Stealing its styling and its design philosophy from the Minimoog, the Prophet 5 was to programmable polysynths what its inspiration had been to a generation of synthesisers before.

THE FIRST REVIEW of the Prophet 5 to appear in a UK magazine was in the July 1978 issue of Sound International. Many of you may not have heard of this magazine (it was, in fact, a sister title to Studio Sound) but there will be few of you who haven't heard of the Prophet 5 - the synthesiser that revolutionised synthesiser design and transformed the bedroom operation known as Sequential Circuits Inc into a first division instrument manufacturer.'

The Prophet 5 was first shown in 1977 but didn't actually make it into the music stores until 1978. It was to become the DX7 of the 70s, and its lifespan has only been bettered by those of the Minimoog and the ARP Odyssey. What made Sequential's synthesiser such a classic instrument? To my mind, a "classic" instrument is one that sells itself, one that gives the player just what he or she wants. The Minimoog was the first classic synthesiser, and the Prophet 5 a worthy successor. It was so far ahead of the competition that it became an instant phenomenon, in spite of the fact that its reliability - or lack of it - was to become almost as legendary as its performance. One employee of Rod Argent's Keyboards (the Prophet's importers) set it to the tune of Buggles' 'Video Killed the Radio Star': "I bought a Prophet from you just the other day, I turned it on and all the programs went away, ooh-wee-ooh we should have told you, ooh-wee-ooh that's what they all do".

To put it into historical perspective, the Prophet 5 was launched at around the same time as Oberheim's Four-Voice, Moog's Polymoog, ARP's Omni 2, Korg's PS3300 and PS3100, RMI's Computer Keyboard and Yamaha's GX1 and CS80. But it was the Prophet 5 that everyone wanted, leaving the CS80 far behind as second favourite.

Two Americans, Dave Smith and John Bowen, were the brains behind the Prophet 5, although they sat on the design for six months because they were convinced the idea was so obvious that somebody was surely pursuing it. They designed and financed the Prophet with funds that Smith had accumulated from a programmer box which could be used to make the Minimoog programmable - if only to a limited degree. He still works for Sequential in a design capacity, though he no longer owns any part of the company following Yamaha's rescue late last year.

A glance at the Prophet 5 will tell you that Smith was influenced by the Minimoog when he conceived the design. The instrument's sleek lines were covered with walnut (or koa wood on the Rev 1). Very classy. The front panel was covered in black and silver knobs (remember knobs?) and momentary switches with integral LEDs. The Prophet 5 was one of the first instruments to utilise a microprocessor - a Z80 - and so its architecture could be quite different to that of its mentor. Being a relatively new company and needing to get their instrument out as quickly as possible, Sequential Circuits decided to use E-mu's keyboard scanning technology while the sound-generating part of the circuitry utilised SSM (Solid State Music) chips.

Initially Smith designed two instruments, the Prophet 5 and the Prophet 10, but the latter was never released onto the market as it never worked properly (although this hasn't stopped some examples of it reaching the public).

MUCH AS WITH today's synthesisers, the five-octave keyboard and all the controls were scanned by the processor - the Prophet scanned the keyboard every 8 milliseconds - and processed sequentially (sic). The Prophet was not touch or velocity sensitive but it did have Moog-style pitch-bend and modulation wheels situated to the left of the keyboard.

As its name implies, the Prophet 5 was a five-voice instrument - although the original design was for ten-note polyphony but was abandoned due to severe overheating problems. Save for its unreliability, this limitation was probably the only criticism launched at it. The keyboard assignment was such that, if you played a sixth note whilst holding down five, the first one was "robbed". This was probably the best system to adopt, however in Unison mode it did present certain problems. If you played and held a single note but triggered another in the process, you'd be left holding nothing. This problem was further exacerbated by a keyboard that had an extremely light touch.

If you've only recently entered the world of synths and samplers you may not have encountered a synth with knobs.

"With early machines, the tuning cycle was like a game of Russian roulette - you might hit the Tune button between numbers in a set only to find you never came out of it."

Forget alpha dials and data entry sliders, knobs are great - you can twiddle them and the sound changes instantly. And the Prophet 5 had just under 30 of them, each one instantly affecting some aspect of the sound. They made programming incredibly quick. However, talking to service engineers who worked on the Prophet reveals that most instruments that came in for repair still had the original presets in memory. Either the ease of programming wasn't as great as it seemed or the malaise that afflicts DX7 owners is not unique.

As I mentioned earlier, the first versions of the Prophet 5 utilised SSM chips for voice generation. These were later replaced with CEM (Curtis Electro Music) chips as they were a lot more consistent and reliable. However, it is commonly agreed that Prophets using SSM chips had a better sound. Each voice consisted of two voltage controlled oscillators (VCOs), the first having sawtooth and pulse waveforms and the second sawtooth, pulse and sine waves. In addition, each voice featured a noise source, voltage controlled filter (VCO) and two ADSR generators. With SSM envelope chips driving the VCF, you could really detect the discrepancies between the voices. Perhaps it was this inconsistency that helped to give the Prophet its distinctive sound. Bob Moog always professed that it was the distortion in his filter circuit that made the Minimoog sound so good.

