I've built a few of these modules but this one seems to be giving me an interesting problem;
When I run an oscillator into Filter 1 it's sound comes out the High Pass and Notch filters loud and clear but when I switch to Low Pass or Band Pass the volume decreases sharply. Further, the Frequency pot has no effect on the sound no matter which selection I make. The CV inputs don't either. The Resonance and Distortion % pots seem to work fine.
The exact same thing happens on Filter 2.
I've wired this module with the -15V going to the Frequency knob rather than 0V and with the spread coming from both CVSN on Filter 1 and pin 3 of the TL072 (where it meets the 2K2 resistor).
This has worked for me on other CGS49 modules I've built but this is a strange problem that I can't seem to figure out
Does anyone have suggestions as to what I might do to test / fix this problem? Any help would be greatly appreciated.