Absolute power

I have enough modules in Kosmodrome to warrant adding a second power supply and bus board — or at least a second bus board, I haven’t yet checked what fraction of capacity the power supply is running, but I figured I’d just go ahead and build a new supply. Or two, actually, because I’d like to replace the Frequency Central one with an Analog Output one.

I drew up a layout for a power supply board last year and had some fabbed a few months ago, but I’ve only just now assembled any. The circuit’s only a little modified from the MFOS wall wart supply. Main differences are I added LEDs in series with the resistors, as well as resettable fuses. As for the hardware implementation, I decided to put footprints for three input-side connectors on the board — a barrel jack and two 2-pin pluggable terminal blocks. The barrel jack lets you plug in a wall wart, but for use in a case I think it’s better to put a barrel jack in the case and run wires from there to the power supply. So one of the terminal blocks is for that. The other is to run wires to another power supply, so you can daisy chain two supplies off one wall wart. They’re pluggable terminal blocks to make it easy to swap a supply in or out of service.

Output is a (non pluggable) 3-pin terminal block for +12 V, -12 V, and ground. Unlike usual Eurorack supplies there’s no provision for a +5 V rail, since Kosmo doesn’t use that.

Unlike the MFOS design, mine has the voltage regulators standing up and screwed to heat sinks.

It’s just 100 × 61 mm, so qualifies for the cheapest fabbing prices at many companies.

I found a few minor issues with the PCB, the worst of which was I used the wrong footprint for the 1.1 amp fuses, one with too small a hole for the leads. I had to get them to fit somehow, and there wasn’t a hammer handy. So I soldered cut-off resistor legs to the fuse leads.

That was the first and messiest. As is so often the case with these things, by the time I did the fourth one, I’d pretty much figured out how I should have done the first one.

When I got the boards assembled I put them in the garage, ran an extension cord to the basement, closed the doors, and plugged it in. Nothing a splode! 2 x ±12 V. Victory.

So the boards are okay, but improvable. I have a new version, with proper fuse footprints and other tweaks, about ready to go next time I want to build a power supply. The repo’s here: https://github.com/holmesrichards/ww_supply.

Then I built a new bus board. This was the last of the first run of 12 x (2 x 5) bus boards (repo here) which also had a few cosmetic quirks, since corrected.

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