Poor Man's Pultec EQP1-A Build Support Thread

[ForthMonkey]

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...

 

[johnnyscotch]

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)

 

[ruffrecords]

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

 

[johnnyscotch]

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

 

[ruffrecords]

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

 

[anjing]

Beautifull built! The pictures will make a nice addition to the gallery!

Regards,

Pierre

 

[johnnyscotch]

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

 

[ruffrecords]

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

 

[ilfungo]

Hi
can someone share  schematics for IC make up / poor man's pultec ( TL071 Based) ?
THANKS!!!

 

[creal]

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
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

 

[ilfungo]

Thanks Creal
It's possible to use PPA board balanced without transformer?
Do you know how?
Thanks!!!

 

[creal]

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

Cryil

 

[Deepdark]

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?

 

[ruffrecords]

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

 

[Deepdark]

sorry wrong forum XD

 

[ilfungo]

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!!!

 

[ruffrecords]

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

 

[ilfungo]

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!!!

 

[ruffrecords]

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

 

[ctechdx]

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,