LM4838: LM4838 has noise sound with speaker

Hi, Yi,

Let me take a look at this issue and I will provide my feedback as soon as possible.

Best regards,

Luis Fernando Rodríguez S.

Hi, Yi,

Thank you for the details you provided.

I took a look at the schematic and I couldn't find anything wrong.

Could you perform some tests for me?

Could you run a single 1KHz sine wave tone and do an FFT at the codec output and then at the amplifier output? This is to verify how the noise floor and the signal level changes.

Best regards,
Luis Fernando Rodríguez S.

Hi, Yi,

Do you have any feedback on this? 

Thank you.

Best regards,
Luis Fernando Rodríguez S.

Sorry for my late reply and thank you for your reply.

Schematic: I have understood that there is no problem.

Could you run a single 1KHz sine wave tone and do an FFT at the codec output and then at the amplifier output? 

→ OK, let me confirm with you.

　1. Play 1KHz sine wave audio

　2. Measurement waveform：Codec output and amplifer output

Hi, 

Thank you for your response.

This is correct. We would like to compare the response on the audio codec and the amplifier output in order to have a better approach to this issue. In some cases, the codec to amplifier connection may require of additional filter techniques to have a clean output. This test will help us to determine what is required and if the problem comes from the audio codec or the amplifier.

Best regards,
Luis Fernando Rodríguez S.

Hi,

Do you have any update on this? Were you capable to try the tests that I mentioned?

Thank you.

Best regards,
Luis Fernando Rodríguez S.

Hi, 

Sorry, It is difficult to present the problem again.

Our test is to use the audio source file specified by my customer first, and I will test 1KHz audio again in the future 

According to the test results, we have seen some differences. Please refer to the attached file speaker_noise_20210218.pptx.

Page 1-2 is LM4838 output, and it can watch video MVI_2004.mp4

Page 3-4 is codec output, and it can watch video MVI_2003.mp4

speaker_noise_20210218.pptx

MVI_2004

https://youtu.be/6AnnhtzVrAw

MVI_2003

https://youtu.be/1G0H-j7-lrI

Beat Regards,
Yi Kaz

Hi,

Thank you for the additional information. Our team will take a look at this and will provide a response as soon as possible.

Best regards,
Luis Fernando Rodríguez S.

Hi, 

I had test 1KHz audio again. Please refer to the attached file speaker_noise_20210219.pptx.

I found that there is noise in the codec output signal (Net HD_FRONT-R and HD_FRONT-L in the schematic). According to your experience, will it be caused here?

speaker_noise_20210219.pptx

MVI_2012 https://youtu.be/NI68O1vlLxE
MVI_2013 https://youtu.be/bDnkLsfB9G0

Hello, 

Thank you for the additional information. We are still looking into this and will provide a response as soon as we can. 

Best Regards, 

Justin Beigel

Hi,

Based on your observations, as you mention, the distortion on the signal comes from the previous stage and LM4838 is only amplifying this signal.

Perhaps this is a faulty digital data (offset, bit count, format, etc) or clock configuration on the codec, however as this is a different part we cannot provide much more insight.

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

Hi,

Always thank you for your reply. I think the same as you now.

I will test if codec and LM4838 are not connected. To make sure it's not caused by LM4838.

I will continue to ask if I have other questions.

Thank you.

Beat Regards,
Yi Kaz

Hello, 

I will close the thread for now while you are testing. Feel free to add any questions you have here or in a new thread. 

Best Regards, 

Justin Beigel