Sequential Prophet T8

Analogue Polysynth (Retro)

 

Reviews : Keyboard

The radical keyboard design of the Prophet T8, thought by some to provide the best feel and response of any synth yet made, had a heavy cost for manufacturers Sequential, delaying the T8's launch by two years and stunting potential sales. ROBERT ALEXANDER reflects on a synth which was ahead of its time.

It's the beginning of 1981. Sequential Circuits Inc are planning to launch a new synthesizer that they believe will push further forward the boundaries of analogue synthesis development. At the same time, they hope to continue to keep the company at the forefront of the electronic musical instrument industry.

The synthesizer that Sequential are pinning so much hope on is the Prophet T8, intended to be the successor to the very popular Prophet 5 series, nearing the end of its production run (of approximately 7200 keyboards, over three revisions between 1978 and 1984). The essential difference for the Prophet 5 is to be the addition of a touch-sensitive keyboard, which at this time is a rare feature indeed.

Unfortunately for Sequential, development problems mean that the keyboard is not to appear until 1983, and by this time, Yamaha's alternative plans for the domination of the market have taken off, with the release of what was (and still is), one of the most revolutionary electronic musical instruments of all time -- the DX7.

 

PIANISSIMO

It was Sequential's commitment to excellence, along with several exhaustive technical problems with the keyboard itself, that brought the T8 to market some two years late. The company thus forfeited the considerable advantage that they would have gained had it been commercially available in 1981. What was so important to Sequential about the touch-sensitive keyboard? Why did they strive to make it so good?

"Some of its deep, distinctive bass synth sounds have become classics in their own right."

With a touch-sensitive keyboard -- a piano, for example -- the force used in the initial keystroke determines the amplitude of the note produced. A synthesizer cannot normally hope to match all the nuances possible from a system as complex as a piano keyboard, yet this is what the R&D team at Sequential set out to achieve with the Prophet T8.

Sequential found themselves faced with a series of technical problems that dogged them throughout the development of the keyboard system. It soon became apparent that using force or pressure alone to dictate amplitude would not result in a sufficiently sensitive keyboard for the T8, and rather than compromise the flexibility of the instrument, the development team decided to design a completely new system based around optical sensors. This was a daring and expensive undertaking. Optical sensors were micro-processor controlled -- cutting-edge technology in 1981. This adventurous attitude to design and development typified the kind of approach that the American musical instrument manufacturers had in the '70s and early '80s.

The reason optical sensors were chosen for the keyboard was that they would give a far more accurate indication of the travel of a key and the duration of a keystroke for the T8's central processor unit (Z80) to compute. Unfortunately for Sequential, putting all this into practice would prove to be easier said than done -- hence the long delay. However, they did eventually iron out the development problems and get it right for the T8. It consequently has probably the most realistic pressure-sensitive keyboard feel of any synthesizer ever made -- so good, in fact, that New England Digital decided to use it on the Synclavier, possibly the most elaborate, and certainly the most expensive, electronic musical instrument ever produced.

Curiously, the keyboard on the T8 is of the 76-note variety, rather than the full 88 notes of a piano. The keys themselves are made of wood, like a piano's, and are almost fifteen inches long -- twice the length of the normal plastic keys found on most synthesizers. This was to help with the 'action' of the keyboard, giving an automatic feeling of weight due to size alone. The keystroke action is very similar to that of a piano, on which it is based, but perhaps just a bit lighter in the downstroke, and shorter in the return.

"Sequential had put so much effort into the design and construction of the keyboard itself that it's hardly surprising if the rest of the T8 bears a remarkable similarity to the Prophet 5 it was intended to replace."

The initial pressing-down of a key initiates a levering action which moves the far end upwards to strike a second padded lever. This, in turn, registers with the optical sensor the amount of depression and the velocity of the keystroke, thereby indicating the amplitude of the note. It's a very complex system, with each individual note being independently sprung. One advantage of this, however, is that the T8 has individually pressure-sensitive keys -- this sensitivity is programmable -- a very rare feature indeed, only found on a couple of the very best synthesizers ever made, because of the incredibly high manufacturing cost.

The velocity sensitivity of the T8 is linked to the front control panel of the instrument by four rotary pots. The first two are for envelope rate control, and individually labelled Attack/Decay and Release. The second pair of pots are for envelope peak control, and are labelled Filter and Amp. These seemingly simple controls give the T8 an enormously flexible 'feel' when you play it, as each note can be fine-tuned to the kind of response the individual player wants.

 

SYNTHESIS FEATURES

Sequential had put so much effort into the design and construction of the keyboard itself that it's hardly surprising if the rest of the T8 bears a remarkable similarity to the Prophet 5 it was intended to replace. The same VCO configuration and filtering as found on the earlier Prophet is implemented on the T8, though the T8 is 8-note, rather than 5-note, polyphonic.

