Hello Alain

I could imagine, that the output potentiometer of one (or all) VCOs does
not "shut" the VCO ouput completely. Though the VCO itself might be not
audible for us, the Filter on high resonance may react on it.

You may try to disconnect the VCO pcb from the VCF/VCA pcb and check the
VCF then.

Florian

> Hi everyone! Lately I've noticed that when I "play" the filter in self-resonance with all VCOs off, it doesn't produce as pure a sine wave as before. I can hear what seems to be faint harmonics at different frequencies. And when I look at a spectrum analyzer, I can in fact see some "other" frequencies at very low levels.
>
> When I sweep the cutoff, they bounce all over the place. A little like aliasing in a way. Don't worry I've eliminated everything else by take the output straight from the synth. So nothing else can add artifacts.
>
> Could it be due to failing capacitors in the filter section Especially those directly connected to the SSM2044
> Or could it be something else. I've already replaced the SSM2044 with a more recent one and they both exhibit the same behavior.
>
> It's a very minor annoyance since it's inaudible when filtering a signal from the VCOs or white noise.
>
>
> Thanks for any suggestions you might have on this. And I'd be curious to know if anyone else has these artifacts on their MP4.