Sequential Fourm

Sequential Fourm is a compact four-voice analogue polysynth with Prophet-5-inspired voice architecture, dual simultaneous-waveform VCOs with sync, a 4-pole low-pass filter with bass compensation, a 37-note slim-key keyboard with polyphonic aftertouch, a hands-on Pro-One-style modulation matrix, an arpeggiator with sequencer mode and per-step glide, a feedback drive circuit, 128 presets, USB and full-size MIDI I/O including Thru, mono and headphone outputs, expression pedal input, and a road-ready steel chassis running from a 12 V DC supply at up to 14 W.

Prophet-5 DNA with modern control

Fourm runs a true analogue signal path and follows envelope response curves modelled on the original Prophet-5, so it captures the punch, warmth and musicality associated with classic Sequential instruments while adding contemporary workflow speed. Each of the four voices carries two oscillators that allow simultaneous waveforms, so the player blends shapes for broader harmonics instead of switching between them. Oscillator B switches into low-frequency mode for modulation, and classic hard sync delivers the aggressive, harmonically complex sweeps that define many vintage leads and basses.

Musical filter with bass compensation

The 4-pole resonant low-pass filter tracks and self-resonates with authority. Bass compensation preserves low-end energy when resonance rises, so the player dials in squelch and peak without hollowing out the fundamentals. This behaviour widens the usable range for pads, monos and percussion, from smooth vintage tones to driven, contemporary textures.

Expressive keyboard with per-note control

The 37-note slim-key bed supports polyphonic aftertouch, so the performer shapes individual notes inside chords with vibrato, swells and timbral moves while other notes remain static. Velocity further opens dynamic control, and the compact format keeps the footprint tight for desktop and stage rigs.

Modulation made fast and visual

A Pro-One-inspired front panel puts routing on buttons with colour-coded feedback. The player assigns envelopes, LFOs, aftertouch or velocity directly to destinations such as cutoff, oscillator pitch, shape and more, then reads the patch at a glance. The knob-per-function layout removes menu digging and keeps programming immediate.

Performance tools that invite interaction

The onboard arpeggiator flips into sequencer mode for pattern programming, with per-step glide to shape lines and accents. A dedicated feedback circuit adds aggressive drive and harmonics for cutting leads and saturated bass. Factory content includes 128 presets that cover vintage leads, lush pads, percussive sequences and evolving textures, ready to play or to use as starting points.

Connectivity for modern studios

Fourm integrates into hardware and DAW setups with USB MIDI plus full-size MIDI In, Out and Thru. Audio leaves on a quarter-inch mono main out, with a separate headphone output for monitoring. An expression pedal input maps to key parameters such as cutoff or volume for real-time control. The steel chassis withstands travel, while the included 12 V DC adapter powers the synth efficiently at up to 14 W.

Why choose Sequential Fourm

• Polyphonic aftertouch unlocks true per-note expression on a compact keyboard

• Simultaneous waveforms and oscillator sync create broader, richer analogue tones

• Bass-compensated filter keeps low-end weight even at high resonance

• Hands-on modulation matrix speeds programming and reveals routings at a glance

• Sequencer mode with per-step glide crafts melodic movement without external gear

• Feedback drive adds instant character from subtle heat to full-on grit

• Robust steel build and full-size MIDI I/O suit touring and hybrid studio rigs

• Four-voice analogue polysynth with Prophet-5-style envelopes
• Dual VCOs per voice with simultaneous waveforms and hard sync
• Oscillator B low-frequency mode for modulation duties
• 4-pole resonant low-pass filter with bass compensation
• 37-note slim-key keyboard with polyphonic aftertouch and velocity
• Pro-One-style hands-on modulation matrix with colour-coded feedback
• Arpeggiator with sequencer mode and per-step glide
• Dedicated feedback circuit with aggressive drive
• 128 factory presets for leads, pads, sequences and textures
• USB MIDI plus full-size MIDI In, Out and Thru
• Quarter-inch mono main out, headphone out, expression pedal input
• Rugged all-steel chassis, 12 V DC power supply, max 14 W consumption

This item, like everything we supply, comes with the complete support of our expert team. Our excellent technicians have been specifying, building and supporting studios for over twenty years. If you have any problems with installation, setup or everyday use, they’re never more than a click away, and always happy to help.

You can contact them here.