Telephone call Voice Changer

Voice manipulation device specially intended for props

9V Battery operation

Circuit diagram:

Telephone call voice changer


P1______________10K  Log. Potentiometer

R1,R10__________10K  1/4W Resistors
R2_______________1K  1/4W Resistor
R3______________50K  1/2W Trimmer Cermet or Carbon
R4,R6,R7,R14___100K  1/4W Resistors
R5______________47K  1/4W Resistor
R8______________68K  1/4W Resistor
R9_______________2K2 1/2W Trimmer Cermet or Carbon
R11_____________33K  1/4W Resistor
R12_____________18K  1/4W Resistor
R13_____________15K  1/4W Resistor

C1,C2,C3,C8,C9_100nF  63V Polyester Capacitors
C4______________10µF  25V Electrolytic Capacitor
C5_____________220nF  63V Polyester Capacitor (Optional, see Notes)
C6_______________4n7  63V Polyester Capacitor
C7______________10nF  63V Polyester Capacitor
C10____________220µF  25V Electrolytic Capacitor

IC1___________LM358   Low Power Dual Op-amp
IC2_________TDA7052   Audio power amplifier IC

MIC1__________Miniature electret microphone

SPKR______________8 Ohm Small Loudspeaker

SW1____________DPDT Toggle or Slide Switch
SW2,SW3________SPST Toggle or Slide Switches

J1____________6.3mm or 3mm Mono Jack socket

B1_______________9V  PP3 Battery (See Notes)

Clip for PP3 Battery


Although this kind of voice effect can be obtained by means of some audio computer programs, a few correspondents required a stand-alone device, featuring microphone input and line or loudspeaker outputs.
This design fulfills these requirements by means of a variable gain microphone preamplifier built around IC1A, a variable steep Wien-bridge pass-band filter centered at about 1KHz provided by IC1B and an audio amplifier chip (IC2) driving the loudspeaker.