The Prophet's filters were also responsible for the character of the sound. Then, as now, Roland and Yamaha (to name but two manufacturers') synths had recognisable characters but only the Prophet had a full, yet transparent, sound quality such that its array of programs could sound completely different - uncoloured, perhaps. Having said that, the Prophet's factory-programmed brass sound was used by just about everyone, and became a vital ingredient of any mid-Atlantic rock band. Session players still use that same patch today, and it can be heard on the odd TV advert and piece of incidental music.

Another problem with the Prophet 5 was its tuning. When you switched the instrument on, it went into a tune routine which lasted around 20 seconds. During this time it looked at all its oscillators and corrected any tuning discrepancies. However, after about a minute it would be necessary to repeat the exercise as the instrument had then warmed up. The trouble was that, with early machines, the tuning cycle was like a game of Russian roulette. You might hit the Tune button between numbers in a set only to find you never came out of it. All the lights apart from the Tune light would disappear, and the instrument would sit happily whirring away to itself. The result was that players were somewhat loath to hit the particular button until other members of the band started to pull faces.

The Prophet's modulation section contributed greatly to the individual character of the sound. This was a fairly complex section - many players couldn't get their heads round it, but it made extensive use of cross modulation of the filter and LFO. Poly-Mod meant that there wasn't just one modulation waveform being applied to all voices. Instead, each modulation waveform originated within its own voice, thus if a simple LFO poly frequency modulation was being applied, all the oscillators would be moving in and out of phase with each other.

The Prophet 5 was one of the first truly programmable synths; every parameter except the tuning and master volume control was programmable. The programmer, originally holding 40 patches, was extremely eager to lose them 30 seconds before you were due onstage. Sequential were quick to realise this was bad news but instead of curing the problem, elected to retro-fit the instrument with a cassette interface. Since loading a bank of sounds took some 45 seconds most bands found it prudent to write a 45-second intro that didn't feature the Prophet. Eventually the problem was cured and the memory capacity increased to accomodate 120 patches.

IF YOU WERE thinking of buying a secondhand Prophet 5, what should you be looking for? A brief rundown of the various versions the instrument appeared as might help.

"Sequential coined the phrase 'my fifths don't beat' to promote the 3.1 revision, but most people's continued to do so as almost no-one used the feature."

Rev 1.0: this was the first model to hit the streets and is not to be touched with a barge pole unless it is either incredibly cheap and warranted or a serial number of 0010 or lower, in which case it's a valuable collector's piece. Rev 1.0s continued up to serial number 0182.

Rev 2.0: this version featured Tune and Edit buttons on the front panel. Both Rev 1 and Rev 2 versions can be retro-fitted with a cassette interface (and most were). As with Rev 1s, this version utilised SSM chips and is supposed to have a better sound quality than other revisions. If you find one that's working, the chances are that it will continue to do so.

Rev 3.0: starting from serial number 1300, the Prophet featured Curtis chips and, although possibly not sounding as good, were generally more stable and reliable.

Rev 3.1: this version came fitted with more reliable memory chips and offered a micro-tuning mode and memory test functions. Micro tuning facilitated different intonations, rather like Yamaha's TX802. Sequential coined the phrase "my fifths don't beat" to promote the revision but most people's continued to do so, as almost no-one used the feature.

Rev 3.2: the rear panel featured a digital interface enabling Sequential's Poly Sequencer to be connected. This was no big deal except that, in later months, a modification enabling Rev 3.2s to be fitted with MIDI appeared. None of the earlier revisions can be MIDI'd using upgrades supplied by Sequential.

Rev 3.3: this revision sported the increased patch memory (120 memories) and MIDI was fitted as standard.

Sequential were, along with Roland, one of the first companies to produce MIDI-equipped instruments - on the Prophet 600, as the Prophet 5 retrofits came later. I'm sure you don't need me to tell you how much more useful an instrument fitted with MIDI is, so I'd have to recommend a 3.2 or 3.3 revision. Having said that, the Synthesiser Service Centre (01-586 0357) have their own modification to equip any Prophet 5 with MIDI for around £200.

With total sales of around 6,500 instruments, it would be fair to say that the Prophet 5 "made" Sequential Circuits Inc. Maybe it was too successful, as they never managed to repeat this level of success with any of their later instruments. The Prophet 5 originally sold for £3000 plus VAT; these days a secondhand Prophet will set you back something like £500 to £750; quite a depreciation. But I'm sure anyone who ever owned one of these classic synths will tell you it was worth every penny - and just look at that real wood finish.