This is an old Austrian army tank operators carbon throat microphone. It picks up the voice through the direct vibration of the vocal chords and does not feedback nearly as much as an acoustic microphone. I had to build a little circuit to make it work as carbon mics need dc power in order to work. After experimenting with a few different setups, the circuit below worked the best and the 9V should last at least 25 hours or so.
The audio transformer is about $3 at RadioShack, but does not transfer much bass as the lowend cutoff is around 300Hz … but then again, these old carbon mics do not have much bass anyway.
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