The 19" Rackmount hm-400 4-channel headphone amplifier offers an incredible amount of versatility and excellent sound quality in a single rack space. Perfect for professional applications including studios, houses of worship, practice spaces, and more. The hm-400 features a main input with level control plus stereo outs, aux inputs and EQ per channel with 12 total headphone outputs.Features: L/R main stereo inputs plus L/R stereo outputs segment LED metering per channel plus main three headphone outputs per channel aux input on each channel with balance control to mix main and aux signal mute and stereo/2-ch mode switches per channel 12 total headphone outputs built-like-a-tank construction Specs: audio performance frequency response: 20 Hz 20 kHz, 1 dB noise: -66 dB [hm-400]; 70 dB [hm-800] distortion (THD): 4 dBu, 1 kHz, unity gain; <0.01% [hm-400]; <0.005% [hm-800] maximum levels: main input - 15 dBu balanced/ unbalanced [hm-400]; 19 dBu balanced/ unbalanced [hm-800];; aux input - 20 dBu unbalanced;; headphone output - 550 mW/ channel @ 47 ( 21 dBu) cmrr (main input):> 42 db @1 kHz [hm-400];> 52 db @1 kHz [hm-800] gain range (main input): 66 to 18 dBu [hm-400]; 67 to 19 dBu [hm-800]input/ output input type: female XLR balanced; Female 1/4" Balanced unbalanced main input impedance: 20 k balanced, 10 k unbalanced [hm-400]; 40 k balanced, 20 k unbalanced [hm-800] aux input impedance: 10 k unbalanced [hm-400]; 13 k unbalanced [hm-800] output type: Male XLR balanced; Female 1/4 balanced unbalanced headphone output impedance: 3 unbalanced power requirements detachable line cord: 100 120V, 50/60 Hz, 24 W; 220 240V, 50/60 Hz, 24 W AC connector: 3-pin IEC 250 VAC, 10 a male display LEDs front power on/off front input level meter front output level meters L/R mute switches [hm-400] St./ 2-ch switches [hm-400] stereo/ mono switches [hm-800] in 1/2 switches [hm-800]physical properties height: 1.8 in/ 46 mm width: 19.0 in/ 483 mm depth: 8.8 in/ 224 mm Weight: 8.0 lb/ 3.6 kg.