fifine headphone amplifier 4 channels metal stereo audio amplifier,mini earphone splitter with power adapter-4x quarter inch balanced trs headphones output and trs audio input for sound mixer-n6 fifine technology flexible control individual level control knob for each output allowing flexible control for different headphones or speakers. excellent sound quality this compact 4 channel amplifier can hold 4 pairs of headphones & maintain the clarity of sound. build like a tank sturdy with a metal housing, the headphone splitter box feels nice and solid. power adapter is included the audio amplifier comes with a 12v ac adapter, so you could use it out of box. attention: 1. mono: if the audio input is mono, or if you use mono cable for connecting the devices to either the input or output of the headphone amp, the output will be mono. 2. stereo: you will need to use stereo cables (2 rings on the tip) to connect your devices to both the input and output of the headphone amp, if you want to get stereo output. 3. please add a ground loop noise isolator on the line from your device to the headphone amp, if there is humming buzzing noise.