Shruthi LPF + Delay infinite feedback?

#1

I just put together this filter board and it seems like the feedback is set to 100% regardless of where the pot is. Is this the “clock latchup” referred to in the build document? I replaced R58 with a 32K resistor (all I had on hand) and it still didn’t fix the problem. Could there be another issue or is this most likely a bad PT2399 chip?

It also seems that when the delay time is put past @ 120, it starts to really distort to the point of sounding like something is wrong. Related to a bad chip problem?

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#2

The PT2399 is fairly low-fi and it is very normal that the delay gets really crunchy and noisy for longer delay times (sound like some a sort of bit crushing particle noise). This should be a somewhat linear change, meaning that it gets increasingly noisy the longer the delay time gets - up to the point where the noise is much louder than the delayed signal itself. I don’t own this board so I can’t tell what ‘@120’ corresponds to… it should be relatively clean up to 300ms of delay and then get quite noisy. If that is what you find on your board, then all is fine.

Regarding the feedback problem, maybe there is a problem with the feedback VCA/Filter around IC8. Check for solder problems around that IC

#3

No. When the “clock latchup” problem occurs, the delay time can’t be controlled.

It looks like there’s a problem with the feedback circuit (VCA).

No, long delay times sound like trash on a PT2399 :slight_smile:

#4

Thank you both so much! I’m not sure what it was, exactly, but after reflowing everything around the VCA chip, I’m back in business!

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