Mon Dec 6 20:07:59 EST 2010

Opamp input

What I see in many guitar effects input circuits

  - Input resistor R1 to ground 1M
  - Capacitor coupling, 1u
  - Resistor R2 100k to ground or 1/2 reference voltage

The C is to bridge the DC difference between ground and the 1/2 ref.
The R2 is necessary to make sure that C gets biased correctly if the
input is zero volts, and R1 is for biasing the other end in case the
source doesn't provide a DC path.