Radio Transmitter

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Wednesday, June 3, 2009


All-FET design Valve-like distortion behavior


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:

  1. Input sensitivity: 30mV RMS.
  2. Output square wave: 6V peak-to-peak max.
  3. Total current drawing: about 1mA.

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.

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