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We were the first Sequential Authorised Service Centre in Britain & Europe.
Servicing more of their instruments than anyone else. This position only ceased when Sequential closed.

Prophet 5 Rev. 3.3 Prophet Five, the Mother of programmables but the maker has gone. 61 steel shafted keys, with screwed on caps & gold wire contacts. Analogue subtractive, 5 voice polyphonic, 2 VCOs per voice, one of the first to use computer control.
A Rev. 3.3 model, this expands the 40 programmes to 120. In all other respects it is similiar to the 3.2, all revisions have a similiar appearance.

Rev. 1 is rare, only 182 made, & is usually considered more troublesome. A good example is a piece of history well worth owning. Very few people have the knowledge to service these effectively, resulting in a bad reputation, not entirely deserved. They can be made to work very well.

Rev. 2 is the one that made Sequential famous, just over 1100 made. Both use the SSM chipset. Neither were supplied with a cassette port but a retrofit was available.

Rev. 3 uses a Curtis chipset and a more advanced computer programme. This allows software calibration of many settings, reducing the trimpot count & improving reliability. It also has a cassette port for data storage. Programmable 'Micro-tuning' of individual patches allows setting up for early or oriental scales etc. another first.

This revision was made in larger numbers & successively improved with 3 main variants.

Rev. 3.1 is an electronic improvement, with a simpler, less unreliable power supply & better EPROMs. It has no additional functions.

Rev. 3.2 has external computer & analogue ports. These can connect to a neck strap held external keyboard or a sequencer & allow a factory MIDI retrofit.

Remember that MIDI was a Sequential innovation! It also has Voltage control of performance modulation.

Rev. 3.3 is pictured at top of page. It is a Rev. 3.2 with hardware & software modifications expanding the 40 patches to 120.

All revisions have a distinctive & popular sound. The portamento is a weak point, only working in unison mode, it is constant speed. When set correctly for semitones, it takes too long on wide intervals, a problem shared with most programmables.

Before all was a pre-production version, (Rev. Zero?) with 10 voices & 2 analogue boards. Only a few made & issued for evaluation. Players loved them but they overheated & were unstable. All or most were recalled & converted into 5 voice REV. 1s.

The power supply is a troublesome area on all revisions & in our view represents a design flaw. Rev 3 series frequently suffer from sporadic editing of panel settings, especially VCF, this is curable. Ensure it all works before purchase, especially voices, custom parts are almost all unobtainable.

With hard playing frequently breaks contacts, these are plain gold clad wires. Ensure that repairs are neatly done, using the right material. Bits of guitar string won't work properly & damage buss bars.

Prophet 10, 10 voice dual manual. Basically two complete Prophet Five Rev. 3.2s in one case. Quite an instrument, one you will either love or hate. The voice boards & manuals can be linked in various ways.

Included, as an option, is a pretty good sequencer, This is essentially a separate unit, but within the same case. With its own CPU, so is quite powerful for the time and was available in a stand-alone form for the Rev. 3.2 Prophet Five.

No less & no more reliable than its single manual sister. However, included was a built in digital tape drive for preset storage, no cassette port. Bad move, the early single spool drive kept wrecking its tapes & the later 2 spool type needs non-standard tapes that are hard to come by.

Capable of Ex-Factory MIDI retrofit, the same hardware as the Prophet Five's but a different CPU programme. Implements many of the dual manual functions & the sequencer.

A couple of previous attempts at a Prophet 10 were made. The first used the same case & boards as the Prophet Five Rev 1. With two voice boards 'piggy-backed', found to overheat & be unstable. Most or all were recalled & converted into Rev 1 Prophet Fives.

A second attempt was made later with a larger case, still using the SSM chipset. This version was not marketed, the whereabouts of the few made appear not to be known. Soon afterwards the REV 3 came out with a Curtis chipset.

Pro-One Pro One, Sequential's first monophonic analogue synthesiser.

Although it has a good sound, liked by players, it is hard to see as a classic. Their first budget model, included here as it has a place in the company's history.

'Cheap & nasty' in construction for the period, cosmetic & external control parts were not to their previous standard.

This enabled a low selling price.
Obviously intended for those who could not afford a Minimoog or Odyssey. The wisdom of Sequential entering this market area is debatable.

The same type Curtis chips as the Rev. 3 Prophet Five are used, no 'Auto-tune', resulting in poor pitch accuracy. Two VCOs, 4 pole VCF, the modulation section has useful routing facilities. A keyboard microcontroller eliminates precision resistors, allowing a rudimentary arpeggiator & sequencer.

Made before MIDI, it has a form of external computer interface. Use of this requires removing the microcontroller, minor modifications & writing a programme for the computer used. At least one company marketed an expansion making use of this feature.


The first release had the Mains Transformer mounted on the single printed circuit. Big mistake & potentially lethal. This serious design error was corrected in later machines. The last batch had a membrane contact keyboard. This did not work for long & these examples are best avoided.

Prophet T8. Analogue Subtractive 8 Voice Polyphonic Programmable synthesiser. Another Milestone from the innovators of computer controlled synthesis. Introduced together with the Prophet 600. The first Sequentials with MIDI , their 'open to all' interconnecting protocol that made everything following possible.

A first in so many ways. 76 wooden keys with weighted 'hammer' action. No key contacts, using instead two light beams and sensors per key. These are crossed in sequence by an opaque vane connected to each hammer. The main CPU times the crossings to give Attack and Release Velocity values.

After Sequential's take-over & unfortunate demise this system was seen, in updated form, on top end Yamaha pianos.

