Stereo 3.7W Class D Audio Amplifier and Teensy Audio Board

[sleitman]

I am having trouble with some of the Stereo 3.7W Class D Audio Amplifiers and the Teensy Audio Board. I made a PCB that connects the line outputs of the Teensy Audio Board and the 3.7W Amp(https://www.adafruit.com/product/987) . Of the 8 boards that I have soldered up, 2 work and 6 have noise issues. Here are the facts for the noisy ones and I will include a diagram of the connections since the PCB hides them.

- The signal coming out of the Teensy Audio board is a simple square wave of variable frequency and loudness.
- Most of the time, I get a horrible level of static noise on the left and right outputs.
- I originally left the G and G' pins floating because that was what I read in the schematic would lead to the 6dB gain.
- I have tried the various other gain dBs and this does not alleviate the problem.
- The headphone output on the Teensy audio board sounds good.
- The line out on the Teensy audio board sounds good when sent to an external amp.
- Occasionally, I have had a small moment where the noise cleared up on two of the "noisy" of the boards. Once this happened when I had connected the ground pins for 6dB with a little jumper wire. When I soldered that connection together, the noise came back.

I know that the most difficult issues are the ones that are intermittent but any advice that you might have would be very appreciative.

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[adafruit_support_bill]

L- and R- on the amp should be connected to GND on the signal source.

[sleitman]

Hi Bill,

Thanks for your response.

They should be connected to audio ground on the Teensy board, right? Not the power ground on the Teensy audio board.

I have definitely connected them to audio ground but accidentally left that out of my diagram. An update diagram is attached.

Thanks for your help with this,
Sasha

[sleitman]

I am particularly wondering if there might be something that I am missing regarding setting the gain levels. Is there any reason that I shouldn't leave the gain pins floating?

[adafruit_support_bill]

With no jumper, you should get 6dBof gain. Please post some photos showing your soldering and connections.

[sleitman]

Solution - In my PCB routing, there was one place where I had accidentally combined the L Out- and R Out-. Once I cut that trace, my noise problems went away. I am very grateful that I did not damage the board.

Clearly, I need to do some more learning about Class D amps.

Thank you for your help with this!

[adafruit_support_bill]

Good to hear you found the problem. Thanks for the follow-up.