Early in my F5's life it was accidentally left on for a couple of days. When I had been using it the heatsinks had never gotten over 48 C but somehow during this couple of days something happened and the fuse blew. I found both output mosfets on the failed channel were now burned out. I had no speaker protection on it at the time but fortunately my speakers were switched to a different amp via a switchbox and weren't connected to the F5. After this I added the store's speaker protection board and lowered the bias from 1.3 to 1A after replacing the mosfets and source resisters. I haven't had any trouble with it since but definitely wouldn't go without the speaker protection again. And also, of course I'm much more careful that it doesn't get left on.