Basic Tone Control
This is a very basic circuit diagram of 3 band tone control. This circuit was originally intended for home audio use, but should be able to be hacked into an effect circuit with very minor modification.
Resistance value of resistor R1 is left up to the user depending on gain needs, R2 is unknown – for experiment purpose. The op-amps are not critical, any standard ones could be used (eq: 741, LM324, etc).
Download basic tone control circuit in PDF document: