AHH yes the faulty
ground connection. I have had endless arguments with electricians on this, the ones used to home office shop wiring simply don't understand. It is very common in churches
etc where in many cases where the volunteer does the work and it is not done properly.
What happens is a variety of the following
Sometimes some one replaces the
outlet, and gets the hot and
neutral connection reversed, or the
neutral and
ground connection reversed. The cheap 3 light tester will find the first problem but NOT the second.
Code allows for the use of metal
conduit for the
ground connection, and to save money, the contractor will not pull a green
ground wire thru to all the outlets. Works fine for lights, but for audio is a mess, over time the
conduit connections corrode, weaken get disconnected, or sometimes wind up touching something that could be a
ground say for instance the
conduit runs in such a way that it is strapped to something else, and that for instance is a water pipe, or the
conduit from another circut, now you have multiple paths to
ground, and you get a potention difference, and a hum
Sometimes a sub panel is installed, and the person gets the
neutral bar grounded to the box, now you have again two
ground connections.
For hum free audio, you either need
To
plug everything into the same
outlet, (if the interconnection of
ground on the same
circuit is bad you will get hum even if it is on the same
circuit. Obviously this many times is not practicle but in some places I have had to run an extension
cord all the way from the
stage back to the
mixer at
FOH just so everything was on the came
outlet.
Isolation transformers on the
line that interconnect also work, and fix the problems also.
Bring a
distro, have it hooked into the main panel and then YOUR wiring is what goes from the
distro to your units.
Get an electrician to fix the
ground, I recommend if at all possible, changingn to
ground isolated outlets, and then having a complete
ground wire pulled. This is not cheap, and sometimes it is easier to have them simply run a new set of circuits for you on
stage and
FOH and have the new connections all have a complete isolated
ground only connected to the service
ground at the main panel.
Another thing to keep in mind that a lot of people miss is that
surge protector strips that have gone bad, will work but have
ground problems. This is why in general for amps for instance people tend to just have a
quad box, no
Surge protector, and a
voltage regulator/
ups for the
FOH equipment, and then have isolation transformers on the
line feeds.
Sharyn