Topping NX1S Portable Earphone Amplifier Portable Amps with 40 Hours Continuous Play Time for Phones, MP3s, 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 150 hours playback