Eurorack Synthesizer
Author’s Current Eurorack Synthesizer

Introduction to Eurorack.

Listen to this generative music composition called “The Seagull and the Walrus”. There are 3 individual components: a beach sound, a strumming sound and a bass part in the background. All of the parts are played simultaneously yet it is done with just a few modules.

  • A noise module
  • A digital voicing generator
  • A second digital VCO
  • A delay and feedback loop
  • An multi-channel LFO
  • An output mixer

So 6 modules is all it takes to make a three part music composition. In fact, there are many artists who can do musically interesting things with less. This is the power of a modular synthesizer. Modular synthesizers, specifically in the eurorack format, have an incredibly wide sound pallet for experimentation, sound design and composition. This is not to say complex, multipart music can’t be performed on a 5u system, after all there is Tonto!

Large (Moog or 5U) format modular systems are too expensive for the average person to start building. A large format 30 module system can easily hit $50,000 or more. Yet a moderately sized eurorack synthesizer with 30 equivalent modules, could be had for just under $7000 or even much less if you buy used. Additionally the space required for the eurorack will be much less as it can fit on a small desk. Eurorack can also be installed into separate cases to provide some portability. Lastly are patch cables. You will need a lot, at least 50 or more of various lengths for a moderately sized modular. Larger formats use 1/4″ phono jack patch cables, and they are very expensive. Eurorack uses 3.5mm (1/8″)  phono jacks, available on ebay, amazon or any supplier for much, much less.

I wrote this article to help introduce some of the issues I faced when thinking about building my own eurorack system. I already knew how synthesizers worked,  I understood how large analogue modulars, desktop polyphonic synthesizers, and recording studios all worked. Eurorack though, offers many more ways get into and the lost in a myriad of choices, marketing hype, technique and sometimes just plain nonsense.

Where to start.

Why do you need a modular system? This is a serious question and will save you some time, money and frustration. If you just want to play house or techno music as a DJ, then turn back now and get a DJ production rig. If you are still serious, then note that some of this article will have terms that you may not be familiar with, but are essential for understanding many of the components and modules. If you are really new to music synthesizers, then a brief background can be learned through a few sites.

For this article, I am going to focus on the decision process I made and not offer a course on music synthesis or modular synthesizers. The people in the links above and others have done a great job in providing learning info already.

The first choice: Voicing

A simple voice in modular synthesis is comprised of a source, filter, envelope and amplifier. So, something to make a sound->something to change the depth of the sound->something to modify the length of the sound->and something so you can hear the sound. In a synthesizer, this could consist of 4 individual modules:  VCO (source), VCF (filter), Envelope Generator and a VCA (Amplifier) which are patched together to form a specific sound. A voice can also come in a single module, with all of the components pre-patched much like a monophonic standalone synthesizer. You can even have both schemes, a couple VCOs, VCA, Envelopes and filters as separate modules and one or two complete voice modules.

Second Choice: Analogue, Digital or both.

I am not going to debate the “analog vs digital” opinionators (yep, another word I made up), out there on the web. The debate is pure nonsense and takes your focus away from creating music. There are pros & cons in using both, there may be some overlap, but that would be minimal and both audio types will contribute to enhance the sound pallet. With that in mind, voicing schemes can implement signal paths in pure analogue or digital (or even both). Because I have so many analogue synthesizers, I decided at first, to consider digital voices and VCOs. I then selected some additional digital and analog filter modules to go with them. Note: In the end of my putting a system together, I added a couple analogue VCOs and an analog voice module.

Third choice: What else do I need.

Voicing gives you the sound and you could go off and make music, but it may sound tonally flat, dead or just blah. You are going to need some method of mixing the levels of your sounds and making it more alive through some effects like delays, reverbs, modulators, etc. These can also be analog, or digital, and come as a single module or even as a multi-effect processor module.

You are also going to need some LFOs and modulation sources to provide timber and other nuance to your sound. Utility modules allow to copy control signals, adjust levels of these signals, provide timing, noise and interface with other devices or synthesizers or trigger signals. Finally, a case and power supply will be required to put the whole thing together and ensure each module can be powered up.

The Korb Pusher triggers signals by touching a pad.

Fourth choice: Who’s brand (what manufacturer) should I use.

Technical note: If you can put a PC together, that is buy the case, power supply, and circuit boards, you should have no issues assembling a modular synthesizer. You are basically plugging standard connectors together and ensuring you don’t short out the modules.

Module Installation can be as easy as ‘Plug & Play”

You can buy an entire modular system from a single manufacturer. In fact, some manufacturers offer them already assembled, ready to go. Alternatively, you can buy various components from any number of manufacturers. Eurorack is a standard that manufacturers are supposed to adhere too, but they don’t always. Since I like the DIY aspect and wanted to start with digital voicing, I decided that I would look toward Mutable Instruments. Mutable Instruments has been one of the largest influences in bringing music synthesis to the masses.

