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Old 12th March 2002, 03:37 AM   #1
BrianGT is offline BrianGT  United States
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Default heatsinks for aleph 2.

I picked up some aluminum heatsinks today from Austin Electronics, a electronics surplus store north of Atlanta, GA today. The dimensions are:

8" x 9" x 2.6"
baseplate - 1/4" thick
19 fins - 8" long x 1/8" thick each

Will these work good for the Aleph 2? Would one work for a channel? or should I use 2, with 6 mosfets on each?

Here are some pictures. I sized them down quite a bit. Hopefully they are not too big.

Click the image to open in full size.
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If you are in the Atlanta Area, if you call them, they can get more in. They cost $24 each. It is north of the city on 85, off Jimmy Carter. Here is their contact information:

AUSTIN ELECTRONICS
6050 CENTER PL NW, NORCROSS, GA 30093, (770) 449-8697

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Old 12th March 2002, 03:48 AM   #2
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There's no such thing as too much heatsink for a class A amp like Aleph. I would be using 4 pieces of those heatsinks per ch. if I were you.....
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Old 12th March 2002, 04:06 AM   #3
BrianGT is offline BrianGT  United States
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4 of these per channel, with 3 mosfets per heatsink? Isn't that overkill?

I was figuring that I would use 2 heatsinks per channel, with 6 mosfets on each. Does this sound like it would work?

They also have heatsinks that are about 12x14x1.5 I figured that they would not work as well.

Anyone have any suggestions on heatsinks, with regard to what they used for their designs?

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Old 12th March 2002, 04:11 AM   #4
BrianGT is offline BrianGT  United States
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There seems to be a problem with the pictures coming up.

I put a mirror of the pictures up at:

http://brian.prohosting.com/heatsinks/

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Old 12th March 2002, 04:26 AM   #5
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Overkill? I'm not so optimistic.....try comparing your heatsink dimensions with the dimensions of Aleph 2.
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Old 12th March 2002, 04:33 AM   #6
13DoW is offline 13DoW  England
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Brian,

I reckon each of your sinks is ~0.5 C/W.
Comparing the profile to the Wakefield extrusion catalogue the nearest match was 0.75C/W (3" length) but yours have slightly deeper fins.
So, conservatively, yours will at least as good and then adding the length factor of ~ 0.7x for an 8" lenght cf. a 3" length gives ~0.5C/W overall.

Now you can figure out how many you want. I don't know the aleph 2 rating but 4 heatsinks for 200W will give you a 25C rise. On top of that you must consider the device junction to heatsink rise (spreading the power between more devices helps).

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13 Duke of Wymbourne
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Old 12th March 2002, 05:21 AM   #7
BrianGT is offline BrianGT  United States
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The aleph 2 was 12" x 12" x 10.5" high

Click the image to open in full size.

I guess that 4 heatsinks would be the best bet. I didn't realize that one channel putting out 100W would take so much.

So, 4 heatsinks with 3 mosfets spaced out pretty good on each heasink will work?

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Old 12th March 2002, 06:03 AM   #8
13DoW is offline 13DoW  England
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Brian,

just checked Aleph2 and the standing dissipation is 300W per channel (for 100W output). With 12x output devices that's 25W each. The junction to sink thermal resistance will be at least 1 C/W (depends on insulating pad)- let's assume 1.5C/W then each device junction will be 38C hotter than the sink.
If the total sinking (4 pieces) is ~0.125C/W then the sink will be 38C hotter than ambient. So, for an ambient temperature of 20C the device junctions will be at ~96C.
96C is acceptable but lower is always better for both longevity and performance (MOSFET gain decreases as temperature rises).

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13DoW
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Old 12th March 2002, 06:55 AM   #9
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96 is theoreticaly good. I think its too hot for the fets.
If the themal resistance of the heatsinks is only 0.5K/W than I agree that 4 heatsinks is better but you could use 2 per channel on lower power. You can use pads with lower than 0.1 K/W thermal resistance.
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Old 12th March 2002, 02:00 PM   #10
BrianGT is offline BrianGT  United States
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What kind of pads are best for this application? If I use good pads, and 4 heatsinks (per channel), will it run reliably as an aleph2 at full power?

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