Pre-amplifier circuit

Discussion in 'General Electronics Chat' started by finding_apple, May 28, 2008.

  1. finding_apple

    Thread Starter New Member

    May 28, 2008
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    Hi all,

    Does anyone know how a simple Pre-amplifier circuit of an electret microphone look like?
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. cumesoftware

    Senior Member

    Apr 27, 2007
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    Now that you mention that, I might have a pre-amplifier project for that kind of mic. That came in a magazine, but it is not copyrighted material (none of the materials inside that magazine are). I will OCR it as soon as I can.
     
  4. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
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    This schematic is for a super sensitive microphone:
    microelectret.jpg

    Connect the microphone to the input. You should consider lowering the gain.
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The preamp for an electret mic is simple:
    1) Use a low noise wideband opamp like a TL071.
    2) Bias the input of the opamp to half the supply voltage.
    3) Have atrimpot to adjust the voltage gain to 22 times.
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    here is a simple schematic.

    http://www.mitedu.freeserve.co.uk/Circuits/Audio/ecmmic.html

    As you see there is a resistor from the mic to plus.
    Did you use this also? if you forget this your signal will be very low.

    Greetings,
    Bertus
     
  7. finding_apple

    Thread Starter New Member

    May 28, 2008
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    Hi,

    i think the circuit is too complicated for my case. I decided not to use the preamp for the mic. Thanks.

    Rgrds,

    apple
     
  8. finding_apple

    Thread Starter New Member

    May 28, 2008
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    Hi i decided not to use preamp in my circuit. now i try to create a DC offset value of 2.5V at the o/p by biasing it with resistors 200k and 100 ohm with the gain of the op-amp=1001. But why the o/p nearly 0v, why the amplification is not done?
     
  9. finding_apple

    Thread Starter New Member

    May 28, 2008
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    Hi bertus,

    The biasing of the electret is done internally. the circuit start from the mic(+pin) to a 2.2k resisitor then to a capasitor the to resistors 200k and 100 acts as a voltage divider to supply 2.5mv to the op-amp then with gain of 1001 , i hope to amplfy the CD o/p to 2.5v . But why the o/p nearly 0v, why the amplification is not done?

    Regards,

    apple
     
  10. finding_apple

    Thread Starter New Member

    May 28, 2008
    6
    0
    Hi bertus,

    The biasing of the electret is done internally. the circuit start from the mic(+pin) to a 2.2k resisitor then to a capasitor the to resistors 200k and 100 acts as a voltage divider to supply 2.5mv to the op-amp then with gain of 1001 , i hope to amplfy the DC o/p to 2.5v . But why the o/p nearly 0v, why the amplification is not done?

    Regards,

    apple
    [​IMG]
     
  11. bertus

    Administrator

    Apr 5, 2008
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    hello,

    Can you post a drawing of your schematic?

    Greetings,
    Bertus
     
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