Building a modular synth rack is the ultimate hands-on experience for musicians. It allows us to create our own unique instrument and get real hands-on with the modelling of our sound.

Modular synthesis has seen a resurgence in popularity in recent years. It was once the hobby of the most dedicated hardware synth engineers, but the barrier to entry is far lower than it used to be and the seemingly daily release of weirder and more wonderful modules can make a newcomer feel overwhelmed.

The hardware itself, even when assembled, often required detailed knowledge so the user could maintain it regularly to get the most out of them and avoid destroying its system. Those without a sufficient bank of money and an understanding of electrical engineering and sound synthesis… designing and building their own modular synth was more of a fantasy.

But times have changed and building a modular is no longer a fantasy that a minority can have. In this guide, we’re going to talk you through how to build a modular synthesis. We’ll examine what Eurorack and other jargon phrases mean, different types of modular gear and what some basic modules are.

What Does Eurorack Mean?

In the 1990s, Dieter Doepfer created Eurorack as a regulation for modules. Eurorack ensures we can be confident that our modules, racks and cases would fit together if we bought them from different manufacturers.

Modules with the Eurorack label on the tin all share the exact same height of 128.5mm/5.06″, but do have varying widths. “HP,” which stands for Horizontal Pitch, is the unit of measurement for module width. 1HP = 5.08mm/0.2″.

The method used to mount each Eurorack module in our rack are always the same module mounting method is also the same for all modules, as well as the method for power distribution to individual units through a standardized ribbon cable.

Thanks to the standardisation that Eurorack brought, We use 3.5mm tip/sleeve (TS) patch cables to route audio, control, and synchronize connections from module to module (otherwise known as patching), and parameter control via control voltages is now universal.

And that is Eurorack summed up. It’s one of the reasons why the barrier to entry to building modular synths is now so much lower. If everything is universal and works together by design, we no longer need an understanding of electrical engineering.

What is a Semi-Modular Synth?

If you’ve never even touched a modular synth but have a keen interest in learning, why not dabble with a semi-modular synth?

Modular synths are a great opportunity to understand how patching works. Semi-modular synths are complete systems that contain input/output jacks for control voltage and audio. They allow you to re-patch their sound and modulation paths and change how they work, as well as patch them to other hardware unis and discover unique sound possibilities!

You can get both poly and mono semi-modular synths. What you get should depend on what you need. Are you looking to make bassy sounds? A mono synth will do the job, but if you’re looking to make some chords then a polysynth will be your desired synth.

Now that we’ve explored the potential of a semi-modular synth and what Eurorack actually represents, shall we jump into the meat of the article?

Plankton Electronics Ants Semi-Modular Analogue Desktop Synth, Source: guitarguitar

What Modules Do I Need to Build a Basic Modular Synth?

You’ve Got the Power!

The first building block to your modular synth always needs to be a power supply. Without power comes no sound.

Not only power but also a case. You can find powered cases, but we’ll cover power supply modules for the time being.

For beginners, we don’t recommend going for anything that requires you to undertake any complex wiring. Investigate power supplies that offer quick and easy integration so you can get on with the fun stuff all the more quickly.

Like when building a custom PC, take note of the requirements of your power supply. Eurorack’s has centralized standards that have helped to reduce the likelihood of damaging modules, but damaging modules does still remain a risk.

Measured in Amps, each module draws a certain amount of power from your power supply. This power will be drawn from either the +12 volt, -12V or +5V outputs of your power supply, so you need to be aware of what power your modules require and be sure that the power needed by your modules is less than the total amount of power provided by your power supply. Should you need help with this, ModularGrid can help you plan your modular synth and calculate what modules need what power.

A lot of power supplies come without a wall plug, but some don’t. Check this when browsing and buy one separately with amp and voltage ratings that match with your power supply if needed.

Something to take note of also is the power connections between your modules and your power supply. If your modular system has the correct power levels, you can actually short-circuit your modules if you plug them in the wrong way round… which isn’t something we recommend.

Many manufacturers adhere to the Eurorack standards, including a red stripe that marks the -12V supply on each module’s power cable. They also include keyed connectors which actually prevent you from plugging modules incorrectly. But be cautious because not all of them do.

Always check the power instructions for each module. Be sure that you’ve matched the positive and negative connection for each module to those of your power supply before you plug anything in.

Tiptop Audio uZeus Micro Power Supply

For beginners, we recommend the Tiptop Audio uZeus for your power. It features keyed connectors, it doesn’t take up much space with a 4hp width and can power up to 10 modules.

You can daisy chain additional power cables together for a bigger case, but the uZeus can deliver up to 1.5 amps of power. This is enough for smaller to medium racks (which depends on how power-hungry your modules are).

Usually, the uZeus doesn’t come with a power cable so you will need to get one separately.

What About Powered Cases?

But maybe you’re not so keen on buying a separate power supply from your case. It’s obvious that a powered case makes life easier and will save space in the case itself. Well then, let’s look at powered cases…

Options here have grown exponentially in the past few years, with a lot more manufacturers selling their own cases with their range of modules.

