WHEN THE ANALOGUE POLYSYNTH FIRST CAME OF AGE IT CHANGED THE COURSE OF MUSICAL DEVELOPMENT. AMONGST THOSE REVOLUTIONARY INSTRUMENTS WERE THE CS80, PROPHET 5, JUPITER 8 - AND THE OBERHEIM OBXA.

IT SEEMS AMAZING to be taking a retrospective look at something that was the state of the art a mere nine years ago - but that seems to be the way of the world of hi-tech music technology. The bad news is that something that you might once have paid a cool four grand for should be worth about a tenth of that now. The good news is if you didn't have that sort of money then, you can pick up an amazing instrument really cheaply now.

And that's the pattern for classic instruments like the Minimoog, Prophet 5 or even the Fairlight: bound to belong to the luxury league in their first few years of manufacture, and only later to become available to the more ordinary punter when a new wave of technology has tarnished the appeal of the old classic.

In the case of Oberheim's OB family of synths (OB1, OBX, OBXa, OB8 and OBSX) they're pretty rare in the UK - not just because of their initial price, but also because Oberheim didn't have a really powerful distribution network here in their heyday.

Cast your mind back to the late 70s. If that brings back memories of tacky uniforms and sweaty changing rooms, then let me cast mine back for you. If you were talking synthesisers, then you were usually talking monophonic. Almost the only real polyphonics (discounting string synths) were the Oberheim 4-voice, 6-voice and eventual 8-voice machines.

At the time I used to gaze longingly at a four-voice in the London Synthesiser Centre, and wonder if I'd ever find the £3000 needed to acquire it; but on reflection, it's amazing how anyone managed to play the thing in public. Imagine a Korg MonoPoly with chronic tuning problems and a worse keyboard and performance controls, and you're getting close. And apart from the sheer difficulty of making it sound good, the limitations of the technology of the time meant that its revolutionary and much-vaunted programmability was arduous and only partially effective. Today you'd be forgiven for laughing, but at the time it was all there was.

Then the Prophet 5 crashed onto the scene, capturing the imagination of musos and the ears of the public. It must have given the likes of Moog, Arp and Oberheim a collective heart attack. By the simple expedient of using a micro-processor to scan the keyboard - and using spare processing power to organise 40 programmable memories - Dave Smith dealt a blow to Moog and Arp from which they never really recovered.

It took Oberheim about 18 months to voice their reply, and that gave Sequential Circuits a huge market lead that even Oberheim's classy reputation was going to find it difficult to claw back.

One of the worst features of early Prophets was their unreliability, both in terms of tuning and in storing patches - if only Oberheim's machine could score in those areas, then they were in with a chance. The trouble was that when the new Oberheim, the OBX, did appear, people quickly realised that there wasn't much improvement at all. The machine looked like an updated version of their earlier machines, with dark knobs on cream background and, although it was a vast improvement on them in programmability and consistency of sound, it wasn't that much better than the Prophet. Two of its better points were its polyphonic portamento and the option of going up to eight voices - against the Prophet's five. But in terms of reliability it didn't seem much better. You didn't know whether it was good or bad that Oberheim had made it so easy to get into the machine to disable malfunctioning voices or perform other repairs... Similarly, it was a mixed blessing that they announced a 'roadie kit' for on-the-road repairs.

It's pretty obvious that Tom Oberheim decided very early on that the OBX wasn't going to crack SCI's domination of the market, and started work on an upgraded version which would incorporate several minor mods to improve reliability, and also go for one more big new feature that would make the pro keyboard player an offer he simply couldn't refuse if he wanted to be in command of the latest technology.

That big new feature (don't snigger) was a splittable keyboard. At the time, that was pretty big news. As far as I can remember, Yamaha's monster CS80 was the only other synth to have this feature then, and the Oberheim sound, programmability, and relative portability were sufficient to make that no contest.

"WHEN THE SEQUENTIAL CIRCUITS PROPHET 5 CRASHED ONTO THE SCENE IT MUST HAVE GIVEN THE LIKES OF MOOG, ARP AND OBERHEIM A COLLECTIVE HEART ATTACK."

Oberheim (sensibly) also re-vamped the whole exterior design, introducing the smart blue pin-stripes on black that determined the "Oberheim look" for the years to come. The shame was that they didn't do so well on a new name. You'd have thought they could have come up with something more meaty and less small-time than changing from the OBX to the OBXa. Still, there it was. A lousy name, but potentially the most powerful synth in the world at the time. Portable, powerful, and with a split keyboard that was going to appeal to ex-Hammond organ players who were used to having separate sounds under their left and right hands and the Wakeman generation to whom banks of keyboards each producing two or three sounds had become a way of life.

