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Coleman Audio M3PH MkII

Monitor Controller
Published March 2006
By Hugh Robjohns

Coleman Audio M3PH MkIIPhoto: Mark Ewing

This unit from Coleman Audio makes a mark with its sonic integrity, despite its apparent lack of operational 'frills'.

Dedicated monitor controllers were rare back when everyone had a console of some sort in their studio. However, now that most of us work entirely with DAWs we have little need for a full console anymore. A few outboard preamps for tracking and a separate monitoring controller are more convenient, more cost effective, and take up a lot less space. As a result, the number of manufacturers offering monitor controllers has grown almost exponentially in recent years, with products spanning all budgets and requirements.

The subject of this review is a no-frills design from America, Coleman Audio's M3PH MkII. The emphasis is very much on quality and simplicity, so there is no provision for talkback or headphone cue mixes — just a simple four-source input selector, three-output speaker router, basic signal-manipulation functions, and an engineer's headphone output. The review model featured an entirely passive signal path, although an active and fully buffered model (the M3A) is also available. The term 'passive' is possibly confusing here — the M3PH does contain active electronics, but only for the headphone output and to derive a summed mono signal. All signal routing and conditioning is performed directly on the balanced signal using the front-panel switches, and the rotary volume control is a quad-ganged stepped attenuator with a claimed tracking accuracy of 0.05dB.

A Peek Inside

The unit occupies 1U of rack space, extending about 260mm behind the rack ears. Internal construction is to a high standard, with good-quality components throughout. There are five separate fibreglass circuit boards, starting with a small switched-mode power supply on the right-hand side of the chassis. A second board runs across the back to carry the XLR connectors — 14 of them (four input pairs, three output pairs) — and a third board occupies most of the central area to carry the selector switches and summing amplifier electronics. The remaining boards are for the headphone amplifier and a vertical card to connect the four sections of the switched volume control. Ribbon cables and header sockets are used to connect the boards.

Coleman Audio M3PH MkIIPhoto: Mark EwingA 'hidden' switch inside the casing on the main circuit board allows the third speaker output to be reassigned as a fixed line-level output (post the input selector), enabling its use as a feed to an external metering system or as a pass-through for the monitored signal. A switch on the power-supply board configures the unit for 230V or 115V mains supplies. There are no protective fuses in the mains or DC supplies, so you are reliant on the mains supply trip (or plug fuse in the case of UK models) should anything go wrong internally.

Since the XLR connectors occupy the entire back panel, there is no space for the mains cable connection. Instead, a captive mains cable exits the unit at the rear of the right-hand side panel. In most cases this unusual construction won't cause any problems, but in tight rack cases or frames this might make installing or removing the unit harder than usual.

In Use

The front panel is clear and intuitive, dominated by seven large white buttons: four interlocking switches to select the input source and three more interlocking switches to select the speaker output. The button caps can be removed and engraved if required, but there is also plenty of panel space for stick-on labels. To the left of the buttons is the rotary stepped attenuator, which has a light detented action, and to the left of that is a conventional volume knob for the adjacent headphone output socket. Over on the right-hand side are four smaller buttons which select the derived mono signal, mute the left or right speakers, and reverse the polarity of the right-hand output channel — this last button being coloured red to differentiate it. Finally, the mains power switch is at the extreme right-hand side.

As already mentioned, the signal path is entirely passive, and I was unable to hear any obvious degradation to the monitor signal when working with balanced sources and destinations. Operation is intuitive: select the desired input source and monitoring speakers using the buttons. The mono, phase-reverse, and mute switches allow quality and compatibility checks to be made as necessary. The two mute buttons conveniently allow mono to be auditioned from both speakers (as a phantom image) or just from one — an important function that few monitor controllers permit, strangely. Mono on both speakers allows the true phantom centre image definition and position to be checked, and mono on one speaker gives a better idea of the spectral balance of a derived mono signal than a phantom image.

The phase-reverse button is located after the mono selector in the signal path, which makes it impossible to hear the stereo difference (Sides) signal. This is a great shame, because being able to audition the difference signal is extremely useful, not least for the 'null' technique. (If you invert the polarity of one channel then sum to mono, equal-level signals cancel each other out, and this is a handy trick for matching channel gains or aligning stereo mic arrays.)

The only function missing completely is a Dim facility to allow the speakers to be turned down — perhaps to answer the phone — without upsetting the reference monitoring level. However, since the monitor volume is a switch, it inherently provides discrete level steps and is therefore fairly easy to reset accurately anyway.

This is a neat and well-built unit, with all the necessary features and facilities a typical home-studio/DAW installation would need. Its fully balanced and passive signal path ensures sonic integrity, and the ability to mute the two speakers separately is very handy for checking mono balances. Few home studios would probably run to three sets of monitors, so allowing the third output to be switched (internally) to provide a fixed output to feed meters or an external recorder is a welcome facility. 

Published March 2006