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PCM5142: + DIR9001 Heavy noise on the output! Signal heavy clipping and when paused i get white noise

ionut remus Remus
Prodigy 25 points
Part Number: PCM5142
Other Parts Discussed in Thread: DIR9001, , PCM5102, PCM2902

Tool/software:

Hello,

I recently started a new project that involves 4x DACs.

I usually use DIR9001 as a receiver and now i chose to get the PCM5142 due to the direct output.
In the past i used WM8740 but since power and simplicity is important now, PCM5102 or PCM5142 was more suited.

I used the same schematic as i usually do for the DIR9001 with a DA102JC transformer, ST3485EBD as a translator and made sure all the decoupling and filtering capacitors are present.

For the PCM5142 i used it in hardware mode only, and hooked it up next (actually 1 cm lower then the DIR9001) and start it up.

I had a PCM2902 sound card to get the Coax SPDIF output and everything was going great, until i hooked everything up to an amplifier and than i heard that the sound is clipping like hell....or it's distorted, as it's so bad that i can't make a difference. Once i stop the music a loud white noise is still on the background (normal operations) and i kind  of hear some clicking (not really sure as it's short) like some clock it's entering the audio stream somehow.

I was tested also with the internal SCK as well with the DIR9001 SCK and the same issue is occuring.

In the past i played as well with PCM5102 and everything went really well. With the PCM5142 is not going as smooth as i though and i will need some suggestions on what to check....or maybe i did something wrong....



The decupling capacitors aren't in the pictures above but i definitely added them together with 10uF capacitors.

Thank you.

  • 0
    Prodigy 25 points

    Hello,

    Over the weekend i have reviewed my schematic and as well the PCB.
    The schematic was ok, and have came back to the drawing board of the PCB.

    This time i paid much more attention on the routing of the I2S signals, made a very accurate AGND and DGND separation where there are meeting only at the power supply through a start configuration and voila.....when i powered up, everything worked from the 1st try without needing to adjust anything.

    Conclusion:

    1, Separate AGND from DGND, it's a must every time you work with mixed signals, and make sure the return is properly adjusted, as well the connection made in only one single point 

    2. Make sure you route the I2S signals no where near AVDD and (as the datasheet also says) no where near the analog signals

    3. Separate the VDD from AVDD, preferably add a secondary regulator, but you can also do it with some resistors or ferrite beads

  • 0 in reply to ionut remus Remus
    TI__Mastermind 30671 points

    Thanks for sharing and the update.

    Regards,

    Arash