This unit is designed for use with Amp Send/Return (Loop) to lower the volume. If you have Loop on/off SW in the Amp, please turn on Loop. If you have Loop-Mix knobs on the Amp, use Mix as 100 Percent. Please note that it cannot be used with parallel Loop. When connecting an effector other than this device to Loop, please connect this unit to the end of the effector. Simply one knob and IN/OUT only. Passive tuning for a good sound drop. Size (W x H x D): Approx. 2.0 x 2.2 x 2.0 inches (50 x 55 x 50 mm) (Including protruding item