Behringer Kobol Expander Synthesizer

Behringer Kobol Expander — Duophonic Analog Synthesizer with Morphing Waveforms

The Behringer Kobol Expander is a duophonic semi-modular analog synthesizer built around two voltage-controlled oscillators that continuously morph through seven waveforms. Drawing on the original French RSF Kobol from 1978, this instrument revives the saturated tone that defined late-1970s European electronic music. A 4-pole low-pass VCF shapes every sound with natural warmth that made the original a cult favorite. With 32 patch points and an 80 HP chassis, the synth fits any modular rig or stands alone as a desktop voice.

What Sets This Synth Apart

Unlike most analog synths that lock you into fixed waveform selections, the VCOs sweep continuously from sine through sawtooth, triangle, square, narrow pulse, wide pulse, and white noise without stopping at preset positions. A built-in voltage processor lets players scale or amplify any incoming CV signal — a feature rarely seen at this price tier. White and pink noise outputs can be routed into the filter or used as modulation sources for evolving textures.

Two Analog Oscillators for Duophonic Voice Architecture

Two fully analog voltage-controlled oscillators run independently, each with its own waveform control, fine tune, and hard sync routing. Oscillator sync unlocks harmonic-rich timbres, while pulse-width modulation adds movement to static tones.

• Polyphony: 2 voices (duophonic) — two notes sound simultaneously for intervals or layered basses
• Oscillators: 2 × analog VCO — independent tuning, sync, and seven morphing waveshapes per oscillator
• Pitch Bend: Not available — pitch controlled via MIDI or 1V/octave CV only

4-Pole VCF, Single LFO, and ADS Envelopes

The 4-pole (24 dB/octave) low-pass filter is specific to the original Kobol architecture, with resonance climbing into self-oscillation while preserving natural low-end weight. A single analog LFO drives cyclic motion, and two ADS envelopes sculpt the attack and decay of every note.

• Filter: 4-pole 24 dB/octave low-pass VCF — resonance and dedicated drive input for saturated tones
• LFO: 1 × analog LFO — square and triangle waveforms routable to pitch, PWM, filter, or external CV
• Envelopes: 2 × ADS — Attack, Decay, and Sustain stages with individual CV inputs

Eurorack-Ready Connectivity and Poly Chain Expansion

The 32 patch points expose nearly every internal signal for external routing, and the housing removes cleanly for installation in any standard Eurorack case. Poly Chain links up to 16 units for 16-voice polyphony, while USB-B and 5-pin DIN MIDI keep the synth talking to modern and vintage gear alike.

• Patch Points: 32 × 3.5 mm CV/Gate jacks — modulate nearly every parameter from external sources
• Outputs: 3.5 mm TS, 6.35 mm TS, USB-B, MIDI Thru — plus a 3.5 mm headphone output on the top panel
• Form Factor: 80 HP Eurorack module — dimensions approximately 424 × 136 × 94 mm, weight 1.65 kg

Ideal for Modular Explorers and Vintage Synth Enthusiasts

This synth is the right choice for electronic musicians, sound designers, and modular explorers who want the saturated character of a 1970s French synth without the vintage price tag. Players building a Eurorack system will appreciate the 32 patch points and removable housing, while desktop users get a complete duophonic voice with no patching required. Beginners can dial in basses and leads from the front panel, while experienced patchers unlock deeper modulation chains through the CV matrix.

The RSF Kobol Legacy Reimagined

The original RSF Kobol was a French synthesizer released in 1978 by the boutique manufacturer based in Saint-Étienne, designed as an affordable alternative to the Minimoog. Its keyboard version found its way into studios across Europe, including those of Depeche Mode, Vince Clarke, and Daniel Miller. Behringer's reissue preserves that patch-heavy architecture while adding USB MIDI and Poly Chain support.