hi eric,
What you did is amazing and I can't wait to try it out. I just want to clarify a few points on the schematic.
1. Can I use the TL072 Dual-OpA? I have a bunch lying around as I am also DIYing guitar gadgets.
2. Should the +vr be connected to the regulated output of the 7808 which is 8v?
No, connect as shown to the junction of the two 470R's
3. V1 is the 7808, U1 is the CA3240 then what is U2?
U1 and U2 are the two parts of the same DUAL opa package
4. Does the Vo1 (the cut line part) points to nowhere?
The vo1 line is for SIM only
5. Are the R4 and R8 variable resistors? Can I use trim pots using only its 2 pins?
Yes, they are variable resistors, connect the centre pole [wiper] to one end of the pot with a wire link.