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I just made my first attempt at making a Bluetooth Stereo PCB, and it was okay. This is a Class D Audio Amplifier, with the main IC being the TPA3122D2. O was planning on powering it through USB C, with a Op Amp Circuit that would disable the speaker if it received an input voltage of under 12V. But I had to settle for a 12V wall adapter since the USB C 12V input was creating issues with how the speaker operates. The one big issue is that there is a low frequency static sound on the speakers that is present, even when there is music is playing (hard to hear, but it's there). This isn't related to the Bluetooth module since it's still present without it. What are ways that I can improve my design in order to eliminate this?

Schematic enter image description here enter image description here Top Layer enter image description here

Inner Layer 1 enter image description here

Inner Layer 2 enter image description here

Bottom Layer enter image description here

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  • \$\begingroup\$ It would be helpful if you added a schematic with components placed according to the layout, and tell us about the power supply and other I/O wiring. \$\endgroup\$
    – P2000
    Dec 20, 2020 at 5:03
  • \$\begingroup\$ @P2000 Schematic added. The power supply is a 12V wall adapter. I was planning on using a USB C cable, but the speakers would not operate properly, and would output sound in short bursts instead of a continuous stream if that makes sense. The only I/O's are the Power On and Mute button, and a DIP switch that controls the gain of the speaker. \$\endgroup\$
    – Jay
    Dec 20, 2020 at 5:20
  • \$\begingroup\$ OK good info. And did you read "Managing EMI in Class D Audio Applications", ti.com/lit/an/snaa050a/snaa050a.pdf, section 4, and if so what measures did you implement? e.g. no traces cut in the supply plane? And what about your PGND, can you highlight it please? \$\endgroup\$
    – P2000
    Dec 20, 2020 at 6:17
  • \$\begingroup\$ @P2000 I didn't read that before designing this board. I was trying to follow the recommended component placement listed in the TPA3122 datasheet. The PGND merges with the AGND on the Top and Bottom Plane. I tried to place the capacitors next to their respective GND, and just merged the two grounds together. \$\endgroup\$
    – Jay
    Dec 20, 2020 at 14:15

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