How I Built my Own Eurorack Module Part 0: Circuits Background

I recently built my own Eurorack module. It was a long and detailed process, but in the end, the reward was well worth it! The goal of this series of articles is to share with the curious DIYer the things I've learned along the way, things that I've found helpful and useful. I will also stress that this is by no means a professional guide to making modules; I am not a professional. Rather, this is a collection of wisdom, things I picked up along the way, things that are good to know.

Without further ado, our first article in this series talks about having a good knowledge of circuits before starting out.

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Part 0: Circuits Background

It goes without saying, but a good understanding of circuits and circuit design is essential for making your own module. You don't need to be an expert, you just need to be knowledgeable about things like components and how to make designs using them. For example, what goes into making a passive versus active filter.

In my case, prior to ever thinking about designing my own Eurorack module, I had a general interest in circuity; analog circuits to be specific. In fact, I had begun self-studying analog circuits shortly after getting into modular synthesis. Not a long time though, only about two years. For me, I was attracted to the idea that some of the best sounds in modular synthesis came from purely analog modules, some designed years before the digital age. 

My self-study of analog circuits was in the form of reading textbooks and working through the problems posed in them. One that I can recommend very highly is "Microelectronic Circuits by Sedra and Smith" (I have the 6th edition, but there are newer ones). In my opinion, this is a great textbook for those who want to delve deep into analogy circuitry. Despite being a university-level textbook, it does a great job of explaining concepts concisely and only assumes a very basic understanding of circuits, mathematics and physics. 

The book is packed with content, enough for two semesters of study, the authors note. It begins with a general introduction, before making a deep dive into analog components such as amplifiers, op-amps, semiconductors, MOSFETs and BJTs, and the physics behind them all. The later part of the book gets into circuit design/analysis and also touches on digital circuits and logic, for those interested. Throughout the book, various smaller circuit designs relevant to each topic are presented and worked through to provide a deeper understanding of how various components all work together. 

Each chapter also has tons of practice questions at the end of it. What's neat as well, and extremely useful for module design, is that several questions in each chapter are labelled as "design" questions. These questions put you in the role of a "circuit designer" and ask you to do things like create circuits, pick component values, etc., based on specs provided in the question. 

Once you feel comfortable with your knowledge of circuitry, another tip I can give is to start looking at existing schematics out there for DIY modules. Not really for inspiration per se, but just to see how things are laid out and if you can, in a general sense, understand what's going on. I wrote an article a few years ago about resources for DIY Euroracking (building rather than designing), where I featured two great builders: Sam Battle of Look Mum No Computer and Niklas Ronnberg. Both offer schematics on their websites for DIY builds and I've built a few of their modules. What's cool about Sam's channel/website is that he usually has a YouTube video to accompany each module, where he breaks down the circuit and explains what each module does. Super valuable for people starting out.

Having this background knowledge of circuit design is the key foundation for making your own Eurorack modules. In my experience, it is the part that takes the longest, but is also the most rewarding. I should also stress that my path to studying circuity is by no means the only way, or even the best way. There are tons of resources available both in print and online to aid in your studies. It's just a matter of finding what works best for you and developing that knowledge.

So, you've learned what there is to learn about circuitry and you feel like you can tackle creating your own module, what's the next step? Stay tuned for our next article.

-Uncle Peter

"Microelectric Circuits" by Sedra and Smith is a great textbook for those who want to delve deeper into analogy circuitry 

Introducing PENTATONES by Patches & Racks

Pentatones by Patches & Racks

Features:

• 5-band bandpass filtering over a range of low, mid and high frequencies
• Band-specific outputs with voltage-controlled amplification/attenuation
• +12dB to -∞dB gain range for each band
• CV control over band weight/intensity 
• Mixed output with gain control
• High-quality components designed specifically for audio use
• Fully analog circuit design

Specs:

• Width: 14HP
• Depth: Variable
• Supply: TBD
• Anodized aluminum front panel

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After many months of researching, developing and assembling, I am proud to present my first Eurorack module, Pentatones!

