From Manufacturer
The E6 Stereo Headphone Amplifier from Fiio is an ultra-compact headphone amplifier that increases the volume and audio quality of your portable music player. The amp has an advanced circuit to offer a high signal to noise ratio, wide dynamic range, and minimal distortion.
The amplifier has standard 3.5mm input and output connectors for compatibility with a variety of music players and headphones. There are power and volume controls, plus 3 types of DSP-based EQ so you can adjust bass and treble. A key lock function prevents accidental changes. The amplifier has a built-in rechargeable Lithium battery that provides approximately 10 hours of operation. The battery is charged via a mini USB connection for convenience. A removable transparent back clip is included so you can attach the amp to your clothes or bag.