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Old 4th November 2012, 12:01 PM   #1
pra3718 is offline pra3718  India
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Default LM1876

I have already 2 chips in my drawer. So I wish to build Bi-Amp. Pls find attached file.
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File Type: pdf LM1876.pdf (39.5 KB, 206 views)
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Old 4th November 2012, 11:29 PM   #2
AndrewT is offline AndrewT  Scotland
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Do we get to see the schematic?

Have a look at the route the fast transient currents must follow into and out of the HF decoupling as they pass from Output PIN to output Zobel and back again.
With a route that long, can any fast transients pass around the loops?
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Old 5th November 2012, 05:27 AM   #3
pra3718 is offline pra3718  India
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Quote:
Do we get to see the schematic?
Input Cap not added, assume can be fitted at crossover output.
Zobel not added.
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Old 5th November 2012, 09:47 AM   #4
AndrewT is offline AndrewT  Scotland
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The schematic shows Cs.
You have placed the four Cs capacitors on the PCB, but in the wrong place.
The fast film or ceramic parts of Cs must be at the power pins and must be connected together in the shortest loop possible. The junction so formed is then connected to the corresponding junction of the electrolytic Cs. This common junction for all four Cs caps must be close to the OUTPUT PIN of the amplifier. Now connect the XZobel from OUT to Cs.
That is the ONLY way to allow the very fast rising and falling transients to pass around the Cs decoupling routes. Your decoupling route goes around the outside perimeter of the PCB and is about 10 (ten) times too long to be effective. The added inductance very effectively prevents the fast transients getting to their destination. In addition you have enclosed all the low level signal traces and components INSIDE the loops carrying those output currents. That makes for a good transmitter and receiver of unwanted distortions.

Start again.
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Last edited by AndrewT; 5th November 2012 at 09:49 AM.
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Old 5th November 2012, 12:55 PM   #5
pra3718 is offline pra3718  India
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I tried my level best.
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Old 6th November 2012, 08:14 AM   #6
AndrewT is offline AndrewT  Scotland
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There are many Threads where Members ask how to layout amplifiers.
Go and read and if you agree then adopt the ideas that suit you.
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Old 7th November 2012, 01:20 PM   #7
pra3718 is offline pra3718  India
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One more try
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Old 7th November 2012, 01:51 PM   #8
AndrewT is offline AndrewT  Scotland
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You still have the decoupling capacitors connected by a long route that passes around the whole PCB. That route can never be short !!!!!!!!!!!!
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Old 8th November 2012, 03:15 PM   #9
pra3718 is offline pra3718  India
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Infact, Post # 4 is well descriptive, I read several times to understand what you want to say. Being not an electronics man, I understood few of them.

I tried to copy the style of "LM4780 SS Pcb" which appreciated by many members. My layout may be looks like pinkmouse's pcb but may not technically similar or correct.

But, if I remember "That route can never be short !!!!!!!!!!!!" I should concentrate to another layout.

Best Regards.

"YOUR DREAM DOESN'T HAVE AN EXPIRATION DATE. TAKE A DEEP BREATH, AND TRY AGAIN."

Pls just look pdf for my todays job.
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Old 8th November 2012, 04:53 PM   #10
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Must the LM1876 have both pins 2 and 15 connected?
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