Pentatones is a 5-band graphic equalizer, but not your typical one, in that it features CV control for each band. The bands are spread over the entire audio spectrum, at frequencies 80, 240, 750, 2.2k and 8kHz, and use active two-pole bandpass filtering (Q-factor: 4.3). 

The idea for Pentatones came out of need. Throughout my search for modules, I was surprised to find that there were no EQ modules (to the best of my knowledge) that had CV control for each band. I saw this as a unique DIY opportunity and decided to take on the challenge. 

The entire process of creating this module was super rewarding. I've learned so much along the way. Because of this, I've decided to release a multi-part set of articles on this site, titled "How I built my own Eurorack module", as a way to consolidate all of the knowledge I've acquired over this process and share it with you all. My hope is that many of you in the DIY world will be able to use the info to make modules of your own. Stay tuned for these!

For those asking if I'm selling Pentatones to the public, I have no plans for this as of now. But who knows, if there is enough interest in the module, I would reconsider. 

Stay tuned for my series of articles!

-Uncle Peter

Additional Images:

Mutable Instruments Tides v2: The Oscillator

Mutable Instruments Tides v2 is a special module to me. Not only is it a multi-outputting wave-generating monster (LFOs, audio rates, and everything in between) with many variable parameters, but it was the first big name brand module that I purchased new; that is, the first one I decided to spend relatively big bucks on.

I've had it for about several months now and you've seen it in many of my videos, where its done things from rhythmic clocked modulation, to acting as a clock source. But for this video, I'd like to show everyone how you can use Tides v2 as an oscillator. 

What I'll be doing in the video below is sending a sequence into Tides, then taking the four outputs of Tides (something new in v2) and varying their parameters to produce some interesting sounds. Enjoy!

I really liked putting this patch together and the sequence sounds amazing, to me, through Tides (see sequence details below). And I love the way the sounds changes even with the slightest turn of the knobs. 

Let's break down this patch now. 

It's not a complex patch I must admit. I have my Arturia Keystep loaded with a 32-note sequence which when started will output this sequence as voltages according to the 1V/oct standard into Tides. Tides is set to "oscillator" mode": 130.8Hz frequency output (red LED), cyclic bipolar oscillations (yellow LED) with its outputs having different frequencies (red LED). The four outputs are mixed together via my DIY mixer, then sent to my DIY Dual VCA, which is opened and closed by a gate signal from the Keystep every time a note in the sequence is generated. All of that is then inputted into Clouds, mainly to add reverb to the sound.

In addition, I have Pam's Workout also receiving the gate signal from the Keystep to set the tempo; i.e. every time a note in the sequence is played. The FutureRetro Transient is triggered from Pam's and adds a bass beat to the patch, to give it a more complete sound. 2HP Arp also makes an appearance, generating a voltage every 16 notes via Pam's to shift the pitch of the sequence (so it doesn't sound like the same thing, note-wise, all the time!)

And that's basically it. Now in the video, I vary three of Tides' parameters. In order, I start with Slope, which adjusts the ratio of ascending and descending segments of the outputted waves. This is sort've like an attack/decay feature built into one and as you can hear, basically changes the sound from a triangle wave to a more sawtooth-like wave. Next, I vary the Smoothness, which depending on how its varied either low-pass filters the wave (counterclockwise) or adds "kinks and bumps" along the slope (clockwise). This made for some funky sounds! Lastly, I vary the Shift/Level. This changes the frequency of each output relative to one another to produce "intonation chords". In the video, I use my DIY mixer to adjust the volume of each output, just to illustrate the difference across outputs. As I said before, changes in a few of the parameters can produce a wide array of sounds; it's quite versatile, and I didn't even touch the Shape parameter for this video!

Before I end, I would like to point out that keen listeners will have recognized that the sequence used in this video is the intro sequence to the song Levels by Avicii (the proper non-radio cut version). I had decided to use this sequence for the video simply because I had always wondered if it could be replicated using an oscillator Eurorack module. In addition to this, last week marked the two year anniversary of Avicii's untimely death, and it was just by coincidence that I had planned to release this video with that sequence, near that date...

