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lm386 and electret microphone problem

Discussion in 'General Electronics Discussion' started by Stratos, Aug 23, 2015.

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  1. Stratos

    Stratos

    2
    0
    Aug 23, 2015
    Hello,
    I have completed an amplifier circuit using the lm386 and an electret microphone as shown in the following link: *How to Build a Microphone Amplifier Circuit

    When I blow onto the electret microphone, I can hear the sound of it. However if I start talking onto the microphone, no sound is coming out of the speaker.

    I have tested the electret microphone on my pc and works fine as I can record myself talking and then hear it back.

    What am I doing wrong?
    Thank you very much for your time.

    Regards,
    Stratos
     
  2. davenn

    davenn Moderator

    13,500
    1,830
    Sep 5, 2009
    hi there
    welcome

    lets see a pic or 2 of your construction, maybe some one will see a wiring error you have made


    Dave
     
  3. Martaine2005

    Martaine2005

    2,575
    696
    May 12, 2015
    Hi Stratos,
    I think your amp is really a pre-amp. Which is why it works fine with your computer soundcard.
    If you want to hear your voice through a speaker, you need a power amp too.
    Those terms are used loosely as in a pre-amp to another amp to amplify the output signal, which is your mic.

    Martin
     
    Arouse1973 likes this.
  4. BobK

    BobK

    7,673
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    Jan 5, 2010
    LM386 is a power amp.

    Bob
     
  5. AnalogKid

    AnalogKid

    2,337
    654
    Jun 10, 2015
    There are a lot of low cost modules from china based on the 386 as a mic preamp. Low parts count and indestructable, but not enough gain, high distortion and noise, and not enough gain to go from mic level to 8-ohm speaker drive. Did I mention the gain?

    ak
     
  6. BobK

    BobK

    7,673
    1,684
    Jan 5, 2010
    I agree, it is not enough to drive anywhere near max output. A 1 transistor preamp (gain 10) would do it.

    Typically, the electret mic will have a sensitivity of -46dB at 94dBA in. The gain is 46dB (200) so you would get 1V out at that level. A normal voice at 1 ft is 70dBA, at 3in it would be 82dbA which is -12db from 94, so you would get 1/4V out. You should hear something if you placed the speaker against your ear.

    Bob
     
    AnalogKid likes this.
  7. Stratos

    Stratos

    2
    0
    Aug 23, 2015
    Thank you all for your replies.
    As far as I understood I need a preamp for the electret mic to work with lm386 as expected.
    Thus I would like to make my own preamp. I have seen that a NPN transistor is needed for this.
    Can I use any NPN transistor, because I have got BC547 (50V 100mA)?
    In such a case what values for transistors and capacitors will I need?
    Cheers
     
    Last edited: Aug 25, 2015
  8. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Stratos likes this.
  9. anjum4

    anjum4

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    0
    Oct 13, 2015
    I think you don't need any preamplifier circuit, as I have also built one without any preamplifier, taking help from below circuit and mine one is working great.
    LM386 Audio amplifier Circuit
    And this mini amplifier article also says that in practical it doesn't need preamplifier
     
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