Stereo effect making your rig hum? Try this test

Hum or buzz is usually a ground loop, and it gets more likely the moment you send signal to two different places — like two amps. Plugging all your gear into the same outlet or power strip reduces the chances. There's a simple test to see if your rig is prone to ground-loop hum: connect a cable between the two inputs you plan to feed the stereo signal into. It sounds strange, but it won't harm anything — it just ties the two grounds together at their inputs. If you get hum or buzz, you'll get the same with a real stereo signal. As the test shows (or rather, lets you hear), ground-loop hum comes from grounding differences, not the source gear. The simple fix is to break the loop with a ground-loop breaker like an Ebtech Hum X on the AC plug of one piece of gear. Running two amps? Put it on one of them. Running to an amp and direct? Try it on just the amp. We prefer this to isolation transformers because it doesn't touch your signal at all — and it keeps a safety ground intact. Never fully disconnect the ground connection; that's dangerous.