Low Noise: Enjoy a low noise monitor distribution and music system. The ultra compact headphone amplifier is easy to carry and can be used anytime, anywhere. Independent Adjusting Knob: Individual volume controls enable each listener to determine their own volume via a dedicated output volume control knob. Metal Material: The shell of this headphone amplifier is made of premium metal, strong and stable, wear and fall resistance, can be used for a long time. 4 in 1 Out Mono Mixer: Ultra compressed 4 channel input and 1 channel output line mono mixer 4580 operational amplifier with superior sound performance. Great Performance: Even at maximum volume, this metal 4 channel headphone amplifier can provide the highest sound quality for each earphone.