Digisound 80 aka Modular Beast

There is an old-skool 'Digisound 80' synthesizer at LAG:

Originally built at the 'Synthese Studio' in Maastricht in the early 80's it was used for a lot of experimental work on audio and visual performances.

It needs some love, but mostly functions. Although many of the labels are worn and many of the knobs and ports are undocumented.

You are welcome to come to the lag to play with this beast from the past!

As the machine is in a fragile state we are in the process of renovating it.


The Digisound modular synth was published in the 80's by Charles Blakey. Some of the modules were described in two British electronics magazines - Electronics Today International (ETI) and Electronics & Music Maker (E&MM). A digital reference for the Digisound 80 system can be found here.

One of the filter modules originates from the 70's electronics magazine 'Elector' (or 'Elektuur' in the Netherlands). A reproduction of the original Elector articles with designs and explanation can be found here.

The Modules

Power Supply

A rather straightforward +/- 15V power supply. We removed the cable-spaghetti in the back and made a powerbus, which has the following pinout:

+15V      0V     -15V     0V
| O   O   O   O   O   O   O   O |
| O   O   O   O   O   O   O   O |
      0V    -15V      0V     +15V

So that's a 16-pin plug with +15V at the sides, -15V in the four middle poles, and ground inbetween. It's symmetric, so it's impossible to plug it the wrong way around.

Unknown control module 1

Likely used for external sequencing with an old 8bit computer.

Unknown control module 2

Likely used for external sequencing with an old 8bit computer.

80-10 VC Envelope Generator (ADSR)

A CEM3310 voltage controlled envelope generator.

Quad VCA I

A Quad VCA module, using both a CEM3330 and a CEM3360.

The CEM3330 part (the two VCA's on the left) looks quite similar to the project 80-9 module, with some changes around the AM and Exp inputs. The exact working remains a mystery thus far.


Looks identical to Quad VCA I.

VCO (project 80-2/3) (3x)

CEM3340 based VCO with a switch to turn it into a VCLFO (project 80-3).

VCF (project 80-7)

Labeled PROJECT 80-7 on the PCB, it has 'State Variable Filter SSM2040' handwritten on it.

IC's: LM13700N , SSM2040 (careful: unobtainium), TL072CP (2x), TL081CP

More documentation on the Project 80 VCSVF page.

VCF (project 80-6)

Labeled PROJECT 80-6 on the PCB, it has 'VC LPF' handwritten on it.

IC's: CEM3320 (careful: unobtainium), TL071CP , TL072CP

More documentation on the Project 80 VCF page.

Processor, likely project 80-5

Clock divider

Formant filter