Have a Peavey Minx 110 '98+ model. Anyway, the guys at church dug it up for me to use this morning. Set it up so that I went from the bass, to the amp input. Then the amp out to these DI units that we have. Even with the amp power off, the church speakers hummed. Actually, even with ONLY the amp hooked up to the church system it hummer.
The DI box has two 1/4 connections. One input, one output. And then a ground switch and an XLR output. And no matter how the amp was wired, on or off; either amp out to DI box in, or amp in to DI box out, the speakers hummed.
So, what's wrong with it
It works fine with just the guitar plugged into it though.