Electro-Harmonix Germanium Overdrive Pedal Controls: Gain, Bias &amp; Volts1/4" input and outputDC power input for battery replacement.LED indicates whether effect is engaged or bypassed. Gain, Bias and Volts controls are on top of the pedal, not hidden inside the case Easily dial in that perfect vintage germanium overdrive The Bias control adds emphasis while the Volts control helps you dial in that that sweet spot produced when your battery's voltage dips Dial up that slightly torn speaker sound or unleash total Germanium satisfaction