-Uncle Peter

Making it Work #1: Clouds, Disting mk2, FutureRetro Transient

"Making it Work" is a new series that I'm launching. It's new take on the classic "3 module challenge". What I'll be doing is picking three modules at random from my rack and find a way to make a decent sounding patch from them. It's something I'm really looking forward to, and I'm hoping I'll be able to learn more about the capabilities of my modules by doing so.

In this first episode of the series, I make a patch using Mutable Instruments Clouds, Expert Sleepers Disting mk2 and FutureRetro Transient. Here's what I managed to come up with:

Not too bad to be honest! From the start, I knew that I was going to use the Transient to make a beat and have it triggered by a square wave from Disting. But I wanted to use a different mode on Clouds just to make things sound a bit different. Luckily, the Parasite firmware I have on Clouds has a cool resonator mode, which allowed me to turn the beat generated by the Transient into a melody-like sound. Who knew!

Here's the more detailed version of what's going on:

Disting mk2 is in "4-B Clockable LFO" mode. Output A generates a sine wave that modulates the FutureRetro Transient. Output B generates a square wave that acts as a clock source for FutureRetro Transient. Both waves are oscillating at a low frequency (1.5Hz or 90BPM). 

The Transient is set to the "RANDOMeYeS" sample and is being triggered and modulated by Disting. Its output is multed to a mixer and Clouds.

Clouds is in resonator mode; an alternate mode in the Parasite firmware. Position is set to 11 o'clock, Size is set to 12 o'clock, Pitch is set to 10 o'clock, Gain is set to 4 o'clock, Density set to 5 o'clock, Texture set to 12 o'clock and Blend set to just over 9 o'clock. It is outputted to the mixer as well, which now outputs both the raw Transient beat and the "melody" generated by Clouds. 

So I think we can call that a successful first challenge. I'm really looking forward to doing more of these challenges, hopefully they all sound as good as this one!

Happy patching friends,

-Uncle Peter

DIY Eurorack Module Resources

Long before I ever got into Eurorack, or even music for that matter, electronics were a big interest of mine. I'd love taking things apart, looking at the weird circuit boards, and trying to understand what was going on. 

Fast forward many years to learning about Eurorack and all its various modules that can perform pretty much anything. It was only a matter of time before I became curious about how these modules worked; what was going on behind the face plate. After a bit of searching, I found the crazy, but fascinating world that is DIY Euroracking. 

Making DIY Eurorack modules is something that is relatively easy, designing them is a whole different story. With a bit of soldering know-how, you can make some pretty cool things.

My goal here is to consolidate all the information and resources I've acquired about DIY eurorack module-making, with the goal of helping beginners or interested people wanting to give it a try. I'm doing this because, to my knowledge, I don't think anyone has put something together like this. 

So hopefully the information below is helpful. I'll keep updating it as I find new resources:

DIY EURORACK RESOURCES

1) Look Mum No Computer 

Look Mum No Computer is a Youtube channel run by Sam Battle that focuses on DIY synthbuilding and music making. Sam is a creative genius and builds some crazy musical contraptions that sound awesome. He also has a collection of modular synth builds that he has created. What's cool about Sam's designs is that he posts the circuit board layout/bill of materials to his website, but also has a Youtube video about each module he designs. I personally think this is great because you can see what a particular module does/sounds like, before deciding to build it. Also, almost all of Sam's designs are stripboard layouts, which makes building them that much easier, and there is a nice forum on his website to ask questions. Sam himself is also pretty friendly and always answered my emails when I had module questions

I should point out though that Sam's modules are not in the typical Eurorack 128.5mm format (since he prefers larger modules), so a bit of front panel layout/design is required, which I personally find to be pretty fun; you can lay things out how you want. So far I've built the multi-channel mixer, 1V/oct oscillator, envelope generator and low-pass filter. Here is a list of Sam's module designs. 

