The Sister Card for EMS Synthi A / AKS / VCS3

New Portabellabz expansion card for the Synthi A and AKS, mostly intended for the experimental Synthi playing but not only, it's able to create crazy droid sounds as well as subtle modulations.

The card simply plugs directly into the 8 pins Jones "keyboard" socket and is powered by the Synthi, no cables no connector, it's plug and play, easy and hassle free.
For use with a VCS3, the Jones plug can be mounted onto the top side of the PCB but an adapted umbilical cable with swapped connections is requested, the standard cable won't work.

Warning : the card's power consumption is close to 50mA on each -9V/+12V power rail, which is the maximum a MK1 PSU can handle according to the VCS3 MK1 users manual.
It *should* work with factory condition MK1 units but will push this old PSU to the limits. I assume no liability in case of problem (anyway, it can be repaired, no worries).
 An extra PSU can be added to MK1 units to power a KS / TKS keyboard and the Portabellabz expansion cards, here are the details.

Features :

Thick PCB for best stability and solidity

2 identical LFOs
Bipolar signal
Square output
Triangle output
Variable shape of both waveforms / fine tune
Hi/lo range switch
Lowest frequency : +/- 25 seconds cycle
Highest frequency : +/- 90Hz
Frequency LED

Sample & hold
Clocked by either LFO (3 position switch 1 - off - 2)
Sample input via the meter column
Slew limiter with rate pot and lin/log response switch
Normal CV output
Slewed CV output
Clock LED

2 identical CV modulation busses
Individual level pot for each output of the LFO's and S&H
Left bus CV routed to input channel 1
Right bus CV routed to input channel 2
Mixed output CV inverter switch
Level LED

2 attenuverter pins
Scale and invert signal

Gate output
Fires the Synthi's envelope generator by either LFO (3 position switch 1 - off - 2)

Handle support
Small plates can be mounted to the back to lock the Spartanite case's handle for better stability.

It is possible to add a female socket onto the top side of the Sister Card.
The card's and KS (or Kenton type Jones-jack sockets cable) CVs are mixed passively via the 100k resistors present on the card's CV outputs and in the KS cable to modulate the incoming CV. Gates from the keyboard and sequencer, from the card and from the Synthi's EG self-retrig are mixed.
With all the card's pots set to 0 and the gate switch in central position, the incoming CV/gate signals are not impacted.

The DIY PCB set costs 120 EUR shipped tracked.
It includes PCB, panel, Jones connector cover and handle support (I do not supply with other parts).

Users manual


BOM and build notes


A pre-built Sister Card costs 380EUR VAT and shipping excl.
Contact me to join the waiting list.


Many thanks to Yoshio Machida for the video