SSM2044 tuning
  • KSDKSD
    Well, it's alive and sounds like a Shruthi. I thought I'd do some rough trimming but I can't seem to get it to auto-oscillate; the trimmer seems to be ineffective. I will try and re-solder the trimmer tomorrow. I'm not too worried about the filter itself not working because the cutoff works as expected and turning the resonance up creates the drop in gain that has been described as characteristic. Perhaps I accidentally used a 20k trimmer, I'll check, but that should only affect the sensitivity of trim-pot, correct? Another thing is that I was only using the test tone at this stage because I haven't hooked up the midi port or momentary switches for the menus. I know the smr-4 tuning page specifically says to use an E4 but I figured while roughing it C4 would do. I have also tried it with the filter mode set to ssm and lpf with the filter page setting at 50 63 0 0. The reason for rough trimming was that I'm hoping to do the tuning after I mount everything in my enclosure but want to make sure everything is working and so far seems like it is save for the auto oscillate.

    Thanks a lot.

    edit: No notes necessary to find auto oscillation(duh). Still can't find it and i did use a 5k trimmer. Tomorrow(6.14) I'll recheck solder joints for trimmer, R4, and hook-up line.
  • KSDKSD
    O.K. I checked and re-soldered those points with no change to the situation. I wonder what should I check next?
  • KSDKSD
    hmmm.... I wonder.
  • pichenettespichenettes

    One way to troubleshoot this would be to remove the SSM2044 and measure the current flowing into pin 2 of the chip.

    Sadly, I don’t have any SSM2044 board here to measure what is the current flowing into this pin on a working board. I’ve ordered some chips, I might have a working board in 2 to 3 weeks.

  • roschrosch

    hmm, i could do some measuring. i have working boards, as long as it’s not required to be absolutely sure that i have them tuned really really well.
    but they do auto oscillate like hell ;-)

  • KSDKSD
    Awesome guys, thanks.

    I'vn't ever measured current before. Shall I probe 2 and 1, 2 and 2, or 2 and 8?
  • pichenettespichenettes

    To measure current you need to break the circuit, and get the current that flows into pin 2 flow through the meter first. This is trickier than measuring a voltage!

    You need to put the SSM2044 on a breadboard and run wires between the supply pins of the SSM2044 and the corresponding points on the IC socket (so that the chip gets power). Then you need to put the meter in series between the board and the chip.

    PIN2 of the IC socket -> input of the meter -> COM input of the meter -> PIN2 of the IC.

  • KSDKSD
    Oh, IC.

    I'll have to get me some breadboard.

    I should be ashamed shouldn't I?
  • fcd72fcd72

    Easier would be putting a 2nd socket into the first with the according pin bent, then soldering a wire to the bent pin and the original pad of the bent pin und the pcb and measuring between the 2 wires… wiring 16(?) wires to a breadboard makes 32 potential spots for mistakes….

  • pichenettespichenettes

    Nice idea! Another way to do that: insert 2 of the 1x8 “Arduino shield connectors” into the IC socket, put an IC socket on top of the two connectors.

    Then you can bend the connector above pin2. See what I mean?

  • KSDKSD
    Good deal.
  • KSDKSD
    OK I'm going to take some readings. The schematics say the 2044 is mirrored so pin 2 is nearest the bottom of the board, correct? Left side of chip when looking notch up?
  • pichenettespichenettes

  • KSDKSD

    Cool graphic.

    Well, here is what I’ve rigged

    and here is my meter.

    Now I just prob the empty socket and the bent pin with the power on right?

    I get big phat 0.00

    I’m I doing this right?

  • KSDKSD

    Could have a bad chip?

  • KSDKSD

    Doing a voltage test on the socket pins 9 and 16 I get proper +5/-5 but pin 1 get 0 in reference to ground. Is this correct?

  • KSDKSD

    I re-soldered ever point on the filter board. Still no self osc.

    Changed the meter to 200u and got a reading of 57.7.

  • pichenettespichenettes

    Regarding the null voltage you have read on pin 1: this looks normal – this is a centered, tiny, AC voltage. If you get sound out of the filter there’s nothing wrong here.

    I think pin 2 is at ground potential, so the current you should read here is the Q CV divided by (6.8k + whatever is set on the trimmer). With full resonance on the Shruthi, this should be between 0.420 mA and 0.73 mA depending on how the trimmer is set.

    So the reading you get is uA?

    Looks like it’s off by a factor of 10. Strange, because even if this was a wrong resistor instead of the 6.8k, you would still get a value from the trimmer. How does this change when the trimmer is rotated?

  • KSDKSD

    Yeah, when I set the meter to mA I get .1 no matter what.

    The range is 56.3 – 60.1 from trimmer min to max with full Shruthi resonance.

  • pichenettespichenettes

    Huhuh, several layers of dead sentences colliding here.

    Which voltage do you read at pin 2?

  • KSDKSD

    .11 in reference to ground

  • KSDKSD
    What next shall I do?
  • pichenettespichenettes

    Sorry, I have absolutely no idea on this. Where did you get the chip?

  • KSDKSD
    From you. ;)
  • pichenettespichenettes

    Ah OK… It can’t be a bad chip because I tested the whole batch before shipping them. Unless the pin somehow got damaged? If you think so, you can send me the chip and I’ll test it again.

  • KSDKSD
    It's not physically damaged if that's what you mean.
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