Extra ceramic capacitor spot on my DSP filter PCB?
  • Hi,

    It may sound farfetched but I was given a Shruthi DSP filter circuit board at a party a few weeks ago. I finally have all the parts from the BOM and I’m getting ready to assemble. However, it looks like there’s an extra spot for a ceramic capacitor on my board. Can anyone identify how many farads I need here? Or can I bypass it since it’s not on the version of the PCB shown on the MI site (or on the BOM)?

    Also, is this an early board or what? It doesn’t look like Laurentide or Tubeohm ever made DSP boards, and my board doesn’t quite look like the one on the MI site.

    Attached are some pics pointing out which capacitor I’m talking about and zoomed out to identify the board. Excuse the masking tape: I was making sure all caps on the BOM were accounted for elsewhere on the board.

    shruthidsp_20170319_111101.jpg
    1328 x 747 - 342K
    shruthidsp_20170319_111110.jpg
    1328 x 747 - 389K
    shruthidsp_20170319_111127.jpg
    1328 x 747 - 281K
  • Also, underneath that spot it says “C33”, though the BOM only lists capacitors up to 32. Annnnd, I downloaded Eagle to view the .brd and .sch files from github. It’s there on the board file, listed as a 68p, but it’s not present on the schematic as far as I can tell (I looked all around the IC2 section).

    68pIguess.PNG
    937 x 615 - 95K
    notOnSchTho.PNG
    1180 x 445 - 20K
  • http://mutable-instruments.net/forum/discussion/7683/shruthi-dsp-c33

  • Ah, thanks. I should have searched once I found the c33 text. Think I can just squeeze 3 parallel 22pF caps in there to get close enough since I have them lying around? Or do I need to order the 68pF to be exact?

    Someone should add this to the BOM on the wiki. =P

  • It works fine with nothing there or rather I didn’t notice a difference.

  • Any value between 47p and 100p is fine.

  • Cool. Thanks!

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