PreSonus HP4 4 Channel Headphone AmplifierTired of straining to hear the headphones? The HP4's four 130 mW headphone outputs are clear, clean, and screaming loud, all packed in a compact, 1 3U chassis. Features include balanced L R line inputs and outputs, global mute, overall level control, and sum to mono. The line outputs can feed another HP4 or an HP60. Features: 4 screaming loud (130 mW per channel) stereo headphone amps 2 balanced 1 4" line inputs Headphone level control Mono summing