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32-ohm earphone speaker as a dynamic microphone

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August 3rd 14, 11:58 PM posted to rec.radio.amateur.homebrew

Lostgallifreyan Lostgallifreyan is offline

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32-ohm earphone speaker as a dynamic microphone

Stuart Longland wrote in news:mig1bb-
:

For the RJ45, it's documented in the handbook. There is +5V, signal
ground, open-collector inputs for PTT, Up, Down and Power/Fast Tune,
then microphone + and -. The microphone input is a nominal 600ohm
impedance, intended for a dynamic microphone.

From the rest of the post I can see you tried more than I know enough to try,
probably.

That quoted bit does suggest that Yaesu's intent for dynamic mic
is the vital thing, and as you say using CAT5 with their connectors works
fine with a dynamic mic. (I agree with you about DB25 though, cheap, good
current, very reliable fir all kinds of stuff (as are BNC connectors for
single core)).

Anyway, if the idea for electret was to reduce size of microphone, then
converting to low impedance might involve some part too heavy or bulky in
comparison to some small dynamic part to be justified as a replacement. I've
read (vaguely) of a thing called a 'gyrator' a kind of virtual inductance,
but while maybe small and lightweight, I have no clue if this thing is in any
way helpful in this context.

You found a small earplug thing, but the older walkman headphones might be
closest. Inch-wide, or a little less, diaphragm of curved (semi-toroidal
surface) mylar with radial ridges to stiffen it, but extremely thin and
lightweight. Tiny NdFeB magnet.. I remember a dynamic mic with extremely
similar structure, the only big difference (apart from casing) was that the
mic didn't use NdFeB to keep the magnet small. Anyway, these tiny flat
headphone capsules might be the best bet, easy to adapt into stuff too.

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