The split facility, despite being one of the first ever, wasn't bad either. For a start, it was programmable. (There were only eight locations available, but that was still the world record at the time.) Secondly, you could transpose one of the halves of the split up or down - and although this was only a temporary edit, not something you could write permanently to memory, it was, again, an unprecedented feature. Selecting a new split point was simplicity itself - just hold down Split and press the key you wanted to be the start of the upper split.

As well as splits, of course, you could layer sounds, which would leave you with a maximum of four-note polyphony but also with the potential for some great composite sounds. Again, this was something only the CS80 could do at the time. The doubles had to share the few memories available with the splits, but at least you could allocate them as you liked.

Polysynths' patch memories of the time were pretty limited by today's standards. They started out at around 32, and it was only towards the end of the OBXa's production run that the number rose to a much more impressive 120 (on the OBXa and Prophet 5). But it was so much easier to program a synth that had dedicated hardware (knobs and switches), and musicians' imaginations had yet to come to terms with the numbers of sounds we expect today, the lack of memory locations on earlier machines wasn't regarded as being that critical.

Like most of its competitors, the OBXa's programming system is simplicity itself. You want to make the sound a little brighter? Just move the VCF frequency knob a fraction clockwise, and listen to the effect. Each control is permanently 'live', so any parameter you need to tweak, you can access immediately. The knob won't necessarily show the right setting - it'll be at the position it was moved to the last time it was touched - but again that doesn't matter so much when you've got such ready access to each parameter. In a way, having 'proper' controls on a synthesiser is the equivalent, in computer terms, of having parallel rather than serial communication. On a modern synthesiser (without an expensive computer and complicated software editing program) you have to address each parameter one after the other - serially. On the OBXa, you can address parameters in parallel - virtually simultaneously. This becomes very important as soon as you start playing around with two parameters which have interrelated effects.

But it's not just in ease of use and human feel that 'traditional' synthesiser design scores. I've sometimes asked myself why I spent almost exactly the same money buying an OBXa when I could have bought myself a natty Matrix 1000 and saved a lot of valuable studio space. The answer could have something to do with snob value; the Matrix 1000 is, after all, a preset synth - the sort of thing that players of my age used to almost regard as not being real synthesisers at all. But you can always get into them with a software editor, and with 1000 sounds to choose from you're extremely unlikely to be using exactly the same set of sounds as anyone else even if you stick to presets. No, it has more to do with the fact that there's something more characterful in an instrument like the OBXa than in any rackmount, even of Roland MKS80 calibre. There might be a character analogy here with guitars - would you rather have a Japanese or American Fender?

The most attractive aspect of the OBXa over the Matrix 1000 is the availability of all of the instrument's controls as realtime performance controls. Quite a few expanders don't really allow you to do this even with an add-on programmer or software editor - you often get digital clicks as you alter parameters or the control doesn't come into effect until after you hit the next note. It's a shame, because there's a lot of expression you can get by judicious use of controls such as filter cutoff, sustain level, and attack. It's analogous to a guitarist 'playing' the volume control with the little finger of his or her right hand to produce different attack characteristics. Primitive, but effective.

Using the controls in real time is something you can do with most of the old classic synths; but there are one or two refinements in the OBXa's dedicated performance controls which give it an edge. The one I really like is very simple: there's a push-button underneath the pitchbend control whose name (Osc 2 Only) explains it all. What that means is that when you use the bend wheel (or lever in Oberheim's idiosyncratic system) you can choose to have just oscillator two affected by pitchbend. There are similar performance refinements on Roland's Jupiter 8.

On some sounds, bending one oscillator against another works a treat. Now, I know you can do that any day with MIDI and a couple of expanders, one of which you set to receive pitchbend messages and one not. But it's certainly simpler on the OBXa and it seems to come out better. Maybe it's the limitations of the machine that make this so - the fact that the two oscillators are subtly different but from the same source, while if you're using two expanders you're somehow unlikely to have them both set up to the same sound. Quite possibly, the effect sounds better because it's immediately accessible without having to stop, alter parameters on a couple of expanders, and then pick up the thread of inspiration again. Whatever the reason, there are some electric guitar-like effects which the OBXa gives you that I've found hard to beat with a collection of much more recent synthesisers and expanders.

