Matt Mc_Carthy wrote in a message to Roy J. Tellason:

 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?

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

Sounds about right.

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

Yep.

 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...

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

Yeah,  with some resistor in series with it.  Looking at the dead one I
still have sitting here,  there's a 1uF cap and a bunch of surface mount
parts (both caps and resistors) right at the jack.

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

 MMC> No experience there at all.   :-((

Yeah well,  it's out there someplace,  I'm sure.  I'll find it sooner or
later,  though I'd probably be spending some nontrivial time dealing with
the piles of stuff I've already snagged,  first.  :-)

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