Building a modular synthesizer

This is the current state of my modular synthesizer.

And here are some sounds it makes:


For those of you unfamiliar with modular, it’s essentially a configurable electronic instrument. For example, depending on the configuration, it could sound like a piano or it could be a an all-in-one techno machine.

Modular has multiple major formats. The format dictates the size of the modules and the power configuration. Right now, Eurorack is the most popular format. If you’re planning to get into modular (or you hate having money), Eurorack is likely the way to go as there is a HUGE variety of interesting modules.

The format I build is the Kosmo format – a format I learned about after stumbling across Look Mum No Computer. Kosmo modules are 20cm high and use Eurorack power supplies. This means they play nicely with Eurorack. You can learn more about it on this website or its corresponding forums.


You might be wondering what a module is. A module essentially a single circuit that does very specific funtions. Here is an example:

This is a photo of three oscillator modules before I completed them. An oscillator module outputs a tone (wiggly voltage) that can be manipulated by other modules to make interesting sounds.

I built another module called a Microkosmos (based on the Music Thing Modular’s Mikrophonie module) that I added a doorstopper to. I use it very often as a way to control other modules. Here’s a weird video showing it off featuring furby samples and other weird stuff:


I was particularly drawn to Kosmo modules because I rather enjoy the build and they are cost effective. Sam (Look Mum No Computer) and a few others from the forums have made PCBs and front panels available to purchase. That means all I needed to do to start off my modular is order the components and assemble the module. It also is somewhat less expensive than purchasing Eurorack modules, which can be hundreds of dollars for a single module.

I started the build around March when Sam started putting more modules for sale. I picked up a few oscillators, a filter, the electronic components necessary for the modules, and a power supply. Then it was time to get soldering. I ended up testing them like this:

Once I had the modules and power supply working, it was clear I needed a case. I took some old rotting plywood and build a case that is designed to be 80cm wide and 40cm tall. This means, it would be two rows tall and could accommodate sixteen or so modules depending on the size of the module. I liked the aesthetic of the aged plywood so I didn’t sand it or anything. I just added a handle and some rubber feet. Here’s how it looks now:


So far so good, here. Almost everything I build comes with a BOM (Bill Of Materials). That means, for the most part, I’m just painting by numbers. Really. It’s fairly straightforward. When I do my next build, I’ll hit the record button and you can see. If something doesn’t work, it can take a little debugging, but if it doesn’t work, it’s usually something silly.

As for the power supply, that build was no different than the modules. I started with the FCUK Microbus kit. It does the job. I have been using two per case, but I suspect that might be overkill.

It is important to test every eurorack cable you get or make. It’s also important to make sure things are plugged in the right way around. mylarmelodies has a video on the topic because it’s likely the biggest cause of magic smoke in Eurorack.


I will admit, the up-front cost per module is pretty high when starting out. As I progressed and accumulated a range of components, the cost per module dropped dramatically. For example, the last three modules I ordered only cost around $30 – $40 each + shipping. I only needed a few new components in addition to my usual resistors, capacitors, etc. I suspect the average cost at this point is likely between $80 and $150 per module, but I don’t really know. That said, I’ve learned a fair bit since I started to help keep the cost down.

Tips to keep the cost down:

  • Avoid Amazon. Yes, you can get the thing in two days, but it’ll cost more and you’ll get less.
  • Source locally from component providers. There is an extensive list of component sources on the forums. In the US, Tayda and Mouser are my go-tos for most things.
  • Buy in bulk. This seemed counter intuitive to me, but saves so much money down the road. Especially with common components like opamps or knobs. This also goes for modules if you’re in the US and ordering from the UK (Sam’s store). Shipping is expensive. Order a few at a time.
  • Buy one of the boxes of resistors of multiple vales. Do the same for both ceramic and electrolytic capacitors. There’s no reason to try to buy resistors one value a time. You’ll go crazy.
  • eBay is a great source for harder to get components or used gear. Just make sure to look at the seller rating. Sometimes there are faulty ICs for sale there.
  • Start saving old electronics and electronic toys. They could make a rad module or pedal down the road.


  • Invest in some way to sort/store components. I have space so I used a parts organizer case. I have seen folks also use slimmer organizers to go into drawers or under desks.
  • It can’t hurt to learn some basics about circuits and components. You really don’t need it to get going, but it will certainly help if you run into issues. This video is a rad overview of components.


If you’re interested, I’d probably watch a bunch of Look Mum No Computer videos starting with some of the DIY videos like “Build A DIY Case And Power Supply For A Modular Synth CHEAP.” (side note: pay attention to the measurements if you build a case so you don’t end up with one that’s 4cm to narrow like I did)

I’d also jump into the forums. Folks there are happy to answer any questions. The builds are incredible and often folks make unique modules. There is plenty of circuit sharing.

From there, it’s a matter of ordering all the things and throwing your wallet in one of those already on-fire rubbish bins.


Let me know what you think or if you have questions. It’s a pretty fun build.

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