HA4 is a compact 4-way headphone amplifier from a DC power adapter power supply. The biggest advantage of this product is that there are four channels can be used simultaneously, each channel with separate volume control knob, the user can monitor the process more easily into Line regulation. All the studio wants to have a more flexible headphone amplifier, and sometimes want to come out of the stereo signal mixer evenly distributed to multiple headsets, and sometimes you want multiple headphone signal can also listen on different channels, HA4 can be very a better solution to these problems is the ideal companion headphone listening.