The A.B unit is an entirely passive router therefore it is completely transparent. It allows routing the signal between 2 amps, to amp A or to amp B. 2 bright LEDs, powered by a 9V battery or power supply (not included), indicate which output is selected. With every Huge Audio router, the power is drawn only when a cable is connected to the input jack plug. Also, if no cable is connected there, the sound is electronically muted on all the amps. This means that absolutely no sound comes out of the unit then, even at maximum volume! Made in Germany.