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Old 4th January 2013, 10:56 PM   #1
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Default toroidal transformer wire identification!

hello

i am making a power supply for my LM1876 chip amp.

here is the schematic im using:

Click the image to open in full size.

the transformer i have is wired like this (according to the datasheet)
Click the image to open in full size.

so.... which wire goes where to the bridge rectifier? the red/brown?

really dont want to fry it up, so any advice would be greatly appreciated!

thanks
úlfur
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Old 5th January 2013, 02:55 AM   #2
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Join the red and brown, that's is your 0v, where you put the ground of capacitors

the green and blue goes for the rectifier
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Old 5th January 2013, 10:36 AM   #3
Mooly is offline Mooly  United Kingdom
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If you are unsure then use a bulb tester (low wattage mains filament bulb) in series with the mains. That will limit current and enable you to check it safely. The bulb should be out (not lit) when its correct and all DC voltages will be correct too.
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Old 5th January 2013, 11:17 AM   #4
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A picture paints a thousand words.
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Old 5th January 2013, 02:59 PM   #5
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thanks for your replies!

alas, i hooked it up like you suggested - and POOF! - my LM1876 chip blew up. i have no clue what could have gone wrong.

i am using this schematic;
Click the image to open in full size.

any thoughts?
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Old 5th January 2013, 03:12 PM   #6
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Try measuring the DC voltages from the power supply. Just check that you do have +/- 25V with respect to 0V.

Have you got bridge rectifier the right way around? The LM1876 would certainly fry if you inadvertently connect + to - and - to +.
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Old 5th January 2013, 03:24 PM   #7
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If all is well just recheck your soldering very carefully - look for any shorts.

Also check your speakers and their cabling for shorts.
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Old 5th January 2013, 03:26 PM   #8
Marra is offline Marra  United Kingdom
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As Mooly recommended use a bulb tester. One has saved my *** on a few occasions.
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Old 5th January 2013, 04:28 PM   #9
Mooly is offline Mooly  United Kingdom
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You're going to have to replace the chip and power it up with the bulb tester to prevent damage. And NO speakers connected either.

I see the diagram doesn't show a zobel network... very unusual... I would certainly add one. Say 6.8 ohm and a 0.1uf cap from the output to ground.
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Old 5th January 2013, 05:34 PM   #10
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just replaced the chip... now nothing happens at all... must have fried something else on the board too.

i guess it's back to the drawing board...
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