This sound enhancer is designed to help improving sound quality for music after MP3 or MP4 compression. Enrich you life with music of quality sound. Enhancer in classic vacuum tube shape, easy for carry. Build in Li-Polymer battery, full charging for 6 hours usage. Suitable for MP3 or MP4 media player. Improve the volume, extend the playback time of media player. Improve the bass performance. Special circuit layout, reduce the pop sound. Two LED indicators, easy to know using or charging. Stereo Line-in. Stereo Headphone-out, Plug and on device, remove to off the device. Standard mini-USB port for charging. Support 16-150 ohms headphone. Output 50 (32 ohms loading). Size: 1.8"L x 0.9"D (45mm L x 23mm D).