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Old 15th July 2010, 04:31 PM   #1
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Default Nelson Pass Aleph 5 - Heatsinks

I'm restarting this question due to the funny buggers that decide to tell me that Nelson is better than my Cat.

I'm planning on building two Monoblock Aleph 4 Amplifiers.

My problem is heatsinks. Reading the many threads that have been listed on this subject I am looking at ditching some 280W of heat from each block.

I'm a bit strapped for cash so I'm trying to keep things within reason.

My Mark Levinson 333 clone failed at Mk 1 due to insufficient heatsinking (well actually the use of SilPads as opposed to Mica). The revised version is now running properly but with the bias reduced and all the SilPads replaced by decent Mica washers.

Getting back to the Aleph 4, each MOSFET will be dissipating around about 25 Watts at idle. I intend to mount each MOSFET - yes 24 in total on their own individual 1.1 K/Watt heatsinks. In my reckoning, the amplifiers will run at about 57C on a warm 25C summers day. In my reckoning this should be OK for long term reliability. The genuine article apparently runs MUCH HOTTER.

Please no comments about roasted hampsters.
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Old 15th July 2010, 04:55 PM   #2
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by Andy5112405 View Post
......
Please no comments about roasted hampsters.
what else you need us to comment ?

(except fact that is wise to keep at least all lower mosfets thermally coupled , and all upper mosfets thermally coupled ....... if not all in one channel )


while you're in planning stage - did you think about Jfet input version ?
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Old 15th July 2010, 05:17 PM   #3
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Go to fleaBay and search for Barredbooss. He has a 10.1"x2.8" extrusion. (4) 8" tall units might just do it. Maybe $200US before shping...
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Old 15th July 2010, 05:36 PM   #4
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Many Thanks but I've got over 110 of the RS 1.1K/W heatsinks sitting in a rather large box in the loft. We bought 250 of them for a stage lighting project that went bust. It's a shame that I can't put half a MOSFET on each one. Hence my earlier question, would I benefit from more output devices. I've just bought 100 IRFP244s for my matching process.
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Old 15th July 2010, 05:38 PM   #5
DougL is offline DougL  United States
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Your heat sink sounds adequate to me.

Just a thought, even modest air flow can make a big difference.

Are sheep jokes off limits too?

Doug
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Old 15th July 2010, 05:55 PM   #6
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Can you visualise the final setup? Each Monoblock will consist of 12 heatsinks. It is aimed to sandwich two sides, six heatsinks each onto a heat spreading plate. How it is it best to distribute the 12 output devices?

Basically there will be two heat plates that are not thermally connected to each other. Each heat plate should be fairly "thermally" linear.
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Old 15th July 2010, 06:23 PM   #7
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Quote:
Originally Posted by Andy5112405 View Post
Can you visualise the final setup? Each Monoblock will consist of 12 heatsinks. It is aimed to sandwich two sides, six heatsinks each onto a heat spreading plate. How it is it best to distribute the 12 output devices?

Basically there will be two heat plates that are not thermally connected to each other. Each heat plate should be fairly "thermally" linear.
As ZM said, six upper devices on one plate, six lower devices on the other.
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