Two CPUs, interconnected via a common RAM, an 8 bit for Main processing etc. and a 16 bit for Envelope calculation etc. ALL calibrations and tuning are handled by this system. Easily programmed, with a separate rotary control for almost everything.

Surprisingly slim & reasonably light. With a narrow, angled control panel & a flat top to allow stacking of another keyboard. How many innovations can one instrument boast? Good looks & keyboard feel. Fairly reliable & repair access is acceptable.

As with all Sequential instruments, there is a serious problem with availability of custom ICs, used in the analogue section. Certain of the digital ICs may also be difficult to source. It is wise to bear this in mind, if you are tempted to buy a faulty model.

Prophet 600, 6 voice analogue programmable synthesiser. Introduced at the same time as the T8 & also with MIDI. This model probably represents Sequential's first serious mistake. More developed computer programme than the Prophet Five & with one more voice. Filter is similiar but combined with the mixing & final VCAs.

Digital envelopes reduce cost. Still no velocity or pressure.

The styling, construction & finish however were drastically cheapened. Even the new interface could not make it attractive to anyone wanting a professional instrument. Despite a similiar sound it was certainly no replacement for its predecessor and had a lower price. The other new model in Sequential's line-up, the T8, was too expensive for many.

To make matters worse Yamaha introduced the DX7 at the same time. This also had MIDI, but for the same size & price as the 600 it offered so much more. Good modern professional style & build quality. Full velocity & channel pressure. Plus a new form of synthesis, Digital FM. Put this together with supreme reliability & the 600 stood no chance.

The 'final nail in the coffin' came from Sequential themselves, & their dealers. The remaining stock of Prophet Fives was sold at much reduced price to clear the shelves for new models. A quality instrument for the same money, which were analogue enthusiasts going to buy?

For the reasons above we do not really rate this one as a classic. However it has a place in history so it is included. If you can find one that works & the price is right by all means buy it. They do sound good, are light & easy to carry. Service may be a problem in the same way as all others using custom chips.

If you are the proud owner of one we apologise for insulting your pride and joy. However everything we say is from the heart. If Sequential had stuck to top quality instruments they would probably still be here & selling well.
Six Trak, their first multi-timbral instrument. Small, neat & cheap subtractive analogue synthesiser. Six Voices, only one VCO per voice. Each uses a single Curtis IC, including everything except envelope generator on a single chip. Velocity but not pressure.

Each voice can be set on a different MIDI channel so allowing fully multi-timbral operation from a sequencer. Probably the first time such facilities became available at such a low price. 'Automatic' auto-tune re-scales voices whenever none has been played for a half minute. Uses successive approximation allowing all voices to be available instantly, neat.

A fairly good internal sequencer makes use of this capability, two sequences can be stored. An arpeggiator is included. This little instrument gave a good indication of the way things would go.


If only they had made a bigger & better version at the same time! A five octave professional model with eight note polyphony & two VCOs per voice might have re-established their pre-eminence. Oh well.

Prophet VS, often know as the Vector Synthesiser. An unexpected departure from the norm & a milestone in musical instrument history. Or was it a 'millstone'.

A most unusual hybrid wavetable machine. Tables held in ROM like the PPG Wave. Analogue filters & VCAs. Eight voice polyphonic, with stereo chorus & outputs. Five octave keyboard, after that the differences start.

Four wavetables are active at any one time on each patch & patches can be layered. A joystick controls real time dynamic shifting between the tables, whilst notes are held (Vectoring). The circuitry to accomplish this is a clever combination of analogue & digital.

This machine should have put Sequential firmly back on the map. It has a following & is still unique. Unfortunately "trouble at t' mill" was well under way. The Korg Wavestation is a design produced after Yamaha's takeover & closure of the ailing company. A capable enough digital machine, but not in the same league. More an M1 with a joystick.

True Vector Synthesis died with Sequential. It need not have.

Sequential Circuits Inc. produced a number of other instruments etc. Some were too cheaply made to be placed here, they appear to have been a vain effort to 'go with the market'. They should have stuck to what they did best.

One of their earliest designs, a programmer, did not set the world alight. An ambitious programmable effects rack was not a success & did not sell well over here. Too bulky, too expensive, too complex, too noisy, too unreliable & too late. How many 'toos' can one product have?

They produced samplers & sample based drum machines. As already stated we do not consider such machines to be classic.
Studio 440 The Studio 440, shown here during service, may be an exception.

Possibly the best sampling drum machine in the World.

However, it uses unobtainable custom parts & was not fully developed during the company's lifetime.
Although controlled by a more advanced 68,000 16 bit CPU, the analogue hardware was based on that of the earlier Prophet 2000 keyboard sampler. Still 12 bit sampling & only 512K of memory. The 2000 came out with 256K but had a memory port, allowing expansion, eventually to 1MB. As the 440 started with twice as much RAM, SCI did not provide an expansion port.

So unfortunately more became less, due to short-sighted economy, a pity.

Some further software development was completed after SCI's closure & a new operating system released. This allows the SCSI port to work properly & improves some other features.

Drum pads tend to perish, going soft & 'squishy'. As with the machine here.

All Brand & Model names are Trademarks and/or Copyright of their respective owners.

All opinions in this section are those of the author, Ron Lebar.

Information given is generally brief & is based on our experience. If you spot any factual mistakes or 'typos' please feel free to let us know. We are not quite perfect & promise not to sulk over constructive criticism.

If you need more information on models listed or can suggest another instrument to add let us know & we will do our best. From time to time we may include comprehensive details of specific models.

For Technical queries, advice on operational problems etc. you are welcome to E-Mail us.

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Sequential. Updated on the 2nd of June 2008. Ron Lebar, Author.