Mic problem

[dvandoornik@xxxxxxxxxxxxxxxxxx]

        I have a microphone related question I hope someone can answer for 
     me.  I use a Astatic JT-30 with a volume control that works great when 
     plugged into an amp.  However, I recently tried to play it through a 
     PA system via the mixing board.  The mic sounded fine, except when I 
     tried to adjust the volume control on the mic, it created a loud, 
     horrendous, sort of crackling sound through the speakers.  I was using 
     a different cord - one with a low impedence plug, to connect with the 
     mic jack.  Is this a high/low impedence problem? (I'm not clear on 
     what the difference is).  Thanks.
     
     Don Van Doornik