Newbie question: why use non-isolated LM3875? - Page 2 - diyAudio
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Old 23rd September 2003, 05:03 PM   #11
joensd is offline joensd  Germany
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If I get you right Ron you´re just lucky that your heatsink is eloxated which isolates to a certain extent.
Slight scratches on the heatsink or some higher voltage and a "fault current" (don´t know the correct expression) will flow from V- to earth-ground (in case your heatsink is earthed).
Of course then the "fault current breaker" will become active and switch of your electricity in the apartment or whatever. (that´s at least how it works in our country)

Cheers
Jens
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Old 23rd September 2003, 05:27 PM   #12
roncla is offline roncla  United States
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No Peter ,no pad.However using the copper bar with the vortex tubes i have to put some type (havent designed it yet) of cover over the top and bottom just to keep Road(my cat) from getting zapped.
ron
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Old 23rd September 2003, 05:49 PM   #13
grataku is offline grataku  United States
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Quote:
Originally posted by roncla
No Peter ,no pad.However using the copper bar with the vortex tubes i have to put some type (havent designed it yet) of cover over the top and bottom just to keep Road(my cat) from getting zapped.
ron
I don't know if this idea is something to be too proud about...
yes, anodized Al is an insulator but it seems to me you are flying too close to the skyscrapers here. A pad is not such a big deal and it puts a nice level of safety between the chip and the heatsink. That way you could use a metal screw and tighten the chip a bit more against the HS.
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Old 23rd September 2003, 09:33 PM   #14
roncla is offline roncla  United States
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Yep!
ron
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Old 23rd September 2003, 10:41 PM   #15
jleaman is offline jleaman  Belgium
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Or do it like this..


Perfect example.
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Old 23rd September 2003, 11:26 PM   #16
Bricolo is offline Bricolo  France
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Quote:
Originally posted by JasonL
Or do it like this..


Perfect example.
You can safely remove the pad on this one, it will never cause a shortcircuit... since it has no pins anymore
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Old 23rd September 2003, 11:30 PM   #17
jleaman is offline jleaman  Belgium
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WHAT are you serious. i just cut the legs off a $34.oo mosfet to make a Sweet picture and i cant use it any more. NOOO..

HAHah jk,

it was a dead one that i kept for this kinda reason. : O )
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Old 24th September 2003, 12:34 AM   #18
Mikett is offline Mikett  Canada
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Someone should try the following. Take the unisolated one, and lap the contact surafce to the heatsink very carefully till it is perfectly flat and smooth. Similarly, also lap the heatsink contact are till it is also perfectly smooth. When you drop the chip on the heatsink it might " stick" because of the perfect contact. Now you can mount the chip with very little heatsink and have the best thermal contact. See if the heavy bass lines improve.

I suggest taping 600 grit emery on a flat pice of glas to do the above. The thermal resistance or lack of will be vastly superior to mica or sil pads. That way, the thermal and current protection doesn't begin to kick in and generate non linearities and compression.
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Old 24th September 2003, 07:45 AM   #19
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Quote:
Originally posted by Mikett
Someone should try the following. Take the unisolated one, and lap the contact surafce to the heatsink very carefully till it is perfectly flat and smooth. Similarly, also lap the heatsink contact are till it is also perfectly smooth. When you drop the chip on the heatsink it might " stick" because of the perfect contact. Now you can mount the chip with very little heatsink and have the best thermal contact. See if the heavy bass lines improve.

I suggest taping 600 grit emery on a flat pice of glas to do the above. The thermal resistance or lack of will be vastly superior to mica or sil pads. That way, the thermal and current protection doesn't begin to kick in and generate non linearities and compression.
computer 'overclockers' do this.
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If it aint broke, don't fix it. If it is broke, fix it.
If you can't fix it, take it apart and see how it "worked".
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Old 24th September 2003, 08:18 AM   #20
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i think the way rowland does it is a shure winner - i use this method and use the insulated chip (lm3886tf).....now if i just could find the rowland pics....
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