Just to get this up here. I hope to make this clearer soon...
This shows how you can modify the Yamaha CS-01 Mk1 to:
1) have variable resonance control, by hijacking the Breath Control VCF potentiometer
a) remove the 10k resistor near the VCF chip.
b) cut the traces (or lift the pins) of the Breath Control VCF pot that connect it to GND and the Breath
Control jack. I lifted the pins just to avoid cutting PCB traces
c) remove the 39k resistor tied to the wiper of the VCF pot.
d) solder wires from one side of the pot and the pot wiper and run these wires over to the holes that
used to contain the 10k resistor near the VCF chip
e) I'd suggest adjusting the resonance trimmer that's near the VCF chip to make your new Resonance
control self-oscillate near the end of the rotation. why? because this filter gets out of control in a very loud
and dramatic way. I don't think this VCF chip was designed for stable self-oscillation - that may explain why, in the
CS-01 Mk2, when they gave you analog control of the resonance, they used a different 24dB VCF chip.
2) have variable VCA "drone" by hijacking the Breath Control VCA potentiometer.
a) remove the 1k resistor that grounds usually-closed terminal of the breath control jack to GND
b) solder a 47k resistor from the ungrounded, non-wiper terminal of the pot to -9V.
c) when the VCA drone pot is now fully on, you'll always get a DCO-VCF signal running to the power amp.
this mod keeps the VCA only partially open, and you can still superimpose the EG over the drone. I did this because
I don't have a spec sheet on the VCA chip and I didn't want to risk having the EG slamming the VCA while the drone was going
full on (basically, I don't know the max CV that the VCA chip can tolerate). so if you just use the drone, you'll have
to increase the volume at the power amp. But now the front-panel VCA slider actually becomes useful, since if you don't
want the EG to affect the drone, just turn that down to nothing!
Sorry I don't have actual pics of the mod up! Perhaps someday soon...