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Old 25th August 2005, 10:38 AM   #1
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Default Input Capacitor Polarity

I'm trying to start an amplifier up (LM3876) but at +-13VDC my speaker starts popping.

I noticed that my input capacitor's polarity is the other way around than National's Datasheets, would this be the problem or does the polarity of THIS cap not matter?
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Old 25th August 2005, 10:41 AM   #2
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Minimum voltage is _very_ near that you have. Have you checked the datasheets about that? You have a feature which is called "under voltage protection". How about the mute resistor?
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Old 25th August 2005, 10:53 AM   #3
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The problem is probably that I'm scared to give it horns. This is a hobby for me and getting cash a tad limited. I don't want to blow the IC since it costs a bit here.

The popping's speed increases with the voltage to up to 17VDC ( there I lose the heart to go higher for now.) It sounds like a Harley

PS I'm running a variac into a 35-0-35 DC supply (No regulation but HUGE caps).

The components aren't getting warm yet, do you think I should go a bit higher?
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Old 25th August 2005, 10:58 AM   #4
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PS It's +-17VDC not just 17V
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Old 25th August 2005, 11:02 AM   #5
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How ldoes your decoupling of the supply voltage look like? Have you any caps near the IC? How does your ground look like?

Have you checked the datasheet and the AN-1192 application note carefully?
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Old 25th August 2005, 11:11 AM   #6
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This is the PCB layout with a copper pour
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Old 25th August 2005, 11:13 AM   #7
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With a copper pour
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Old 25th August 2005, 11:18 AM   #8
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With a copper pour
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Old 25th August 2005, 11:23 AM   #9
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And the schematic. Please note that I changed the 4700uF Caps to 220uF.
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Old 26th August 2005, 05:22 PM   #10
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even i had such a problem before.

but my problem was solved when i placed the cd player on a pillow.

the speaker vibrations were making the cd player pop. looolll

i think ur problem might be due to caps. have u places caps at the chips psu pins? and also a cap at the mute pin and ground.

and i would suggest using 2 4700uf caps instead of one 10000uf cap. in psu.

i think ur problem might be solved.

and if ur not so confident i would suggest to put a fuse near the speakers so that they dont blow up.
usually this doesnt happen in chip amps as they have lots of protection circuitry
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