The E3 Portable Headphone Amplifier from Fiio is a compact and portable headphone amplifier that allows you to increase the play time of your music player and improve the audio quality. It also has a bass boost function for enhanced bass. The amplifier has standard 3.5mm input and output connectors, providing compatibility with a variety of headphones and music players. Simply place the amplifier in the signal path between your music player and your headphones. Features: Signal to Noise Ratio - 90 dB (A Weight) Distortion - 0.05% (10 mW) Frequency Response - 10 Hz - 40 kHz Suitable Headphone Impedance - 16 ohms - 300 ohms Dimensions - 2 x 0.9 x 0.57 inches Weight - 11g (Battery not included)