Product Details： 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 Greater Than 100db, Thd+n=0.0, 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 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 Lightweight] - 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