LM4780 and noise (question)

john_lenfr said:
My problem is:

I can hear a very low noise (into speakers) when I sleep in my room (so it's very low but when I turn at max volume, it increases).

How can I remove this thing?


Are you using a preamp?
If the noise increases when you increase the volume, the noise may be coming from your preamp or from your source (CD player, etc.).

We really need more information before we can offer too many suggestions.
 
john_lenfr said:
My problem is:

I can hear a very low noise (into speakers) when I sleep in my room (so it's very low but when I turn at max volume, it increases).

How can I remove this thing?
Is it a "random" noise (like the inter-station FM noise), or an "oscillatory" noise like motorboating? IF you havent' used the supply bypass caps which national semiconductor recommends -- THEN use the supply bypass caps which national recommends. (100nF in parallel with 10uF).

also check the DC offset of the amplifier -- the noise on the supply lines is amplified through the ampchip.
 
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I did this, exactely the same. (but cs7 & cs8 are not on the pcb because of the size)


So:

@ jackinnj :

You think of cs1 & cs2. So no need to add.


@ SRMcGee:

You think of Rm. So no need to add.


The sound is like a motorboard. But for accuracy, I tried to record it.I was at max level when I record with my mp3 player and a mic. I was at 3cm of the speaker:

NOISE (.mp3)