LM3886 Amp - Transformer Question

[ApexJr.]

Also for heatsinks:

www.apexjr.com/Sinks.htm

Steve @ Apex Jr

[mydementia]

Yeah, Steve, I saw those sinks on your site...
I also dug around chipamp.com in the 'completed builds' section and saw one guy using a 3x4x0.5" hunk of copper - that sounds better to me than trying to accommodate a big finned heatsink (something in the 4x6x8" range). 
I'm still looking...
mike

[joecool85]

The problem is with a solid piece of metal is that it will only work for a certain amount of time without shutting down.  It will basically absorb heat, but not disperse the heat into the air.  Fins are really required to get the job done well.

[mydementia]

This reminds me of a heat transfer problem from college...

Which dissipates more heat, a heatsink exposed to a volume of ambient air constantly increasing in temperature (Conduction path: Chip-->Heatsink-->Air-->Aluminum Enclosure), or a highly conductive heatsink (copper chunk) thermally coupled to the aluminum enclosure (thus conducting to the larger aluminum enclosure to an ~infinite volume of constantly 'cool' air (Conduction path: Chip-->Copper chunk-->Aluminum Enclosure)

Here's a snapshot of the 'gainclone' that caused me to raise this question:

[teemuk]

In case it was unclear to someone, that enclosure is a heatsink and the copper mainly just a thermal conductor to it.

Basically, if you want to use small heatsinks you better decrease all thermal resistances and/or use a fan. The answer to your college problem depends on many variables, see:
http://www.ssguitar.com/index.php?topic=404.msg2976#msg2976

[mydementia]

How about an old P4 CPU Heatsink?  Looks like 1.25" tall, 2.75x3.25" with 23 fins...
I'm running a single LM3886 (PS and Amp boards/kits from Brian at chipamp.com) with 22-0-22V from the transformer into an 8-ohm load oughtta give about 35W... maybe this will work?

[joecool85]

Running at 35 watts you *might* be ok passively, with a fan it would be perfect.  You could always try it and see, the chip has thermal protection so it will shut down before damage occurs.