Lm3886t / Lm3886tf ?

[matt09]

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?

 

[CJ900RR]

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...

 

[jackinnj]

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.

 

[matt09]

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 ?

 

[jackinnj]

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.

An externally hosted image should be here but it was not working when we last tested it.

 

[matt09]

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?

 

[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?

 

[jackinnj]

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

 

[facundonu]

i thought a mica layer and thermal compound added almost 1ºC/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...