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3 pronged mike

Discussion in 'Misc Electronics' started by Little Monster, Oct 24, 2003.

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  1. Hello all,

    I got a second hand microphone the other day for recording interesting
    sounds on a little piano-key type mono tape recorder.

    The mike is made by Grundig, model GDM 311 seems very well made, and looks
    like the sort your parents/grandparents might have used to record baby's
    words on the family reel to reel.

    It has screen + 3 wires terminated in a 3 pin DIN plug, these are the
    outputs from some kind of matching transformer (I had a look) a low
    impedance side which seems to match the recorders input, and a higher
    impedance side. (I could only measure the DC resistance though)

    So what I would like to know is, why the 3 wire arrangement? Is to
    provide an alternative match for a non standard input, or is it to provide
    some kind of offset earth connection - I'm guessing to feed a differential

    Any suggestions, anybody? It would be nice to know even if I'm not going
    to use the extra wire.

    Tia, Monster
  2. Agreed, the actual voice coil is connected to 2 of the pins and the ground
    is the third. Many Microphone designs used this inclusive of Shure. Been too
    many years for me to remember the configuration tho.
  3. So, without removing the shield to have a look, could this be an
    auto-transformer sitting in there?

  4. Given that most of the older Shure mics had a switch to select output
    impedance, yes.

    Harry C.
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