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Telephone call Voice Changer(LM358)

2016-02-05 10:12  
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This article describes a Telephone call Voice Changer (LM358). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: LM358.

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.


The pass-band filter can be bypassed by means of SW1A and B: in this case, a non-manipulated microphone signal will be directly available at the line or loudspeaker outputs after some amplification through IC1A.R3 sets the gain of the microphone preamp. Besides setting the microphone gain, this control can be of some utility in adding some amount of distortion to the signal, thus allowing a more realistic imitation of a telephone call voice.R9 is the steep control of the pass-band filter. It should be used with care, in order to avoid excessive ringing when filter steepness is approaching maximum value.P1 is the volume control and SW2 will switch off amplifier and loudspeaker if desired.C5 is optional: it will produce a further band reduction. Some people think the resulting effect is more realistic if this capacitor is added.If the use of an external, moving-coil microphone is required, R1 must be omitted, thus fitting a suitable input jack.This circuit was intended to be powered by a 9V PP3 battery, but any dc power supply in the 6 - 12V range can be used successfully.
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