Difference between AGND and DGND (AMP2.1)?

Hi,

I am currently designing an extension PCB with a headphone output and have a questiom about the AUX-Input on the AMP2.1 board. What is the difference between AGND and DGND on the 4P JST connector next to the AUX-Input? First I thought one of the pins is for detecting if the 3.5mm jack is plugged in, but both pins seem to be always connected to each other. When I measure between them, there is always a connection. Both, when a 3.5mm jack is installed and when it is not installed. So what is the purpose of having two grounds there and which one should I use to connect to my headphones?

Also what is the purpose of the NUM1-NUM4 buttons that can be seen in the schmematics in the manual?

Hi, welcome to Arylic forum.
The AGND is for analog signals like audio circuit, and the DGND is for digital signals. These 2 are sure connected as they are both GND. The difference is the DGND might have some unwanted noise because of the jumping digital signals, and which might affect the analog. So we extended 2 GND for better conneciton to external boards. For single headphone, you should use the AGND.
NUM1~4 button is used to play the preset playlist, you can assign a playlist (for some music sources, not all) as a preset on APP.

Thank you for the response. That makes sense.
I just finished the PCB design and am now waiting for them to be manufactured. I really appreciate the expandability with all the extra connectors and available information about these boards.

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