LM3886 amp

[kristopher612]

Hi there.  i just bought Brian GT's 3886 stereo chipamp kit, and need to get a good heat sink.  is this http://www.apexjr.com/Sinks.htm 9.95 one good enough for both.  they're going into an old 31 band EQ 2U rackmount enclosure, so there is plenty of ventilation, and i'm not opposed to a small fan either. or would the 15.00 one just below be better?  thanks for any help given.

[Filament]

I have the same kit.  It is my understanding that you need to mount the left and right channel boards in such a way that the LM3886 actually screws onto the enclosure.  I'm sure you could do the same with a heat sink but I've seen lots of guys put some thermal paste on the back of the chip and mount it directly to the chassis.  I believe Graydon at GDS amps has some pictures on his blog.  Also, Brian has a number of pictures on his website.  When in doubt, steal some inspiration.

[kristopher612]

yeah i guess i should see what some other people have done with these.  some interesting ideas could be had.  but i will definitely need a big heat sink to run 2 of these at 50W output each.  but there is enough room that i guess i could think a little more out of the box on the how to part.  thanks for the advice!

[petemoore]

  LM3886-TF [if I remember the TF suffix correctly] has an insulated heat sink package, otherwise use mica spacer, the chip body of the 3886/ IIRC needs to be isolated from stray connections.
  Paste recommended, I used salvaged heat sinks...

[mydementia]

I used an old Pentium4 heatsink for my mono kit... tapped a #4 hole, used arctic silver for the thermal junction, and screwed it down - works great.
Have you checked out ssguitar.com for ideas?  Also, there are a lot of build pictures on the chipamp.com site (as well as the web).

Check it out - I'm sure you'll be pleased with the end result - Brian's boards are excellent!

Mike

[R.G.]

or would the 15.00 one just below be better?

The $15 one would be better. It's wide and short and has deep fins.

Heatsinks 101:
- for natural convection you want the fins to run vertically
- fins longer than about 3" give you diminishing returns because the air is preheated by the lowest part of the fins
- short and wide is good; fins about 1" to 2" deep is good; body plate of 1/4" or more is good
- fins closer than about 3/4" obstruct natural convection
- never use a fan unless you absolutely have to
- a heat sink that's 1% too big is a thousand times better than one that's 1% too small

[kristopher612]

wow thanks for the responses!  R.G., i was looking at apex jr again, and there is one below that that i think would be even better 15-1/2"x6-1/2"x1-5/8"  and it's already got 2 holes to screw into.  i htink that's the one i'm going to go with, unless you think the 15.00 one is still better.  having read the super long thread started by RDV and commmentated by yourself, i kind of figured that too big was better than just enough or too small, so i was really wanting to make sure that i wasn't wasting my time/money on something i would need to increase.  i dont mind spending the money, but i would rather pay shipping once instead of twice you know. 
i have looked at some of the build pics at chipamp, but haven't looked at pictures at ssguitar yet.  i will be looking at more build pics before i finish, just to get some ideas of what i like, and make that work with what i need.  thanks again guys!