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Electret condenser microphone questions

Discussion in 'Electronic Basics' started by Andrew Howard, Aug 9, 2003.

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  1. I have a circuit for an ECM preamp but the microphone in the circuit has
    three pins. The only types I can get hold of are the 2 pin variety. Is there
    an easy way to convert the circuit so that I can use a 2 pin electret?

    Thanks
    Andrew Howard
     
  2. tempus fugit

    tempus fugit Guest

    Where is the schem? I think that the 3 pin variety has 1 pin for ground, 1
    for signal, and 1 for V+. The 2 pin kind has 1 for ground, and the signal
    and V+ is shared by the 2nd pin. The signal output must use a DC blocking
    cap between it and the amp in.
     
  3. The schematic is located at:
    http://www.mitedu.freeserve.co.uk/Circuits/Audio/ecmmic.html
    I think it me be as you described it, but if so, do you know how to use the
    2 pinned type with the circuit?
    Failing this, if you could direct me to any good electret microphone preaamp
    circuit for ecms with 2 pins, I would be grateful.

    Thankyou
    Andrew Howard
     
  4. tempus fugit

    tempus fugit Guest

    All you have to do is use a blocking cap from the output of the mic to
    prevent sending the DC supply voltage to the preamp. The schematic you've
    pointed to has a 10uF cap between the output of the mic and the base of the
    transistor, so that will do the job. So, the only adjustment that you need
    to make is to connect the 1K resistor to the same mic pin as the 10uF cap.
    IOW, connect the top pin of the mic in the schem to the middle pin, and that
    will be the same as the 2 pin ecm that you have. Make sure that the cap is
    on the transistor side of the resistor, though, so it blocks the DC (like it
    is in the schem).

    One caveat - I notice the whole thing is powered by a 12v supply. Most of
    these types of ecms recommend a 2-10v supply voltage (oddly, it even says so
    in the article). You may want to either use a regulator to drop the mic
    supply voltage down to 9v, or use a simple voltage divider. Keep in mind
    though, that the 1k resistor effectively sets the output Z; this will change
    if you use either the regulator or the divider method.

    One other thought - these ECMs can be had very cheap (I'm asuming you're not
    using an expensive element here) so you might want to just go ahead and try
    it with 12v, and see if it works OK. Where are you getting your mic element
    from?
     
  5. Rob

    Rob Guest

    Simply conect the 1k resistor to the 10uF cap. Connect the 'ground' of
    the mic to ground of the circuit and connect the second pin of the mic
    to the junction of the 1k resistor and 10uF cap.
     
  6. I am getting the microphones from Jaycar, an electronics store in Sydney,
    Australia. They cost about three Australian dollars.

    By the way, thanks for helping me out with this problem with your quick
    responses.
     
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