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Modification kits for EMS Synthi

The kits come assembled, tested and ready to install. I do not offer spare PCBs only for these.
All modifications are at your own risk and I assume no liability for personal injury or damage to equipment or loss of use caused directly or indirectly by the use of any of the kits. Although the installation is quite simple it should only be performed by those experienced in electronics.

Sustained/transient external gate push-pull pot
Transforms any external gate signal into a short trigger.
When pushed, the envelope behaves as normal.
When pulled, the "on" time depends on the knob setting only and is not related to how long you press your keyboard key, very useful for snappy envelopes.
Works with both keyboard Jones socket and jack (if installed) gate inputs
Mounted in place of the "on" pot.
A LED fills the former anti-rotation hole and shows the mod is active.
Comes with detailed installation schedule for the kit and for the optional jack gate input mod.

80 euros including worldwide shipping.

Installation into a Synthi A needs to temporaly remove the reverb tank


I play the KS in normal position, you can see the notes length depends on howlong I keep my finger on the key, then I pull the knob and the notes length is independent and fixed.
Second part is the same with a sequence.

Trapezoid polarity push-pull pot
Controls the trapezoid output polarity.
When pushed, the trapezoid behaves as normal.
When pulled, the trapezoid polarity is inverted.
Mounted in place of the "trapezoid" pot.
A LED fills the former anti-rotation hole and shows the mod is active.
Comes with detailed installation schedule for the kit.

80 euros including worldwide shipping.

Inverter pins PCB
2 pins are wired to an inverter circuit and can be used to invert the signal polarity.
Comes with detailed installation schedule for the kit and grey shielded cable for the pins.

45 euros including worldwide shipping without the pins.

120 euros including worldwide shipping with 2 pre-wired pins.

Installation needs to slightly enlarge 2 pin shaft holes of the pin park for the cable


First with the trapezoid polarity control push-pull, then with a normal pin and the inverter pin.
Trapezoid controls osc 1 frequency and is patched to scope out.
I don't change the pin patched to the scope out, so you can see that with the push-pull the signal is inverted before to be patched and with the inverter pin it's inverted when it's patched, you can patch the inverted signal to a destination and the normal signal to another destination at the same time.

Simple Random Voltage Generator / Sample & Hold

It uses 2 push-pulls on both noise pots.
As long as the mod is not enabled by pulling the push-pull pot, the Synthi works exactly as unmodified.

2 wiring options are possible, more details and demos here.

Demos direct from the phones out of my Synthi A :


Thanks to Really Nice Audio for the video

The kit costs 150 euros and includes
- populated and tested ready-to-install PCB mounted to the 2 push-pull pots
- clear and detailed installation instructions for both possible RVG and S&H wiring
- cables and cable ties for the connections
- worldwide registered shipping

Kit for VCS3


Kit for Synthi A and Synthi AKS

rvg/sh pcb