Poor Man's Pultec EQP1-A Build Support Thread

duantro said:

Thanks for the description Ian. I've sent .775V 1k signal in, that measures .680V at bypass switch and on CCW of High boost pot/switch. At CW pin of High boost switch (the divider between the High boost and cut that should be -20db lower) my signal is 26mv. Am I correct that this isn't what I should be seeing? I apologize, I'm a horrible trouble shooter.

Click to expand...

You are correct, that is not the right level. You should see something in the region of 75mV at that point but make sure you have the high cut turned fully off as well. I suspect there is something funny happening with you extra mid sections which are also connected between this point and ground. I would advise disconnecting the mid completely and just concentrate initially on the hi and lo boost/cut. Get that working first and then add in the mid circuits one at a time. it's a bit laborious but it is the only sure where to eliminate things.

Cheers

Ian

Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.

duantro said:

Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.

Click to expand...

OK then you need to trace and  check the circuit you have in detail. Try disconnecting the gain make up and the EQ bypass circuit and measure again. Something somewhere is pulling down that signal.

Cheers

Ian

Am I correct in assuming that the DPDT switch for the EQ bypass switch should be ON-ON, not ON-OFF-ON?  Sorry if this has been covered.

JohnWatkins said:

Am I correct in assuming that the DPDT switch for the EQ bypass switch should be ON-ON, not ON-OFF-ON?  Sorry if this has been covered.

Click to expand...

That is correct. Also, if you are using the mid section add on, the SPDT switch to select mid boost/off/cut should be an 0n-off-0n type.

Cheers

ian

Thank you!

Ian... I need to know the input impedance of the Poor man's Pultec for calculating one cap in the unbalancing stage. Can you tell me what impedance is at the input of the circuit?
Thanks

I measured the impedance in my unit.
Input impedance is over 50k in both channels. Output impedance is also over 50k, though I expected over 10k as you told me, Ian.
Is this normal?  ???

pacorro said:

I measured the impedance in my unit.
Input impedance is over 50k in both channels. Output impedance is also over 50k, though I expected over 10k as you told me, Ian.
Is this normal?  ???

Click to expand...

How did younmeasure the input and output impedance?

Cheers

Ian

With a multimeter, red on hot at T2 and black at the ground in pin 3 for the input.
At the output with red on xlr pin 2 and black on ground at xlr pin 3.
One channel is 49,4 k input and 51,6 k output. The other is similar, 50k input and 51k output.

That is dcr,not the impedance.

Udo

Sorry, but... What is dcr?

pacorro said:

Sorry, but... What is dcr?

Click to expand...

DCR=Direct Current Resistance.

Thanks. How can I measure the input impedance in my device?

pacorro said:

With a multimeter, red on hot at T2 and black at the ground in pin 3 for the input.
At the output with red on xlr pin 2 and black on ground at xlr pin 3.
One channel is 49,4 k input and 51,6 k output. The other is similar, 50k input and 51k output.

Click to expand...

I am confused about the putput XLR - is this directly out of the EQ or after a gain make up amp? What positions were the pots when you made this measurement?

Cheers

Ian

ruffrecords said:

duantro said:

Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.

Click to expand...

OK then you need to trace and  check the circuit you have in detail. Try disconnecting the gain make up and the EQ bypass circuit and measure again. Something somewhere is pulling down that signal.

Cheers

Ian

Click to expand...

Upon disconnecting the output amp at the center pin of the bypass switch, I go from 12v to 58v, at this connection.

duantro said:

ruffrecords said:

duantro said:

Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.

Click to expand...

OK then you need to trace and  check the circuit you have in detail. Try disconnecting the gain make up and the EQ bypass circuit and measure again. Something somewhere is pulling down that signal.

Cheers

Ian

Click to expand...

Upon disconnecting the output amp at the center pin of the bypass switch, I go from 12v to 58v, at this connection.

Click to expand...

Is that dc volts or signal?

Cheers

Ian

ruffrecords said:

duantro said:

ruffrecords said:

duantro said:

Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.

Click to expand...

OK then you need to trace and  check the circuit you have in detail. Try disconnecting the gain make up and the EQ bypass circuit and measure again. Something somewhere is pulling down that signal.

Cheers

Ian

Click to expand...

Upon disconnecting the output amp at the center pin of the bypass switch, I go from 12v to 58v, at this connection.

Click to expand...

Is that dc volts or signal?

Cheers

Ian

Click to expand...

AC signal from 775mv input signal generator

duantro said:

ruffrecords said:

duantro said:

ruffrecords said:

duantro said:

Yes Ian, I have my mids disconnected as per your suggestion earlier. The center pole/wiper of the boost cut pots on mids are unhooked.

Click to expand...

OK then you need to trace and  check the circuit you have in detail. Try disconnecting the gain make up and the EQ bypass circuit and measure again. Something somewhere is pulling down that signal.

Cheers

Ian

Click to expand...

Upon disconnecting the output amp at the center pin of the bypass switch, I go from 12v to 58v, at this connection.

Click to expand...

Is that dc volts or signal?

Cheers

Ian

Click to expand...

AC signal from 775mv input signal generator

Click to expand...

I don't understand this. With less than one volt input and no gain make up amp, how can you get a gibber output than the input. Or did you mean 'goes from 12mV to 58mV which would be about right.

Cheers

Ian

Sorry Ian. Yes I meant 12mv when output is connected and 58mv when disconnected.