W6NEK wrote:
If you connected the SM20's Pin 2 (+8V DC Input) to K3 front panel Mic
Pin 6 (8V Output) then the SM20 internal preamp will provide mic bias to
the SM20 electret element. That's how I wired my SM20 and it works
great on the K3. No additional Mic Bias is required.
Actually, the so called bias on electret microphones only ever powers
the pre-amplifier. Electrets are permanent electrostatic dipoles, and
provide the electrostatic field needed for the microphone transducer.
Those transducers are very high impedance, which is why you need a
pre-amp very close to them. Typical electret units phantom feed the
power, so it looks, at first sight, like bias.
Condenser microphones, that were historically used as broadcast
microphones, do need a high voltage bias to generate their electrostatic
field. Electret transducers work on the same basic principle, but get
their field from the electret. Electret "bias" voltages are far too
small to be used directly to provide the field in the microphone.
--
David Woolley
"The Elecraft list is a forum for the discussion of topics related to
Elecraft products and more general topics related ham radio"
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