The BOSS BD-2 Blues Driver Pedal delivers the creamy yet crunchy sound associated with great blues guitar. This popular pedal provides instant access to the kind of warm overdrive and emotive distortion usually reserved for 30-year-old tube amps.Level KnobThis adjusts the volume of the effect sound. When turned counterclockwise, no sound will be heard.Tone KnobThis adjusts the tone of the sound. Rotating it clockwise will create a sharp sound with emphasized treble while turning it counterclockwise will create a soft sound with a cut tremble.Gain KnobThis adjusts the gain of the blues driver. Rotating the knob clockwise will increase the gain creating harder distortion.Input JackThis jack accepts input signals coming from a guitar, some other musical instrument, or another effect unit.Output JackThis output jack is used to connect the unit to amplifiers or other devices.DC IN JackIt accepts the connection of an AC adaptor. By using an AC Adapter, you can play without being concerned about how much battery power you have left.Check IndicatorThis indicator shows whether an effect is ON/OFF and doubles as the battery check indicator. The indicator lights when an effect is ON.