Please open a support ticket
. Please let us know your results with the headphone output on the pre-amplifier. Also, if you have an external source with a volume control, such as a smart phone, you could use the headphone output and test two amplifier channels at a time. You would need to use a stereo 3.5mm to stereo RCA cable and plug directly from the headphone output into two amp-channel RCA inputs. Make sure the volume is low when starting to play something, and make sure all equipment is off when plugging or unplugging connections.