Polivoks filter screeching

I finally started to look in depth on my polivoks shruthi and realised that a horrible screech I get with default patch is not normal. I originally thought this was part of the noise and character of the polivoks! Looking on youtube I see that others have quite nice smooth sounding filters before adding overdrive.
It seems on mine the screech can be tamed with the cut off and envelope settings, but presumably somethings wrong it shouldn’t sound so horrible with the presets, right? Also I’ve set the control to (pvk) so it’s not that.
Anybody have any ideas what would cause a high pitch screech/yelp when the filter opens? I’m guessing I chose a wrong capacitor somewhere?
Thanks for any pointers!

Can you post a recording of the screech?

I got 2 working polivoks, and i can give you some waveforms form an oscilloscope, so if you have one, you could compare the waveforms, that would be easiest for troubleshoot i think, if you dont have an oscilloscope i think its rather random troubleshoot, or you resolder all the crucial joints of the filter, might help.

@mex - If it’s not too much trouble, then yes please do post them. In any case I’ll post a recording when I’m home.

Attached is a sample file from my polivoks: (1) junon, (2) moof?, (3) init patch.
Any help would be welcome, thanks!

It seems that the resonance is locked to the maximum value - probably due to an assembly mistake. Can you confirm that adjusting the resonance setting has no effect on the sound?

Yes correct! - not sure why I didn’t notice that before when playing with the filter - I guess I was overwhelmed by the noise… Thanks!
Looking at the schematic it’s pin4 on J4, right? Is 127 “high” or “low” - i.e. should I look for a short or a disconnect?

127 is almost always high.

I’m not sure what “127” is supposed to be, but yes, the resonance CV is generated at pin 4 of J4. It should be 0V (with a multimeter - a 0% square wave if you use a scope) when resonance is at 0 ; and 5V (average - or a 100% square wave) when resonance is at 63.


Not sure where the “127” came from ;). Although coincidentally the filter board only was reading 9.9V on pin 4 of J4! I found/solved the problem somehow the track of pin14 on IC2D (TL084P) was not connected to anything at all. I guess my middle night of soldering 4 years ago was not precise enough :-(.

@Olivier thanks so much for your detailed help and fast responses - I now have a very nice sounding polivoks Shruthi to go with my standard one