Donner Golden Tremolo Pedal Classic Tremolo Guitar Effect 1.Dedicated Speed, Bias and Depth knobs allow you to dial in your desired sound. 2.Classic Tremolo Sounds. 3.Whole Aluminium-alloy classic, stable and strong. 4.True bypass provide transparent tone.LED indicator shows the working state. 5.DC 9V Adapter power supply. Working Current: 26mA. Power Supply9V DC (Negative in the center). Depth KnobControl the depth of tremolo effect. Bias KnobAdjust the bias of the optical of tremolo unit. Speed KnobAdjust the speed of tremolo effect. Input &amp; Output JackAnalogy though 1/4 mono audio jack. LED LightLED indicator shows the working state. Full metal shellAluminum-alloy classic, stable and strong. True BypassTrue bypass for zero tone coloration.