This is Fan Music MKII MK2 Portable Earphone Headphone Amplifier! This portable headphone amplifier connects directly to the line out of a digital audio player, and it also can control the volume directly by using the function of a volume control. In order to have a higher power output, this best headphone amplifier is with better signal of noise ratio and lower distortion. And this headphone portable amplifier is featured by the pocket-sized design. This portable headphone amplifier perfects sound quality and greatly enhances the reliability.Moreover, this portable headphone amplifier with built-in rechargeable Lithium-Ion battery and short-circuit two-way protection system. Why not choose it.