The HA4000 from On-Stage is a four-channel headphone amplifier, allowing up to four people to personally monitor an audio signal at the same time, all while individually setting their own volume levels. High quality sound is maintained even at full volume. With 20 dB of gain available per channel, the unit is suitable for use in playback or recording scenarios. Routing audio to the unit is accomplished via one 1/4" stereo input jack, and from there, the signal is routed to channels, each one boasting its own volume up and 1/4" headphone output jack.