2) Niklas Ronnberg

Niklas Ronnberg's DIY synth page is another great website I've found with a massive collection of various Eurorack-sized modules. His designs are also in stripboard format and some have instructions and audio samples to go along with them. 

A downside however is that Niklas doesn't provide an explicit bill of materials for his builds, although all the required components can be deduced from the stripboard and schematic layouts (see image). He is also friendly and responds to questions about his builds and required materials. So far I've built the dual VCA and distortion unit. 

3) Mouser Electronics
Mouser Electronics is a website that sells pretty much every single electrical component you'll ever need for these DIY builds. It's a pretty user-friendly website and what I like in particular is the filtering system they use for the a search query; you can filter down search results in super detail to get the exact component you want/need.

Mouser also has a really cool shipping policy (for Canada at least). For about $20 of shipping or free for orders over $100, you'll get next-day/two-day shipping on your orders; perfect if you are like me and want to get right into building ASAP.

Updated: 03/03/2020

So that's what I've come up with so far. As I said before, I plan to populate this list as I come across more resources. If you have any resources, post them in the comments below and I'll add them to the list. It would be great to see more people getting into this sub-hobby!


Happy patching friends,


-Uncle Peter

A Dual VCA schematic by Niklas Ronnberg

Ambient Strumming with 2HP Pluck, Clouds, Rings and a DIY Dual VCA

It's exciting times for me at the moment, in terms of Eurorack. I've just finished building my new DIY 2-row rack. Because of the extra space now, I've been able to add some DIY modules that I've built to the rack. Posts about both of these topics are coming soon!

I've been on a "ambient patch" binge lately as well (mostly because of my purchase of Mutable Instruments Clouds), trying to see what cool and different sounds I can come up with, while still making it sound ambient in nature. 

I decided to see how one of my favourite modules, 2HP Pluck, sounded when it is passed through Clouds. But I wanted to incorporate some of my DIY modules also, mainly a Dual VCA and a mixer. I kinda felt that I needed to, since they were the newest additions to the rack.

So here's the result of all that, something I'm calling it "Ambient Strumming", featuring 2HP Pluck as the main voice, Rings as a backup voice and some gate sequencing with the DIY Dual VCA and Pam's Workout, all sliced and diced together with Clouds!

To be honest, this is probably one of the most awe-inspiring (to me, of course) patches I've managed to wire up to date! I was completely surprised by the sounds that this patch produced. It's such a relaxing sound, delicate, yet clear when each note is triggered, from both of the voices. What's also cool is the different feeling the sound gives off at different tempos (who knew a change from 40 BPM to 60 BPM could make that much of a difference)!

Let's break down this patch now, since there's some pretty neat tricks I've included it in.

As I said before, two voices are present here. The first is 2HP Pluck, acting as the main voice. It's being triggered rhythmically by 2HP Euclid and given quantized voltages by 2HP TM and 2HP Tune every quarter of a beat (16th note). The other voice is Rings, in quadriphonic (red) modal (green) mode, acting as the backup voice. To be honest, I wanted to play down the role of Rings in this patch, mainly because I didn't want this to be another "Rings into Clouds" patch.

Each voice is then sent through a VCA, via the DIY Dual VCA, which receives gates from Pam's Workout (gate sequencing). Each gate is one beat in length, thus a beat's length of sound is outputted from each VCA; Pluck on the first beat and Rings on the third beat. This is something that I found to sound similar to call-and-response pattern found in various types of music.

The VCA-controlled voices are mixed together via the DIY mixer and inputted into Clouds. Clouds is in granular mode, with all its blending parameters set to 12 o'clock except for reverberation, which is set to ~4 o'clock. A gate from Pam's Workout that opens every fourth beat also controls the freeze parameter. I particularly like this setting of Clouds that I've found. As I said in a previous post, many people find Clouds very finicky, so I'm content to keep this setting for now.

