About the size of a cigarette pack, amazingly it can drive a 4 x 12 cabinet. (We didn't believe it either, so we tried it. And, sure enough, through the magic of technology, it was actually loud and sounded great, though the battery didn't hold out long.) It responds to the volume knob on your guitar and generates a sweet and convincing tube amp overdrive when cranked. It has its own built-in speaker. It can also be used on the input of another amp as a fuzz box. Check the drop-down menu to the right to select colors and/or other options.