Nuforce - iCON Mobile - Headphone Amp or USB/DAC (Black) Two headphone/line outputs: a 3.5mm 4-pin mini stereo (with mic) jack and a 3.5mm 3-pin mini stereo jack for driving earphones and line-level sources such as active speakers. A Gain Select switch provides compatibility for a wide range of headphones and earphones. A high-quality rotary volume pot for maximizing USB and iPod signal-to-noise ratios. A built-in, rechargeable Lithium Ion battery with USB featuring a 2.5 hour charge-time for 13 hours of continuous playback at maximum power.