The ABY Mix is designed to route two input signals to two output sources. Each input has its own level control to balance different input levels. Each output channel is turned on/off via a footswitch for that channel. Each output channel has an LED indicator that lights when that channel is on. Unity gain is at approximately 10 o'clock on each input knob. From 10 o'clock to 1 o'clock, will add clean boost and turning up beyond 1 o'clock will add slight overdrive. The ABY Mix powers up from one 9V battery or optional Morley® 9V 300mA adapter (center polarity is negative). Remove bottom cover via 4 Phillips head screws to gain access to battery compartment. Hooking two output sources together via the ABY Mix may create Ground Loop Hum in one or more of the output sources, this is a normal occurrence and can be easily solved. Please visit www.ebtechaudio.com for information on why Ground Loops occur, tips on diagnosing hum and learn about products that solve hum and signal problems.