All-FET design

Valve-like distortion behavior

Circuit diagram:



P1______________10K  Log. Potentiometer

R1_______________1M  1/4W Resistor
R2_______________3K3 1/4W Resistor
R3_______________2K2 1/4W Resistor
R4_______________5K  1/2W Trimmer (Cermet)
R5_____________100K  1/4W Resistor

C1,C4__________100nF  63V Polyester Capacitors
C2_____________100pF  63V Ceramic Capacitor
C3,C5___________22µF  25V Electrolytic Capacitors

Q1,Q2,Q3______2N3819  General-purpose N-Channel FETs

J1,J2__________6.3mm  Mono Jack sockets

SW1_____________DPDT  Toggle - Slider or Pedal Switch
SW2_____________SPST  Toggle or Slider Switch

B1________________9V  PP3 Battery

Clip for PP3 Battery


This circuit was designed to obtain a valve-like distorted sound from an electric guitar or other musical instrument.
For this purpose a very high gain, three-FET amplifier circuit, was used. The output square wave shows marked rounded corners, typical of valve-circuits when driven into saturation.
Therefore, the distorted sound obtained from such a device has a peculiar tone, much loved by most leading guitarists.

Technical data:

Circuit set-up using oscilloscope and sine wave generator:
Connect a 1KHz sine wave generator to J1 and the oscilloscope to J2.
Adjust R4 until the output square wave shows equal mark-space ratio.

"By ear" circuit set-up:
Connect a musical instrument to J1 and an amplifier to J2.
Carefully adjust R4 in order to obtain as maximum output sound intensity as possible.