[Elecraft] K3 and SM20

[Jim Brown]

On Fri, 15 Aug 2008 08:04:31 +0100, David Woolley (E.L) wrote:

>Condenser microphones, that were historically used as broadcast 
>microphones, 

Condenser mics have historically been used for MUSIC, both 
recording and broadcast (and they still are). Most broadcasters use 
dynamic mics for speech. Most US broadcasters wouldn't know a 
condenser mic if it bit them you know where. 

>do need a high voltage bias to generate their electrostatic 
>field.  Electret transducers work on the same basic principle, but 
> gettheir field from the electret.  

Electret condenser mics need a different form of bias. The capsule 
(the transducer) is permanantly biased when it is manufactured -- 
it doesn't need anything from the circuitry. The very small signal 
produced by the capsule is amplified, usually by a FET follower 
circuit. This amplifier circuit is what needs DC voltage and 
current from the radio.  

>Electret "bias" voltages are far too 
>small to be used directly to provide the field in the microphone.

See above. 

73,

Jim K9YC