The Doepfer LFO is generating three LFOs; a triangle wave, attenuated by Shades, to modulate Pluck's decay parameter, an inverted sawtooth wave, to modulate Euclid's outputted rhythm, and a sine wave, to modulate Rings' brightness parameter.

So that's pretty much what's happening. On a final note, I was really torn about what tempo to set for the patch, simply because each tempo generated a completely different mood. That's why I decided to go with both.

What did you think of this patch? Let me know in the comments below!


Happy patching friends,


-Uncle Peter

First Look at Mutable Instruments Clouds

I've gone into much detail about the Mutable Instruments brand in a few of my posts. They really do offer a vast range of powerful modules and are some of the most recognizable.

One of their most famous (now discontinued) modules is the texture synthesizer Clouds. Clouds is a really genius module that takes incoming audio, divides it up into tiny samples and, frankly, does some pretty crazy things with them in terms of reverberation . Early on in my patching career, way before I even owned a module, I heard some ambient patches using Clouds and was instantly hooked!

So I took the plunge. The good thing is that there are plenty of manufacturers that make a replica of Clouds, or its thinner counterpart uBurst; the original models can be very expensive no doubt. My first impressions of it were positive, from the bit that I've explored. The reverberation feature is pretty mesmerizing, to say the least, and the density parameter can really do some funky things when modulated.

After playing around with it for a bit, here's a patch I'm calling the "Mutable Instruments Trifecta"! Rings into Clouds (a very common practice), both modulated by Tides v2.

Not that bad. I'm getting a cool space-like vibe from this, "space strings" or something to that extent. The contrast between the background hum and sharp sequence of notes is pretty cool as well.

Let's look into this patch a bit more.

Clouds is in its basic granular mode, with all its blending parameters set to 12 o'clock except for reverbation, which is set to ~4 o'clock. This is what adds that nice reverberation to the patch.

Rings is in quadriphonic (red) sympathetic strings (yellow) mode and sends both its odd and even outputs to Clouds. The reason for using the quadriphone mode here is to add as many notes into the mix as possible, all of which contribute to the ambiance. 

Tides is in 1/8 Hz (green) cyclic bipolar oscillation (yellow) mode, set to output different shapes (LED off). Output 1 is an LFO that modulates Rings' damping parameter. Output 2 is a low-frequency triangle wave that modulates Tides' own shift/level parameter, which in turn attenuates Output 1's signal. Output 3 is a gate that controls Clouds' freeze setting. It opens at the end of the attack phase of the main signal and closes at the end of the oscillation.

The Doepfer LFO sends LFOs of various shapes to Tides' slope and frequency parameters, Clouds' position parameter and Rings' brightness parameter. Yes, that's six LFOs in total now, which may actually be a record for me at this point!

As always, perhaps a personal favourite of mine, 2HP TM sends random voltages (quantized via 2HP Tune) to Rings. 2HP Euclid sends a Euclidean rhythm to trigger Rings. Finally, Pam's Workout is set to 126 BPM, and triggers TM every quarter of a beat (sixteenth notes) and Euclid every half beat (eighth notes).

I will admit, many users of Clouds experience finickiness with their patches and to a lesser extent that was the case with this patch. It was a bit challenging to figure out the exact sound I wanted Rings to send to Clouds such that the reverberation did not die away too quickly. In my case, varying the damping parameter of Rings even the slightest has dramatic effects on decay time of the reverberation. But hey, it was pretty fun experimenting around with it, so I don't see this challenge as something negative. 

That sums up my first attempt at using Clouds. Naturally you can expect more videos featuring Clouds for anything ambient-related; I really want to learn the ins and outs of this module and what each mode is capable of.

Also, if you've been following me on Twitter ( @UnclePeterMod), you'll know that this is my last video in my current 1-row case. I just finished building a new 2-row case, maybe I'll make a post about that too, it was pretty fun to make!

Do you have any suggestions on patches to make using Clouds? If so, leave a comment below!

Happy patching friends,

-Uncle Peter