This device adds a preset amount of gain, using a single control. With a guitar, this lets you boost your signal for lead work, adjust between two different guitars with unmatched output (i.e, humbucker to single coils), or it can supply a permanent boost in a long effects chain where signal drop off is a problem. Controls: Footswitch toggles amp on/bypass (red LED indicates on) Gain knob adjusts total output volume when micro amp Is engaged. Power: Single 9 volt battery or Dunlop ECB-003 AC ada