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Sequential Circuits Prophet 5 Rev 3.3. Courtesy of cyborgstudio.com

A polyphonic synth introduced by Sequential Circuits in 1978, the Prophet-5 was the company's first synthesizer, although not its first product (it had marketed a hardware sequencer previously). The Prophet-5 was one of the first polyphonic synths to be priced within reach of working musicians, and one of the first with patch memory.

Design[]

The Prophet 5 revolutionized the way that polyphonic synths are designed, in two ways. First, most previous polyphonic synths had been designed as fully polyphonic, that is, they had one set of voice circuitry for each note on the keyboard. This was a very expensive way to build a synth, and most such synths actually marketed were string synthesizers, special-purpose synths with very limited voice circuitry designed to produce only a few specific sounds. Sequential reasoned that most players will seldom actually play a huge number of notes at once, and that they could build a synth with a smaller number of complete voices that would suit most players, offer a much wider pallette of sounds than the string synths, and be less expensive to build. Using a scanning keyboard design licensed from E-mu Systems, a microprocessor could detect the notes being played and then assign each note to a voice using a voice allocation algorithm. Relying heavily upon voice component ICs from SSM to miniaturize the circuitry, the works of the P5 could be condensed to fit in the space underneath the control panel.

Second, since the synth already had a microprocessor onboard, the designers incorporated patch memory. The ability to instantly recall patch settings was a boon to live performers, who no longer had to spend time tweaking knob settings between songs and using patch sheets or bits of tape on the panel to help them remember settings. With 40 (later expanded to 120) memory slots, the P5 displaced most other polyphonic synths from live performance. It became an instant hit with synth players, even at a price of $3500 in 1978 dollars. The P5 remained in production until 1985.

(It is worth noting that the Oberheim Four Voice was a polyphonic synth that used a scanning keyboard and voice allocation, had patch memory, and preceded the Prophet-5 by two years. However, the Four Voice did not have fully integrated patch parameter controls; there were some parameters that were not stored in memory and had to be set for each voice individually whenever a patch was changed. Plus, it cost far more than the P5 did.)

The voice architecture was fairly conventional by today's standards, consisting of two VCOs, one four-pole low pass VCF, and a VCA. One LFO was provided with sawtooth and triangle waveforms, and was routeable to VCO frequency or pulse width modulation. An ADSR envelope generator was hard-wired to the control input of the VCA, and was also routeable to the VCF cutoff frequency. An outstanding and much-used capability of the synth was cross modulation, in which VCO 2 could be detuned and then used to frequency modulate VCO 1.

Rev 1 & 2[]

Prophet 5 Rev 2. From an expired eBay listing; photographer unknown. Note the differences from the Rev 3.3 unit, in the controls on the right side of the panel

Production of the P5 was divided into several revisions. The Rev 1 (as Prophet aficiandos number them) units were hand-assembled, and it is said by service personnel that no two are exactly alike, the result being that many techs will not service them. The Rev 2 was the first mass-production version; it made more use of the SSM integrated circuits to reduce the amount of circuitry required. Being that the concept of patch memory was almost unknown at the time, the Sequential engineers were at first unsure about how patch editing should work. Accordingly, the Rev 1 and early Rev 2 units ignored the patch parameter controls until the user selected an "edit mode", at which time the CPU noted all of the current positions of the knobs. Moving a knob added to or subtracted from the parameter value in memory. Depending on the positions of the knobs when edit mode was entered, the performer sometimes found that they reached the limit of the knob's rotation before reaching the desired parameter value; when this happened, it was necessary to exit edit mode, re-center the knob, and then enter edit mode again. The Rev 1 and 2 units provided 40 patch memory locations.

After 1980, some Rev 2 units were retrofitted at the factory with Rev 3.1 style controls and patch editing software. Later, a MIDI retrofit was available for some Rev 2 units, but it required extensive modification, and the resulting MIDI capability was very basic.

Rev 3[]

In 1980, Sequential redesigned the Prophet to use ICs from Curtis. The reasons why are unclear; the stated reason was that some of the SSM parts had reliability issues. This may have been true, but it is also true that at that time Sequential was about to initiate a patent dispute over the scanning keyboard with E-mu, which owned an interest in SSM at the time. This redesign became the Rev 3, and these units sound somewhat different from the earlier ones; some aficionados claim that the Rev 2 units sound "thicker". The Rev 3 design expanded patch memory to 120 locations.

The Rev 3 is further subdivided into the 3.0, 3.1, 3.2, and 3.3 versions. The 3.1 introduced the patch editing paradigm used by most synths with patch memory today, in which moving a panel control instantly edits the associated parameter. Also, the 3.1 revision introduced a remote control bus, intended for use with the Prophet Remote keytar, but later useful as a convenient hook for easily adding MIDI retrofits. The 3.3 was the final version, and some of these had MIDI installed at the factory. Other rev 3 units can be retrofitted, with varying degrees of difficulty.

The Prophet-10[]

Sequential Circuits Prophet 10. Courtesy of Vintage Synth Explorer.

The Prophet 10 moniker applies to two different ten-voice variations produced by Sequential. The first was basically a P5 with five additional voice circuits installed, for additional polyphony. This model had severe thermal problems, and Sequential eventually re-purchased most of them from the buyers, scrapping them and using the parts in other synths. The second version became the definitive article, a two-manual extravaganza with additional modes for dividing and layering the voices between the manuals, and a built-in sequncer. This was also one of the first multitimbral synths, as each manual could be set to play a different patch. All of these P10s are based on the Rev 3 P5 circuitry.

Dave Smith Instruments Revives the Prophet Name[]

In 2008, Dave Smith Instruments introduced the Prophet 08, a successor to the Prophet line. The Prophet 08 includes two DCOs per voice, a step sequencer, an arpeggiator, and greatly expanded modulation possibilities. Dave Smith was a co-founder of Sequential Circuits and contributed greatly to the design of the original Prophets. Smith regained the rights to the Sequential Circuits name in 2015, and DSI officially changed its name to Sequential inc. in 2018.

Rev 4 Prophet 5 and Prophet 10[]

In 2019, the new Sequential introduced a revival of the Prophet 5, referred to informally as the "Rev 4". Sequential claims that most of the original circuitry has been duplicated in the new version, including using some of the same Curtis and SSM integrated circuits used in the Rev 2 & 3. A "Rev" switch allows switching between Rev 2 and Rev 3 VCF circuits, as well as emulating some other behaviors of the two different versions. Unlike the originals, all Rev 4 units have a velocity and aftertouch sensitive keyboard, and come from the factory with a full MIDI implementation. Additionally, a Prophet 10 is offered; like the original Prophet 10, this is simply the Prophet 5 with five additional voices, lacking the dual-manual setup or the sequencer of the previous Prophet 10.

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