08 Nov 2003, 12:06, Roy J. Tellason (1:270/615), wrote to Matt Mc_Carthy:

Hi Roy.

 MMC>> If there is _no_ battery _in_ the mike, then one of those leads 
 MMC>> is common to ground on the equipment chassis, the second lead
 MMC>> connects to B+, and the third lead is capacitor coupled 'audio',
 MMC>> and usually connects to a medium or high impedance input.

 RJT> So I should be able to tell with an ohmmeter,  then?

Most likely the sleeve would be the ground, and since it is a mono mic, the
tip would have to be the 'output', that leaves the ring for the B+.

In that case, an Ohmmeter would likely give a reading from ring to sleeve,
and a different reading if any, with reversed leads.  The output would show
as an open being in series with the cap.

 MMC>> No impedance matching is needed, but connecting to a _low_ 
 MMC>> impedance input effectively shorts out the coupling capacitor.   

 RJT> Ok.  As I posted before,  it works with the sound cards I've 
 RJT> tried it with...

Hmmm...  they must be putting B+ on the ring in the socket, and that
therefore would have to be current limited to protect against jacks that
aren't plugged in all the way.

 RJT> Know of any pointers to info regarding the impedances,  levels,  
 RJT> etc. for typical sound card inputs and outputs?

No experience there at all.   :-((


     Good luck...  M.

--- Msged/386 TE 06 (pre)