Product Information: If you're tracking more than one musician at once, or if everyone in a group wants to listen to a playback, you need a monitor distribution system. The compact, flexible HA400 can power up to four pairs of headphones and up to four independent volumes. You can use this super-compact stereo headphone amplifier with practically any headphones - four of them at the same time, to be exact! Let up to 4 different people in your studio listen to the main mix while recording, and each listener can determine their own volume level using the dedicated output level controls. The HA400 contains 4 high-power stereo amplifiers that maintain the highest sonic quality even at maximum volume levels. Ultra low-noise 4580 operational amplifiers are included for outstanding audio performance - these are the same op amps found in “full-size” audio equipment—plus, a DC 12-Volt adapter is included. Specifications: 4-channel stereo headphone amplifier for use with all types of headphones