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Thread: Audio shield noise Teensy 4.0 / Raspberry Pi 4

  1. #1

    Audio shield noise Teensy 4.0 / Raspberry Pi 4

    Hi there,

    I am experiencing high-pitched noise over both the line-out and the headphone jack of the SGTL5000 audioshield. The sound that is programmed to be there comes through too, but there is just this lasting high-pitch in the back (It seems very much in line with the power supplying my LED matrices). Maybe someone has some more knowledge about this and could advise me. I've had a tip about using audio ground-loop isolators. However, the pitch is there both when I plug in externally powered speakers and using my headphones. So I assume that my headphones won't create a ground loop.

    An explanation of my setup;
    I have a Teensy 4.0 hooked up to a Raspberry pi 4 (Broken out RX/TX pins -> FTDI converter -> USB cable -> Raspberry Pi). The power to the Teensy, the audioshield SGTL5000, and an XBee along with some indicator-LEDs is also coming through this USB cable and distributed over a custom PCB. The Raspberry Pi itself is powered by a 5V power supply that also powers a whole lot of LED matrixes. This particular power supply powers the Raspberry pi and 8 32x64 matrixes. Though the Raspberry Pi also PWM's another 16 of those matrixes (total of 49152 leds distributed over 3 power supplies).

    Thanks in advance!

  2. #2
    Senior Member
    Join Date
    Jul 2020
    Posts
    472
    The USB power comes from the RPi?

  3. #3
    Yes, the USB cable feeds the power from the RPi -> Teensy so everything on the board is sharing that power. I can't see a way to upload an image here, but you can check out a photo of the board here for reference; https://www.instagram.com/p/B-9OcW2n39V/

  4. #4
    I had a general midi sound board (send midi in, get basic instrument sounds out) hooked up to a little sparkfun audio amplifier. They shared a 5v power source and I had a similar situation to you, the ground loop was going between the two boards and making noise on the audio signal (it didn't matter if I had headphones or a speaker plugged in since the loop was between the two devices themselves). I installed one of these: https://www.digikey.com/en/products/...-0505S/8550767 on the power source input for one of the boards, and it immediately fixed the issue. It takes 5v in and puts 5v out, but separates/isolates the input and output. So it prevented the ground loop and my audio signal became clean afterward. I'm sure there are many methods of ground isolation that would work for these issues, you just need to figure out what one best works for you.

  5. #5
    Thanks, that definitely looks like an option to check out. I might need one that allows for slightly higher output current, but will look into it and update if this solved my issue.

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