Introduced in 1980, the Sequential Circuits Prophet-10 represented the most ambitious development of the original Prophet concept. Built around ten independently articulated analogue voices and two five-octave keyboards, it effectively combined the capabilities of two programmable five-voice Prophet synthesizers within a single instrument. The Sequential Circuits Prophet-10 could operate as a ten-voice instrument, divide its voices between the two manuals, layer two independently programmed sounds, or alternate between them, while retaining the direct front-panel programming approach that had helped establish the Prophet series.
The Sequential Circuits Prophet-10 provided ten complete voices, each incorporating two voltage-controlled oscillators, a noise source, a voltage-controlled 24dB/octave low-pass filter and two four-stage envelope generators. Twenty oscillators were therefore available across the instrument. Unlike synthesizers that relied on a single common sound across the entire keyboard, the Sequential Circuits Prophet-10 maintained separate Upper and Lower programs, normally assigning five voices to each five-octave manual. Each section had its own stored program, allowing two completely different sounds to be played simultaneously.
A total of 64 programs could be stored, with 32 programs available for each of the Upper and Lower sections. Front-panel controls within the Program section were stored as part of a program, enabling complete sounds to be recalled rather than merely providing preset approximations. Programs could be selected independently for the two manuals, making the Sequential Circuits Prophet-10 particularly flexible for layered and split configurations.
Each voice incorporated Oscillator A and Oscillator B. Oscillator frequency was adjustable in semitone steps across a four-octave range, while Oscillator B also included continuous fine tuning over approximately one whole tone. Oscillator B could be switched into a low-frequency mode covering approximately 0.1Hz to 10Hz and could be disconnected from keyboard tracking. Multiple oscillator waveforms could be selected simultaneously, pulse width was continuously adjustable from 0 to 100 per cent, and hard synchronisation allowed Oscillator A to follow the frequency of Oscillator B.
The mixer combined Oscillator A, Oscillator B and noise before feeding the filter. The Sequential Circuits Prophet-10 used a 24dB/octave low-pass filter with cutoff frequency, resonance and envelope amount controls. Its filter envelope provided attack, decay, sustain and release, with attack, decay and release times extending from approximately 1 millisecond to more than 30 seconds. A separate ADSR envelope controlled the amplifier.
Modulation facilities were extensive. The Poly-Mod section combined the filter envelope and Oscillator B as modulation sources, which could then be routed to Oscillator A frequency, Oscillator A pulse width or filter cutoff independently for every voice. A separate LFO operated over approximately 0.01Hz to 20Hz, with selectable waveforms. The Mono-Mod section allowed programmed LFO modulation to be directed to Oscillator A frequency, Oscillator B frequency, the pulse width of either oscillator or the filter. Pitch and modulation wheels were positioned beside the upper manual, with the pitch wheel providing a range of approximately a fifth.
Four keyboard assignment modes substantially expanded the way the ten voices could be used. Normal mode assigned five voices and the Upper program to the upper manual and five voices and the Lower program to the lower manual. Single mode placed all ten voices under one program and allowed them to be played from either keyboard. Double mode layered the Upper and Lower programs, allocating one voice from each program to every played note and providing five-note polyphony. Alternate mode switched successive notes between the Upper and Lower programs.
The Sequential Circuits Prophet-10 also included programmable detuning between its two five-voice sections, programmable volume, independent octave transposition for the Upper and Lower manuals, Upper and Lower balance control, a Drone function and a Release control that could override the programmed amplifier release time. A three-band programmable equalisation section provided low, mid and high frequency cut or boost.
Two control-voltage pedals could be assigned to functions including oscillator frequency, filter cutoff, amplifier level, volume or Mono-Mod amount. A Program Increment footswitch allowed programs to be advanced without removing the player’s hands from the keyboards, while a separate Release footswitch could control the amplifier release function.
The instrument also incorporated facilities intended to make its considerable analogue circuitry manageable in practical use. A Tune button automatically tuned and scaled all 20 oscillators, while Master Tune provided simultaneous adjustment of every oscillator for tuning with other instruments. An A-440 reference tone could be routed to the output for accurate tuning. Voice Assignment indicators showed which voices were currently active, providing a visual indication of the voice allocation system.
The rear panel provided balanced and unbalanced audio outputs for the Upper and Lower programs individually, together with a mono mixed output. Control-voltage inputs accepted the two pedal voltages, while gate and voltage outputs followed notes played by the Upper program. The instrument also incorporated an interface for the Sequential Circuits Model 800 Digital Sequencer and other compatible equipment. Selectable mains operation accommodated 100, 120, 220 and 240 volts AC.
An optional polyphonic sequencer could be installed either when the Sequential Circuits Prophet-10 was ordered or subsequently. It fitted inside the main instrument and was operated from the lower manual. The system was designed to record performances directly from the keyboard and provided editing, overdubbing, programmable timing and external clock operation. The supplied documentation describes a capacity of 2,500 notes across six memory banks, automatic program changes during sequences, sequence transposition and a built-in microcassette deck for storing sequence and program data.
## Historical significance
The Sequential Circuits Prophet-10 arrived only two years after the Prophet-5 had established a new model for the programmable polyphonic synthesizer. The Prophet-5’s ability to store complete synthesizer programs under microprocessor control was a major step in the development of professional electronic instruments, and the Sequential Circuits Prophet-10 extended that concept into a much larger performance system.
Rather than simply increasing the number of available voices, Sequential Circuits designed the Prophet-10 around two independently programmable five-voice sections. The dual-manual arrangement, separate Upper and Lower programs, layering, alternate voice assignment and ten-voice Single mode gave the Sequential Circuits Prophet-10 capabilities that went considerably beyond a conventional ten-note polyphonic synthesizer. In practical terms, it placed two programmable Prophet instruments under the control of a single integrated keyboard system.
The Sequential Circuits Prophet-10 also demonstrated the increasing integration of analogue synthesis with digital control at the beginning of the 1980s. Program memories, automatic oscillator tuning, sophisticated voice allocation and the optional polyphonic sequencing system addressed many of the practical limitations that had characterised earlier large polyphonic synthesisers.
Its place in recording history was reinforced by its use by prominent musicians and composers. Tony Banks used the Sequential Circuits Prophet-10’s Dual capabilities to construct layered sounds and incorporated the instrument into his early 1980s keyboard setup. A Sequential Circuits Prophet-10 was also part of the synthesizer system used by John Carpenter and Alan Howarth during their early 1980s film work, alongside instruments including the Sequential Circuits Prophet-5, ARP Quadra, Oberheim Four Voice and E-mu Emulator.
With its dual five-octave keyboards, ten programmable analogue voices, four voice-assignment modes, extensive modulation facilities and optional sequencing, the Sequential Circuits Prophet-10 became one of the most elaborate instruments produced during the first generation of microprocessor-controlled polyphonic analogue synthesisers.
Features
- Ten-voice programmable analogue polyphony
- Two independent five-octave keyboards with separate Upper and Lower programs
- Two voltage-controlled oscillators per voice
- 24dB/octave voltage-controlled low-pass filter per voice
- Separate four-stage filter and amplifier envelope generators
- 64 program memories, with 32 programs for each manual
- Normal, Single, Double and Alternate keyboard assignment modes
- Poly-Mod, LFO and Mono-Mod modulation systems
- Programmable three-band equalisation
- Optional polyphonic sequencer with built-in microcassette storage