Music and Synth DIY

Eurorack, Synth DIY

H Block – linear bipolar Eurorack PSU (part one)

I’m in the process of building a large case to consolidate all my smaller ones – 24u of 168hp.

Turns out power is more of a headache than I was anticipating, and I’m going to have to upgrade the power supplies I’m currently using.

They’re either 7812 & 7912 or lm317 & lm337 based, so max 1A and 1.5A respectively. That’s assuming your heatsink is up to it, and you’re not working them at maximum currrent draw, which they’re not overly keen on.

I’ve got a load of 5a 12v AC adapters, so I’m reworking the typical linear power supply design (again, thanks Ray Wilson etc ) that works by half rectifying the AC wave and then having a bank of large “reservoir” capacitors feeding the voltage regulators.

Firstly I’m upgrading a couple of components (the 2A 78s12 instead of the 1A 7812, and 1N5422 3A rated diodes for half rectifying duty) and allowing for much larger heatsinks. I’m using 2A polyfuses, and I’m also using 2 oz copper on the PCBs with wide traces copied on both sides, and copper pours for ground and +12v.

2A rated 78s12

The 12v rail is the main problem, digital modules draw much more current on +12v than they do on -12v. I’m allowing one PSU per rail, rated at 2A to draw 1.5A max, and two per rail for really power hungry modules (hello Bitbox Micro).

The heatsinks I’ve been testing out are these – FA-T220-51E.

Having been reading through some posts on PSU design by Graham Hinton and others, I’ve also decided to go with crimp terminals and heavy duty wiring instead of using DC barrel jacks and the usual Eurorack IDE cables between the busboards and the PSUs.

So, this is a work in progress. The design is off to JLCPCB now, let’s see if it works, and whether it stands up to soak testing at these sort of loads…if it’s all good, I’ll upload the design files and gerbers here.

I’ve also designed another heavier duty low noise busboard, incorporating soldered copper bars carrying the power nets (though it can be used without if it turns out not to make much difference). Won’t be uploading this one – it’s a shamelessly stolen idea from a commercial product that I don’t think ever made it to market – and therefore for personal use only.

Part two of this post here.