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Old 17th July 2003, 08:37 PM   #1
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Default Is LM3875 chip waterproof?

I'm working on a new project, where GC chip would not be mounted to the heatsink (after reading pads thread I have some reservations about mounting the chip to piece of metal) but would be immersed in copper cylinder filled with water or some other fluid. My question is if this will effect the chip in a long run? I would be using an isolated version of a chip.

There are possible advantages to this approach of heat dissipation, mainly better damping and avoiding vibration pick up from the chassis. It is also more original way of building an amp, as I promised the members of AA to come up with something refreshing and original
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Old 17th July 2003, 08:41 PM   #2
Bricolo is offline Bricolo  France
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I think that the chip is water proof. You'll just have to take care about the pins. They musn't touch the water!
Or use a dielectric (like oil)
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Old 17th July 2003, 08:42 PM   #3
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So, if using oil, the pins can touch it?
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Old 17th July 2003, 08:43 PM   #4
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Hi,

Quote:
Or use a dielectric (like oil)
And it has a better damping factor too.
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Old 17th July 2003, 08:45 PM   #5
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Quote:
So, if using oil, the pins can touch it?
Of course not. You trust dielectric absorbtion of oil? Great risk of contamination, especially long term.

cheers
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Old 17th July 2003, 08:46 PM   #6
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Hi,

Quote:
So, if using oil, the pins can touch it?
Some oils have dielectric properties that isolate upto 23KV/mm...think that should be good 'nuff?

Cheers,
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Old 17th July 2003, 08:46 PM   #7
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Any fluids that are "pins" friendly?
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Old 17th July 2003, 08:46 PM   #8
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Most parts today can withstand cleaning with water..BUT...they need very often to be dried in a oven for quite some time.

Normal plastic (epoxy) absorb moister (failure eventually) so I unrecommend this! Maybe if you use some insulating fluid, oil but the idea seems not to be very good.

You could make a tin box of copper, brass and then sink box down in the fluid. Make it completely fluid proof.

As answer to your question: NO part is water proof unless the datasheet tells you so.
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Old 17th July 2003, 08:54 PM   #9
UrSv is offline UrSv  Sweden
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Peter,

Are you sure that the heat dissipation is better like that? Sounds to me that it would be worse than when mounting with pad on sink. I suspect hotspotting would be way worse. Obviously I don't know for sure, it just seems logical, to me at least, that it would be way worse.
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Old 17th July 2003, 08:56 PM   #10
fedde is offline fedde  Netherlands
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Kewl, a gainclone that's running on oil ;-)

Watch out though that certain countries do not get interested in your oil though! Also, watch out for excessive volumes or your amp will explode

But now more seriously:

I think that it's risky to use oil or water on the chip. Even if the pins are not in the fluid, they will be during transport of the amp. Though what you COULD do is to make a metal box filled with oil (and closed well!) and mount the chip on top of it. The resonances of the metal will be damped by the oil and the heat of the cheap will be dissipated quick by the fluid. Though maybe the thermodynamic effects of the fluid will also cause resonances...

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