The features which made the 'Sequential sound' so popular are still there to be found on the Prophet T8, particularly the Sync function, which allows oscillator B to modulate the filter, frequency or modulation width of oscillator A. Oscillator B was also now able to offer the elusive triangle waveform that was so obviously lacking in the Prophet 5 (oscillator A on both synths already had the triangle waveform). The filter panel would now allow fully variable keyboard tracking, and an additional rotary knob in the LFO mod section gave control of the initial LFO modulation amounts.

Some brand new features were also added, namely: polyphonic glide; programmable volume (which allowed a patch to be stored at a pre-settable amplitude); and digitised envelopes, to allow more flexibility. (The essential sound-generation components -- the oscillators and filters -- remained analogue.) In fact, the T8 was given two central processors to cope with all the functions it offered. As mentioned, the keyboard scanning was taken care of by a Z80 CPU, while the remainder of the synth's functions (routings, presets, envelope generation, and sequencing) were handled by the newer Z8000 CPU.

 

SEQUENCER

A rudimentary sequencer (even by 1983 standards) was included. This allowed 670 notes to be programmed, though unfortunately only in real time. (Sequential were, for reasons known best to them, not very keen on step-time recording until later on in their history). One of the most significant drawbacks of the sequencer was its inability to be clocked externally, especially in early software revisions of the T8. However, before Yamaha took over at Sequential on January 1st, 1988, the last software revision for the synth was released (Rev 3.8 upgrade) and this did, finally, offer full external sequencer control via MIDI.

The sequencer does have its redeeming factors, though. The notes stored include program information, as you would expect, but significantly they also contain the velocity information of each event -- such an important part of the T8's design. This is vital to the use of the sequencer as a 'scratch pad' for songwriting (its only practical use), as without the ability to save the nuances of the work, when played back each sequence would sound totally different to how it was originally played. Once written, sequences can be saved into one of eight different sequence locations, or 'songs'.

 

SOUNDS

The Prophet 5, in its many revisions, went from an original 32-sound instrument, to 40 sounds, and lastly to 120 sounds. The T8 goes a little beyond this, with 128 factory presets, which can certainly be described as typically 'Sequential' in nature.

"...it is in the hands of a good programmer that the T8 really comes to life..."

First impressions of the T8 sound is that it is warmer and, in some subtle way, different to a Prophet 5. The same Curtis 3340 oscillators and 3372 VCFs (Voltage Controlled Filters) were used, but Sequential upgraded the VCAs from 3280s to the newer 3360s. The T8 standard sound set consisted of the usual electric and acoustic pianos, strings, harps and wonderful Prophet brass sounds. There are percussive sounds too -- marimbas, bells, and a passing attempt at Simmons electronic drums.

As ever, though, the best sounds that Sequential instruments produced were those that only a Prophet synthesizer could make, and the T8 carries on this fine tradition in style. Some of its deep, distinctive bass synth sounds have become classics in their own right (listen to The Thompson Twins, Swing Out Sister, and some of the later Human League from the mid '80s). While all the preset sounds are mostly quite usable, it is in the hands of a good programmer that the T8 really comes to life, with the power and flexibility to create enormous, fat analogue sounds that growl when the oscillators all kick in.

 

CONCLUSION

In the end, sales of the Prophet T8 (or rather the lack of them), meant that it did not equal the success of the Prophet 5, as had been envisaged. Nor did it restore the market supremacy that Sequential had enjoyed earlier in the decade. However, this was in no way due to the quality of the instrument, which is without doubt one of the finest ever constructed. Sequential's problem with the T8 was due to the extraordinary amount of money that had been invested in its research and development, and this, of course, had to be carried across to the customer. In 1983, a Prophet T8 would set you back the quite staggering sum of £4727! You could buy three flightcased DX7s for that and still get a MacDonald's lunch and a taxi home!

While the DX7 did represent better value for money and was a remarkable instrument in its own right, did you long for one? Would you have considered a second mortgage for a DX7? Probably not. For me, there's no nostalgia in owning a DX7 (even though I did buy one in January 1985 and still have it to this day). But the T8? That's made of different stuff -- it has wood, it has style, it has a monster sound, and very, very few people own one.

As part of the research for this article I contacted much of the original development team at Sequential in the United States (who incidentally, to a person, all said they felt it was the best synth Sequential ever made), and they tell me that there were only around 350 Prophet T8s ever made. That makes them amongst the rarest, and therefore most collectable, of the large analogue synthesizers of the early '80s. They rarely come up for sale in good condition now, but if you did want to buy one, a couple of years ago (like so much of the analogue gear) you could pick one up for £1000. Today, you'd better be prepared to pay £2000 to £2500 for one in reasonable condition, and perhaps as much as £3000 for a T8 in mint condition.

Sequential have long gone, but the legacy of the musical instruments they built remains with us to this day, and through a small number of determined collectors, these masterpieces of analogue circuitry will be kept safe forever.

My thanks to Bruce Wismer, John Bowen, Dave Sesnak, and Dave Smith for their invaluable help and expertise during the research for this article.

Published in SOS October 1996