Sequential Circuits Prophet-5 (1978–1984)
Five voices, forty memories, and a microprocessor in an analog polysynth.
Overview
Forty patches. That's twenty factory presets and twenty user-defined, held in memory by a microprocessor that Dave Smith designed into an analog polysynth. The Prophet-5 was the first truly programmable polyphonic analog synthesizer. It's remembered as the most classic synthesizer of the eighties rather than a curiosity of 1978.
The architecture underneath is modest. It has five voices, two oscillators per voice, selectable sine, triangle, sawtooth and square/pulse waveforms, and a 24dB/oct resonant low-pass filter (plus 12dB/oct high-pass) that can self-oscillate. Two ADSR envelopes, one for the filter and one for the amplifier, and a single LFO with triangle, square and sample-and-hold waveforms round out the modulation.
The keyboard is 61 keys, velocity and aftertouch sensitive. That was not a given on a 1978 instrument, and it's still the part owners mention first when they talk about feel. Every parameter has a dedicated knob or slider. There are no digital displays and no layers to dig through. The physical package is 38.5 x 14.5 x 4.5 inches and 36 lbs, powered from an internal supply at 100-120V AC, 60 Hz. Measured performance is respectable for the period: frequency response of 20 Hz - 20 kHz (+/-1 dB), THD under 1% at 1 kHz, signal-to-noise greater than 80 dB, and a maximum output level of 10 Vpp into a 1 kΩ output impedance.
It sounds like five voices of dual-oscillator analog synthesis, warm and gritty. It defined the sonic palette of an entire decade, and engineers would reportedly leave it powered on for weeks just to avoid retuning.
Key Features
Microprocessor-Controlled Patch Memory — 40 Patches
Smith's approach was to embed a microprocessor into an analog synth to store and recall settings. Before the Prophet-5, polyphonic synths like the Yamaha CS-80 existed, but they were temperamental and had no reliable way to save sounds. You'd sculpt a patch and lose it at power-down. Forty memories (20 factory, 20 user) turned the polysynth from a laboratory instrument into something you could take onstage. It was the first polyphonic synthesizer with fully programmable memory.
Two Oscillators Per Voice, Five Voices
Each voice carries two oscillators with selectable sine, triangle, sawtooth and square/pulse waveforms. Ten oscillators across the keyboard give the Prophet its thickness: detuned pairs for pads, stacked unison for leads, single-oscillator patches for basses that need to stay defined. Five voices is not a lot of polyphony by later standards, but the voice architecture is the reason the instrument is still sought after four decades on.
24dB/oct Resonant Low-Pass Filter with Self-Oscillation
The filter is a 24dB/oct resonant low-pass with a 12dB/oct high-pass alongside, and it will self-oscillate, so it can be played as a sine source when you push the resonance. Early revisions used discrete components. The shift to Curtis CEM chips in Rev 3 improved stability. The filter is described as CEM 3320-based, and it's the part of the signal path most often cited when owners argue about which revision sounds best.
Two ADSR Envelopes and a Sample-and-Hold LFO
One ADSR handles the filter and one handles the amplifier. That's standard architecture, but the envelopes are fast enough to snap and slow enough to breathe. The single LFO offers triangle, square and sample-and-hold waveforms. Sample-and-hold is the one that turns a static pad into something that moves.
61-Key Velocity- and Aftertouch-Sensitive Keyboard
Sixty-one keys with velocity and aftertouch sensitivity, on an instrument from 1978. Dynamics can shape filter cutoff or amplitude in real time. The keybed is also the first thing to check on a used unit - see the collectibility notes below.
No MIDI — Stock, By Design
The Prophet-5 has no MIDI. It predates the standard, which emerged in 1983. Studios adapted with custom control-voltage solutions at the time. Modified units with aftermarket MIDI do circulate on the used market, but those are modifications, not factory spec, and should be priced and evaluated accordingly.
Historical Context
The Prophet-5 was designed by Dave Smith and John Bowen in 1977 and introduced in 1978, produced through 1984. Its success spawned the Prophet-10, a 10-voice machine made by stacking two Prophet-5s, and later the Prophet-600, which added MIDI. By the time Rev 3 rolled out in 1981, the Prophet-5 had become the gold standard for analog polyphony, influencing everything from the Roland Jupiter-8 to the Korg Poly-800. Monosynths of the era, like Sequential's own Prophet-1, couldn't offer the polyphony and recall the Prophet-5 did.
The instrument's recording credits include Michael Jackson's Thriller sessions, Toto's "Africa," and Vangelis's score for Blade Runner. Period advertising from Sequential Circuits positioned the Prophet 5 as the instrument that "took the industry by surprise" and had become "the new keyboard standard," with the company claiming near-universal adoption among major keyboard players. That's marketing copy, not a verdict, but the independent press of the period treated the machine as a serious compositional tool. Modern Recording (November 1980, p.23) pitched the Prophet 5 at both the largest automated 24-track studio and the smallest home setup, calling it an excellent instrumental investment for sound capability and creativity, and noting that its sounds could be subtly reshaped - longer attacks, brighter or darker - to suit personal taste. Mix (November 1980, p.25) ran Sequential's own family advertisement in the same season, positioning the Prophet 5 alongside the new Prophet 10 and the Model 700 programmer.
Collectibility & Value
Desirability is rated very high; rarity is uncommon. As of 2025, prices range from $8,000 to $15,000 USD depending on revision, condition and service history, though the market is wider and messier than that band suggests. Recent eBay listings have run from roughly $3,240 for a 61-key unit up to $29,999 for a fully restored Rev 1 with MIDI, with Rev 2 and Rev 3.3 examples landing in the $8,000 range. Treat listing prices as approximate. They're snapshots, not appraisals.
Revision matters. Rev 3 models are often preferred for their superior tuning stability and Curtis CEM 3340 VCOs, though some purists swear by the raw character of the Rev 1's discrete oscillators. Early revisions, Rev 1 and Rev 2, are notorious for tuning drift, a result of analog component drift and temperature sensitivity. The CEM 3320 filter chips can fail, and decades-old electrolytic capacitors often need replacing. A thorough service means recapping, calibration and voice card inspection, and it is not optional on a machine this age.
Buyer advice: look for units with clean keybeds, responsive aftertouch, and stable pitch across all five voices. A unit with its original carry case and manual is a minor bonus.
eBay Listings
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