JOYO mini guitar amplifier is small enough to clip to your belt or hang from guitar body. 1/8-inch stereo in allows you to play along with music. Features 3 controls: Gain (dist.), tone (treb.) and volume. Includes the 2 AAA batteries required for operation. Quality sound. Just plug your headphones into the JOYO JA-03 mini amp and you've got a cool sound, directly from your guitar amplified to your headphones. Walk around the house and practice wherever you want, all without disturbing anyone around you.