The MXR M133 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. Powered by a single 9 volt battery or Dunlop's ECB-003 AC adapter.
Footswitch toggles amp on/bypass (red LED indicates on) Gain knob adjusts total output volume when micro amp is engaged.
Get an overview of the MXR M133 Micro Amp Boost Pedal in this video demo: