Features: brand new and high quality This Hifi headphone amplifier supports impedance 16-150 , delicate, compact and portable, which make it convenient to carry, Can output remarkable sound without distortion. 3.5mm AUX Input and Output. High quality audio, suitable for your mobile phone MP3 MP4 laptop PC. Noise reduction function, and distortion with enhanced dynamics, perfect pure stereo effect, high definition voice music sound quality optimization. Aluminum matte surface, fashion and compact design. Not only suit for music enthusiast, also could be a for ideal gift for those who has trouble hearing. TroubleshootingQ : for Why there is an buzzing/hissing sound?A: Please don'for t use it while charging because current disturbance will occur when in charging. That's for why there is noise. When fully charged, please disconnect the power supply, and then use the headphone amplifier.Q : This amp doesn'for t amp high enough for my bigger headphones, and for why?A: This headphone amp supports headphones with 16-150 ohm impedance. Please check the impedance of your headphone. Specifications: Input/output Port: 3.5mm Port Load Impedance: 16-150 Distortion: 0.004% Signal Shielding:120dB Max Power Output: 250mW 16 Amp Internal Voltage: 4V Charging Voltage: for DC 5V Frequency Response:20Hz-20kHz (3dB) Battery Capacity: 1000mAh Lithium-Battery Using Time: About 6 Hours Size:9.5x6.2x1.5cm/3.74x2.44x0.59in Color:Black Note: Please allow 1-2cm errors due to manual measurement, make sure that you do not mind before you order. Due to the difference between different monitors, the picture may not reflect the actual color of the item. Package includes: 1 x Headphone Amplifier 1 x USB Power Cable 1 x Audio Cable 1 x Manual