Poor Man's Pultec EQP1-A Build Support Thread

[JohnWatkins]

Ian, looking at the midbottomchrion.jpg, I assume that the pointer for pin 5 should actually go to the terminal just to the right since it's currently pointing to one of the switch terminals?  That's the only thing I can find that I did differently.

 

[JohnWatkins]

The saga continues;  I realized that I had connected the 'screen' to the right-hand lug of the bass boost pot instead of the 0v, left lug.  However, after moving it, I have no mid boost or cut at all.  Honestly, I don't get how it can have so much impact on the circuit when it's only connected to the metal clips on the side of the inductor.  Clearly, I'm still not understanding something.

 

[duantro]

I have ChrioN's Inductors hooked up as following:
Hi Mids 9042: Ground Clip to "S"
                      tap 0 to "ind"
                      tap 1 to "D"
                      tap 2 to "E"
                      tap 2 to "F"
                      tap 3 to "G"
                      tap 4 to "H"
Lo Mids 9047: Ground Clip to "S"
                      tap 0 to "ind"
                      tap 1 to "E"
                      tap 2 to "F"
                      tap 2 to "G"
                      tap 3 to "H"

Hey JohnWatkins there are a lot of confusing elements to decipher in this.
This quote is from my earlier post as to how I hooked up Chrion's inductors.

First- I'd double check how you have your Cut and Boost caps (on high and low boards) arranged on the pcb's-i.e: cut caps first and boost caps second, or vice versa. Then confirm that you are using the correct wiring diagram. Between this and the opposite direction of Chrion's inductor wiring pattern, I nearly had to put earplugs in to keep my brain from leaking out of my head!

Second- go over wiring and confirm everything else is connected correctly. I believe you are using mid boards, so my merged Daves wiring hookup should work, PROVIDED your cut boost caps are arranged as mine are on high and low boards.

When my mids would boost and not cut, It was do to my trimmers being reversed, which I think was messing with the impedance.

So if everything else is hooked up correctly, run a test signal thru it and measure to see if it drops down somewhere.

 

[ruffrecords]

Ian, looking at the midbottomchrion.jpg, I assume that the pointer for pin 5 should actually go to the terminal just to the right since it's currently pointing to one of the switch terminals?  That's the only thing I can find that I did differently.

Yes you are right, it ahould be the terminal to the right. I will update the picture.

Cheers

Ian

 

[ruffrecords]

The saga continues;  I realized that I had connected the 'screen' to the right-hand lug of the bass boost pot instead of the 0v, left lug.  However, after moving it, I have no mid boost or cut at all.  Honestly, I don't get how it can have so much impact on the circuit when it's only connected to the metal clips on the side of the inductor.  Clearly, I'm still not understanding something.

You are right, it should make no difference which seems to imply that maybe it's not connected to the metal parts of the inductor or that the metal parts are also connected to something else. The screen connection is not essential so if I were you I would just delete it for now.

Cheers

Ian

 

[JohnWatkins]

Ok, I found one more incorrectly wired terminal and now I REALLY think I've got everything hooked up correctly in terms of wiring.  Everything now works as expected except the mid cut.  The mid boost seems a little pronounce (almost harsh), but I can't tell if that's a problem or expected behavior. 

I have run a 0db signal through it (skewed by using my DAW instead of a proper signal generator) and the results, with the tube makeup gain fully cw, are as follows;

Input voltage  - 1.71v
Bypassed output - 1.54v
EQ in, mid in the cut position - 2.01v
EQ in, mid in the boost position - 3.5v

Can any conclusions be drawn from this?

Also, should C12 on the mid-board be jumpered?  I'm having trouble reading the traces with everything connected, but it seems like I've got an orphaned inductor lead because there is no cap in that spot.  Thanks,  John

 

[JohnWatkins]

I've taken the mid board out of one of the EQs and connected the leads that fed it to one another.  (the center of the mid pot and the center of the mid boost/cut switch)

The voltage result are now;

input    - 1.74v
bypassed output    -  2.03v
EQ in with mid cut enabled  -  2.07v
EQ in with mid boost enabled  -  3.91v

What could be causing that big jump?  All knobs are at fully ccw.  Thoughts?

 

[JohnWatkins]

Trying to find where exactly it makes that jump in voltage.  So far I'm tracing from the inputs and after the input transformer it's 1.5v everywhere until it hits the other side of any of the pots where it drops to about 200 millivolts.  I'll try from the output side backwards now.

 

[ruffrecords]

Trying to find where exactly it makes that jump in voltage.  So far I'm tracing from the inputs and after the input transformer it's 1.5v everywhere until it hits the other side of any of the pots where it drops to about 200 millivolts.  I'll try from the output side backwards now.

If you are doing this at 1KHz then that is about right. The basic pot divider consists of the treble boost and treble cut pots which together should give an insertion loss of about 20dB so you would expect a 1.5V input to drop to 150mV or so at the junction of these two.

Regarding C12, the 'standard' poor man's mid has all 12 capacitors defined so you will probably be missing the 15KHz setting.

Cheers

Ian

 

[JohnWatkins]

Fixed and sounding fantastic!  Thanks so much to everyone who helped me.  The biggest obstacle was my own arrogance.  I kept looking for inconsistencies in the diagrams as clues to what was wrong when ALL of my problems were basic oversights on my part.  Live and (hopefully) learn.  I'll post pics as soon as I get them buttoned up.

 

[JohnWatkins]

Here are a couple of pics as promised.

 

[JohnWatkins]

And the obligatory gut shot.

 

[3nity]

A simple question.
Make up gain related, is there a chance i could use an IC make up gain? or the 325 style

 

[duantro]

Congrats JohnWatkins! Looks pretty sweet!

 

[ruffrecords]

Well done John! It just confirms my theory that there is no such thing as a subtle fault - they are all pretty obvious once you find them.

Can you email me the pics for my gallery?

Cheers

Ian

 

[JohnWatkins]

Absolutely Ian.  I'm going to take some proper pics once they are racked, but I'll send you copies of these for now.  Thanks so much for making your designs and expertise available to the rest of us.  Your generosity with your time is very much appreciated.

 

[ForthMonkey]

A simple question.
Make up gain related, is there a chance i could use an IC make up gain? or the 325 style

And i think like you,too.I'm planning use JFP gain module.I think it's possible.

 

[3nity]

Yeah sounds good.
I think i have 2 options since i have parts for Neve outputs and Api.
Thanks.

 

[mitsos]

Trinity, for solid state gain makeup:

http://groupdiy.com/index.php?topic=48328.msg612931#msg612931

If using an IC, either get one that is 600 capable, to ensure it can drive the trafo sufficiently, or put a BD139/140 output stage after it.  I think there is a schematic in the original(not the updated one, because we stopped making those adapter PCBs) EQP-1S5 build document, at the beginning of the thread.  Works very nicely with an OPA604, but I'd like to try one of the LME ICs as well.

 

[ruffrecords]

A simple question.
Make up gain related, is there a chance i could use an IC make up gain? or the 325 style

You can use an IC based gain make up for the poor man's pultec BUT you need to make sure it has a high enough input impedance. The poor man's Pultec prefers to be loaded with not less than 470K bot you can get away with as little as 220K. Any less than that and the bass boost loses range and the bass cut becomes more severe.

An FET input op amp is ideal. I think several people used an IC gain make up in the original thread.

Cheers

Ian