DOD 680 analog delay

[lowell]

Been researching this pedal and sad4096 circuits. Havent found anything directly relating to this circuit. I have replaced all electrolytics in this pedal as they are some 30-40 yrs old I think. This issue was there before I recapped it. Initially the thing had no delay but a little twist of the bias trimmer brought it to life. The issue: high pitched squeal (clock noise?), and the delay turns into straight distorted noise as it repeats if i turn up the repeat pot. Basically the repeats sound like touching the tip of the input cable if the repeat pot is turned up to the point of compounding. Finally, the frequency of the squeal lowers as the delay time is adjusted. My main question; how do I adjust the clock to reduce noise, and what IS the clock? Is it the NE571?

Here is a link to the schematic.http://www.dirk-hendrik.com/temp/dod680.gif

[Jazz P Bass]

The 'clock' is the TL081 JFet opamp driving the CD4013 flip-flop IC.
The 4013 sends a clock pulse to SAD4096 pin 2 (Q) & pin 16 (Not Q)
Pin 16 will be an inverted pulse.

[lowell]

Thanks for clearing that up. Do you know how I'd go about reducing clock noise? My guess is that the CD4013 is old and not producing equal out of phase pulsing?

[Jazz P Bass]

I would imagine that you have to prove where the noise is at.

The CD4013 is a simple 'flip flop' IC.
Though it may be bad.
Scope the Q & Q Not output pins.
If it is bad, it will be grossly apparent.

[Jazz P Bass]

In looking for a 'noise' source, I would advise scoping the Flip Flop Q/ Q Not outputs.
If you have a dual scope, that would be ideal.
(The SAD datasheet has some real good waveform info.)
SAD4096.pdf

Allowing that they are good, you should scope the I/O pins of the SAD. (Turn the Repeat control Off)
The output, being unfiltered , may be ragged.
If so, jump down to U2 & scope it's output pins.

You may also have an issue with the compander IC (NE571).
Again, scope the I/O.
NE571 Compander.pdf