The Sequential Fourm is a compact analog synthesizer that invites you to play, shape, and perform with unprecedented expression. Combining legendary Sequential tone with hands-on modulation and a uniquely responsive Tactive™ keybed, Fourm serves as a creative partner that brings your musical ideas to life with authenticity and nuance.

At its heart, Fourm delivers four genuine voices of Sequential analog sound, built on the legendary Prophet-5 voice architecture—right down to its characteristic envelope response curves. With dual oscillators offering simultaneous wave selection and a classic 4-pole low-pass filter with bass compensation, Fourm captures the warmth and punch that shaped a generation and takes it to the next level.

Authentic Analog Voice Architecture

Fourm's analog voice path is built around a modern oscillator chip inspired by the design used in the original Prophet-5 Rev 2. It delivers the same rich, musical tone as its vintage predecessor, now enhanced by the benefits of contemporary engineering—improved stability, reliability, and consistency. This creates the perfect foundation for Fourm's 100% analog sound.

The analog 4-pole lowpass filter chip is based on a classic design known for its rich, organic tone and musical resonance. The modern implementation faithfully preserves that sonic character while adding bass compensation, allowing you to crank the resonance without sacrificing low-end power—keeping your sound full, bold, and unmistakably analog.

A New Form of Expression

From its solid steel chassis to the custom-engineered Tactive slim-keys keybed with responsive polyphonic aftertouch, every element of Fourm was designed to deliver a fully integrated, high-performance playing experience. It's a no-compromise, all-analog instrument built for the next generation of synthesists.

Custom-designed by Sequential, the Tactive™ keybed features 37 slim-keys tuned specifically to complement Fourm's analog synthesis engine. For the first time in 40 years, Sequential has returned to polyphonic aftertouch—an incredibly expressive performance feature that brings per-note articulations to your fingertips.

Polyphonic aftertouch is one of Fourm's most expressive features, offering a direct and nuanced connection between your playing and per-note synthesis parameters. It opens up new possibilities for articulation—from subtle dynamics to dramatic gestures—including note bends, arpeggiator accents, volume and filter shaping, and independent timbral control. These capabilities go far beyond what's possible with other high-performance musical instruments and controllers.

Hands-On Modulation

Fourm's modulation section is inspired by the legendary Sequential Circuits Pro-One, a highly sought-after classic monosynth that has propelled the bass lines of synthpop for decades. The Pro-One style top-panel modulation matrix offers immediacy and flexibility, featuring two modulation buses with multiple sources and destinations and the ability to combine both buses at the destination. Explore this hands-on approach and let your latest sonic inspirations take Fourm.

Creative Sequencing Power

Tucked into the arpeggiator section, Fourm's polyphonic step sequencer is a creative powerhouse. Yes, it can play back musical phrases—but it can also be used as a modulation source, perfect for triggering rhythmic filter patterns and more. With support for chords, ties, rests, Acid-style per-step glide, and deep modulation routing, the sequencer transforms Fourm into a dynamic, hands-on composition tool.

Technical Specifications

Sound Generation

• Polyphony: 4 voices
• Architecture: 100% analog signal path
• Oscillators: Two Prophet-5 lineage analog oscillators per voice
• All oscillators feature simultaneously selectable waveforms, including the LFO
• Oscillator B supports low frequency modes for use as polyphonic LFO modulation
• Classic Prophet-style Sync
• Variable square wave pulse width per oscillator (PWM)

Filter

• Type: 4-pole resonant lowpass filter drawn from the Prophet-5, revs 1 & 2
• Bass compensation for thick sounds even with high resonance
• Filter can be driven into self-oscillation with the resonance control
• Filter keyboard tracking: Quarter, half, full
• Feedback with an aggressive drive circuit for extra edge

Noise Generator

• Types: White, pink, and violet noise for greater sonic variation

Envelopes

• Filter Envelope: Four-stage (ADSR) for tone shaping and assignable modulation
• Amp Envelope: Four-stage (ADSR) for volume shaping
• Velocity modulation of envelope amounts for dynamic performance

LFO

• Configuration: One global LFO for creating movement in the sound
• Waveforms: Seven shapes - sine, sawtooth, reverse sawtooth, square, S/H (sample and hold), noise, and DC
• Four LFO wave shapes can be selected simultaneously for complex modulations
• LFO can synchronize to tempo at different step values

Modulation

• Modulation Matrix: Pro-One style top-panel modulation matrix
• Two modulation buses with multiple sources and destinations
• Ability to combine both buses at the destination
• Top panel modulation sources: Filter env, oscillator B, LFO
• Top panel modulation destinations: Oscillator A frequency, oscillator B frequency, pulse width A, pulse width B, filter cutoff, amplitude, LFO frequency, LFO amount

Polyphonic Aftertouch

• Up to six polyphonic aftertouch destinations selectable simultaneously
• Destinations: Oscillator A frequency, oscillator B frequency, filter cutoff, amplitude, LFO frequency, LFO amount

Performance Features

• Polyphonic glide (portamento)
• Unison mode: Monophonic mode with configurable voice count (one to all four voices), plus chord memory
• Vintage setting: Recreates classic synth characteristics by adding voice-to-voice variations in component behavior
• Pitch wheel: Spring-loaded with selectable range per program (1 to 12 semitones up and down)

Sequencer & Arpeggiator

• Arpeggiator with step sequencer mode
• Polyphonic step sequencer: Up to 64 steps with rests
• Supports Acid-style glide per step
• Sequencer can be used as a modulation source

Keyboard

• Tactive™ keybed: 37-note slim-key keyboard with polyphonic aftertouch
• Custom-designed by Sequential, tuned specifically for Fourm's analog synthesis engine

Controls

• Intuitive, knob-per-function layout

Connectivity

• Audio outputs: Main output mono (1/4" jack), Headphone output mono (1/4" TRS phone jack)
• MIDI: In, out, and thru ports
• USB: USB-C for bidirectional MIDI communication
• Control inputs: Footswitch/expression pedal input (also supports trigger and gate signals)

Power

• Power supply: 12V DC 1.2A, center-positive (included)
• Compatible with AC outlets: 100V to 240V at 50Hz/60Hz
• Separate power switch
• Power consumption: 14 Watts maximum

Construction

• Chassis: Pro-quality, all-steel construction
• Dimensions: 22.13″ L × 9.88″ W × 2.75″ H (56.2 cm × 25.1 cm × 7.0 cm)
• Weight: 8.76 lbs (3.97 kg)