Released in 1978, the Sequential Circuits Prophet-5 was one of the pivotal instruments in the history of electronic music. It was the world’s first fully programmable polyphonic analogue synthesiser and the first musical instrument to incorporate an embedded microprocessor. By combining five-voice polyphony with complete storage and recall of synthesiser settings, the Sequential Circuits Prophet-5 established an operating concept that became fundamental to generations of programmable synthesisers that followed.
Sequential Circuits founder Dave Smith developed the Prophet-5 during 1977, with the instrument making its public debut at the Winter NAMM show in 1978. At a time when most analogue synthesisers required musicians to recreate sounds manually by returning every control to its previous position, the Sequential Circuits Prophet-5 could electronically memorise an entire sound and recall it at the press of a button. It placed the immediacy of a conventional knob-based analogue synthesiser together with computer-controlled patch storage, creating an instrument that remained straightforward to programme while introducing a fundamentally different way of working.
The Sequential Circuits Prophet-5 was a five-voice polyphonic synthesiser, with each voice containing two voltage-controlled oscillators, a noise source, a voltage-controlled low-pass filter and a four-stage envelope generator. Across its five voices, this gave the instrument a total of ten oscillators. An internal computer monitored the system and could automatically tune and scale all ten oscillators, substantially reducing the periodic internal tuning traditionally associated with large polyphonic analogue synthesisers.
Each voice began with Oscillator A and Oscillator B. Oscillator frequency could be selected in semitone steps across a four-octave range, while Oscillator B also included continuously variable fine tuning over approximately one whole tone. Oscillator B could be switched into a low-frequency operating mode and disconnected from keyboard tracking, considerably extending its usefulness as a modulation source. Waveforms could be selected independently, while pulse width was continuously adjustable from 0 to 100 per cent. Oscillator synchronisation allowed Oscillator A to follow Oscillator B in hard synchronisation.
The oscillator signals were combined in the mixer along with the Prophet-5’s noise generator. Independent controls determined the amount of Oscillator A, Oscillator B and noise passed into the filter section.
Filtering was provided by a resonant 24 dB-per-octave low-pass filter. Cut-off frequency and resonance were continuously adjustable, with the filter capable of self-oscillation when resonance was advanced fully. A dedicated envelope amount control determined how strongly the filter envelope affected the cut-off frequency. Attack, decay, sustain and release controls provided the four-stage envelope, with attack, decay and release times extending from approximately 1 millisecond to more than 30 seconds.
The amplifier section incorporated its own attack, decay, sustain and release controls, allowing the amplitude contour to be programmed independently from the filter envelope. A dedicated Release switch could force the amplifier envelope to its minimum release time regardless of the programmed release setting, while the master volume control determined overall output level.
One of the Sequential Circuits Prophet-5’s particularly important facilities was Poly-Mod. The system allowed a mixture of the filter envelope and Oscillator B to become a modulation source. This could then be routed to Oscillator A frequency, Oscillator A pulse width and filter cut-off frequency. The amount contributed by the filter envelope and Oscillator B could be independently controlled, providing substantially more complex modulation possibilities than straightforward low-frequency oscillator modulation.
A separate low-frequency oscillator provided three selectable waveforms and operated over a frequency range of approximately 0.1 Hz to 20 Hz. Its output could be directed through the Poly-Mod system, while the wheel modulation section allowed noise and the LFO to be mixed together and controlled from the modulation wheel. Modulation destinations included Oscillator A frequency, Oscillator B frequency, Oscillator A pulse width, Oscillator B pulse width and filter cut-off.
The five-octave keyboard was accompanied by dedicated pitch bend and modulation wheels positioned to the player’s left. These controls allowed modulation and pitch changes to be applied to complete polyphonic chords as well as individual notes, making the Sequential Circuits Prophet-5 equally suited to chordal and monophonic performance.
The defining feature of the Sequential Circuits Prophet-5 was its Programmer section. Forty complete programs could be stored internally, organised as five banks containing eight programs each. Selecting a program recalled the complete synthesiser setup under computer control. The factory memory included orchestral sounds such as brass, strings, organs and electric pianos, together with effects and synthesised sounds, but every program could be modified or completely replaced.
