AS3350 (CEM3350) Eurorack filter DIY – from schematic to PCB and panel production in KiCad.
Using a mix of the schematic in the datasheet and (mainly) the schematics from the old Digisound 80-16 module, plus a standard Eurorack power filtering section, I knocked up the circuit boards and panel in KiCad and ordered them from JLCPCB.
Uploading the panel was a headache – as it’s not the typical electrical circuit JLC’s online ordering system expects, it wouldn’t recognise the board dimensions until I added a via as a workaround. Something to do with expecting two layers.
Now waiting for the boards to arrive from China…first time I’ve tried to make a skiff-friendly split main/pots board PCB joined by male/female headers, so whether v0.1 works is anyone’s guess.
As a side note, if you’re reading this and you have a copy of the Syrinx schematics with the component values filled in, I’d love to see it!
OK, I wasn’t expecting to get this right first time, and I didn’t…but it wasn’t too far off.
The panel fits:
…and the upper and lower PCBs line up with the headers.
Again, human error crept in: I got an electrolytic the wrong way round in the power section (bang), set the resonance pots up at a divider between +12v and GND when they should be +12/-12v, mislabelled a 200r resistor as 200k, and missed a ground connection on one of the IC pins.
But – with a couple of flying wires – it works.
I’ve (hopefully) corrected the mistakes and am now waiting for the version 0.2 boards to arrive.
The Syrinx and the Spirit both had two of these 3350s, with a switchable mixing circuit to give combinations of low pass, band pass etc in serial or parallel. But let’s get this simple version working first…
Version 2 boards arrived. Forgot to take the bloody JLC order number off the panel. Never mind. Built them with an interactive BOM I exported from KiCad’s PCBNEW, so I could test out how someone else might build it.
The second part of the filter worked, but the first didn’t. In an object lesson about the importance of version control, I pulled the IBOM from the board with the mislabeled 200k resistor mentioned above, which took me an hour to find with an audio probe and an oscilloscope…
Swapping that out – it all works. I will now allow myself a brief period of rejoicing.
Here are the corrected build documents – the KiCad files, gerbers and IBOM for the main board and the jacks/panel board.