To put together a strong modular system, aim for a case with at least 84hp of width.

Tiptop Audio Mantis 2x104HP

Tiptop’s Audio Mantis case brings two rows of 104hp in width that has keyed connectors for 36 modules!

This may be a lot of space that you don’t necessarily need, but buying a case with more space than you need is only saving you money down the line.

Delivering up to 3 Amps of power, the Mantis is the first choice for those looking to future-proof their modular synth or those looking to expand it!

Generate Some Sound!

Voltage-controlled oscillators are our sound source. In the same way that oscillator functions on a VST synth such as Serum, VCO generate a repeating signal that we can route to our other effects.

You could choose from a range of analog or digital oscillators, but oscillators aren’t the only sound source you could run through your oscillator.

Available to you are also sample players, drum modules, or even external audio sources.

Mutable Instruments Braids

Braids is probably one of the most popular oscillators in Eurorack, and it’s digital.

If you’re looking for a digital sound with a powerful array of functions in a compact unit, Braids is the oscillator for you. Although it is expensive, it provides a lot of bang for your buck.

Braids feature over 40 individual waveforms, including simple square waves to complicated FM synthesis sounds. Not only this but percussion sounds and polyphonic chords.

It features modulation inputs that allow for evolving patches, and it also features a built-in quantizer to lock its output to specific musical scales if and when needed.

Triggers and Gates

As well as an oscillator, you can use a controller or a MIDI keyboard, as well as hardware like a sequencer to generate signals that trigger your modules into action.

You can grab yourself a MIDI to CV interface and then use MIDI data via your computer to send different information to your modular synth.

Such information can include trigger, pitch, and gate information!

If you don’t want to get your computer involved, you can actually incorporate a hardware sequencer into your Eurorack system.

Example of a Eurorack modular, Source: Intellijel

Signal Processors Allow You to Shape Your Sound

So, we have the modules to generate and shape our sound. But how can we control the sound?

If you were using an oscillator, you’re not going to get much out of the repeating signal unless you apply some processing to it…

There are a plethora of ways to generate CV that adjusts our VCF and VCA parameters. But, as we briefly touched on, two of the frequently used methods are Envelopes and LFOs.

Filters (VCF)

Voltage-controlled filters allow you to cut different frequencies of the oscillating signal. This in turn gives you the frequencies that you want to work with. Filter modules also come with time-based modulation effects too. Basic filter modules may only remove frequencies as if you were undertaking subtractive synthesis, but others allow you to modulate the filter at 1/2, 1/4, 1/8 and other intervals!

High pass, low pass, and bandpass are filter modules that allow you to manipulate their parameters using voltage inputs over time.

An example of an affordable VCF module is the Behringer Multi Filter/Resonator.

It’s worth noting that a lot of the character of a synthesised sound comes from the sound generators and the filters!

Amplifiers (VCA)

We use filters to manipulate the tone of our synth over time. But we use voltage-controlled amplifiers to control the volume of our synth!

Without a VCA, you would actually end up with a drone sounding oscillator that has 0 variations in volume. These get boring pretty quickly.

An example of an affordable VCA is the Doepfer A-130-2 Dual linear VCA.

But, with that said, you can actually modulation sources like Envelopes and LFOs to manipulate the volume of your synth over time. This makes VCA’s less important, but still handy if you’re looking to have direct control over the volume of your synth.

Envelopes and LFOs can control volume either constantly or when triggered by a clock or sequencer, or maybe even an instrument input.

Modulation is in the Name

Envelope Generators

An envelope generator creates a one-time modulation control voltage whenever it receives the go-ahead.

The CV changes based on parameters such as Attack, Decay, Sustain, and Release (ADSR).

But this is just one type of envelope generator. There are also envelopes that use Rise and Fall, as well as other variations of the voltage level changing over time.

An example of an affordable Envelope generator is the Behringer System 55 911 Envelope Generator

Low Frequency Oscillators (LFOs)

LFO’s oscillators oscillate at much lower frequencies. So much lower, in fact, that you can actually hear the movement they generate.

LFOs create ongoing changes over time. Unlike envelopes, they continuously oscillate rather than when than just one time once triggered.

An example of an affordable LFO module is the Doepfer A-145 LFO Modulation Generator

You have control over parameters such as rate and depth, as well as shape! There are other parameters that give your VCFs and VCAs other controls too, but we’re only covering the basics!

Mixers and Clocks

It’s time to wrap up this article of basic modular units with the boring, but necessary, stuff…

You’ll need to consider how you’re going to attenuate the level of your Eurorack signal to a line level so you can hear it through speakers or send it through a headphone amp or send it through signal into your computer via an audio interface.

If you have an advanced setup, you may need a mixer module to combine multiple signals together.

If you wanted to control the timing of multiple modules at once, you could look into a clock module. The more you experiment with your modular, you will find that there are tools that would come in handy. You’ll discover that you need this and that over time, and there is probably a module that does what you need!

There are modules that bring a premium sound at an affordable price. That too is our mission.

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