The HA43 is for expanding or generating headphone channels. It has a 1/4" stereo input, 4 volume controls, 4: 1/4" stereo output jacks and is powered by an AC adapter (included). The HA43 has a 20Hz - 20K Hz response, small size, and is very easy to use. Specifications: Input Impedance: 100K Ohms unbalanced Max Input Level: +14 dBV Input Connectors: Stereo 1/4" TRS phone Outputs: (4) 1/4" Stereo 1/4" Max Gain: 20 dB/Channel S/N Ratio: >90 dB THD: <.008% IMD (SMPTE) <.008% Weight: 1 lbs (.45Kg) S