Mike: In my only vaguely-informed opinion, the situation with two power supplies as you describe is not unreasonable, but a ground loop may or may not be the problem. What is the exact nature of the symptoms? Hum? Buzz? Controller freaking out? If you're running a DC cooling fan (or fans) temporarily disconnect same and see if the problem goes away.
Over the years in the broadcast biz, I've seem situations where lifting a ground provided a miracle cure, and almost exact same situations where adding a ground did likewise. I'm convinced that ground problems fall under the heading of FM--"freakin' magic"! That said, try some experiments: Tie the two power supply grounds together. If none of the gear is floating above ground (or otherwise in a configuration that could result in a difference of potential between cabinets), see what happens if you bond all the various chassis together (but avoid daisy-chain grounding). Try lifting the ground of the AC cord (use one of those 2-to-3 prong adapters); this is only for diagnostic purposes--long term you don't want to leave things this way. Use a voltmeter--one probe on the ground of the P.A., one on the exciter's ground--to see if there's any potential. Then, after you complete all these various science projects, double check the fan situation again. Switch to a DC-relay switched AC powered fan. Good luck. Keep us posted. 73 de K5IQ Bob
