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Old 5th August 2011, 02:24 PM   #1
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Default Heat sink size, Need help in determining.

Hello people,

I'm currently and slowly building a stereo power amp with power of 200w/ch into 8ohms and 400w/ch into 4ohms , But I'm no expert in calculating heatsink size.

My question is , will this chassis on the link below, be sufficient for the power of my amp? It is stated that the dimension of the heatsink per channel is 160mm height x 32mm width x 380mm depth.

After the cabinet-level pure amplifier AR998 [After the cabinet-level pure] : HiEndKing Online Stroe
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Old 5th August 2011, 02:29 PM   #2
AndrewT is offline AndrewT  Scotland
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What is the range of ambient temperatures you need to design for?
What is the range of supply voltages you need to design for?
What is the quiescent power that you expect the sink to dissipate?
What class of amplifier are you cooling?
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Old 5th August 2011, 02:37 PM   #3
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Ahh, Sorry I forgot , The amp is ordinary class AB, Will be used in an air-conditioned room 25 degree C. The supply voltage on the amp board will be +/- 70V supplied with 1000VA trafo and 80,000uf caps per channel.

I don't know the actual quiescent current dissipation though, But I assume it won't be hot when it is in idle.
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Old 5th August 2011, 02:46 PM   #4
AndrewT is offline AndrewT  Scotland
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You need the quiescent power. You cannot proceed with hardware selection without that.

What are the ranges of operating conditions for that amp? Voltage supply has a big influence on heatsink loading.
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Old 5th August 2011, 03:01 PM   #5
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And what output devices are you using? Is it a metal or plastic package?
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Old 5th August 2011, 03:08 PM   #6
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That chassis should be okay for an 8 ohm load if you don't bias too hard.

You'd have to bias real light and blow a good deal of air past it for an actual 400rms per channel.
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Old 5th August 2011, 03:30 PM   #7
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One thing you would want to keep in mind using that chassis is getting the most out of it requires distributing the output transistors evenly along the depth of it, half of one channel transistors on one sink, and half on the other. Packing the power transistors in close, which is better for high frequency performance, would require a very heavy block of interface material to go between the transistors and along the length of the split (pair of) sinks on each side. Don't mean to complicate, just the way it is.
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Old 5th August 2011, 03:36 PM   #8
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Hi Andrew T, I can't really answer that question, as I'm not expert in that subject either.

Hi, Sofaspud, The devices are plastic, similar in form to the ones commonly used in Pass amps projects. With 8 devices per channel.

Hi Andrew Eckhardt, Yes I intend to use it on 4 ohms load or maybe slightly lower, And I don't want to use fans , So I think I'll just gonna find a bigger chassis, How about this one, Do you think this will be enough for 4 ohms load?

Large aluminum amplifier chassis (15 kg) [Large aluminum amplifier chassis] : HiEndKing Online Stroe
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Old 5th August 2011, 03:45 PM   #9
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I'd say that'll do it just fine.
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Old 5th August 2011, 03:51 PM   #10
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Good lord, you could put a Nelson Pass class a amp in there.
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