Output noise EVAL-ADAU1787Z
Hello,
I have an issue with my EVAL-1787Z board. If I connect headphones to the stereo output of the board I hear an audible broadband hissing noise. I don't know what the expected noise level is, but to me it sounds much louder than I would expect. The noise is audible even if I have no output block in my schematic and mute the DACs. I have added a SigmaStudio project to this message. I hope you can help me resolve this issue.
Thank you in advance.
With kind regards,
Thijs Hekman
/cfs-file/__key/communityserver-discussions-components-files/396/8171.Project.zip
hardware
ADAU1787
sigmaStudio 4.7
Integrated/Special Purpose A/D Converters
noise
sigmastudio
ADAU1787 evaluation board
EVAL-ADAU1787Z
Audio CODECs
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Hello Thijs,
The ADAU1787 is designed for differential headphone output only. It cannot be guaranteed to meet d/s specifications or other system level requirements (pop for example) in single-ended operation.
The EVAL-ADAU1787Z uses a stereo 3.5mm jack and routes HPOUTL+ and HPOUTR+ through 470uF AC coupling capacitors to allow for a stereo connection to headphones, but this is not recommended for system-level design or final use. It is meant just to provide a convenient way for folks to verify that they are getting sound, in case they do not have headphones to accommodate the differential output of the ADAU1787.
We will be updating the documentation for the EVAL-ADAU1787Z to make this distinction clearer moving forward.
But it is expected that noise performance will not be the same in single-ended mode compared to differential mode. Differential is the only mode supported by the ADAU1787 where the d/s specs can be guaranteed.
Dave T
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