Clean boost pedal. From the manufacturer:
The MXR M-133 Micro Amplifier Pedal adds a preset amount of gain, using a single control. With a guitar, this lets you boost your signal for lead work, adjust between 2 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. Power: Single 9-volt battery or Dunlop ECB-003 AC Adapter - Controls: Footswitch toggles amp on/bypass (red LED indicates on) Gain knob adjusts total output volume when the Micro Amp is engaged.
$50 shipped domestically.