Sound Modifier

Posted in Tone control, on 2015-07-27

Circuit diagram:

Sound Modifier


  • P1,P3,P4________22K Linear Potentiometers
  • P2_____________220K Linear Potentiometer
  • R1,R15_________150K 1/4W Resistors
  • R2_____________220K 1/4W Resistor
  • R3______________56K 1/4W Resistor
  • R4_____________470K 1/4W Resistor
  • R5,R13,R14______22K 1/4W Resistors
  • R6______________10K 1/4W Resistor
  • R7______________33K 1/4W Resistor
  • R8,R10,R12______47K 1/4W Resistors
  • R9_______________1K 1/4W Resistor
  • R11_____________68K 1/4W Resistor
  • R16____________100K 1/4W Resistor
  • C1,C3,C5_______220nF 63V Polyester Capacitors
  • C2______________47nF 63V Polyester Capacitor
  • C4______________22nF 63V Polyester Capacitor
  • C6_____________100µF 25V Electrolytic Capacitor
  • C7_______________4µ7 25V Electrolytic Capacitor
  • D1,D2_________1N4148 75V 150mA Diodes
  • IC1____________LM324 Low power Quad Op-Amp IC
  • J1,J2__________6.3mm. Mono Jack sockets
  • SW1______________1 pole 3 ways rotary or slider switch
  • SW2______________SPST Switch
  • B1_______________9V PP3 Battery Clip for PP3 Battery


Compared to common Fuzz-box devices, the Sound Modifier circuit allows a choice amongst a wide variety of output waveforms, thanks to its capability of mixing three different modified versions of the input signal. This stand alone unit, primarily intended for electric guitars, is based on a low power quad op-amp IC and draws a very low current from a common 9V transistor battery.

Circuit description:

IC1A is the linear input amplifier. The input sensitivity of the circuit can be varied from -10dB to +10dB in three fixed steps by means of SW1, in order to cope with almost any pick-up type and model. IC1B forms a rather straightforward fuzz circuit, based on the squaring property of two back-to-back diodes connected across output and inverting input of the op-amp. IC1C and related components convert the squared output signal coming from IC1B into a triangle-shaped waveform. IC1D is wired as a virtual-earth mixer, summing the linear, squared and triangle-shaped signals coming from IC1A, IC1B and IC1C respectively. A very accurate mixing of these three different signals can be done by means of P1, P3 and P4: the result will be an almost endless choice of different fuzz-effects.


  • The circuit can be used also as a linear amplifier by rotating P3 and P4 controls fully anti-clockwise, or as a straightforward Fuzz-box by rotating P1 and P4 controls in the same way.
  • P2 is the fuzz deep control.
  • Total current drawing is less than 2mA.

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