The filter feedback on one Shruthi-1 SMR4 mkII filterboard is kind of low. So low that if I turn off osc and just feedback the VCF, the tone almost disappear. I have swapped the op-amp, the 13700, and checked that the Q CV is stable all the way to the chip. Could I change the two 10k feedback resistors (R16 and R19) or would that interfere with the VCF output balance? (using the 4P)
The best way to increase the resonance would be to replace R21 (18k) for something lower like 15k.
R21 is in the circuit creating the current for the resonance control and not in the resonance path itself.
I also recently had a SMR4mkII that needed an even lower resistor to get full resonance across the whole spectrum. Apparently it has to do with part tolerances in the circuit.
Thanks! I will give it a try and report back.
Yes, that was the right thing to do. I used a 13k3 spare resistor I had (odd value), so now the feedback is slightly hot, starting the filter tone around 7 on the pot, as to the usual 8 on the pot, but that is fine by me. Thanks for the help!