1875 heatsinking (bolt to steel plate?)

[wicked1]

I'm making a computer speaker system w/ sub and lm1875 amp for the fullrangers. I built the 1875 amp, and bolted both channels to one relatively small heatsink, and the thing doesn't get warm! I'm really surprised at how cool it stays.

I want to build all of the amps into the sub cabinet. My sub amp is a purchased plate amp. I am thinking about modding the plate amp by removing the power transformer, and moving it somewhere else. Then I will have plenty of free space for my chipamp.
Do you think I can just bolt the 1875's to the steel plate of the plate amp? The plate is 10x10, but the area that is just a solid open plate, w/ no holes or other heat generating parts is about 4x10x1/8"thick.
As w/ all plate amps, it also has a heatsink which the sub amp parts bolt to, and that is below the area I'm thinking of using for these 1875's.

what do u think????
thanks,
Scott

[pacificblue]

Originally posted by wicked1
I built the 1875 amp, and bolted both channels to one relatively small heatsink, and the thing doesn't get warm! I'm really surprised at how cool it stays.

Did you use thermal grease? If not the metal stays cool, although the LM1875 is already cooking.

Originally posted by wicked1
Do you think I can just bolt the 1875's to the steel plate of the plate amp? The plate is 10x10, but the area that is just a solid open plate, w/ no holes or other heat generating parts is about 4x10x1/8"thick.
As w/ all plate amps, it also has a heatsink which the sub amp parts bolt to, and that is below the area I'm thinking of using for these 1875's.

Have a look at the datasheet. On page 4 there are graphs that show the power dissipation for several supply voltages and speaker impedances. On page 3 there is a graph that shows the possible power dissipation for several thermal resistances of heatsinks.

At the bottom of this page you can download a calculator to find out the thermal resistance of your heatsink.

[wicked1]

Thanks! That website should help.

On the 1875's now, yes, I used some 'arctic silver' thermal grease, and I do know how to use it properly. I'm used to class A amps, which is why to me, this 1875 is staying cool. The heatsink does get slightly warm, but not hot. And I think it's pretty small. 5"long, 1.5" tall, and 3/4" deep fins, and both channels are bolted to it. Also, it's the clamp type mounting, not just the single bolt through the hole on the chip.