All of Mutable’s designs are open source and anyone can freely use, modify, build and even sell under your own brand, any one of their designs. Several desktop synthesizer projects on this site are designed by Mutable, so building some Mutable eurorack modules was a great choice. Mutable also offered their own assembled version through retailers. Since 2022 however, Mutable Instruments has ceased operations. Its founder and creator just wanted to pursue something else.

Digital Voice Module

With all that, I purchased the circuit boards for the Elements and Rings modules through synthcube, and my initial voicing was now selected. Note here that you can still get them, fully assembled, from anywhere a google search will take you. Again in the end, I changed my mind about doing the whole process as DIY. Component shortages slowed up the process and I thought more about supporting the module designer’s efforts, so most of my modules were purchased assembled. 

Back of the Rings DIY module

Digital VCO & Resonator

I also liked the Intellijel brand. I tend to support manufacturers by locality first. city, province, country, continent. Since I am in the same country as Intellijel and I wanted to use portable cases for performances, I chose to use the intellijel performance case. I also considered Intellijel for most of my utilities, including:

For additional digital modifiers, I chose to go back and consider Mutable Instruments for them:

Finally, I considered the following additional modules from other manufacturers:

Planning it out

Once I had these ideas, I needed to plan more in depth and required someway of ensuring all these modules would fit in the case I wanted. For this, we can turn to Modular Grid. This is a fabulous tool that lists almost every module you can get, both recent releases and older unsupported versions should you want to purchase used modules. I used this extensively to plan the layout. You choose a case and then select and drag the modules you want onto the case image, move them around and adjust how they fit. It even provides overall power consumption for power considerations and costs for your budget. Modules can also come with different or custom panels. Even though the modules on Modular Grid may not have your exact panel, the module specs (size, power, price) are what is most important. Several of my modules on the Grid don’t match the ones I actually have.

Filling the case, playing and more planning.

Within 6 months of my conception, I had one case partially filled with enough modules I could start composing music and really trying to understand the functionality of each module. This is the most important aspect in a successful outcome: Know what each module does, what effect it has on inputs and what functions it performs. Then. if you need another VCA, utility or clock or you need an extra sound source, you can add. My process was focused toward putting together two 15 minute performances. Digression time!!

There are two ways you can design a  “Modular Performance”.

  1. Preconceived & fully patched. Come up with an interesting composition. once it is wired up take a photo of all the wires, switches and knobs incase someone changes it. Practice changing parameters and develop the composition’s flow. Then pack it all up as is, without unplugging too many wires, and off to the show you go. Many shows are done like this, and it allows you to focus on your composition and give the audience a perfect performance.  Face it, synthesizer shows that are ill conceived or unrehearsed can be very boring. Which brings us to the second way to can perform flawlessly.
  2. Practice patches and memorize compositional themes. Some performances start with a clean slate. A totally unpatched synthesizer. The artist arrives, sits behind his/her machine and starts plugging in wires, turning knobs, throwing switches generating musical bits and bobs, all evolving into a fabulous composition. “Wow” you ask yourself. “Was that just made up”? Well,  yes and no. They just know their synthesizer and have practiced a long time on it. They have memorized specific patches and know what the outcome will be and even what an audience will like. It is much like a chess master who has memorized dozens of moves and countermoves based on board position. They know what the outcome will be.

Your first time on a clean slate synthesizer, without preconditioned notions, will be just like everyone’s first, second or hundredth time. It will start with bleeps & bloops, cats screaming, fart noises and uninteresting things. Only with patience, practice and a bit of luck do you develop a cool idea that you can build on. Time is the key. You need to spend time on your modular and your music. Anyone who tells you otherwise is full of donkey doo doo. Digression, over.

That is the basis for me choosing to utilize a portable case system, and after 18 months of building, buying, and playing, I had filled two cases with modules!

Author’s bottom case on Modular Grid


Author’s top case on Modular Grid

What to do when you have more modules, than case or rack space?

That is where things can go aria. If you look at image above of my top case, there is an analog voice module called ‘Atlantis’. This module is about 1-1/3 larger than my original ‘Elements’ digital voice card. For a specific performance I will swap out the analog for the digital, and visa-versa. Basically I am satisfied that I have enough modules that I stopped getting more. I have 4 that don’t fit in the case, but I will swap them out when needed. I forced myself to use what I have, rather than try the “next big thing”. Many people just keep buying larger racks, more modules, more racks, more modules, etc. And that’s ok if you just want to focus on modular synthesis. Some people’s eurorack systems are huge!

This article became larger than I originally wanted, and we could still go on, but I am going to end this here. You need to thing about this whole thing, investigate other people’s opinion and develop your own process. There are/will be many more articles on the site about controllers, MIDI, utilities, connectivity, etc. They will be available through the landing page or menu above. I wish you much enjoyment.