RSF Kobol Expander

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The RSF Kobol was the French synth company's first compact keyboard synthesizer, certainly inspired by the Minimoog. It is a much more compact instrument than the Modular Model 11 series of synthesizers they had been making thus far. It is a monophonic analog synthesizer with traditional controls, knobs, switches and two oscillators for a good solid analog synth sound. Initally released as a keyboard in 1978, a 3-unit rack-mount system was later released in 1979.


Although it is mostly a traditional analog synth with stable oscillators and lots of knobs that allow you to control the ADS envelope, the filter section and the nice LFO, it did offer some unique features for its time. Most notably, the oscillator waveforms can be continuously swept across for a very cool morph from square to saw to pulse, etc. This, as well as note on/off and other parameters can be controlled via CV/gate. External sounds can be processed through the Kobol filter and envelope sections too.

RSF Kobol Rack Image


The rack version came in four different components. The Kobol Rack (Expander I) was essentially only the VCO/VCF/VCA/LFO sections of the Kobol in a rack module. The Expander 2 was an add-on to the Kobol that added some new processing modules such as ring modulation, sample-hold, and envelope followers as well as extra VCA and LFO modules. The Programmer rack module contained the memory circuits for storing patches and sequencing. And the KM8 was an 8-channel rack-mount mixer. The connections between modules were normalized but could be bypassed by external patches, similar to other semi-modulars like the ARP 2600 and Korg MS-20.


The Kobol looked and sounded great, and was quickly snapped up by the big names in synthesizers of the time. But being a small French company, RSF were never able to truly mass produce these on the same sort of scale that Moog, Arp, Roland or Korg could. Less than 200 Kobol keyboards were made, around 800 Kobol Racks, 200 Expander 2's, 200 Programmer's and only a handful of the KM8's. This makes them quite rare and quite pricey too! They have been used by Vince Clarke, Vangelis, Jean-Michel Jarre, Depeche Mode, Peter Gabriel, and Hans Zimmer.

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Polyphony - Monophonic
Oscillators - 2 VCO's; triangle, square, saw, pulse; variable sweep
LFO - 1 LFO, triangle, square waveforms, rate knob
Filter - 1VCF 24db low pass
VCA - 2 ADS envelopes
Keyboard - None on rackmount, mini-keys on keyboard model
Sequencer - 2x8 steps
Memory - 16 memories
Control - CV/Gate 1 volt / octave
Date Produced - Kobol: 1978
Kobol Rack (Expander): 1979


Thanks to Garmendia pascal for providing information.

Original images from RSF official web site.