Hi all, hope this forum is still active?
I did the VCO out / VCF in mod exactly as described here: http://www.ladyada.net/wiki/x0x/vcfmods (Updated Mod for VCO out/VCF in) and now the following happens:
If I connect an external synth, the external signal just doesn't seem to fully "get in there" and I hear a weird distorted version of the signal, and the x0x filter cutoff just kinda warbles and barbles (and only if I turn the resonance fully CW). But if I simply send the VCO out signal back to the VCF in via the mod, everything works fine.
Now this: If I run any external signal (including the x0xb0x' own VCO) through a guitar pedal (EHX Holy Stain) and then into the x0x filter input, everything works fine. I have the feeling it might have to do with input and output impedances? (The Holy Stain's output impedance is 570 ohms, not sure about the other synths' impedances)
I experimented with different values for the cap (anything from 100nf to 100uF) and resistor (4.7k to 47k) that run from the input jack tip to the VCF input but get very similar results. I am currently going with a 10uF cap and 22k resistor.
Does anyone have an idea what could be happening here? Thanks all