MATRIXSYNTH: RSF Kobol Expander

Tuesday, February 18, 2020

RSF Kobol Expander


via this auction

"Rare semi-modular rack mount mono synth, made by the Fernandez Brothers Ruben & Serge, in France between 1979-82. Only 800 units are estimated to have been produced.

This functions as a standalone synth, unlike the Expander 2 which offers additional features for the Expander. I sold my Expander 2 many years ago to a buyer in Spain under my redstartradingltd eBay user ID.

For recent feedback see the Oberheim DMX sold a year ago on this account & other high end audio items.

The Kobol Expander was serviced by synth Prof Andy Jury back in 2014 for which I have a pdf copy of the receipt but would benefit from another service for calibration as below.

VCOs #1+2, VCF, LFO, both ADS#1+2 Envelopes and the output VCA are all working & so it can be used 'as-is' but VCO#2 would benefit from a proper calibration as the range was up outside of the audible scale. I have now manually tuned VCO#2 to match VCO#1 with trimer.

NOTE: All features work and I will make a demo video tomorrow to upload to YouTube for reference.

It is in overall good cosmetic condition, with some minor marks to the face plate and more around the holes on either side where it is rack mounted, though those can’t easily be seen when racked of course. It was given a new rear case/housing as the old one did not comply with modern mains safety requirements within UK/EU. However the fit is not snug to the face plate so there is a small gap of around 1/2 cm whenj looking from above, though which can't be seen when racked but has been shown in the photos for clarity. Also there are 2 x caps missing from the SIFAM type collect knobs as can be seen in pictures on the left section for Voltage Processor, which was never used by me.

Please view all pictures for full cosmetic details, as these are in support of the item condition description.

NOTE: You will need a suitable CV+Gate source - keyboard/sequencer, etc. to operate & play this synth. One lead to Gate IN and one for CV IN V/Oct are the minimum requirements to hear the synth, with a single 1/4" jack for the audio output.

That is not provided with this sale but simple & cheap sequencers are now plentiful. As it is rack mounted, the Kobol Expander interfaces easily with other modular gear including the Eurorack variety provided suitable cables are used, ¼” to 3.5mm jacks, etc.

Note also that the filter on this can process external audio as mono & it’s the most liquid filter I’ve ever heard, including comparisons to the Moog ladder type, Oberheim state variable type & Sequential Prophet Curtis chip revisions. The SSM2040 filter is the same as in the early Rev1+2 Prophets. That along with the super fast response times of the ADS envelopes makes this a very unique sounding analog synth, with wave-morphing oscillators controllable by hand or CV & notably with a host of other parameters for CV control of modulation signals; VCOs, VCF, VCAs, etc. In total 15 parameters offer external CV control & there is also an external audio input to the VCF/filer."


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