Electrical quirks - Need help diagnosing

Hi all,

I’m having a couple issues with my Zynth that are hindering usability - I think they are related and hoping that if I share my symptoms we can find the root cause. They all are electrical.

  • If I rub my finger along the case, I can feel a “buzz” of electrical potential. It doesn’t hurt, it’s not like shock, but it’s noticeable. It’s much worse when I’m touching my macbook, plugged into the same power strip (also metal case)
  • If I plug zynth into one of my home-made amps, I get a rhythmic blipping that is in sync with the rhythmic blinking of my power strip light. I also can hear the interface.
  • These sounds change depending on the state of connection of my Zynth, worse if the screen is connected.
  • On a commercial practice amp made for guitars and line-in, I DON’T get the noises
  • The sounds from synths are not reliable
    • Notes “stutter” pretty often (maybe 1 in 20 or so), there is a very short, audible (and visible in the ALSA overlay) click, feels like this might be zynth not being able to keep up with big soundfonts, but also could be related. This happens on midi but also just when making notes in the pattern editor - is Pianoteq super smooth for everyone else, or do you get stutters? I have a pretty fast card, but could that be faulty?
    • I very often get “stuck notes” where the zynth doesn’t pick up the off signal, so the note keeps playing until I press it again


I have another older RPi 3… would replacing that out do anything? What is the culprit here? Is it something electrical with my amp? But then why do other inputs not do that? I can plug my anything else to the amp and I don’t get any weird audio. But this happens with Zynth with all my diy amps.

I would start with a different known good power supply.
The Pi is rather PSU sensitive and that would be the simplest starting point.

It sounds like there might be earthing issues, but I would start with the PSU. If you really want to be sure, try with a battery pack. These can be a little bit low on power sometimes you see the lightning in the status, but it will, at least, ensure that the problems ain’t power supply related.

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It smell like a PSU issue …
Also, seems that your DIY amps produce some kind of ground-loop with Zynthian …
Remember that Zynthian output is unbalanced and referenced to ground, that is connected to the case, etc.

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Yes, once you’ve changed the PSU, be careful about the lift every ground till the buzz goes away technique favoured by guitarists…
. There are well understood ways of dealing with this sort of thing. You don’t talk about hums but the effects you are describing are the result of things that should be at Ground potential ain’t.

Don’t worry it’s normally pretty simple. We once had a weekend to kill off all the ground loops in 15 45 U bays of audio patching…

It came down to two dodgy solder joints.

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Threw out the DIY amp - too many variables. It’s likely faulty anyway.

Found a proper Apple charger from somewhere… looks old but Apple hardware was as reliable as I could get. Found a quality Anker usb cable. Plugged directly into the wall on known good wall socket.

Every issue I documented above is resolved. Pianoteq and all my soundfonts play flawlessly.

I knew this thing was going to be trek, given that it comes in pieces. Thank you both so much for taking the time to patiently and kindly assist. Ok enough typing back to hitting keys.