Nady TR-20 Tremolo Pedal &ndash; Wave, Rate, and Depth control - All Metal Casing &ndash; 9V battery operation or use optional AC adapter Widest variety of vintage tremolo guitar sounds available Wave knob offers extensive range of altered waveform tremolo variations Rate knob varies tremolo speed All-metal casing for years of roadworthy reliability Operates with one 9V battery or the optional PAD-1 AC adapter