Chris,

 A carbon mike has to have a voltage (current) source in series with it to
 make it work.  It is basically a voice adjusted resistor.   Carbon granules
 are packed inside the button on the back and the diaphram is connected
 to a plate in fron of the button.  So at rest, it will have some
 resistance. (Generally rather high  ie. several hundred Kohms to several
 Megohms.)   So, with a battery and an ammeter in series with it, you
 should see a varying current when the microphone is spoken into.
 Feeding this varying current into a resistor and connecting an op-amp
 across this resistor should give you a usuable output capable of driving
 a hi-fi amp such as your stereo.

                                             Regards,

                                               Jim



> I have a handset, identical to a regular telephone handset. It has one
> of those carbon electret microphones in it. I cannot get any sort of
> signal on my scope when I holler in the mic. I am used to the active
> mics, like the two pin device that takes a 1K pullup to power it. Does
> anyone know what sort of amplifier is necessary? Impedance of the mic
> element? Gain that is necessary?
>
> Thanks all
> Chris~
>
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