Started playing notes by itself

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  • #7790 Reply

    I assembled my mini synth yesterday and played it for a long time with no issues. It’s been a ton of fun. However this morning when I turn it on it starts playing random notes by itself. I imagine the capacitance touch keyboard is triggering by itself somehow. I can override the default notes by pressing elsewhere on the keyboard but it makes making music difficult if not impossible. Is there any way to fix this problem?

    #7792 Reply

    Hmmm… Yes, that sort of behavior us usually associated with instability in the cap. touch keyboard. Sometimes, here in the Lab, a synth will sound just because it’s humid. Does this happen consistently, all the time, or is it pretty erratic? Try placing a finger on the edge of the PCB, on the blue border but beyond the printed keys. Does that stabilize performance? How about when it is plugged in to a power supply vs a battery? How about when you’ve got earbuds or something else plugged into the line out? All these things affect the grounding of the PCB and stability of the keyboard.

    If the random-note behavior is unaffected by any of these factors, then there’s something goofy with the circuit. Each key has an associated resistor; if any of them are damaged or loose it could create this behavior.

    Macchiato inventor Brach may have other suggestions when he is back from holiday.

    #7794 Reply

    I do live in a humid area and it has been pretty humid outside today. That was my first guess since it worked perfectly all day yesterday. So I removed it from the housing and placed it in front of a fan for a while. This didn’t solve the problem.
    I believe I’ve narrowed the noise down to a specific note on the keyboard and have yet to attempt re soldering the resistor associated with it. That is what I plan to try next.

    The behavior is consistent with that note for the most part. If I leave it alone it will occasionally flicker in and out other notes. I can cancel it out by pressing two other keys in succession (since it’s two note polyphonic) and sometimes it will stop the ghost noise for a few seconds. Another interesting thing that makes me think it may not just be the cap. keyboard is that the release knob no longer changes the length of the notes after release. On the occasion that I get the ghost note to stop it seems to ramp down the notes after release over a long time regardless of the release knob position.

    I tried placing my finger outside the keys to no avail in several places around the board.

    The power supply vs battery does not change the behavior either.

    It doesn’t matter if there is anything plugged into the line out.

    Something I did notice this morning is that I did not install the capacitor associated with the DC jack as the instructions said I didn’t need to if I have a 3.0 board. However, I found a missing place for it on the board afterwards. I’m assuming this has to do with the noise floor when the power adapter is being used. But since I didn’t pay that much attention in circuits class I don’t know if this could cause the issue.

    Thanks so much for the quick reply!

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