slipmip said:
Just played a show last week and ran right off the battery. That seemed to keep any strange static noises to a minimum. I also got a tip that using a 2 prong adaptor on the power supply might work, but that kind of bothers me. I suppose it really would be best to just find a correctly grunded outlet, but that would be to easy. thanks for the input.
peace
Bad idea to use one of those adapters. Your outlet is probably grounded just fine, but your computer's power supply probably isn't.
The noise you are hearing is almost certainly caused by the GPU generating noise on your computer's ground plane (and power plane) which isn't being properly shunted to the earth ground because your computer's power supply isn't grounded well enough. My old (first generation) PowerMac G5 had the same problem.
Best way to cure this is probably to actually ground the system properly. Take a three-prong power plug, fasten about a 10 AWG stranded wire to the ground. Make sure you connect it to the right pin!
Fasten the other end of the wire to the shield on an audio plug and connect it to a spare jack on your audio interface. If you don't have a spare jack, build yourself a short extension cable with a plug and jack and tie the extra ground wire into the shield on that. Plug the opposite end of the wire into a spare power outlet.
In all likelihood, the noise will vanish after that. My guess is that the reason that running on battery works is that you are probably running the GPU at a lower core voltage while on battery, but there's another possibility that's even more bizarre.
Most of this noise is on the hot side of the circuit---basically, the 5v PSU output line. When you run on a power supply, the charge circuit is engaged. You now have... possibly a pair of diodes in the power supply's FWB, possibly a transformer, possibly something else entirely... but either way, you now have a very low resistance path between hot and ground.
Audio interfaces are designed to be immune to tons of noise on the hot side. When they get noise up their ground plane, they misbehave almost universally. Since here is probably only a modest resistance between the signal ground and the signal input in your audio interface, some of that noise will leak into the input.
At least I -think- this is what happens. Either way, ground bussing does generally help, in my experience.