Power megaphone circuit

admin April 7, 2010 8 Comments

Description.

Just about any power transistor can be used in  this megaphone.Its suitable for boats,playing fields etc.the transistors Q1  & Q2 are the HEP-230 type which are easily available in the market.The transistors are parallely connected to handle the required power and speaker matching.The microphone is a carbon type like that used in telephone hand sets.If  a regular carbon mike is used the push-to-talk (PTT) switch can be connected in place of S1 to provide PTT operation.There will be no warm up or “capacitor charge time.

Circuit diagram with Parts list.

power-megaphone-circuit.JPG

Notes. 

  • The circuit can be powered from a 12V battery or 12V DC power supply.
  •  The POT R1 can be adjusted to obtain maximum volume with minimum distortion.
  • It will be always better to mount the transistors on heat sink.
Comments
  • December 25, 2013

    what is the maximum output power of this circuit? What type of a mic should be used?

    • Seetharaman
      December 26, 2013

      Hi Mic should be carbon type and with the shown germanium transistors the power output will be around 2 to 2.5 watts.

  • Rex
    October 7, 2013

    What are other Replacements fo HEP230 Transistors?

    • Seetharaman
      October 8, 2013

      Hi Rex HEP 230 is a PNP power transistor similar to AD149 or 2SB337. As the transistor is pnp collector should get connected to negative and emitter to positive. Mic should be carbon type only. To start with keep R1 at maximum value and by talking into mic slowly adjust the pot till god quality (un distorted)sound is heard with good volume. by adjusting R1 further will increase the current consumption and reduce the volume also. Never try with a car battery you may blow the transistors instantly in to smoke.

  • Rex
    October 7, 2013

    Apart from Carbon mic, Can i use Electret mic, dynamic mic, or Condenser mic.

  • steven
    October 9, 2010

    what type of mic will be the best to this circuit??

  • Steven
    May 24, 2009

    If R1 (potensio) turn to zero ohm, the base Q1 and Q2 are + 12V. Speaker not burn ???

  • February 5, 2009

    it sick outa proportion member mi tell yuh dat!!

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