Roland Micro Cube Bass RX Battery-Powered Bass Combo Amp Battery driven (6 x AA, up to 13-hour continuous use) (Best with Polaroid AA Batteries) Stereo power amplifiers and four newly developed 4" (10cm) speakers Eight COSM amps, six digital effects Rhythm Guide function for practical rhythm training Stereo AUX input for CD/MP3 player Phones/Recording out