Maxon 9-Series Overdrive Soft Distortion Input Impedance: 500k ohms (Output Impedance: 10k ohms or less) Maximum Gain: 41.5dB(700Hz) Equivalent Input Noise: -107dB or less (IHF-A) Operating Voltage: 9V Battery: 9V battery (6LR61 or 6F22) x 1 or Maxon AC adaptor