Many classic amps feature multiple input channels, ours don’t. We did this because we strive for simplicity, and frankly didn’t see the point. This accessory is a four channel active mixer. It has four input channels, with two unity gain active amplifiers, as well as two channels with 10x amplifiers for microphones or a nice little preamp overdrive for an instrument. A fifth active amp drives the single output channel that can be hooked up to your amplifier for small gigs, home practice, busking, or anything else you can think of. It is on whenever an output cable is plugged in, and runs on an internal 9V battery.