we use your LM4871LD audio amp on ten similar double-layer PCBs on our university. We have a strong noise on some of the PCBs. You can hear a "scratchy sound" when there is no signal input on the IN- Input and you can hear it also when music is played.
To eliminate the noise on that PCBs we have to touch the two 20k resistors on their solder areas next to the IN- Input. The sound output is then (almost) perfect.
We still did a re-design (see last page of the attachment) because we haven't used capacitors exactly as mentioned in the LM4871 datasheet. But the effect is still the same on some PCBs in the re-design.
Do you have an idea or re-design proposal what we can do to avoid that behavior in our actual design and in further designs?
Any help would be great.
All the best