Programming retained the traditional direct-control approach of an analogue synthesiser. A stored sound could be selected, any front-panel knob or switch altered, and the resulting sound stored into memory. The original stored version could still be recalled if the edited result was not required. This combination of immediate physical controls and digital storage became one of the Prophet-5’s most important contributions to synthesiser design.
Program memory was protected by an internal backup battery designed to retain sounds when the instrument was switched off. Sequential Circuits specified a battery life of approximately ten years. An Enable/Disable switch on the rear panel could also deactivate the Record function to prevent accidental erasure of stored programs.
Programs could additionally be transferred to ordinary cassette tape through the Prophet-5’s cassette interface. Save-to-Tape transferred all 40 stored programs to cassette, while Load-from-Tape restored previously archived programs to the synthesiser’s memory. This provided musicians and studios with a practical means of building larger libraries beyond the 40 sounds held internally.
The Sequential Circuits Prophet-5 also incorporated an unusual programmable tuning system. Its Variable Scale mode allowed each of the 12 notes within the octave to be individually tuned in approximately two-cent increments around its normal equal-tempered value. Complete alternative scales could then be stored in program memory and recalled like other settings. This allowed conventional temperaments as well as just intonation, meantone, Pythagorean and individually created tuning systems to be programmed.
A crystal-referenced A-440 oscillator was incorporated for tuning, specified as accurate to within 0.1 Hz. The Tune function could automatically tune and scale all ten oscillators in less than ten seconds, an important practical feature for an instrument containing ten analogue voltage-controlled oscillators.
The rear panel extended the Sequential Circuits Prophet-5 beyond standalone keyboard operation. Control voltage inputs provided external access to the filters and amplifiers, while trigger and voltage outputs followed the last note played on the keyboard. Gate and voltage inputs could directly control voice five, automatically disconnecting that voice from the keyboard when used. A dedicated sequencer interface provided compatibility with the Sequential Circuits Model 800 Digital Sequencer and other suitable equipment.
A Release Footswitch connection allowed the envelope release function to be controlled during performance, while the audio output provided a line-level signal. The Prophet-5 could therefore be integrated with the control-voltage, gate and sequencing systems that formed the basis of electronic music studios before MIDI became established.
The Sequential Circuits Prophet-5 remained in production from 1978 until 1984 and underwent several revisions during its original production life. While its internal electronics evolved, its fundamental concept remained intact: five analogue voices, immediate front-panel programming, microprocessor control and the ability to store and recall complete sounds.
Its historical importance reaches considerably beyond being an early polyphonic synthesiser. The Sequential Circuits Prophet-5 established the practical model of a programmable polyphonic keyboard synthesiser in which musicians could create a sound using conventional controls, save it electronically and instantly recall it later. That approach became standard throughout the synthesiser industry.
The Sequential Circuits Prophet-5 also became deeply embedded in recorded music. Hall & Oates used the instrument prominently on 1981’s “I Can’t Go for That (No Can Do)”, while the Prophet-5 was used for several parts of Michael Jackson’s “Thriller”, including the opening chords of the title track. It provided the pad part on A-ha’s “Take On Me”, and decades later remained sufficiently relevant to appear on Radiohead’s “Everything in Its Right Place”. Its use across different periods demonstrated that the Prophet-5’s importance was not confined to the first generation of late-1970s and early-1980s analogue synthesis.
The design also formed part of Dave Smith’s wider contribution to electronic musical instrument technology. Sequential Circuits subsequently developed the Prophet-600, which became the first commercially released MIDI-equipped synthesiser, while Smith played a central role in developing the MIDI standard itself. The Sequential Circuits Prophet-5 therefore stands near the beginning of a technological progression that moved electronic instruments from largely self-contained analogue systems towards programmable and interconnected studio instruments.
Features
- Five-voice programmable polyphonic analogue synthesis
- Two voltage-controlled oscillators per voice for a total of ten oscillators
- Resonant 24 dB-per-octave low-pass filter
- Independent four-stage filter and amplifier envelope control
- Poly-Mod system using the filter envelope and Oscillator B as modulation sources
- 40-program internal memory arranged as five banks of eight programs
- Automatic computer-controlled tuning and scaling of all ten oscillators
- Programmable Variable Scale tuning system
- Cassette interface for saving and loading complete program libraries
- Control voltage, gate, trigger and sequencer connections for external integration
