Polivoks FM mode


When using the FM mode it doesn’t seem to modulate too well. The cut off freq doesn’t seem to do much. It is okay in other modes. Which components are most critical in this part of the filter? or is there something I need to set to make it work?

I’ve stuck to the BOM as much as possible in terms of recommended parts.

Maybe I should RTFM :slight_smile: is the FM mode only useable with an external signal?

No, it works with the internal signal OK… should sound like this .

Hmm okay. I guess I have some fiddling to do.

“Please make sure that both the analog (CV1 to +5V) and digital (RX to +5V) ports of the filter and control boards are connected.”

I initially forgot to do this. Sounds like it could be your problem? J6 FTW!

I have both ports connected :slight_smile:

It switches to band pass and low pass fine. Distortion works, FM engages fine too. Perhaps I need to play with the patch a bit more, there may be something in the presets that upsets it.

Sorry for a waste of time. Works fine now, env and lfos were stopping it all.

Glad it all works. 100% success rate with my boards so far :slight_smile:


Actually, I think it may be a bug or quirk in the firmware I have. It seems like as I switch FM on the cut off and res don’t do anything much (res is on or off) until I turn the right most knob (lfo2>vcf) down. It works then.

Could be patch related I guess. But I can live with that.

I have built a dozen of Polivoks units and the FM works as expected on all of them. FM works best:

  • When no other modulation source is widely modulating the VCF (otherwise its effect is “masked” by the other modulation).
  • With high resonance.

You can decrease the 47k resistor below the TL084 for a more drastic FM effect.

It works fine, it was more me wondering what i had done wrong, 'm not doubting your genius :slight_smile:

Filter cutoff seemed to be doing nothing until I reduced the modulation of the filter by LFOs.

I should spend more time playing and less time typing.

Found what was really wrong. After swapping ATMega chips it worked fine so that made me realise there was some setting to blame.

After doing some reading and experimenting it seems it was the CV mode. I had it set to ‘pedals’ somehow and that was causing all sorts of odd things like param1 not changing etc.

Set it back to 4cv and all is well :slight_smile: