Mackie HM-400: A Personal Monitor System in a Single Rackspace

The Mackie HM-400 is a four-channel rackmount headphone amplifier that delivers twelve headphone outputs, per-channel aux inputs, EQ, and metering from a single 19-inch rack space. It is built for the moment a simple headphone splitter is no longer enough - when every musician in the room needs their own mix, their own tone, and their own volume. Housed in Mackie's Built-Like-a-Tank steel chassis, it turns a rack into a complete personal-monitoring hub for a studio, stage, or house of worship.

Twelve Outputs Across Four Custom Channels

Each of the HM-400's four channels carries three 1/4-inch TRS stereo headphone outputs, for twelve jacks in total, so a whole band or a booth full of talent can plug in at once. Every channel is fully independent, meaning four different groups can each dial in a distinct mix while the three outputs within a channel share that feed - ideal for pairing up singers on one blend and the rhythm section on another.

Blend Your Own Mix With Per-Channel Aux

What sets the HM-400 apart from a plain distribution amp is its per-channel aux input. Alongside the main stereo mix arriving over XLR and 1/4-inch inputs, each channel has its own 1/4-inch stereo aux input and a balance control to blend that personal source against the main feed. A drummer can fold in a little more click, or a vocalist can lift their own line, without changing anyone else's monitor mix - the essence of a true personal-monitoring system.

EQ, Muting, and Stereo/Mono Control

Every channel includes a 2-band EQ to shape bass and treble for each listener's taste and headphone, independent L and R mute switches, and a stereo/mono mode switch that collapses the feed to mono when a player wants both ears fed the same focused signal. Seven-segment LED meters on each channel and on the main bus keep every level in view, so setting clean, distortion-free feeds is a matter of watching the lights rather than guessing.

Clean Signal and Road-Ready Build

The HM-400 keeps the audio quiet and honest, with a noise floor of -66 dB and total harmonic distortion below 0.01 percent at +4 dBu and 1 kHz at unity gain, so the mixes players hear stay faithful to the source. XLR and 1/4-inch main outputs let you daisy-chain the signal to another amp or a recorder, and the internal supply runs from AC mains through the included IEC cable inside a rugged single-rackspace steel chassis made for permanent installs and touring racks alike.

Who the HM-400 Is For

Recording studios cutting full bands, houses of worship feeding a platform of musicians, rehearsal spaces, and quiet-stage productions reach for the HM-400 when everyone needs their own headphone mix. If a four-way splitter has left your players asking for more tone, more level, and their own source, the HM-400 is the rackmount upgrade that gives each of them real control.