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gray_wolf gray_wolf is offline
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Default Pultec EQP clone problem

On 25/02/2021 7:01 pm, Scott Dorsey wrote:
gareth magennis wrote:
The Gearslutz post says 100 Ohms in series with 25pf, which I thought made a lot more sense.
I'm reluctant to accept that without comfirmation from the company, though, which I still haven't received.

Is that a typo? should it be 22pF, or even 22nF? I struggled to find a 25pF cap.
Hence my reluctance.


Put a 1 KHz square wave through. Does it look nice and square at the output or
does it ring?

Mild ringing: http://www.panix.com/~kludge/xformers/DSC00263.JPG

Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG

If you add a 600 ohm termination resistor (which everybody should be using
running a Pultec into a modern output anyway) does it get better or worse?

If the square wave looks good, things are good.

You can use the calibration output from a Tek scope as a 1kc square wave
generator. It's convenient and comes free with the scope.
--scott


Any idea what the catastrophic ringing harmonics would look like on a spectrum
analyzer.