"WHY BUY AN OBXA WHEN YOU COULD BUY A MATRIX 1000 AND SAVE A LOT OF VALUABLE STUDIO SPACE? WOULD YOU RATHER HAVE A JAPANESE OR AMERICAN FENDER?"

There was one more major feature, however, that really made the OBXa stand out from the '70s polysynth crowd, although it's only really of historical interest now. Always an innovative company, Oberheim designed the OBXa as part of the Oberheim Performance System. Connecting up different manufacturers' synthesisers, sequencers and drum machines had always been at best difficult and at worst impossible, and so Oberheim set out to design a complete system interface. I think the OBXa actually came out first, with an enigmatic 37-pin connector socket on its back panel, entitled Computer Interface. That was followed by the DSX sequencer (a superb machine for its time - nine tracks and the ability to drive eight CV/gate synths as well as the OBXa); the DMX drum machine; and also the OBSX synth (which presented Oberheim sounds as presets for people who weren't into programming). One of the synths combined with the drum machine and the sequencer made a really powerful system, which could produce very acceptable instrumentals or demos of arrangements. '

We've come to be very blase about sequencing nowadays, but this was the forerunner of today's computer-based sequencing system, and at the time it was as much of a breakthrough - as the Atari/Pro24 combination was only a few years later. So much so, in fact, that huge numbers of influential musicians splashed out on the OBXa and members of its family: Miles Davis, New Order, Japan, Eurythmics, Thompson Twins, Lenny White and Sting all used them extensively, and Prince bought a couple of OBXas and a couple of OBSXs to tour with.

There was just one fly in Oberheim's Performance System ointment: there were still going to be times when you wanted to introduce equipment from a different manufacturer: that was OK if they used CV/gate, but that left most of the best synths like the Prophet right out of it.

To Oberheim's credit, they did embrace the new MIDI standard when it appeared in 1983, despite having technical reservations about its long-term viability. They had been working on a replacement for the OBXa called the OB8 and, although they didn't put MIDI in from the start, they soon sanctioned a retrofit, and included MIDI on all future instruments.

You can get OBXas retrofitted for MIDI these days, and that's going to be pretty essential if you rely wholly on a sequencer or a master keyboard system. But for recording, if you've got enough tape tracks to spare, and you can play well enough not to have to use quantising or note correction, it's often worth putting something like an OBXa onto tape. It helps to keep the individuality of the instrument intact, and means that you're much more likely to use its own special features, like the Osc 2 Only pitchbend and polyphonic portamento, to good effect. And as well as features like these, the OBXa has dedicated sockets for a hold footswitch and foot pedals to control vibrato and filter - something that I could never understand a lot of synths being without.

There are omissions in the OBXa too, of course. In addition to its lack of MIDI and touch sensitivity, one of the worst is the lack of decent mixing facilities for the two VCO's and the noise generator. For the noise, it's either all or nothing, and for VC02 it's all, nothing or half - not very versatile. And it's annoying that with the rest of the instrument so easy to program, something as simple as this should have been neglected. It also loses out to something like the Prophet 5 or Oberheim's own later Xpander in the flexibility and complexity of its cross-modulation facilities.

Even so, I'll never sell mine if I can help it. Sure, it takes up a lot of space, but it's a source of inspiration and a pleasure to program and use. Its sounds vary from raunchy fuzz guitar to fat brass, lush pads to meaty clashes, and in all of them there are the advantages of analogue - relative warmth, and ease of real-time alterations. There's no way something like the OBXa can seriously rival a D50 or M1 in what they do, but what the OBXa does, it does far better than their imitations of it.

I've never heard the Matrix 1000 and OBXa together, so I can't really comment on which sounds better. I suspect a well-programmed OBXa would be some way ahead, but I can't prove it. As for the OB8, Oberheim claimed that they had been able to reduce the component count hugely, which may be good for price but doesn't necessarily make the sound as rich. Don Snow, who owned both models, says he liked the OBXa's sound more and he didn't have an axe to grind, as he was selling me his OB8 at the time.

Hold on, if I've got both versions, why can't I do a quick comparison? Ah, there's the rub. I bought the OB8 knowing it needed a service to coax some sounds from it, and haven't been able to afford that yet. In the meantime, if you like analogue, enjoy programming and playing in realtime, and see an OBXa in good nick for under four hundred quid, snap it up. You won't regret it.