Feature: 1. High Quality Material: The headphone amplifier is made of aluminum alloy, which is sturdy and durable to ensure a long service life. 2. HiFi Headphone Amplifier: 3.5mm AUX input and output for MP3, MP4, mobile phones, computers, CD players and media players. 3. Good Sound Effect: Not only can output louder sound, but also output clearer and more vivid stereo without distortion. 4. High Quality: Support most high impedance 16‑150Ω headphones, 3.5mm AUX input and output, signal to noise ratio>116Db, THD+N=0.001%, and fully filter out noise. 5. Two Stage Gain Switch: Enhance the signal input to the amplifier circuit to achieve the best performance of the headset. Specification: Item Type: Headphone Amplifier Material: Aluminum Alloy Shell Colour: Black Size: Approx. 94 x 52 x 13mm/3.7 x 2.0 x 0.5in Battery: Lithium Battery (Built In) 1000mAh Working Voltage: DC3.7-4.2V Charging Voltage: DC5V Maximum Output Power of Earphone: 130MW 32Ω Load Load Resistance: 16-300Ω (Can Push the Resistance Range of Earphones) Distortion: 0.001% Signal to Noise Ratio: ≥116dB Response Frequency: 20Hz-20KHz (±3dB) Parameters: the Appearance is Small and Easy to Carry, with Independent Two Stage Gain Control Switch 3.5mm Aux Input and Output in MP3, MP4, Mobile Phones, Computers, CD Players and Media Players, etc.. Package List: 1 x Headphone Amplifier1 x 3.5mm Cable1 x Manual Note: Please allow 0.1 ‑ 0.2cm/0.04 ‑ 0.08in error for manual measurement