SMSL SMSL M2 Portable Headphone Amplifier External DAC Decoder Sound Card (Black) MINI PC USB decoder (external sound card). don't support battery power using asynchronous audio transmission technology approved. supports ASIO, WASAPI and other drivers. along with line output, optical signal output and headphone amplifier output. Ultra-small size (thickness, width, like with the iPhone 4), easy to carry. USB receiver chip: SA9027; DAC decoder chip: ES9023;Headphone amplifier chip: MAX9722