For the orchestrally minded, the combination of strings, organ and brass in one machine has definite possibilities. There are several versions on the market, but the Opus is one of the more successful.

First the strings: sliders vary the frequency and resonance of the filter which can be swapped between low, high and band pass so removing the top or bottom frequencies, or a chunk from the middle. All the settings are romantic and can be low and mellow or high and ethereal. The chorus unit is quiet, if a little unsteady, but does have the benefit of depth, delay and speed controls, not usually offered.

The organ is a weak department. Five sliders take the place of the traditional drawbars and offer 16, 8, 4, 2 and 1 footages. Sadly Moog have missed out the harmonics such as 5⅓ and 2⅔ which serve to fatten and enrich chords.

I suspect they've taken the easy way out in the circuitry, for while octaves are easy to create electronically, harmonics are a subtler task. The basic tone is flutey but can be brightened by another tone slider which is a useful tool.

But if Moog excel anywhere it's on their filters and brass, which are recognised as being tops in synthesiser manufacture and the standard to which everyone aspires.

The Opus brass has 16, 8 and 4 footages, its own attack, decay, release unit and slider for contour amount, frequency and emphasis. You can either use the one preset sound — a pleasantly rounded and soft "blaartt" — or switch to the variable mode and set up your own sound.

The brass section is immensely powerful and with a slow attack and a high emphasis setting, chords surge in from somewhere down in the basement to a lofty scream up in the attic. But the sharpness can be tailored for a muted background swell if needed.

Each of the sections has its level control in the bottom right hand corner of the panel, plus a sliding toggle switch to turn it on. They're very easy to reach and swift to change for onstage playing. The Opus also has a stereo output and all three sections can be panned left or right.

The last two sliders are attack and release "articulators" and work in two ways. They are primarily to fade in the strings, then give them a gentle decay. In position two that applies to the organ as well, but in position one only the strings will fade in while the organ retains its sharp attack, and any new note pressed immediately cuts the sustain dead.

So you can play choppy chords on organ or brass, but once the keys are held down for a little longer, the strings swell to the fore for extra power, then vanish once the next key is pushed down.

Juggling with the 2 and 1 footages of the organ, plus a touch of sustain creates a vibrant tinkly harpsichord, helped by being fed through the chorus unit, though that's an unnecessarily complex job. You have to turn on the strings, bring up the level but move the balance slider all the way over to the organ side to ensure the strings themselves don't creep in.

However, it does have the advantage of becoming an ADT unit since you're left with one control for the plain organ, another for the delayed chorus half of the organ and the ability to take them separately from the stereo outputs. Clever, eh?

The organ is best as a reinforcer. The 16 foot slider deepens the bass end for strings, while the higher octaves supply a gorgeous burbling backing to brass chords. Left alone it lacks any real punch or percussion, but the envelope generator on the brass can be brought back to zero to duplicate the key click of old Hammonds.

The Opus falls short in three areas. You can't put the strings through the chorus, the keyboard cannot be split (say organ one side, strings the other) and there's no choice between multiple or single triggering. The last two are the most inhibiting since while you're holding down a bass note, the brass can't sweep through its full wang on any other chords. Also I found the front panel layout awkward to follow.

Not all these points could be easily (or cheaply) corrected by the designers but they have at least ensured it has a vibrant and big hearted sound.

£699