LM1971: LM1971: Output slight hearing when Mute

Hi, Pramod,

Welcome to E2E and thank you for your interest in our products!

The mute attenuation level (96dB) should be enough to mute the device. Have you tried to measure the attenuation level so we can see if there's another attenuation level being configured instead of the mute level?

Best regards,
Luis Fernando Rodríguez S.

Actually I don't have such device with me to measure attenuation. Anyway I set "address register = 0b0000 0000" and "data register = 0b0011 1111"  but it didn't work because I can slightly hear the audio at the output. Then I tried "data register = 0b1111 1111" but it still didn't work... 

As per the datasheet, it says when muted it physically disconnect the output from the input. I wonder how it still leak some signal.

Thanks...

Hi, Pramod,

Thank you for the additional information you provided.

Have you measured the attenuation that you get at the output? I think this could give us a better approach to this issue. As you mentioned, we shouldn't expect to hear anything on muted state.

Best regards,
Luis Fernando Rodríguez S.

The leakage is likely caused by your PCB layout. You show us a two-layer board with no planes and no defined path for signal returns.

The data sheet recommends buffering the reference input (pin 1) so your 1/2-rail reference doesn't vary.

The LM4558 is a lousy choice for the output buffer. Something with a FET input is recommended to minimize loading on the resistor ladder which does the attenuation.

While the data sheet doesn't explicitly recommend it, I would buffer the input with an op-amp, too.

I have already installed the attenuator in the amplifier and I am satisfied with the current situation... anyway I will try to change the output buffer to a FET input buffer.. could you please explain me more about no defined path for signal returns thing..

thanks for the valuable tips..

Hi, Pramod,

Do you have any update on this issue? Did you get additional observations?

Best regards,
Luis Fernando Rodríguez S.

No any updates yet... I'm still trying to understand above mentioned no defined path for signal returns thing. After that I will probably try a new PCB and will certainly post updates here.

Thank You.

Pramod Wickramasinghe said:

No any updates yet... I'm still trying to understand above mentioned no defined path for signal returns thing. After that I will probably try a new PCB and will certainly post updates here.

Thank You.

Signals need a return. Follow the traces. Where does the return current go?