Interface with EMS Synthi A

After a long time of not being busy with real electronics due to the move of the whole orgnisation to the new building – it has a hugh impact – I slowly see more time for being busy with my core activities: make new instruments and electronics.

For one of our teachers, who owns a EMS Synthi A (see picture), I created a setup to be able to interface with the CompLex module.

A short quote from Wiki:
“The EMS Synthi A and the EMS Synthi AKS are portable modular made in England. The Synthi A model debuted in May 1971 and then Synthi AKS model appeared in March 1972 a with a built-in keyboard and sequencer. The EMS Synthi models are notable for its patch pin matrix and its functions and internal design”.

EMS Synthi A

The Synthi A has a pin-matrix but also a 32-pin connector that is directly connected to the 16 ins and outs of the matrix (located directly under the pin-matrix). Instead of connecting the pins to the matrix, I created a first version of a connector that is directly connected to the CompLex matrix. So instead of placing the pins in the matrix we can change the setup with OSC and software!

Connector version 1
Synthi A Connector pin-out
CompLex Matrix with Synthi A connector

I’m looking forward to the first test results!

Simple LFO

Design by Ray Wilson:

Lately more students ask for an oscillator that is capable of generating real low frequencies, a so called Low Frequent Oscillator (LFO). So I made a simple and small LFO.

LFO with frequency range from 500Hz – once every miniute

If I have to look for a good design circuit related to synths, I always visit the website ‘’ with designs from Ray Wilson. Great designs! For an more extended explanation and circuit description, please check this page: The only thing part that I did not implement in my version, is the LED and the extra capacitors making the power supply ‘smooth’.

I made a real small version, since it had to be placed into a really small housing. Instead of the switches, I used two jumpers, changing the frequency-range and the waveshapes..