LM3886 works in a few seconds then it shut off. - Page 2

wintermute · 14th November 2009, 09:52 PM

Quote:

Originally Posted by Cyberzim

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?

Sounds like you have a short between Ground and the negative rail. though how it would work at all with that is beyond me... Also the fact that when you connect gnd to the speaker out instead of the gnd connection tends to imply that you have a break in the circuit between the main ground (between the caps) and the speaker out gnd... though looking at your board that seems unlikely...

I'd check for solder bridges between the negative rail and the Grnd lines (close to the chip they seem pretty close together.

Tony.

Cyberzim · 14th November 2009, 09:57 PM

There are no short cuts between gnd and negative supply.
Maybe it's the chip that there someting wrong with?
I took it from an old amplifier my brother found at his apartment at the garbage.
It was from an old PA speakerbox.

Regards,
Simon H.A.

Piggy · 15th November 2009, 04:35 AM

Quote:

Originally Posted by Cyberzim

There are no short cuts between gnd and negative supply.
Maybe it's the chip that there someting wrong with?
I took it from an old amplifier my brother found at his apartment at the garbage.
It was from an old PA speakerbox.

Regards,
Simon H.A.

Hi Cyberzim,
The 1uF cap looks like Cin, but where is Rin, the resistor connect the +ve input to ground? Did you measure the DC voltage at the output pin?

Piggy · 15th November 2009, 05:11 AM

Please read LM3886 datasheet Fig1 to see the +ve input arrangement. Cin should be connected to the "input". If you don't use a pot, Rin may be replaced by a fixed resistor. I hope this will solve your problem.

Cyberzim · 15th November 2009, 12:45 PM

I'm a bit unsure of what you mean, could you maybe draw it for me?
And the output measures -5.5V with ground as reference.

Regards,
Simon H.A.

Piggy · 15th November 2009, 01:20 PM

Sure...

Cyberzim · 15th November 2009, 01:45 PM

Okay I give up.
It can only be the chip that there are something wrong with since I just took it from an old PA box.
Thanks for all your help everybody.
I will now wait for my TPA3122's that will arrive tomorrow and start building a class-d amp.

Regards,

Simon H.A.

Juergen Knoop · 15th November 2009, 02:29 PM

simon, the chip is probably ok, the layout too. Your schematic is wrong! Solder a 47k resistor from pin 10 LM3886 to ground.
Regards

Cyberzim · 15th November 2009, 02:38 PM

Wow thanks!
Now it finally works.

Regards,
Simon H.A.

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14th November 2009, 09:57 PM	#12
Cyberzim diyAudio Member Join Date: Apr 2009 Location: Gentofte	There are no short cuts between gnd and negative supply. Maybe it's the chip that there someting wrong with? I took it from an old amplifier my brother found at his apartment at the garbage. It was from an old PA speakerbox. Regards, Simon H.A.

15th November 2009, 05:11 AM	#14
Piggy diyAudio Member Join Date: Nov 2009	Please read LM3886 datasheet Fig1 to see the +ve input arrangement. Cin should be connected to the "input". If you don't use a pot, Rin may be replaced by a fixed resistor. I hope this will solve your problem.

15th November 2009, 12:45 PM	#15
Cyberzim diyAudio Member Join Date: Apr 2009 Location: Gentofte	I'm a bit unsure of what you mean, could you maybe draw it for me? And the output measures -5.5V with ground as reference. Regards, Simon H.A.

15th November 2009, 01:45 PM	#17
Cyberzim diyAudio Member Join Date: Apr 2009 Location: Gentofte	Okay I give up. It can only be the chip that there are something wrong with since I just took it from an old PA box. Thanks for all your help everybody. I will now wait for my TPA3122's that will arrive tomorrow and start building a class-d amp. Regards, Simon H.A.

15th November 2009, 02:29 PM	#18
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	simon, the chip is probably ok, the layout too. Your schematic is wrong! Solder a 47k resistor from pin 10 LM3886 to ground. Regards

15th November 2009, 02:38 PM	#19
Cyberzim diyAudio Member Join Date: Apr 2009 Location: Gentofte	Wow thanks! Now it finally works. Regards, Simon H.A.

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