The Fetzer Valve is a guitar pedal that is based on a vintage Fender 12AX7 input stage. It is a popular circuit that can be used as a standalone booster or as a building block in larger circuits. The circuit is a solid-state version of the familiar input stage used in many tube amps.

The pedal features high and low gain inputs, with the low gain input providing 6 dB attenuation and a relatively low impedance to the guitar. The frequency response of the pedal is limited to around 20 kHz, which is ideal for guitar audio and prevents interference from RF and radio stations. The harmonic content of the pedal can be adjusted by choosing the appropriate source resistor for the JFET amplifier.

Summary created by AI from the original source.