Behringer Kobol Expander Synthesizer

Behringer Kobol Expander — Duophonic Analog Synthesizer with 7 Morphing Waveshapes

Built around two analog VCOs that morph continuously through seven waveshapes, the Behringer Kobol Expander is a duophonic semi-modular analog synthesizer inspired by the rare RSF Kobol from late-1970s France. It revives the saturated character that made the original a favorite of Vince Clarke, Daniel Miller, and Depeche Mode. The Kobol Expander is the right choice for players who want genuine 1970s analog tone with modern semi-modular flexibility.

What Sets the Kobol Expander Apart

Unlike most reissues that lean on standard 3340 oscillator chips, this model uses a discrete transistor architecture with TL04 op amps and V13700 OTAs to emulate the original RSF tempco wave generators. The unique 4-pole "Kobol" VCF produces the natural saturation that gives the synth its voice, while 32 CV patch points open up modulation routings beyond a typical semi-modular.

Two Analog VCOs with Continuous Waveform Morphing

The dual VCO architecture gives players two independent voices to layer, sync, or detune. Each oscillator sweeps through seven waveshapes on a single continuous knob, so the timbral shift from triangle to sawtooth to PWM happens in real time.

• Polyphony: 2 voices — duophonic layering from two independent VCOs
• Oscillators: 2 analog VCOs with seven morphing waveshapes and oscillator sync
• Pulse-width modulation: Yes — built into the waveform morph for evolving PWM tones

4-Pole Kobol VCF, LFO, and ADS Envelopes

The 4-pole low-pass filter is the heart of the Kobol sound, adding the warm saturation that distinguishes it from standard ladder designs. Modulation sources include an analog LFO with two waveforms, two ADS envelopes, a noise generator with white and pink outputs, and a voltage processor for scaling control voltages.

• Filter: 4-pole VCF with resonance and natural saturation character
• LFO: 1 analog LFO with two selectable waveforms and multiple destinations
• Envelopes: 2 ADS envelopes for shaping amplitude and modulation

Eurorack-Ready with MIDI, USB, and 32 Patch Points

Designed to drop into a standard Eurorack case, this unit ships with a ribbon power connector and removable housing. The I/O covers vintage and modern setups with 5-pin DIN MIDI in and thru, USB-B, a 3.5 mm headphone output, and a 6.3 mm main audio output.

• Inputs: MIDI IN via 16-channel 5-pin DIN
• Outputs: 3.5 mm headphone, 6.3 mm jack, USB-B, MIDI Thru
• Patch points: 32 CV patch points for semi-modular and Eurorack patching

Who Should Buy the Behringer Kobol Expander

The Kobol Expander is the right choice for synth players who want the character of a rare late-1970s French analog at a home-studio price. It suits electronic musicians exploring duophonic bass lines and leads, plus Eurorack builders who want a discrete analog voice with deep modulation routing. Players with a MIDI sequencer will appreciate the built-in MIDI and USB-B, while modular users can integrate it via the 32 patch points.

The RSF Kobol Legacy

The original RSF Kobol was a French boutique synthesizer produced in very small numbers, with the keyboard version arriving in 1978 and the expander following in 1979 as a more affordable Minimoog alternative. RSF instruments — including the Kobol and Poly KB — found their way onto Depeche Mode and Vince Clarke recordings. The Behringer reissue revives that lineage with discrete transistors emulating the original tempco wave generators.