Restoring EMS Synthi AKS, Museu de la Música de Barcelona

The restoration of the EMS Synthi AKS from the Museu de la Musica de Barcelona has been completed. Yes it is not an ARP instrument, but I feel a deep connection with this instruments and I love to work at this kind of restorations. After many Synthi and VCS3 restorations this was so special.

It has been around 2 months of intense work to restore this historical piece that belonged to the Phonos Foundation and now is part of the museum.

The unit was in non working condition from many years, mostly all parts were working bad or non functional at all. The shape was considerable good taking in consideration the age and use during the Phonos years, used for musicians and artist of the foundation.


About physical restoration it was mostly clean the dirty and some stain of paint drops in some areas. The most intense work was to restore the vernier knobs, not only the clean an lubrication process but especially the oscillator 1 vernier that was with a beat damage, that need to repair the internal mechanism from bent pieces and align it again. A handcraft clockwork job.

Also replace some old rusted or damaged screws. It seems that this unit was previously serviced, due to the sign of manipulation of the screws and head damages. This also was confirmed when checking at some areas like power supply and reverb area, were signs of cut traces and de solder/resolder signs appeared.

Lot of polarized capacitors were with leakage and out of specs, so need full recap to repair and prevent future failures. Also most of the trimmers were working bad, so time to replace with new ones. At same time looking to resolder some cold joints.

All active components were safe fortunately. The Reverb amplifier driver was without the classic heatsink so probably since the last service it was working without the proper cooling part. Fortunately the amplifier still works so we installed a proper heatsink for protect the valuable chip from overheat and damage.

This unit was using the matched transistors in metal can, but not using tempco resistor, so we made the bulletin suggested thermal compensation and also replacing for better capacitors at the oscillator timing circuit. Now the oscillator can keep tuning nicely for long time, and using multiturn trimmer can adjust the VCO tracking perfectly for very musical tracking for 5 octaves or more. This modification keeps the wonderful sound and behaviour of the instrument and adds the interesting feature of keep the tuning and musical scale for more tonal purposes.

All the potentiometers and electro mechanical parts need intense clean, also the card connectors contacts and pcbs. Also the pin matrix connections and some pins need clean and some crackled joints of the base and the pin. It was a dirt of so many years. All the parts now works smooth and free of noises. Added 4 extra pins that was missing, now the instrument have all the pins at the pin holder. Also all the pin holder surface must be replaced with new one for keep the pins safe during use, because the old surface lost all the retain feature.

After the intense restoration and repair of the Synthi A part is time to the calibration process. The units responds so nice to the calibration procedure and is a pleasure to finish it as it was from the first day of the factory.

The KS part was so intense too. Cleaning the case and the pcb with care and proceeding also with the proper recap process, and detecting some defective film capacitors. We detected many cut traces and solder marks from previous service works, most not done in very elegant way… Using hi grade turned sockets for place the valuable chips of this historical piece. Some TTLS were dead or non working, so time to replace it and taking care in some areas that need the vintage series for work properly. Repairing some cut traces and checking the memory stage. The unit was working weird at the record function so we spend a time checking the rare memory chips MF7104. Fortunately we have stock of this old parts and can replace the dead memory chips.

Resoldering cold joints and cleaning the very rusted cinch jones PCB connector. Clean the dial potentiometers and replacing old and defective trimmers for proper adjusting.

Now the units works so nice with the original behaviour, time to make the proper “On the run test” at the Synthi

With all the AKS finished only need to make a keyboard cable of 1,5 meters that allows better distances and ways of use instead the classic short cable.

Time to return to the museum and be ready not only for exhibition but also for the use of different artist and musicians, this kind of instruments should be keep running and available for show the unique sound and beauty that can bring so people can understand and feel why after 50 years this instruments are so valid for creating art today and also explain many things of the evolution of the electronic musical instruments and the impact at the music. This Synthi AKS is really a piece of art by itself. Is really crazy when you notice the amount of hand work dedication and idealism that is behind of the construction and design of an instrument like this.