ROLLS HA204 Battery Headphone Amp. Stereo 1/8 (3.5mm) Input. Four Stereo 1/8 (3.5mm) Outputs with Level controls. Operates on a single 9V battery, or optional AC adapter. Comes with a single 1/8 to 1/8 adapter cable, and a stereo RCA to 1/8 adapter cable. NOTE - DO NOT PLUG IN THE POWER ADAPTER WHILE A BATTERY IS INSIDE, IT COULD DAMAGE THE UNIT!