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mki x es.EDU VCO & Dual VCA

Eurorack Modules By William Stokes
Published July 2022

mki x es.EDU VCO modulemki x es.EDU VCO module.I wouldn’t ordinarily claim to be the perfect person to review any of the hardware that comes my way, but in the case of Erica Synths’ collaboration with Moritz Klein as mki x es.EDU I’ll make an exception. The range of DIY modules is designed for complete beginners with next to no prior experience of electronics or DIY synthesis, walking them through the process of constructing its fundamental circuits from start to finish. Suffice to say, I can comfortably be counted in that target market: I can tell you a great deal about the world of synthesis and how to sculpt complex sounds with electronic instruments of all kinds, but a synth‑builder I am not — to the extent that upon receiving my soon‑to‑be review units, it was time for a trip down the local Wilko to grab a soldering iron, a coil of solder and something called a ‘multimeter’.

The premise of the range is for users to work towards building an entirely self‑sufficient system, including the case. It’s ambitious in all the right ways: one gets the sense that mki x es.EDU indeed want users to feel that such a thing is within their reach, and for their confidence to grow with each successive build. It certainly went that way for me: the ability to play with a fully functional Eurorack system that was once a pile of PCBs and resistors on my kitchen table was, prior to this, nothing short of laughable, but as I completed my second kit I found myself more and more fluent in telling my capacitors from my transistors.


It’s partly for this reason that I was almost surprised to see the manuals for the mki x es.EDU modules available online for free. Far more than a simple step by step, it’s more accurate to say that each is a brilliantly measured, carefully worded booklet explaining what each component that constitutes these modules is, what they do, why they’re included and, importantly, how not to break them. Even without purchasing any of the mki x es.EDU units, the manuals make for a brilliantly educational read, complete with cute hand‑drawn diagrams, water‑in‑pipes metaphors and preliminary breadboard assembly instructions.

They are clearly the fruit of hard work, with all sorts of gems and notes included that could permissibly have been left out but generously haven’t. Moritz Klein has even put a series of demonstration videos online to elucidate certain parts of the process. All this counts towards the reason you should absolutely not open the manual simply with a view to getting your modules up and running as soon as possible. This is not Ikea. Read it before you start, cover to cover, because the process of learning and understanding as you go is the product here — the module itself is simply your take‑home at the end. I would go as far as to say that a hard copy of the manual with a nice cover is something I’d happily pay extra for.

All of the modules are astonishingly good value for money.

Build Your Own

My two review units — or rather, soon‑to‑be units — were the VCO and Dual VCA. Having laid out all my resistors, thermistors, capacitors, PCB, faceplate and so on, I used my multimeter to measure each resistor, as recommended by the manual. Despite being tempted to skip this part on the assumption that mki x es.EDU are unlikely to have included the wrong resistors, I found it incredibly helpful to get my own readings of the components and also ensure that I hadn’t muddled any of the similar‑looking ones. This is an apt microcosm of the wider process. Once again, I told myself: to skip steps is to defeat the point.

mki x es.EDU Dual VCA modulemki x es.EDU Dual VCA module.Once everything was accounted for and labelled correctly I set about soldering everything to the PCB, following the manual step by step. The instructions are clear but rather macro, so once again it’s wise to read through all of them before beginning and make sure you know exactly what it is you’re doing before you start. If you have no prior experience with soldering, spend a few minutes practising and getting to know how solder behaves when hot. These PCBs can get crowded, and if you make a big mistake or break a component it’s very difficult to go back. Slow and steady is the name of the game, a lesson I almost learned the hard way when I incorrectly soldered one of the very many vertically-mounted resistors on the VCA and had to take great care to extract it again from the PCB.

As I absolutely knew would happen without any doubt whatsoever, my VCO and VCA both worked. Success! With the VCO, next came the extraordinarily fiddly process of tuning, which ostensibly comes down to adjusting the trimmer potentiometer with a precision screwdriver while inputting a sequence of octave intervals to find the right relative value between pitches. This in fact threatened to be the only part of the process I felt genuinely unable to achieve, but with a little perseverance I managed it in the end. In Moritz Klein’s words, the finished VCO offers "reasonably accurate Volt/octave tracking," which is technically true but a modest chalk‑up, considering I was able to achieve a difference of cents between frequencies five octaves apart.

So, there they were in my system: A fully organic VCO and Dual VCA, both working happily away next to my comparatively uncool‑looking factory assembled modules. It’s difficult to fault them in terms of function: the VCO sounds beefy, and has a choice of saw or pulse waveforms with a PWM and FM input, while the VCA has two identical, smooth‑sounding circuits, each with an offset knob. Perhaps a couple of LEDs would have been a nice visual inclusion on the VCA, but then again I would have asked for no more or less complexity when it comes to the building process, which as we know is the priority here.

And then there’s the price. All of the modules are astonishingly good value for money. Erica make it clear that they will not provide any customer support for these modules should they fail to function — highly reasonable considering the amount of hand‑holding they provide. I say, take the risk and dive in. If I can do it, so can you.


VCO £62.10, VCA £55.20.

VCO $74, VCA $69.