FiiO E9i Desktop Pre-Amp and Headphone Amplifier Dock for iPod and iPhone Ultra low noise and low distortion with enough power output to drive 600Ohm headphones Two channel power output, with jacks for both 1/8"(3.5mm) and 1/4"(6.35mm) headphones Smooth and low noise ALPS sealed potentiometer for volume control Audio buffers using ultra-low distortion and low noise Burr-Brown OPA2134 op amps Dock connector for iPod and iPhone, also provides charging power