I've wanted a modular synth of my own for some time, but frankly, between the costs of modules and the existence of VCV Rack (and my general lack of wealth :) ) I never really got around to getting one.

However, I did have a few ideas for Modular Synth-adjacent tech --- say, modules you could mount in a Eurorack style rack with non-sound-processing purposes --- and so I got around to researching how you could make your DIY Eurorack case.

(Because, really, have you seen the prices of those things? 0)

There are some interesting solutions for the rack itself which are based off of IKEA modules; see 1 and 2 for example. However, the case still needs a power bus board, and (as it seems to be tradition in the MS world), those are also quite expensive. LOOK MUM NO COMPUTER (of whom I'm a big fan) has a video on building your own rack 3, and he suggests the Frequency Central FC POWER bus board 4.

A look at the build document for this board revealed it was little more than a series of decoupling capacitors, some diodes providing reverse polarity protection, voltage regulators and debug LEDs. So, in the spirit of making a board which I could customize I made my own schematic and PCB design (using EasyEDA, which is JLCPCB's schematic/PCB design tool).

I will not provide the Gerber files for the PCB so that malicious actors can't just go and start selling counterfeit FC boards; I feel like this would be a severe disservice towards FC, and I set out to make something hackable, not a bootleg. However, you can find the PDF document with the schematic attached, from which it should be pretty easy to get an idea of how the bus works/apply whatever modifications you have in mind. I will (for largely the same reason) also leave the bill of materials as an exercise to the reader, sorry! :) Finally, please note:

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Regarding the PCB design itself, I have no experience with that field (even less than with electronics :) ) but I took a hint from Ossman's talk on RF-related PCB design 5 and had the top layer be all ground, and route all of my connections using just the bottom layer. I used THT components only, but I think it'd be easy to replace at least all the resistors and diodes with SMD equivalents.

In the end, COVID happened and I never really got around to ordering the PCBs, so I'm not even sure they work at all! :) It was, regardless, a very fun experiment with AC circuits/PCB design and with negative DC voltage!