Yamaha CS80

I thought about your project for a while and here is how I would do it, if I had to :

http://joachim.milson.free.fr/cs80-interactive-diagram/CS-80-brilliance-pedal-control.jpg

 

This is not a full design since the resistor values need to be computed (with a ratio 1/3 between FH and FL to generate the CS-80's characteristic filter opening) and the voltage/current should be checked so that they comply with the existing circuitry.

Hope this helps,

Joachim