I'm using an SWR Super Redhead which has its own XLR send on it. We used it on our rehearsal the other night and it worked fine. We set up for our first gig last night, and got a horrible hum on my channel in the mains. Flipping the ground lift switch just made it worse. So I pull out my Fishman Platinum Pro that I use for my upright and use it for a direct box. It sent the signal fine to the board, but the second i plugged into my amp, the hum came back in the mains. Just before we gave up and left, the dj told us that we had our power amp for the mains plugged into the same power as the stage lighting system. My amp was plugged into a seperate outlet. Could this be the problem? The gigs this weekend, any suggestions?