Guitar preamp problems
If this op-amp uses a single-ended supply then it should work ok unless your resistor values are too high as as mentioned in the comments. Change 10M to 500K. Delete R1 as it would reduce the bias voltage, which should stay at 1/2 Vcc, as set by R3 and R4.

If your using a quality JFET op-amp it needs a negative supply rail (ideally) so it can bias itself, but there is a way to cheat and you have already stumbled into it. Install a 10K resistor from the outputs of U1 and U2 to the 12 volt supply rail.

This forces an internal bias current to correct for the slight offset the 10K resistor creates and stabilizes the op-amp. I replaced a lot of LM324 op-amps in car stereos with TL074 JFET op-amps which had MUCH better qualty sound, and this was the trick I used to get it to work with just a single supply rail.

NOTE: If you add an input volume control it needs to be ten times less than R2, and before the input capacitor, or you will upset the bias voltage at the + input of U1-A. Note that this pre-amp is not designed to drive a speaker of any standard impedance. It is designed to drive a medium to high input impedance power amplifier.