Poor Man's Pultec EQP1-A Build Support Thread

3nity · Nov 5, 2013

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
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
Clock wise side is connected at T1.

Can you clear that for me please!

ruffrecords · Nov 5, 2013

3nity said:
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
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
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

ruffrecords · Nov 5, 2013

anjing said:
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

ForthMonkey · Nov 13, 2013

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://j1311.hizliresim.com/1h/f/uhtl8.jpg

ruffrecords · Nov 13, 2013

ForthMonkey said:
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

ForthMonkey · Nov 13, 2013

ruffrecords said:
ForthMonkey said:

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!

Click to expand...

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

If it's not good,can you recommend easy to build gain stage?

ruffrecords · Nov 14, 2013

ForthMonkey said:
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

JohnWatkins · Nov 16, 2013

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?

ruffrecords · Nov 17, 2013

JohnWatkins said:
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

JohnWatkins · Nov 17, 2013

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.

JohnWatkins · Nov 17, 2013

I checked the other EQ in the same way and got the same result, but much less pronounced.

3nity · Nov 19, 2013

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.

anjing · Nov 19, 2013

How about comparing your curves with the ones Ian made available...

Regards.

Pierre

3nity · Nov 19, 2013

what are you using for the curves?

anjing · Nov 19, 2013

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

ruffrecords · Nov 20, 2013

I use an audio test set made by Lindos in the UK.

Cheers

Ian

3nity · Nov 20, 2013

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...

ruffrecords · Nov 20, 2013

3nity said:
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

3nity · Nov 20, 2013

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??

3nity · Nov 20, 2013

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?

EQP-1A3Schematic%20mod%20for%20most%20opamps.jpg

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