GranVela TOPPING NX3 Portable Earphone Amplifier Portable Amps with Bass Turbo for Phones, MP3/MP4, Digital Players and Computers -Black Small, compact, and sleek for convenient and easy use. New amplifier circuit, low noise and distortion with enhanced dynamics Offer high-quality audio, ideal for portable music devices Universal for MP3/MP4/mobile phone/computer Charge: Built-in lithium battery comes with protective circuit, it usually takes 3 hours for the charge but 25 hours playback