Some of your answer depends on what is driving the XLR output jacks on the equipment. It could be transformer driven, but more likely these days it is an op-amp in a differential configuration.
If you can find the spec sheet on the mixer board (or whatever you are using for a feed), see if it is OTL (output transformerless) or if it uses transformers.
If OTL (might also be stated as "Active output"... Pin 1 to shield, pin 2 to tip and leave pin 3 floating..... don't ground it... Pin 3 is also an active output... just the negative side of the signal. It is not needed in this case. Pin 2 will carry the full signal. If it has transformers on the output... you will need to ground pin three to complete the circuit path through the transformer.
In my experience, a better way to handle this situation is to put an adaptor on the AMPLIFIER end of the wiring. Once you convert the system to unbalanced, the signal is much more likely to pick up hum and other noises... including CB radio and other unpleasant surprises... Nothing like hearing a trucker running a 1,000 watt linear amp on his CB cursing over a churches sound system... then having that rebroadcast over a radio station. One learns quickly that way.
Unbalanced lines have two things going against them. There is no out of phase cancellation of noise picked up along the wire path... and they are usually high impedance circuits which invite more noise to enter them. The only reason you find them in consumer electronics at all is that they are cheaper. Professional equipment always operates with balanced lines.
What I did with commercial radio stations was this:
Feed the full blown balanced line over to where the amplifier is located. Radio Shack sells a plug in Balanced to Unbalanced line adaptor. Use that on the AMPLIFIER input, and your signal will stay cleaner along the path. It won't become unbalanced until it actually enters the Amp and at least it has some shielding there.
Normally I wouldn't recommend Radio Shack for much of anything but I have used many of those adaptors in radio stations before and never had a moments problem with them. It's kind of hard for them to screw up a simple transformer which is all that will be inside the shell you buy.
Ernie touched on one other important item.... hum because the source and the amp are not at the same ground potential. The best way to handle this is to have an electrician make sure that the source and the amplifer are on the same circuit. If that is not an option.... run a ground wire along with the rest of the wiring and connect it to metal on both pieces of equipment. Normally the shield connection would do that for you... but there are some pieces of equipment that float grounds.... and you need a solid ground connection in this case.
This message was edited by Warren on 08/23/04 21:58 ET.
