Poor Man's Pultec EQP1-A Build Support Thread

[ruffrecords]

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

 

[ilfungo]

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!!!

 

[ilfungo]

PSU is out of the case...

 

[ruffrecords]

Very nice build. Well done.

Cheers

Ian

 

[ilfungo]

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?

 

[ruffrecords]

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

 

[ilfungo]

Perfect Thanks!
But for output which Could be the best make up in this applicazions?
Thanks!!!

 

[ruffrecords]

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

 

[ilfungo]

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!!!

 

[ruffrecords]

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.

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

 

[ilfungo]

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!

 

[ruffrecords]

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.

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

 

[ilfungo]

Thanks Ian
It's not a  problem It's a great sounding EQ!!!
Thanks to share this great project!!!

 

[ilfungo]

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!

 

[ruffrecords]

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

 

[fazeka]

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

 

[ruffrecords]

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

 

[fazeka]

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

 

[Michael Tibes]

I'd suspect the power transformer magnetically coupling into the filter coils. You could try turning it and see if that changes anything.

Michael

 

[fazeka]

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?