I have an older speaker with an iPod dock that I would like to extend with a Raspberry Pi as a streaming music player. At first, I tried powering the RPi from the dock connector with a Micro USB adapter cable but apparently this does not provide enough current.

Since I do not want to add another power supply to the setup, I have soldered a step-down buck converter to the power connector of the speaker's PCB. (I also replaced the original 12 V / 1.5 A power supply with a 3 A supply which should be sufficient for both the speaker and the RPi.)

This is what it looks like: drawing of the setup

The problem that I'm now facing is that this creates a ground loop that adds switching noise to the output of the speaker. I could put an isolator between the RPi's audio connector and the speaker but there also seems to be a lot of interference coming through. Depending on the power supply, it can happen that the GPIO pins detect phantom phantom button actions when e.g. I turn the room lights on and off.

So my current idea is to replace the buck converter with an isolated one like this one.

My questions are:

  • Is my understanding correct that the isolated converter should remove both the interference and the ground loop?
  • What also makes me wonder is the fact that while buck converters are all over the place, it is hard to find even one of these isolated converters on amazon or ebay. Is this such an unusual application? Or do these isolated converters have another serious drawback?
  • Is the general setup OK? While I have basic electronics knowledge, I usually don't deal with power supply (and sure keep my hands off mains), so I want to be sure that I'm not missing anything that makes the whole thing a safety risk.

Thanks in advance for your input, it's highly appreciated.

  • \$\begingroup\$ Add a schematic of your hookup. It is always a good idea to first determine the root cause of the issue, you say it is a ground loop: why do you think that? Then learn about star grounding (read: analog.com/en/analog-dialogue/articles/… ) in order to avoid such issues. As a beginner you're extremely likely to chase a "red herring", you think the problem is A, you try to solve it but since the actual issue is B, fixing A doesn't help. \$\endgroup\$ May 26, 2020 at 11:33
  • \$\begingroup\$ I have added a picture of the setup. Regarding the ground loop, I am pretty confident after reading this question and the comments: electronics.stackexchange.com/questions/17379/…. Also, adding an isolator on the AUX between the RPi and the speaker does remove the noise (but not the interference problems, of course). \$\endgroup\$
    – Tilman
    May 26, 2020 at 12:37


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