?Support Headphones with 16-300?? This HiFi Earphone Amplifier Is Specially Designed for High-end Headphone with High Load Impedance, Support Impedance up to 300?, SNR>120Db and THD+N 0.0003%, Make It Possible to Output Remarkable Sound without Distortion from Your Laptops, Phones or MP3. ?With Power Bank Function? Built-in Power Bank, It Adopts a Rechargeable Lithium Battery with 3000mAH Capacity, Which Allows It to Stay Working More than 15 Hours or Fully Charge Your Phone Once. (Including 1.2m/3.9ft USB Power Cable) ?Gain Switch and Bass Switch? Two-stage Gain Switch and Bass Switch Can Effectively Enhance the Input Signal, Achieve Optimal Performance of the Headphones. ?Improve the Output Power of the Headphone? 3.5mm Input and Output Headphone Jack, on the Basic of Increasing the Output Power of the Headphone, Can Modify the Sound Quality, Output More Realistic Stereo Sound. ?Aluminum Matte Surface? Aluminum Shielding Can Effectively Improve the Anti-interference and Heat-resistance, Providing You Comfortable Handheld Feeling, Be More Durable than Other Material. Be Compatible with MP3 Players, iPods, Personal Media Players, Mobile Phones, Laptops, Notebooks or Portable CD Players.