Modular Synthesiser Project

 Back in the '80's, when I was still at college, studying for an HND in Electronic Engineering, I built a modular synthesiser. I loved listening to electronic music, Like "Switched on Bach", by Walter Carlos, and realised that it was possible to create circuits to make these sounds.
I was inspired by a book called Electronic Synthesiser Projects by M.K.Berry, published by Bernard Babani - though I would not recommend that you use the book yourself, because it is complete rubbish. Almost none of the circuits will work as printed, and it was the source of great frustration. 

Electronic Synthesiser Projects - Bernard Babani BP81
The book is also missing any circuit for a voltage-controlled filter - which is a big omission in my view!

However, I did manage to make some of it work, and added many other circuits and ideas that I gleaned from magazines and text-books (no internet back then!). The project taught me an enormous amount about op-amps, as almost all the classic op-amp circuits are used somewhere in an instrument such as this.

Here is a photo of the modular synth in 1987. The modules are 8 inches high, and 1/4" jack sockets are used for patching. From left to right: dual Voltage Controlled Oscillator VCO (you can only see half of it in the picture), ADSR envelope generator with a Voltage Controlled Attenuator, Low Frequency Oscillator, Voltage controlled delay (using a bucket brigade delay line chip), and a 2/4 pole voltage controlled filter. In addition there is a home-made mixer to the right and the power supply is the wooden box, beneath the corner of the bench. 

I modified the Hohner Symphonic 65 drawbar organ so that it provided a Control Voltage output at 1V per octave, from the white part of the keyboard, and also the standard 12V trigger signal when a key was pressed. Although I made an attempt at an exponential input to the VCO, unfortunately it was neither very accurate or temperature stable, and was not really in tune over more than an octave. I had more success musically, by using the organ as an oscillator and feeding that waveform through the modules - although the two VCO, were very good for creating weird sounds and for FM modulating each other.

Eventually, I acquired other keyboards and discovered Yamaha FM synthesis and MIDI sequencing. The Hohner was sold and the synth dismantled and put up in the loft.

Earlier this year, on a day out in Ramsgate, we visited "This Museum is not Obsolete", which is curated by Sam Battle.

This Museum is (not) obsolete

I spent a happy time playing all the wonderful instruments that he has there, and feeling nostalgic for my own modular synthesiser! Sam Battle, aka "Look mum no computer" has a Youtube channel, and is also a musician who performs using his own, home-constructed, modular synthesiser. Look Mum No Computer on Youtube

Following links on the internet, I discovered that there is a very active community of enthusiasts building and playing home-made synths. Modwiggler Forum

Sam's "Cosmo" synthesiser that he performs with, has 20cm high panels, and 1/4" jacks very much like my original design. But I just don't have the space for something like that. I wondered if I could rebuild the modules that I had kept into the smaller "Eurorack" format. So I cut down the cabinet to accommodate 128.5mm high panels, and set about making some new front panels out of an old sheet of aluminium that I found in the garage.  

So here is the project so far. On the left is a new module which generates a control voltage and trigger pulses for test purposes. To the right is a dual Voltage Controlled Oscillator (not the original, I decided  to build a new one - the old one was a bit of a mess), then there is a 3 input mixer circuit, the original Voltage Controlled Filter, the original ADSR envelope generator, and finally a new module that has a second Voltage Controlled Filter and a noise source. I still have the Voltage Controlled Delay circuit which needs putting on a new panel, but the old Low Frequency Oscillator is lost - so I will need to build a new one.

I already have a big long list of possible new modules to add. But for the time being I am having great fun making some very satisfyingly weird (if not very musical) sounds.