LM3886 works in a few seconds then it shut off.

Cyberzim · 14th November 2009, 06:57 PM

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.

littlerick · 14th November 2009, 07:23 PM

Sounds like its getting hot

Cyberzim · 14th November 2009, 07:25 PM

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.

PMA · 14th November 2009, 07:26 PM

HF oscillations.

Cyberzim · 07:37 PM

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.

gfiandy · 14th November 2009, 07:52 PM

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

Cyberzim · 14th November 2009, 07:56 PM

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.

Cyberzim · 14th November 2009, 08:04 PM

I will try change the resistor for the mute to 2K7, then I have at least 8mA of current.

Cyberzim · 14th November 2009, 08:10 PM

Didn't work

Cyberzim · 08:48 PM

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?

14th November 2009, 07:26 PM	#4
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	HF oscillations. __________________ Pavel Macura, consultant http://cz.linkedin.com/pub/pavel-macura/4/783/637

14th November 2009, 07:28 PM	#5
Cyberzim diyAudio Member Join Date: Apr 2009 Location: Gentofte	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 07:37 PM.

14th November 2009, 08:30 PM	#10
Cyberzim diyAudio Member Join Date: Apr 2009 Location: Gentofte	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 08:48 PM.

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14th November 2009, 07:23 PM	#2
littlerick diyAudio Member Join Date: Nov 2009 Location: Lincolnshire UK	Sounds like its getting hot

14th November 2009, 07:25 PM	#3
Cyberzim diyAudio Member Join Date: Apr 2009 Location: Gentofte	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.

14th November 2009, 07:52 PM	#6
gfiandy Audio Engineer diyAudio Member Join Date: Jul 2003 Location: Cambridge UK	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

14th November 2009, 08:04 PM	#8
Cyberzim diyAudio Member Join Date: Apr 2009 Location: Gentofte	I will try change the resistor for the mute to 2K7, then I have at least 8mA of current.

14th November 2009, 08:10 PM	#9
Cyberzim diyAudio Member Join Date: Apr 2009 Location: Gentofte	Didn't work

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