Let’s take a look at the particulars of the eurorack format and setup I’m using.
Have you heard the Stranger Things soundtrack, or a Trent Reznor soundtrack, or R2D2’s voice? Then you’ve heard modular gear (it is also found in millions of other musical places). Basically the format revolves around the following concept: it enables sound synthesis in a completely flexible way, through a series modular building blocks that create and alter sound in a very hands-on and configurable way. So one module creates the core sound (a VCO), another module adds or removes frequencies to that sound (the VCF), and another changes the volume over time (VCA) to result in different musical impact. You connect and control these different modules with wires that carry electrical signals where changes in Volts are mapped to functional changes in the module. The wires could be carrying audio signals, control voltage signals (CV), or other digital signals….but at the core they are all falling within a particular voltage range and so you could connect an audio output into a control voltage input without breaking anything – you just might not get the sound you’re expecting. In control voltage, the basic idea is that if voltage is high something happens, and if voltage is low something else happens. More on this later.
Modular synth gear comes in several different formats. Moog 5U like their System 15, which began in the 50’s and uses 1/4″ jacks like telephone switchboards did, Doepfer/Eurorack 3U which is a scaled down version of Moog’s 5U using 3.5mm jacks, 4U Serge, etc.
For my eurorack I went with the Doepfer 3U format because its currently the most prevalent, and also a great balance between size, functionality, and price.
I built the case myself, and you can see the process about building the eurorack case itself: build thread here.
I did a decent amount of research on this front both because I’m kind of a power snob both from experience designing and building project recording studios where clean and well-laid-out power is essential, and also from building relatively complex guitar rigs where the same is true. So I kind of over-indexed on high quality power for this build. There are a few considerations to take into account.
Type. There are two types of power supplies: switching and linear. I’ll spare you the electrical details and summarize it as switching supplies are smaller and cheaper but can be guilty of adding noise to your modular system, and linear supplies are more expensive, much larger, sometimes hotter, but when done correctly are much cleaner sources of power.
Voltage Supplied. The Doepfer Eurorack power spec indicates the supply of three direct-current voltages: +12V, -12V, and +5V. These three different types of voltages are useful to module designers, and it helps keep the module sizes minimized by providing all three voltage types from the power supply instead of requiring the module to include regulators to scale the power. Most DIY power supplies don’t include the +5V power, but I had a few modules that needed it (more on that later) so I wanted a supply that had it so I didn’t have to fool with getting it some other way (like a stepdown daughterboard that converts +12V to +5V, etc).
Maximum Current. Any power supply has a finite amount of current it can reliably deliver. In terms of electrical outlets in your house, this would be like “how much stuff can I plug up to my wall outlets before my circuit fuse blows?” In eurorack terms it wouldn’t blow a circuit fuse, it would just “starve” your modules of current to the point that they don’t work correctly or at all. So you need a power supply that is capable of providing the amount of current you need for the modules you want to have. How do you know what the current draw is? I knew you’d ask. You build a layout of your modules at ModularGrid.net. This is both an indispensable tool for planning any eurorack build, and also a great resource for finding new modules and collaborating with others on eurorack info!
After considering the above, and using this awesome comparison guide here, I decided that the Metatronic Mods DIY PSU was the one for me. It checked all the boxes: a linear power design, all the voltages I wanted, a good amount of current, a convenient DIY circuit board with a mouser shopping cart with all the parts you need, and a well-written build guide. Perfect!
The Building Block Modules
Ok now the hard part. A challenge with modular systems is that you become your own synth designer. So if you don’t know much about sound synthesis you’re either going to learn or you’re going to spend a lot of time experimenting (and probably not understanding what is coming out and how to control or influence it).
The building block modules are those modules that provide the core functionality and character of the sound that will come out of your modular system. I think about these in a few groups of functions. Really, you benefit from having these building blocks proportionally represented in your setup. If you have a dozen voices but only one modifier tool, you are probably limiting your sound palette.
Clocks. Long story short, music usually has a tempo in beats per minute (BPM). In eurorack, one or more clocks creates this BPM.