These articles may be of interest.
http://www.rane.com/note151.html
http://www.rane.com/note110.html
I have worked at the same venue for many years and have noticed more frequent problems
recently with hum and buzz
with some bands' equipment while most are perfectly fine. I suspect changes in the
grounding such as corroded
ground rod connectors or dryness in the soil they are in. The boss is investigating.
I always try to run all PA and band equipment from the same circuit if capacity is
sufficient. The previously
mentioned 750 foot run may be a problem though with probable significant voltage drop.
Cheers
Roger