Prophet-5: the first polyphonic synthesizer with full memory

Why memory changed everything

Before the Prophet-5, a synthesizer sound existed only as the current position of its knobs and cables. Changing sounds meant re-setting them by hand, with no guarantee of getting the same result twice. Sequential Circuits used a microprocessor — then a new technology — to scan the panel, store every parameter and recall a sound instantly. Synthesizers moved from making unpredictable sounds to offering "a standard package of familiar sounds", and the Prophet-5 became a market leader in pop music and film scores.

Sequential Circuits had been founded in San Francisco in 1974. Its first products were an analog sequencer for Moog and ARP synthesizers, a digital sequencer and the Model 700 Programmer, which added programmability to the Minimoog and the ARP 2600. The Prophet design started as a ten-voice instrument, but that prototype was unstable and overheated, so half the electronics were removed: five voices remained. It was demonstrated at the NAMM convention in January 1978 and shipped later that year.

Five voices was modest even then — the polyphonic instruments of the 1970s in this guide range from 4 to 8 voices — but its closest rival, the Yamaha CS-80, had no patch memory at all. Memory, not voice count, was the breakthrough.

Revisions 1, 2, 3 and 4 compared

Players and reviewers still debate the difference: one magazine judged Revision 3 "impressive and pleasant to play, but slightly cold and featureless" next to the SSM-based earlier models. The Rev 4 of 2020 includes both filter characters, so the two can be compared on one instrument.

Inside a voice: two oscillators and Poly-Mod

Each of the five voices has two voltage-controlled oscillators, a four-pole resonant low-pass filter and an amplifier, with envelopes for filter and loudness. One LFO and the pitch and modulation wheels sit to the left of a 61-note keyboard. Revisions 1 to 3 have no velocity or aftertouch.

The Poly-Mod section is what gives the Prophet-5 its metallic, bell-like and sync-sweep sounds. In every voice it routes the filter envelope and the second oscillator to the first oscillator's pitch or pulse width, or to the filter. Because the modulation runs at audio rate inside each voice, it is a form of analog frequency modulation — years before FM synthesis went digital.

Connections: CV, a private serial port, and MIDI

The original Prophet-5 offers control voltage and gate connections and a proprietary serial interface, which drives Sequential's Prophet Remote, a keytar-style controller worn on a sling; the interface cannot connect the synthesizer to other devices. Sequential later sold a MIDI interface that could be retrofitted to later Prophet-5 models, and third-party MIDI kits exist.

Sequential also helped create MIDI itself. In 1981 Roland approached the company about a standard way to synchronise instruments from different makers; Sequential's engineers designed the interface with Roland, and in January 1983, at the Winter NAMM Show, a Sequential Prophet-600 was connected to a Roland Jupiter-6 to demonstrate it.

The Prophet-10 and later Prophets

The ten-voice idea returned in 1981 as the Prophet-10: 10 voices, 20 oscillators and two keyboards, built with CEM chips like Revision 3. Early units saved patches and sequences on an Exatron Stringy Floppy tape drive; Sequential later switched to a more reliable Braemar tape drive that held about four times as many sequencer events. A new Prophet-10 with the Rev 4's design appeared in 2020.

Sequential went out of business in 1987, after releasing the Prophet 3000 sampler, and was bought by Yamaha, which closed it in 1989 without issuing products under the name. Yamaha returned the Sequential Circuits trademark to its founder's new company in January 2015; that company released the Prophet-6 in 2015 and renamed itself Sequential in 2018, on the Prophet-5's 40th anniversary.

Using a vintage Prophet-5 on a session

1. Ask which revision it is. It decides the chips (and much of the character), the number of memories and whether MIDI is possible.
2. Back up the patches first. Revisions 2 and 3 can save their memory to cassette; do that before anyone edits the factory or owner's sounds.
3. Check for MIDI. Only Rev 3.3 units, retrofitted units and Rev 4 have it. Otherwise plan on CV/gate or playing the part live.
4. Write down favourite edits. Memory makes recall easy, but edits made during a take are lost if the patch is changed without saving.