Radio Transmitter

For your comments, suggestions, or your looking for a circuit or design, or a electronics designer, please send you Inquiries to We are happy to help and attend to your concerns.

Wednesday, April 1, 2009

Telephone call Voice Changer

Voice manipulation device specially intended for props
9V Battery operation

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.

  • 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


  • 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.

No comments:

Post a Comment