Audio amp output volume become lower or quiet.

Aug 15, 2006 4 Replies
B

Dear All,



My audio output sometimes has no output.


The situation is :


  1. The output volume become lower. ( but I didn't change VR yet ), sometimes I re-plug power, it become normal again.
  2. The output volume become quiet.


The circuit is no change, the different is only plug power time, I debut the poewr AMP too hot, and lost its operation point. ( but I am not sure )



I remember that when I was 17, I bought a audio amplifier, the boss told me, when you are going to power on amplifier, remember to change volume to lowest first, or may hurt the amp. I didn't do that too much, about 5 years later, the amp become the situation as my audio circuit now - volume become lower or quiet sometimes.


Could you please advice ? Thank you very much.



Best regards, Boki.



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Boki =E5=AF=AB=E9=81=93=EF=BC=9A

Hi All,

Sorry, "plug power time" that I means "power on time".

Thanks. Boki.

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E

So, you think the power amp *may * be overheating ? It might be 'thermal shutdown'.

More likely hurt the speaker actually. It's the trouble with non dc-coupled ampliifers.

What's the amplifier chip ?

Graham

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Eeyore =E5=AF=AB=E9=81=93=EF=BC=9A

Today, I am testing it without housing. Now I think it may not this problem.

ed

My circuit that extends the original PCB.

The original PCB has AV output for audio.

The original circuit is:

pcm1742ke -> lmc6482aim -> Audio output jack.

Now:

pcm1742ke -> lmc6482aim -> LM386 -> Speaker. (The original audio jack keep there, no cut )

The problem now is:

The audio is quiet in the most time, if I adjust the VR ( variable resistor ), sometimes ( about 10% ) the speaker will output audio abruptly.

If I volume down by VR slowly, and then volume up, the problem come again, very low volume.

Best regards, Boki.

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E

Ok.

Have you checked the LMC6482 output at the same time ? I assume it's OK ?

I don't recommend the LM386 btw. It's ancient and not really very good. Are you using low supply voltages too ? I'm sure it's not suitable for that.

Consider some of the TI PWM ( Class-D ) ampliifers that are intended for low voltage operation, they're obviously much more efficient too.

What's your output power spec ?

Graham

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