LM3886 works in a few seconds then it shut off. - diyAudio
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Old 14th November 2009, 05:57 PM   #1
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Default LM3886 works in a few seconds then it shut off.

Hi,
I have made my first pcb for lm3886 chipamp.
When I add supply it works because I can hear a little noise from the speaker and when I touch on the input it reacts, but after a few seconds it suddenly shut off.
Anyone have an idea of what the problem could be?
I have attached my pcb-layout.

Thank you,

Simon H.A.
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Old 14th November 2009, 06:23 PM   #2
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Sounds like its getting hot
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Old 14th November 2009, 06:25 PM   #3
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It's not hot at all. I have mounted it to an oversized heat sink and if I touch the chip it's cold.

Regards,

Simon H.A.
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Old 14th November 2009, 06:26 PM   #4
PMA is offline PMA  Europe
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HF oscillations.
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Old 14th November 2009, 06:28 PM   #5
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Is there a way I can test if it's HF oscillations? I don't hear any whizzing noice or so when it plays music.

Edit:

I checked with my oscilloscope to the output, and I see no oscillations at all.

Last edited by Cyberzim; 14th November 2009 at 06:37 PM.
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Old 14th November 2009, 06:52 PM   #6
gfiandy is offline gfiandy  United Kingdom
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hi, What are your power rails as you may not be drawing enough current from the mute pin to keep the amplifer out of mute.

Data sheet indicates you need RM = (|VEE| − 2.6V)/I8 where I8 >= 0.5 mA.

Regards,
Andrew
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Old 14th November 2009, 06:56 PM   #7
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here is the output when playing music.
It seems like when having no load it can work for much longer time before it shut down.
My powersupply is about +/- 25V.
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Old 14th November 2009, 07:04 PM   #8
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I will try change the resistor for the mute to 2K7, then I have at least 8mA of current.
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Old 14th November 2009, 07:10 PM   #9
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Didn't work
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Old 14th November 2009, 07:30 PM   #10
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Okay, I've discovered that if I connect the gnd from the supply to the speaker instead of the gnd from my amplifierboard It works until it starts clipping.

Edit:

I also discovered that the voltage from gnd -> "+" on my board measures 48V and from gnd -> "-" measures 0volt. How can that be true?

Last edited by Cyberzim; 14th November 2009 at 07:48 PM.
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