It's been so long since I've worked on this I went back over the schematic I drew up and of course I find an error after the fact, U2B's inputs need swapped.
I also put it into a simulator to try to "see" how it...
While I have yet to build the full product hopefully I can still answer your questions.
The P&G faders in question need increasing amounts of torque towards the top and bottom of its travel, this was an...