Hopefully Jens might come across this....or any keyboard players out there who made this mod for the DX7!!!
I actually built this thing as you have it on your site...but you left one detail out and thats the blue resistor you used to connect directly to the "zero" point, because without that resistor everytime i turn the "pitch knob" it automatically stabilizes the voltage back to normal (as it should), so which resistor is it that i hook the capacitor to before i feed it into the wheel??
-Mike