Heat sink size, Need help in determining.

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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.
 
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.
 
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
 
Heat sink size, Need help in determining
bias real light ..................for an actual 400rms per channel
What has bias got to do with output power
Everything.
What is the total quiescent power that the sink needs to dissipate?
That could be anywhere from 1W to 200W for a ClassAB 400W into 4r0 amplifier.
This quiescent power could be the most significant load for the heatsink. Or it could be completely insignificant and when in this situation the average output power becomes the most significant heatsink loading.
 
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It depends on what average power he is dissipating. Is he playing music at home, is it a sound reinforcement system, is he listening to continuous sine waves into low impedance speakers. The requirement has to be fully qualified before you can calculate a economic heat sink size.

If he will be running it at 400 watt average power using seriously compressed signals then the heat sink would substantially larger than if he is listening to music at an average of 10 watts with the occasional peak at 400 watt.

The question remains what does bias have to do with output power.
 
Use a rule of thumb. About 30% of the output power of a class AB amp is dissipated as heat by the transistors. Assuming that the average power will be 400 watt, then 120 watt needs to be dissipated.

If the ambient is 25 degrees centigrade and one would not like to cook on the amplifier then allow for a 40 degree rise. Find a heat sink that satisfies this specification which is given by the manufacturer. It is that straight forward.
 
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.
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AB class amp right?


If your output stage is biased heavily it will build up a bunch of heat just sitting there running. If it were me in that case I would consider either more heatsinking area or adding a fan to help cool the output stage.

If the output stage is biased lighter then sitting there running without a signal it will produce less heat.

Now we consider the problem associated when we supply signal to the amplifier. We must now consider the power supply voltage, number of outputs per channel, duty cycle, room heat, and so forth.

The size of the heat sinks is similar to that of the old ill fated Quatre power amplifier. The one rated in the 200 watt per channel area did fine with this amount of heat sinking.

It is my assumption based on my building such projects that you should be fine as long as you don't beat the **** out of it everytime you turn it on. I'm assuming that your B+/B- voltage is going to be around 75 and not 100 or more.


The larger chassis in my opinion would be better.

Dimension: 430MM (W) * 368MM (deep) * 170MM (panel height).
Weight: 15 kg:
Materials: aluminum, panel 430MM (length) 170MM (high) 15MM (thick)
Panel weighs about 7 pounds. Gold, silver two colors to choose from.
Efficient radiator 5 +5 kg (with all hot section 4).
Surface cover, bottom, after the board 3MM aluminum.
Internal Dimensions: 351 (D) * 258 (W) * 143 (H).
For Power: 50W Type A, 200W AB. DIY used for most of the size of the family.


Seems to be rated 200 watts AB amplifier.


Very nice chassis
 
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If one would try to scale the heat sink in the picture of your first choice of box, it would be 368 long and 170 mm wide. There is 35 fins on it and again by inspection it would appear as if the fins are about 30 mm deep. Go here and down load Rod's calculator
ESP Download Page
Plug the numbers into the spread sheet and you get an approximate value of degree C/watt = 0.35. Thus if your amp need to dissipate 120 watt then 120 x 0.35 = 42 degrees above ambient of 25 degrees. Your heat sinks will therefor rise to 67 degrees centigrade above an ambient of 25 degrees centigrade. Is this good or bad, it will surely burn you if you were to play music and an average of 400 watt. Would the transistors die - NO.
 
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