This pedal features an effects loop in a minimal size. One Control is the world's first manufacturer to successfully produce a 1 Loop Box of this size using a PCB, thanks to its groundbreaking PCB layout. The 1 Loop Box is a versatile pedal. When it's OFF, the signal input from the INPUT is output from the OUTPUT, but when you press the footswitch, the signal input from the INPUT is output from the SEND, and the signal input from the RETURN is output from the OUTPUT. To minimize the impact on the signal, the One Control Minimal Series 1 Loop Box employs true bypass with a mechanical footswitch. When used as an effects loop, it allows you to turn multiple effects pedals on and off at once, and even vintage effects pedals that drastically change their sound when bypassed can be used as modern true bypass pedals. By using only the INPUT, SEND, and OUTPUT terminals, the 1 Loop Box can be used as an AB Box. Pressing the footswitch switches the output between SEND and OUTPUT, making it suitable for use as a tuner output or amplifier switching. By using only the INPUT, RETURN, and OUTPUT terminals, it becomes a convenient input selector for switching between multiple instruments. By connecting instruments to the INPUT and RETURN terminals respectively, you can switch between active instruments using a footswitch. By using only the INPUT and OUTPUT terminals, this pedal functions as a mute switch. Pressing the footswitch mutes the output, and pressing it again restores the output. The One Control Minimal Series 1 Loop Box uses passive circuitry, so no power supply is required to use these functions. For improved visibility, if you wish to display the ON/OFF status with an LED indicator, a standard center-negative DC 9V adapter (EPA-2000 recommended) is required. Batteries cannot be used.Condition: No problems with use. Parts requiring acknowledgment: None. Accessories: Box. Warranty: No warranty. Sold as is.