Rockboard HA 4 4-Channel Headphone Amplifier, compact headphone amplifier system for stage and studio applications, four separate high performance stereo amplifiers, separate volume control for each output, suitable for all types of headphones, top sound quality at all volume levels, high-quality components and robust construction with metal enclosure, 12V DC / 40 mA, 2.1 x 5.5 mm barrel plug, center negative, power supply included, input : 1 x 6.35 mm (1/4") TRS jack, output: 4 x 6.35 mm (1/4") stereo (TRS) jack, SNR: 82 dB, THD: 0.009 %, frequency response: +1 dB / -2 dB @20 Hz -22 KHz, gain: 20 dBu, dimensions (L x W x H) incl. knobs and feet: 102 x 58 x 45 mm / 4.02” x 2.28” x 1.77”, weight: 182 gr / 0.40 lbs