[Elecraft] K3 and SM20

[David Woolley (E.L)]

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
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