Modular Synth – An Introduction

As an electronic engineer and amateur musician, I’ve become fascinated with electronic music. More specifically, at how analogue electronic circuits can produce, filter and shape a variety of different signals to create sounds and music. This inspired me to begin building my own synthesiser from scratch, assembling together the circuits and controls used to generate my own electronic music. I have included some pictures of my progress below!

Building a synthesiser rather than buying a pre-assembled one has several benefits; first of all, it is significantly cheaper! For example, a simple voltage-controlled oscillator (VCO) Eurorack module usually costs at least €100, while the components for a DIY version can often be sourced for less than €20. But more importantly, building a DIY synth helps you to understand exactly how each circuit works and how it influences the overall sound. Once you become familiar with how a circuit works, you can also begin adding your own extra features and quirks! There is quite a large DIY synth community where people show off and share their own designs. For me at least, I find that building my own synth is just as much fun as trying to make music with it once it is complete.

What is a Modular Synth?

Synthesisers are devices which can create sounds and music from electronic circuits. A sound can be created very simply by generating an oscillating electrical signal, which is varying at a frequency which we can hear (usually between 20 to 20,000Hz). By changing the rate at which this signal oscillates we control the pitch of the tone, while the volume can be controlled by adjusting the peak-to-peak voltage of the signal. Diagram 1 shows what changing the volume and pitch of an sinusoidal signal looks like. However, generating a basic signal is only the starting point when using a synth! By combining multiple signals and filtering them in weird and wonderful ways, it is possible to create some truly unique sounds and music.

Basic synthesisers have multiple functions hardwired together to give you a specific type of instrument and tone. Modular synths are special, because each unique musical operation is broken out into a separate device/module. For example, you could have one module to generate an initial waveform (oscillator), then one to change the tone of the sound (filter), followed by a module to control the volume (amplifier). Each module has an audio jack for every input, output and control signal, allowing you to automate and change the way in which the module operates. This allows you to hook up the modules in a large number of different ways! Diagram 2 shows one way in which 4 common modules can be linked together to produce music.

So what does the result sound like? I’ve attached an early video of my DIY modular synth below, showing a demo tune I put together to see if all of the modules were working. I have since added some extra modules to my synthesiser, which I will talk about in a later post. At the top of the box is an 8-step sequencer which is used to control the pitch and duration of each of the notes. On the left (blue) is a single oscillator which can produce three different types of waveforms (sinusoid, triangle, square), as demonstrated at the start of the video. Finally, next to this is an amplifier (grey) which can control the volume of each of these waveforms. It is interesting to hear all the different types of tones which this basic synthesiser can produce, without needing to introduce any filtering.

Up next in this Tutorial Series…

As I continue building and improving my own DIY synth, I hope to post several tutorials describing various electronic circuits commonly used to create music. Using a variety of diagrams and practical demonstrations, I will try to show how each synth module affects the audio signal. I will also try and model parts of the circuit mathematically, to illustrate the process and consideration made by the designers when developing the designs. Here is a list of the modules I have already built, and may discuss in my future tutorials:

• Dual +-12V Power Supply
• Voltage Controlled Oscillator (VCO)
• Voltage Controlled Amplifier (VCA)
• 8-step Sequencer
• Attack, Decay, Sustain and Release module (ADSR)
• Voltage Controlled Filter – Low Pass and High Pass (VCF)