DAC noise on ADAU 1787

I am experimenting with the ADAU 1787Z eval board and have run into a pesky noise issue. When I plug my earbuds into the the stereo output, and download any program whatsoever (e.g., a simple ADC input) to the 1787, I experience a low level broadband noise. This occurs even when no output pin has been added to the design (also happens when I have a simple ADC -> DAC passthrough muted / or no mics even connected to AN0 or AN1). I have the jumpers set to the default positions specified in UG-1532 (page 3) and the registers in their default config. I have experienced this when running the DACs from FSDP0 / FDSP1 as well we SDSP0 / SDSP1. I have also tried a bench power supply to verify that the noise is not emanating from my PC. 

Is what I'm hearing the DAC noise floor? I suppose the speakers in the earbuds that I'm using may be fairly sensitive, but I wouldn't think so much so that I can hear the DAC noise floor. Any suggestions are greatly appreciated. 

-Jake

  • 0
    •  Analog Employees 
    on Feb 21, 2020 6:46 PM

    Hi Jake,

    Please note the Stereo output on J23 is provided as single ended output through an coupling capacitor. If you are trying to measure the noise, I would recommend to use the full differential output i.e. available on J21 (Left) or J19 (Right). With the DAC muted it should be quiet. 

    The DAC when measured differentially would offer 105dB SNR A wtd. I suspect some configuration error in your setup. Is it possible for you to share your SStudio project to look at?

    Regards

    Rajeev