EMS Synthi A – Eurorack

Overview Back in 1977 when I had by first proper job as a computer operator at the University of Essex, and I nearly got a loan of their VCS3, but I got by bike stolen and had to to move to London before I got to try it out. I was mad keen on the sound of the VCS3 and Synthi A(KS), and all my most loved records had it playing. My Minisonic 2 from 1974 had a similar kind of out of tune diode filter sound, and I played that for a few years until I moved to the USA in 1979.

I never came across a cheap Synthi in my analog collecting years in the 1980’s and only briefly played one in the 1990’s. Fast forward to 2010 and I built the Snowfall filter which was very popular and by 2014 I started to collect components and PCB’s for a VCS3.  It turned out to be one of my most difficult projects to get moving on, never mind completing. A set of PCB’s, rare transistors, a 20×20 way patch panel ratted around in a box for more years than I care to count.

Project Re-started In late 2020 I dusted off the box of bits and gave up on the idea of making a prototype looking VCS3 with its wooden cabinet or a Synthi A in a suitcase. I have a new form factor in mind, a Euro Rack Tiptop Mantis case. The PCB’s just fit in between the rails, so all I need is a set of front panel PCB’s and the front panels. A modern Synthi A, which would not take long to build…

Design The front panel follows the Synthi A design but with some minor changes. The meter is in the center top with output jacks. The patch panel is in the lower row, with joystick, reverb and output channels. There is space for a couple of speakers as well.

Modifications Here is a list of all the upgrades and changes I have made, based on a a set of three Phutney PCB’s:

  • Dumped the X board, a rubbish power supply and I have no room for a spring reverb.
  • Fitted the Y and Z boards to new PCB’s that hold the pots.
  • Fully buffered 20×20 Ghielmetti patch panel.
  • Added voltage controlled resonance.
  • Added switch for VCF lag on/off
  • Added an extra capacitor at base of ladder filter.
  • Recreated the Output Tone, Level and Pan controls on a new PCB
  • Added an ARP S&H circuit.
  • Added modern Class D power amps to drive the upgraded speakers.
Copyright AMSynths 2019