Poor Man's Pultec EQP1-A Build Support Thread

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Yes (at least, that's what I used for both low mid and high mid boost/cut in my build). I had a bit more time to play with the EQ lately. God, it sounds really good!

Ralph
 
Great to hear Ralph!
Your build is very inspiring. I look at your pics almost every day and I'm progressing on my project because of yours.
I should be getting my first batch of parts from Mouser tomorrow to start building my stepped concentric switches.
Can't wait!
Dave
 
wave said:
The mid boost/cut pot is 47K Log, correct?

Dave
Click to expand...

Yes, 47K log is what I have put on the schematic and also what I noted on the simulations. The problem is we really need one pot law for boost and another for cut. For boost a LIN pot is best and for cut an anti LOG pot is best and I guess I thought a log was a reasonable compromise. However, I have just done some more simulations at different pot positions and I think now that a LIN pot would be better. If you use a LIN pot then the boost and cut you get at 50% and 100% rotation are:

Code: 
Rotation                Boost                Cut
50%                     7.5dB                1.2dB
100%                    15.6dB               14dB

As you can see the boost is spot on but nearly all the cut happens in the last 50%. I thought at first a log pot would cure this but it doesn't because the way the pot is wired means at 50% the pot will still be 90% of the pot total so the cut and boost will be even less.

So, on balance, I would now say the best bet for the mid cut/boost pot is to use a LIN type.

Thanks for getting me to think this through again and apologies to all those who have purchased log pots! (me included)

I will update the documentation.

Cheers

Ian
 
rmaier said:
No wonder my mid cuts were so SUBTLE  ;D ;D ;D ;D ;D
Click to expand...

You could always try wiring your log pots as backwards reverse log pots. To do this you swap the wires going to the pot and also swap the pair of pot tags that are wired together. The pot now works backwards i.e. fully clockwise is off and anticlockwise is full boost/cut.. This should make the cut a bit smoother.

Cheers

Ian
 
Thanks, Ian, but I think I'll probably make up a new set of linear switches and see how they compare. 3rd time lucky?
 
Gentlemen,
I have created a diagram for my stepped switches (I need these visual aids) and I'm wondering if you can give it a look and make sure that I'm going to do this right.
The switch is viewed from the front (shaft) side and I have labeled the connections as Pin 1 Anti CW...etc.



So if looking at my diagram, if I were using this switch as the Hi Boost Lin pot (switch) then Pin1 would be connected to T1 of the High PCB.
Pin 2 would be connected to T2 of the High PCB. Pin 3 would be connected to Pin3 of the Hi Cut switch, correct?

Conversely, if this were the Lo Boost Log pot (switch), Pin 1 would be connected to T1 of the Lo PCB while Pin 2 would be jumpered to Pin 3 and Pin 3 would be connected to T2 of the Lo PCB as well as Pin 1 of the Hi Cut pot (switch).

Does this sound right? Basically I'm trying to make sure I'm connecting the wires correctly to the switch (pot).

Thanks
Dave
 
wave said:
Gentlemen,
I have created a diagram for my stepped switches (I need these visual aids) and I'm wondering if you can give it a look and make sure that I'm going to do this right.
The switch is viewed from the front (shaft) side and I have labeled the connections as Pin 1 Anti CW...etc.

So if looking at my diagram, if I were using this switch as the Hi Boost Lin pot (switch) then Pin1 would be connected to T1 of the High PCB.
Pin 2 would be connected to T2 of the High PCB. Pin 3 would be connected to Pin3 of the Hi Cut switch, correct?
Click to expand...

Looks right to me.
Conversely, if this were the Lo Boost Log pot (switch), Pin 1 would be connected to T1 of the Lo PCB while Pin 2 would be jumpered to Pin 3 and Pin 3 would be connected to T2 of the Lo PCB as well as Pin 1 of the Hi Cut pot (switch).
Click to expand...

That looks right too except to say that Pin1 and T1 are also connected to signal 0V.

Cheers

Ian
 
Hi,

First post for me.

Quick explanation:  Don't move house whilst DIYing - I have been really tight on money recently so couldn't afford the I/O transformers for this ace project.  After speaking with Ian these two circuits were contrived/built for I/O duties with the Poormans Pultec.

They are geared toward presenting the correct impedance at each stage, unbalance/balancing duties and variable makeup gain.  The circuits have been tested (powered by PeterCs Green PSU @ +/-15v) with the correct EQ curves confirmed.

The attached file is .zip with BOM, self-etch tracks and layout.  Save the file and rename to a .zip (file type not allowed for attachments).  You can open directly with rar/zip if you right-click and 'open with'.

Hope it's useful to someone,

Ian



EDIT: See post below for corrected version  ;)
 
 
irfrench - thanks for that contribution. I would love to see schematics of these 2 circuits if possible. I am teaching myself to think in terms of schematics, I find it helps me understand better.
 
surfkat,

Sorry for the delay, the less enjoyable form of DIY has kicked in!  ::)

I've (hopefully) attached the schematic(s) for the I/O.  The circuits were inspired/used/copied/modified from the ESP site, chosen on their apparent suitability.  Ian - ruffrecords - then kindly suggested some tweaks and reading material re:impedance to gear the circuits to the requirements of the Poor Man's Pultec.

I hope it's useful.

Regards,
Ian

EDIT: See post below for corrected version    ;)
 
Ian,

I am not sure if we covered this in our email discussions but there should be an extra 10K resistor on the input board between pin 3 of the input XLR and pin 3 of the TL072. Also R4 is not needed and should be replaced by a shorting link or zero ohm resistor.

Cheers

Ian
 
Ian,

Ha ha, Thanks for getting back.  I'll update the schematic & layout to include those changes.  If you don't mind airing laundry in public - what do those changes provide/produce/prevent?

Thanks,
Ian
 
irfrench said:
Ian,

Ha ha, Thanks for getting back.  I'll update the schematic & layout to include those changes.  If you don't mind airing laundry in public - what do those changes provide/produce/prevent?

Thanks,
Ian
Click to expand...

Adding the 10K at the input ensures that the gain for the inverting and non-inverting inputs is the same which is necessary for proper common mode noise rejection.

The 10K at the output just raises the output impedance to about 10K. The EQ prefers to be fed from as low an impedance as possible which removing the 10K at the output does.

Cheers

Ian
 
Evening,

Sorry it's taken this long to tweak such a small thing.

Please see attached the revised docs, as before this has needed to be a .txt to be attached, but should be downloaded and renamed as a .rar.

The archive contains 6 files: layout, tracks and schematic for each input and output sections.

Thanks for your help Ian.


Regards,
Ian
 

Attachments

  • Poormans Pultec IO v1.2.txt
    62 KB · Views: 72
My finally finished unit:

p1010306v.jpg


p1010304d.jpg


p1010309dy.jpg


Hope to don't open this box again in a couple years....
 

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