boost cap is becoming rather small (about 1500pF at 30KHz) so stray capacitances, especially in screened cables, may begin to affect the response.

Would it be better to use unshielded cables for the Hi boost then?


baadc0de

Re: Poor Man's Pultec EQP1-A
« Reply #321 on: June 22, 2011, 04:13:21 AM »
The inductor was only added as an afterthought because someone asked for it and there was space for it on the PCB.

Could the inductor be rerouted to the topmost frequency with some trace cutting?

ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #322 on: June 22, 2011, 10:54:38 AM »
The inductor was only added as an afterthought because someone asked for it and there was space for it on the PCB.

Could the inductor be rerouted to the topmost frequency with some trace cutting?

I would think that should be possible. Alternatively you could just fit the caps in reverse order so the frequency increases as you turn anti-closckwise.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #323 on: June 22, 2011, 11:19:27 AM »
If you look at the capacitor calculator spreadsheet you will see I have included 20KHz and 30KHz frequencies. Note that the boost cap is becoming rather small (about 1500pF at 30KHz) so stray capacitances, especially in screened cables, may begin to affect the response.

Would it be better to use unshielded cables for the Hi boost then?

A lot depends on your physical layout - how far the pots are from the PCB, how directly you route the connections, where you site the power supply and whether the whole thing is in a screened box or not.

If you mount the hi boost/cut pots right next to the hi switch PCB you can make very short direct connections form the PCB to the pots - there are only two such connections to each pot. The same argument holds true for the lo boost/cut PCB and pots. There should be no need to screen these connections.

The connection from the hi boost pot to the hi cut pot probably does not need to be screened if the two pots are on the same side of the switch PCB, but if they are on opposite sides then it might just be necessary to screen it. The connections from the hi cut pot to the lo boost and cut pots might be quite long depending on your layout and might well benefit from screening.

Where you definitely should use screening is from where the EQ output is taken (from the low cut pot) to the EQ in out switch and from that switch to the input of the gain make up amplifier but try to keep these screened cable lengths as short as possible to avoid introducing unnecessary stray capacitance. Connect the screen to ground only at the gain make up amp input, carry it across the EQ in/out switch and leave it unconnected at the EQ output.

The EQ output is relatively high impedance and hence can be susceptible to interference from external sources of from the local power supply transformer. That's why I recommend screening the output connection. I would also recommend keeping the PSU transformer as far away from these leads as you can and enclosing the entire EQ in a screened enclosure.

Cheer

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

creal

Re: Poor Man's Pultec EQP1-A
« Reply #324 on: June 22, 2011, 08:24:53 PM »
Hi Ian, hi all

Here is work in progress
One channel tested and works,  i used a trim pot instead the 470k.
also, i experiment with the format 500
The amp is a vero/325 API
input xfrm 10K:10K LL1540 Lundahl
ouput xfrm 600R:600R ??? (from old UREI EQ)

Here is the picture and the front.


Thanks Ian for this great projet ;)
This PM eq sound very nice.

Best,
Cyril

ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #325 on: June 23, 2011, 04:54:27 AM »
Hey Cyril,

Thanks for the pic. I like the way you have remoted the switches - is that a short length of ribbon cable??

Glad you like the sound.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

creal

Re: Poor Man's Pultec EQP1-A
« Reply #326 on: June 23, 2011, 05:19:59 AM »
Hey Cyril,

Thanks for the pic. I like the way you have remoted the switches - is that a short length of ribbon cable??

Glad you like the sound.

Cheers

Ian

Yes, it's shord ribbon cable.

ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #327 on: June 23, 2011, 08:07:44 AM »
I also noticed, Cyril, that you have only 5 lo frequencies and 4 hi frequencies marked on the front panel and also that the hi include 20K and 30K.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Holger

Re: Poor Man's Pultec EQP1-A
« Reply #328 on: June 23, 2011, 08:43:34 AM »
Cyril needs the EQ for his upcoming 'symphony for dogs and bats' (sorry, couldn't resist)  ;D

creal

Re: Poor Man's Pultec EQP1-A
« Reply #329 on: June 23, 2011, 12:46:27 PM »
I also noticed, Cyril, that you have only 5 lo frequencies and 4 hi frequencies marked on the front panel and also that the hi include 20K and 30K.

Cheers

Ian
thx you for advices.
i changed plan, i think i put the pair in à 19" 1 or 2U.
May be with the tube Amp
I'll post the new FP soon

@Holger

Yes, i use many compressors and eqs for my symphony.
It's just, i like my toys

Cheers


pigsnoot

Re: Poor Man's Pultec EQP1-A
« Reply #330 on: June 27, 2011, 10:18:45 PM »
hello I got the boards! thanx a lot

Are there any replacements for the sowter ST3575?

I can only find them here
http://www.canford.co.uk/Products/23-155_SOWTER-ST3575F-TRANSFORMER-Analogue-audio-leads-line-bridging-10k10k

sorry to bother y'all pro-builders!
grtz!
M

ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #331 on: June 28, 2011, 05:12:59 AM »
hello I got the boards! thanx a lot

Are there any replacements for the sowter ST3575?

