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Minimum Heat Sink Size for F5 / Aleph 30
Minimum Heat Sink Size for F5 / Aleph 30
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Old 5th February 2018, 05:01 PM   #1
TheNuge is offline TheNuge  Germany
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Default Minimum Heat Sink Size for F5 / Aleph 30

Hi!
I've acquired some "2nd hand" boards, a stereo set of F5 and a stereo set of Aleph 30, which I obviously want to turn into working amps.
I'm married, so WAF is somewhat important...
What's the smallest size Modushop heat sink I can get away with?
2U is 0,45 C/W
3U is 0,40 C/W

Would either of those do, or do I need to go 4U or bigger?
Cheers
Es
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Old 5th February 2018, 05:15 PM   #2
Zen Mod is offline Zen Mod  Serbia
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Minimum Heat Sink Size for F5 / Aleph 30
4U/400 for stereo amp
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Old 5th February 2018, 05:44 PM   #3
TheNuge is offline TheNuge  Germany
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Thanks!
4U/300 would probably also do, no?
Es
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Old 5th February 2018, 05:55 PM   #4
Zen Mod is offline Zen Mod  Serbia
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Minimum Heat Sink Size for F5 / Aleph 30
only with Babysitter
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Old 5th February 2018, 06:18 PM   #5
AudioSan is offline AudioSan  Norway
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3U 400mm should do the job just fine for a single pair F5.
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Old 7th February 2018, 09:12 AM   #6
nr12 is online now nr12  Germany
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Hmmm, so what about the "Deluxe 4U Aluminum" from the diyaudio store?
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Old 7th February 2018, 10:08 AM   #7
El Reino is offline El Reino  Finland
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Quote:
Originally Posted by nr12 View Post
Hmmm, so what about the "Deluxe 4U Aluminum" from the diyaudio store?
Look here.
Modushop by Hi-Fi 2000 | Contenitori per Elettronica | Electronic Enclosures | Hi Fi Chassis
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Old 7th February 2018, 11:39 AM   #8
nr12 is online now nr12  Germany
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Let me rephrase my post: is the chassis from the diyaudio store not suitable for aleph 30 or F5 without babysitter?
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Old 7th February 2018, 11:59 AM   #9
ColinA123 is offline ColinA123  United Kingdom
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This is my experience in the UK. (So not hot climate.)
Dissipante 04/300N 4U 10mm front.
Has been fine with F5, and now with F6 running bias at levels recommended in build instructions.
The 10mm front does seem to aid heat dispersion and looks better.
The 4U depth of 165mm does allow mounting the toroidal tranny vertically leaving plenty of space for caps and rectifiers.
To aid wife acceptance you could get nice vinyl lettering for the front, easy to find suppliers on E-bay.
You may get away with a 3U, but no smaller!

If you order direct you will get best price in the EU.
Dissipante 04/300N 4U 10mm NERO

Last edited by ColinA123; 7th February 2018 at 12:01 PM.
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Old 8th February 2018, 02:29 PM   #10
Eric is offline Eric  United States
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Minimum Heat Sink Size for F5 / Aleph 30
A more generic and long-winded approach to heat sink size:

Thermal ratings of heat sinks are specified in units of c/w, or thermal rise (measured in degrees centigrade) divided by the wattage that they need to dissipate (w). This measure assumes a reasonable ambient air temperature (typically 20-25c), that the heat sinks are black anodized, have free air circulation (not using a fan and given plenty of breathing room-usually 8 inches on all sides and don't sit directly on the floor), and that the fins of the heat sink are oriented vertically. Be aware, though, that different vendors will have different assumptions when measuring and quoting the thermal dissipation of their heat sinks - some of the measures of thermal dissipation are made at 70-80c, thus you cannot reliably trust the figures. The bottom line is that you need BIG and HEAVY heat sinks - and LOTS of them. Here is my recommendation to get an idea of what you need:

1) Divide 25c (max thermal rise that you want) by the quiescent power consumption of your amp (per channel for building monoblocks or for 2 channels together if building a stereo chassis, keep in mind this is the wattage dissipation (draw from the AC wall socket), NOT output wattage - they are very different specifications).

2) Take this number and de-rate it by 25% (derating by more is often desirable). This de-rating takes into account all of the inefficiencies of mounting your output transistors to the heat sink and the less than favorable conditions that you are likely to create in building your amp. It also accounts for the higher thermal rise that many heat sink manufacturers use to specify their products. No matter what you do, it won't be "ideal."

3) Take this number and round it down to the nearest 100th decimal place.

4) This is the minimum size of a heat sink that you really need. Then think of a way to get more...

So here are a few examples:

Nelson's a40 amp is specified to dissipate 200w total for two channels (I built mine as a stereo chassis). Dividing 25c by 200w yields 0.125c/w. Next, derate this by 25% by dividing your c/w rating by 1.25. This yields a more realistic figure of 0.10 c/w. Then round it down (resulting in a larger heat sink specification). Thus, the final heat sink rating should be about 0.09c/w in order to dissipate 200w and keeping thermal rise limited to 25c. How close does this come to reality? My completed a40 amp actually draws 190 watts from the wall socket (slightly less than specified), has a total heat sinking capacity of 0.084c/w (slightly more than calculated), and has final thermal rise is 24c (almost exactly to target specs).

As another example,the Pass Labs Aleph2 monoblock delivers 100wpc into an 8 ohm load and dissipates 300 watts of heat all of the time. Nelson states that the Aleph2 requires heatsinking of 0.06c/w per monoblock. Using the theoretical calculation dissipating 300 watts of power while limiting thermal rise to 25c above ambient (25c/300w) should require 0.083 c/w worth of heatsinking. Derating the theoretical result of 0.083c/w by 25% (0.083/1.25) provides us with a more realistic figure of 0.0656c/w and rounding down to the nearest 100th yields exactly the target value of 0.06c/w.

Finally, more is always better...
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