This is an upgraded version of the old version with Bluetooth function. Supports most high-impedance 16-300ohm headphones, 3.5mm AUX input and output, signal-to-noise ratio 100Db, +N=0.0003%, fully filter out noise and enjoy high-quality audio. [Two-stage gain switch] - This headphone amplifier enhances the signal input to the amplifier circuit to achieve the best performance of the headphones. It can not only output louder sound, but also output clearer and more realistic stereo without distortion. [Rechargeable lithium battery] - Adopts 1000mAH rechargeable lithium battery, which can make the headphone amplifier work for more than 8 hours. In addition, there is a volume control knob to adjust the volume. [Portable and ] - This headphone amplifier is designed to let you enjoy music anytime, anywhere; the sleek and sturdy shell and chassis can achieve long-lasting use [Wide compatibility] - The amplifier is very compatible with a variety of digital devices, such as for MP3, MP4, for , for , for , computer, CD player and personal media player, for , for , for , etc. [Good Sound Quality] - Restore the real sound quality with a wide dynamic range, reduce the distortion rate to create a wide and deep sound field, and the sound quality is delicate and accurate. Colour:Black Material:aluminum alloy Package Contents: 1 * Earphone Amplifier 1 * Audio cable 1 * USB Power Cable Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.