Any 10K:10K bridging transformer will do. I am sure Jensen, Cinemag, Lundahl and others will have suitable transformers.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

creal

Re: Poor Man's Pultec EQP1-A
« Reply #332 on: June 28, 2011, 06:51:56 AM »
hello I got the boards! thanx a lot

Are there any replacements for the sowter ST3575?

I can only find them here
http://www.canford.co.uk/Products/23-155_SOWTER-ST3575F-TRANSFORMER-Analogue-audio-leads-line-bridging-10k10k

sorry to bother y'all pro-builders!
grtz!
M
hello I got the boards! thanx a lot

Are there any replacements for the sowter ST3575?

Any 10K:10K bridging transformer will do. I am sure Jensen, Cinemag, Lundahl and others will have suitable transformers.

Cheers

Ian

I use a  10K:10K LL1540 Lundahl for the input and it works and sound well

pigsnoot

Re: Poor Man's Pultec EQP1-A
« Reply #333 on: July 13, 2011, 09:51:34 AM »
Is the Bridging transformer really Necessary? If you're coming from a line level or really hot signal?

Another probably stupid question : This unit doesn't need any power source, so where does the 0v lead go to? is it just to show there's isn't any current needed, or does it effectively go somewhere?


ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #334 on: July 14, 2011, 10:14:31 AM »
Is the Bridging transformer really Necessary? If you're coming from a line level or really hot signal?

No, it is not essential. You can run the EQ unbalanced at line level if you wish

Quote
Another probably stupid question : This unit doesn't need any power source, so where does the 0v lead go to? is it just to show there's isn't any current needed, or does it effectively go somewhere?

The EQ does not need a power source but it needs a gain make up amplifier after it to make up for its insertion loss and obviously the gain make up amplifier needs a power supply. The 0V of the EQ connects to the zero volts of the gain make up amplifier.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

0dbfs

Re: Poor Man's Pultec EQP1-A
« Reply #335 on: July 14, 2011, 11:54:27 AM »
I am interested in learning what I might need to change around or add to make the output of this low impedance like a microphone. 150 or 200 ohms... 40dB of overall attenuation would be fine. It would be awfully convenient to feed line level to these and patch into a mic-pre-amp for makeup similar to the passive-summing-mixers that are all the rage.

Looking at possible t-pad configs and how perhaps various output transformers may work with that. Also noted that previously in this thread we could possibly use different pot values and use the spreadsheet to re-calc the caps for the desired freq's...

Would be pretty flexible to be able to make this look like a normal bridging destination for the input and like microphone source for the output while remaining passive.

Maybe it's not feasible or the noise would be too much but I am playing with some calcs at the moment.

Any thoughts?

Best,
jonathan
Music is everything!
Audio is everything else!

abechap024

Re: Poor Man's Pultec EQP1-A
« Reply #336 on: July 14, 2011, 12:00:31 PM »
that would be sweet
AC Sound - some DIY circuitboards

ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #337 on: July 14, 2011, 01:45:40 PM »
I am interested in learning what I might need to change around or add to make the output of this low impedance like a microphone. 150 or 200 ohms... 40dB of overall attenuation would be fine. It would be awfully convenient to feed line level to these and patch into a mic-pre-amp for makeup similar to the passive-summing-mixers that are all the rage.

The poor man's EQP1A uses larger value pots than the original to get the input impedance up to around 10K bridging. The penalty for that is the output impedance is even higher and needs to be loaded with no less than around 470K. The EQ has an insertion loss of about 20dB so for a 40dB overall attenuation you can allow only a further 20dB for an pad - so you could use 420K and 47K for example but you still have an output impedance of over 40K.

You could possibly change the 56K resistor to 5.6K plus 51K and tap off across the 5.6K with a 10:1 transformer to give a mic level output of about -60dBu but that is about as good as it gets I am afraid.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Jean Clochet

    Currently taking a break to smell roses and the coffee
  • Posts: 387
Re: Poor Man's Pultec EQP1-A
« Reply #338 on: July 14, 2011, 01:56:21 PM »
I don't know what the real output impedance is on this new higher Z version but how about a traffo?  I've before used something like a direct box transformer which took my eq source impedance of 10K or near and transformed down to 150 ohm.  I made up the gain with a mic pre which had typical 2K input Z so the eq was not loaded downwards very much.
Is there a place you can point me to for the higher impedance eq?  Maybe it's in this thread but I'm just not seeing it  :o

Merci

Never mind, I'm an idiot :-[ - the doc is on the first page.  I just assumed it was the usual pultec one when I looked the other day.

Will look again now ::)
« Last Edit: July 14, 2011, 02:03:36 PM by Jean Clochet »
John Roberts:  I am generally not enthusiastic about the project with or without trimpots...

Jean Clochet

    Currently taking a break to smell roses and the coffee
  • Posts: 387
Re: Poor Man's Pultec EQP1-A
« Reply #339 on: July 14, 2011, 02:07:10 PM »
Back again.

I don't see why you couldn't use a Direct box traffo on the out but I'll let the designer answer for himself  8)

Jean
John Roberts:  I am generally not enthusiastic about the project with or without trimpots...


 

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