I bought a used Iamp800 and haven't yet bought a cab for it. I thought I'd check out the sounds with the headphone but couldn't get anything but hiss out the phone jack. Power switch was on in the back, speaker button was off in front, output was on on 3, input on 3, tuner was registering, and the amp was getting input (green input light was firing when i hit the amp), headphone was in the proper jack, passive bass in the passive input. Am I missing something? Took the bass, the cord, and the phones to another amp and it worked, so nothing wrong with the cords or headphone or bass. Any suggestions? Thanks in advance.