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Old 27th August 2009, 07:35 AM   #1
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Default PC-like cooling?

Hello everyone
has everyone tried to use a CPU cooler in building a class A amp?
i'm thinking about something like the photo attached (or maybe something less ugly), which are commonly available and quite cheap.
This heatsink are designed to work without a fan, and nowadays computer
produce heaps of heat...so i guess it will work even for audio.
any feedback?
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File Type: jpg cooler.jpg (47.6 KB, 301 views)
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Old 27th August 2009, 11:16 AM   #2
flg is offline flg  United States
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Without a fan maybe but, in a box with airflow. There are extra quiet fans available and you can even lower the speed of the fan for very good results
These things work more efficiently at a relatively high temp.
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Old 27th August 2009, 11:17 AM   #3
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I found that coolers for CPUs with a very high thermal design power (TDP) are perfectly suited for smaller amps, if you don't use the fan. Passive CPU coolers for such CPUs, like the one above, are probably perfectly suited for higher powers. Just take a look at the TDP of the CPU they were designed for.

My "guesstimates" are the following: a passive cooler for a CPU with a TDP of let's say 100 Watts will probably allow for a 70-80°C die temperature if you pump the whole 100 Watts in there at room temp. So if you have a stereo class A amp with 2 transistors per channel, you could in theory safely put out 2x 40 W RMS while keeping the output transistors at about 80°C.
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Old 27th August 2009, 11:33 AM   #4
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Edit: I was thinking that way, that every transistor has it's own heat sink. All 4 together on one heat sink will probably allow for 2x10 W RMS only.
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Old 27th August 2009, 02:51 PM   #5
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I've built several pieces using the Zalman products, including
the water towers. They work great.

I pick Zalman because they are the quietest I have found.
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Old 27th August 2009, 03:39 PM   #6
frags is offline frags  Canada
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There is no passive cooling for CPUs with 100W TDP. You must use a fan with any of such heatsinks because the gaps between fins are so small that they need forced air to work effectively. Additional problem with heatpipes is that they stop working at all if you would not cool fins properly.
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Old 27th August 2009, 03:47 PM   #7
CBRworm is offline CBRworm  United States
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I have thought about trying the large Scythe Ninja series sinks - the fins are spread far enough for good heat transfer with just a light breeze - basically passive with a single quiet case fan pulling air through the box.

They are also available in copper which might be slightly better. I am not sure about orientation with heat pipe solutions. I am also not sure of the best mounting solution - seems like a clamp would be required to avoid drilling holes through the heat pipes.

The copper version they say can dissapate 65 watts with no fan, 130 with a 'silent' fan.

Pictures: http://www.xbitlabs.com/articles/coo...-copper_2.html

Last edited by CBRworm; 27th August 2009 at 03:49 PM.
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Old 27th August 2009, 03:54 PM   #8
frags is offline frags  Canada
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CBRworm,

All those "fanless" solutions suppose that you have well ventilated case where the air flow is provided by a case fan (a light breeze).
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Old 27th August 2009, 07:01 PM   #9
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I did a quick google and I'm afraid it's true that no passive cooling can be accomplished for TDPs of 100W. I found notes that passive cooling is only for "light loads" like "browsing, emailing" and so on. I stand corrected.

On topic of (forced) ventilation. I have an AMD K6-350 underclocked to 166 MHz. I stripped the heat sink of it's noisy fan. The processor got rather hot with some 52°C according to the mobo's sensors. Then, I installed a large fan on that heat sink running on 5V instead of 12V. You almost can't hear that fan when it's on. The temperature never rose above 25°C, ambient being 20-21°C. Looks like forced ventilation is a must.
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Old 27th August 2009, 07:03 PM   #10
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I got a pair of laser diode water blocks and two 2-fan radiators.

http://cgi.ebay.com/Water-Cooled-Hea...d=p3286.c0.m14

I am going to run the it all in one loop for temp stability between channels. I am going to use two water pumps in parallel in case one fails, same goes for the fans. The fans are wired to a 29amp 12V smps along with all of the lighting for the house to keep the noisy fans isolated. The temp/fan control is my only gray area. I don't want to use a PC fan controller because I don't want the PC on ifI am not listening to that source.

For the temp/fan control I was going to use a 3-pin voltage reg with a 5k pot, a 5K thermistor and a temp probe to monitor it. I can fire up the amps and wait for the water temp to reach 55F and then adjust the pot until the fans start. This way as the temp increases the fan speed increases. I think this will work and be as close to fail safe as possible. I am not doing this for the cost savings because it will cost me more. I am doing it for the weight saving for when I ship it overseas to my new home and for the heat to be remove from my tropical house. Radiators outside will save me a fortune on cooling the house after two F4's heatit up. I was also thinking of running a huge resevoir and using it for a hot water heater, 55deg water will make a nice shower temp. If I go this route I would use DC water pump that are hooked to the thermistor setup to run the pumps at higher speeds when the temp starts to rise. I was also going to seal the PC, DAC, amp, preamp, all in one box so that it is airtight with a rad inside and rad outside to keep the humidity and animals out. Remember, this might be needed to make it last in the rainforest.
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