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Old 17th January 2008, 10:33 AM   #1
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Default Chipamp lm3886 qns

hi guys,

I was wondering the ecaps at c1,c2,cm have any impact on the sonic qualities of the amp.

Would it matter if the C1 and C2 are of different value, I busted 1 C2 on the amp board, and i couldnt get a replacement of the same brand and value, I only have some 220uf with me.

I am wondering if it will affect any thing if I am going to use some 220uf/50v on the c2 spot on both amplification board.
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Old 17th January 2008, 02:04 PM   #2
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any help from anyone?

someone, pls help me here..
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Old 17th January 2008, 02:09 PM   #3
ratza is offline ratza  Romania
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Why don't you just place them on the board and see yourself how it sounds?
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Old 17th January 2008, 02:22 PM   #4
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Quote:
Originally posted by ratza
Why don't you just place them on the board and see yourself how it sounds?

Would it cause any imbalances?
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Old 17th January 2008, 02:51 PM   #5
AndrewT is offline AndrewT  Scotland
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can you post a link to the schematic you have used for referring to C1 & C2?
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Old 17th January 2008, 03:37 PM   #6
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hi andrew, nice to see you.

I have gotten the boards from chipamp.com
and the manual from here, http://chipamp.com/lm3886.shtml

I just soldered in a 220uf in the c2 and the whole amp is working, on a chopping board though. Sounds okay, but am not sure cos its a little weird as of now and I am thinking it might need some run in.
Do you see any potential problem for this c2 to be of a different from the 100uf stipulated in the manual?

The next concern i have is regarding the heat. It was on for a moment and ts running hot. I am planning not to use any heatsink but mount the chip on the bottom panel of the chassis, which is rather large, at about 45cm x 30cm, would that be sufficient.
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Old 18th January 2008, 04:22 AM   #7
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That cap value is okay; however, if its a main rails cap, it needs to be the same value as its partner.

The weird sound you're experiencing is probably coming from clipping and / or the metal 1k resistor.
See my post here on how to "unscreech" the kit.
http://www.diyaudio.com/forums/showt...86#post1403686

Thermal paste like Artic Ceramique, should be used. For direct to chassis mount, you need a heat spreader. That's a 3cm square thick metal plate with thermal paste on both sides. The chip bolts to that thing and that spreads the heat *away* from the chip and onto the larger metal surface beneath it.
A chassis also needs an air intake below the chip and an air outlet above the chip for venturi/convection ventilation--otherwise you have created an oven.

EDIT: In this case, the small, thick, heat spreader bolts to the case with four screws. The chip bolts to the heat spreader plate.

Have fun with the little kits. They *can* be good.
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Old 18th January 2008, 04:46 AM   #8
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Assuming that i dont do the unscreehing of the treble, would it be alright for me to just mount the chip directly on the base panel.
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Old 18th January 2008, 09:46 AM   #9
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by marcusdeming
........would it be alright for me to just mount the chip directly on the base panel.
probably not.
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Old 18th January 2008, 12:38 PM   #10
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Quote:
Originally posted by marcusdeming
Assuming that i dont do the unscreehing of the treble, would it be alright for me to just mount the chip directly on the base panel.
This depends on:
Voltage?
Thickness of the base panel?
Can cool air get into the enclosure?
Can warm air get out of the enclosure?
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