XD-01 is a multi-functional portable headphone amp that consists of USB, coaxial, optical fiber decoding amp.  It accepts up to 24Bit/192KHz high resolution audio signal.  It has a SRC function that can increase sampling up to 24bit/192KHz, and has a 2-Setting Gain Switch to set gain according to the headphones.  Its power supply is built-in a 4.2V li-polymer rechargeable battery.