From: rcrowley@xp7rt.net   
      
   "Randy Yates" wrote ...   
   > Thanks for the confirmation and education, Richard! Before you wrote   
   > this, I didn't even know there were "non-electret" condenser mics.   
      
   The original condenser mics were externally charged. Most higher-end   
   condenser mics are still externally charged.  I have a pair of Sony C-37   
   mics which use external voltage. They also have power supplies the   
   size of a lunch-box to handle the power and output transformers and   
   use a 6AU6 in the mic head for impedance buffering.   
   http://www.rcrowley.com/SonyC37/index.htm   
      
   While the charge-storing electret was first described back in the late   
   1800s, it wasn't used commercially for condenser microphones until   
   the 1960s.   
      
   > And I guess that C = Q / V means V = 0 if Q = 0 (i.e., you have to   
   > power the bloody things).   
      
   Exactly   
      
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