PCM6340-Q1: PCM6340 collects reference noise from power amplifier feedback, with continuous buzzing background noise

Is this understanding of the system correct?

The analog referenceof the amplifier is fed as a Left and Right signal to the PCM6340 ADC. This is digitized and combined with the MIC signal that comes from the AKM Codec. It is observed that a Buzzing sound is coming from the PCM6340 Circuit?

Does the noise go away if the analog input to the PCM6340 is disconnected?

Hi Sanjay

I will confirm and ask you to check if there are any obvious issues with the following schematic diagram

I have been looking at this schematic. It's a bit hard for me to understand the connection of nets since I do not have an overall idea of the scheme.

Lets wait for the response

Hi Sanjay,

Your understanding is correct, there is noise in the sound recorded in PCM6340.

The sound is transmitted to the SOC, which can record and the recorded file can hear noise.
Unable to input disconnect, once disconnected, sound cannot be recorded,

Hi Sanjay,

We are synchronizing a customer's information with you. There is no noise in the input pcm6340 of the microphone, but there is noise in the input pcm6340 of TAS6424

This noise that you have in the Amp signal path may be an earthing issue.

Is the ground of the power amplifier physically joined to ADC Ground?

Hi Sanjay,

They are the same GND

OK

Does the noise stop if the Amplifier is switched off? I would suggest to try this as a first step.

Hi Sanjay,

It has been confirmed that there is background noise in the sound recorded by PCM6340 from 6424

Is the sound coming from the amplifier noise free? I mean is the sound through amplifier noise free when heard through a speaker?

Hi Sanjay,

There is no noise heard by the speaker

Hello, 

Sanjay is out of office today but he will get back to you tomorrow. Thank you for your patience here!

Regards,
Sydney Northcutt 

In this case i would suggest the below.

1.Keep the amplifier on driving the loudspeaker.

2. Connect the side of C14 coming from the amplifier to ground. Since the ampo and ADC Ground are tied together a single ended input to the ADC should be fine. Choose I2C Setting for single ended input.

Check if noise is gone . If not:

1. Keep amp on.

2. Disconnect ADC From amp output. Replace with a signal generator giving 1VRMS at 1K and check for noise in output.  This will let us know if there is some grounding issue.

Please let me know the results