Sequential Fourm – compact analog synthesizer for a new generation

Sequential Fourm is a 4-voice, fully analog synthesizer built on the legacy of the legendary Prophet-5. It blends classic Sequential sound with modern features such as the Tactive™ keybed with polyphonic aftertouch, a hands-on Pro-One-inspired modulation matrix, and an intuitive knob-per-function layout. Designed for expressive playability, Fourm is equally at home in the studio and on stage.

Main Features

• 4 true analog voices
• Prophet-5 heritage architecture with classic envelope response
• 2 analog oscillators per voice with simultaneous waveform selection
• Classic 4-pole low-pass filter with bass compensation
• Tactive™ 37-key slim keybed with polyphonic aftertouch
• Hands-on modulation matrix inspired by the Sequential Pro-One
• Built-in arpeggiator with 6 modes + 64-step polyphonic sequencer
• Durable all-steel chassis – compact and portable

Oscillators and Synthesis

• Two Prophet-lineage analog oscillators per voice
• Simultaneous waveform selection
• Oscillator B can function in low-frequency mode (as LFO)
• Prophet-style oscillator sync
• Pulse width modulation (PWM) per oscillator
• Noise sources: white, pink, violet

Filter and Sound Character

• Classic 4-pole resonant low-pass filter (Prophet-5 Rev 1 & 2)
• Resonance can be driven to self-oscillation
• Bass compensation ensures strong low end at high resonance
• Keyboard tracking options: 1/4, 1/2, full
• Feedback/drive circuit for added edge and aggression

Envelopes and Modulation

• Two ADSR envelopes: one for filter, one for amplitude
• Velocity modulation of envelope amounts for dynamic expression
• 1 global LFO with 7 waveforms:
  • Sine
  • Sawtooth
  • Reverse sawtooth
  • Square
  • Sample & Hold
  • Noise
  • DC
• Up to 4 LFO shapes selectable simultaneously
• LFO sync to tempo at multiple subdivisions

Pro-One Style Modulation Matrix

• Two modulation buses with multiple sources and destinations
• Panel sources:
  • Filter envelope
  • Oscillator B
  • LFO
• Panel destinations:
  • Oscillator A & B frequency
  • Pulse width A & B
  • Filter cutoff
  • Amplitude
  • LFO frequency and amount
• Polyphonic aftertouch with up to 6 destinations simultaneously

Arpeggiator and Sequencer

• Arpeggiator with 6 modes
• Functions include relatching, repeats, step values
• Range up to 3 octaves
• Polyphonic step sequencer with up to 64 steps, featuring:
  • Chords
  • Rests
  • Ties
  • Acid-style per-step glide
• Sequencer can also function as a modulation source

Voice Modes and Expression

• Unison mode with configurable number of voices
• Chord Memory – store and recall chord voicings
• Vintage setting introduces subtle per-voice variations for organic feel
• Polyphonic portamento (glide)

Tactive™ Keybed

• 37 slim keys designed for expressive play
• Full support for polyphonic aftertouch
• Engineered specifically for the Fourm’s analog engine
• Enables individual note articulations and nuanced control

Construction and Interface

• Professional-grade all-steel chassis
• Compact dimensions: 56.2 × 25.1 × 7.0 cm
• Weight: 3.97 kg
• Knob-per-function interface for immediate access
• Spring-loaded pitch wheel with configurable range (±1 to ±12 semitones)

Connectivity

• Main mono output (¼″ jack)
• Headphone output (¼″ TRS)
• MIDI In, Out, Thru
• USB-C for bidirectional MIDI communication
• Footswitch/expression input (supports trigger/gate)
• Power: 12 V DC 1.2 A (supply included)

Why Choose Fourm?

• True analog signal path with Prophet heritage
• Rare polyphonic aftertouch capability
• Immediate hands-on control – no menu diving
• Portable yet rugged for stage and studio
• Rich modulation and sequencing options

Conclusion

The Sequential Fourm is a modern analog polysynth that combines the soul of classic instruments with cutting-edge expressive tools. Compact, powerful, and intuitive, it’s the perfect choice for musicians seeking direct connection to sound without compromise.