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Old 8th August 2006, 12:15 PM   #1
matt09 is offline matt09  United Kingdom
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Default Lm3886t / Lm3886tf ?

Very simple question.

Are these chips the same

I can get some cheap LM3886T but not LM3886TF, as stated on chipamp.com

Will there have to be any changes to a standard gain clone in using an LM3886T?
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Old 8th August 2006, 12:20 PM   #2
CJ900RR is offline CJ900RR  Sweden
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It's the same chip. No changes are needed to be done. The only differens between those two is that the TF has a insulated tab. The T-tab is not insulated, and are connected to V-

If you attach a LM3886T to a heatsink and dont isolate it (no plastic screw and isolation-plate) you will have 35V at the heatsink...
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Old 8th August 2006, 12:24 PM   #3
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the LM3886TF is the insulated version and has a thermal impedance considerably higher than the LM3886T -- the difference is 1 C/W which means that you will need a heat sink almost double the surface area of that using the LM3886T -- or a fan.

I see no benefit in using the LM3886TF in DIY applications -- there is no sonic benefit, the chips are identical. Perhaps there is a metaphysical benefit -- you could get the same effect with a tumbler of gin.
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Old 8th August 2006, 12:24 PM   #4
matt09 is offline matt09  United Kingdom
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Hello, thanks for the quick reply.
So no changes to the psu are needed atall - the snubber psu would be fine? and likewise brians amp circuit could be used without a problem aslong as the back plate was insulated?
no changes?
I am a total newbie, just want to make sure theres nothing else

jackinnj you talk as if I am chosing to use an LM3886TF as oppose to an LM3886T which is what I am actualyl using.
In regards to the thermal insulation does this mean that the LM3886T will only need half the size heatsink of a LM3886TF ?
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Old 8th August 2006, 12:35 PM   #5
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with a +/- 35VDC supply for the "T" version you need a heat sink with a thermal impedance of 2.8 C/W -- about 22 square inches of surface area. For the LM3886TF you have to increase the surface area very substantially. Here's a heatsink nomograph to help you out. This is not trivial.

Click the image to open in full size.
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Old 8th August 2006, 12:43 PM   #6
matt09 is offline matt09  United Kingdom
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Hello,

Does this therefore mean that using LM3886T's would be a bad idea as a massive heatsink would be required?

Could I get away with not insulating the back plate if I isolated the heatsink from everything else, then there would be no problem of needing a bigger heatsink?
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Old 8th August 2006, 01:14 PM   #7
matt09 is offline matt09  United Kingdom
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anyone? Would it be ok if the heatsink was isolated away from grounds, etc to not insulate the tab so that I get more heat dissapated per square inch and not need a larger heatsink?
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Old 8th August 2006, 02:39 PM   #8
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Quote:
Originally posted by matt09
anyone? Would it be ok if the heatsink was isolated away from grounds, etc to not insulate the tab so that I get more heat dissapated per square inch and not need a larger heatsink?
with heat sink compound and a mica insulator you add 0.2 C/W to thermal impedance.

for the Bridgeclone (which will throw off 120 watts around the clock into an 8 ohm load) I insulated the heatsinks. If you are just starting out this is not a good idea -- besides -- the thermal protection of the Overture series chips really does work.

jack
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Old 9th August 2006, 01:38 AM   #9
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i thought a mica layer and thermal compound added almost 1șC/w, so it would be the same using one or the other if you don't want to have 35v at the heatsink.
but i guess i was wrong...
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