Aleph-X Heatsink Requirements

[systemerror909]

Hello,

I've been working on a project to build the high powered Aleph-X design and I've been concerned about heat sinks.

According to this site:

http://www.facstaff.bucknell.edu/esa...s/aleph-x.html

The high powered version dissipates 320w heat/channel.

He later goes on to describe the process for calculating heat sink requirements, for this case I've calculated:

25c/320w = .078 c/w

0.078/1.25 = .0625 c/w then round down to nearest hundredth:

.0625 = .06 c/w requirement

Is this number correct?

I had been interested in the Conrad Heatsink group buy. These looked like nice heat sinks at a good price. Initially I had thought this would require simply 4 heat sinks, two per monobloc, but reviewing the specs for this heat sink I am now uncertain. According to Conrad the MF35-151.5 model can dissipate 0.21c/w at 80c. I am unfamiliar with heat sink specs, but I am assuming this is a linear measure? That two of these heat sinks could dissipate .105c/w, four dissipating .05025c/w, meaning that I would need 4 of these per monobloc to satisfy the heat sink requirement. Is this correct? At $123/pair (x4 for 8 total) I really am thinking I cannot afford this. If someone could please confirm my calculations, or possibly offer suggestions for a cheaper heat sink source I would be very appreciative.

Ryan

[Blues]

The MF35-151.5 can dissipate about 100W...

[hifimaker]

Just a reminder... These Conrad heatsinks (MF350-151.5) are very well made, but you need to apply an ambient room temp correcting factor to the C/W rating of about 1.4. The corrected C/W is 29.5. Perfect for 100w.

-David

[systemerror909]

Yeah, I meant to ask about the phenomena as well, cause I had briefly glanced at a post mentioning the need for such correction.

So the way I'm interpreting this now is that the ambient temperature is working against me right? 4 heat sinks now dissipate: .295/4 = .07375c/w, which doesn't meet my requirement of .06c/w, so I would be looking to have potentially another (total 5) of these heat sinks per monobloc?

[jacco vermeulen]

Even worse, place 2 heatsinks at a close distance and they'll cross-influence eachother's thermal efficiency number.

The "ambient" factor is not a constant temperature reference, for the thermal resistance calculation it's an average across the (3D) surface of the heatsink.
Put 2 heatsinks in-line and the heat coming from the "touching" side of the 1st heatsink elevates the temperature of the surrounding air for the 2nd heatsink.
Comparable with putting 2 heatsinks on top of eachother, though less dramatic, expect a 10% drop in efficiency for choo-choo heatsinks.
Or in numbers : 2 times 0.295=> 0.16C/W

You can save a lot of cash by going forced air or water cooling at these dissipation levels.

[hifimaker]

Two of these heat sinks forming one side each of your amp box works great for most current stereo F series FirstWatt designs, Aleph3, Aleph30, stereo AlephX (HifiZen's boards), stereo Aleph J 30 watt, and mono Aleph60.

If you are planing on pushing the envelope of heat dissipation, make sure there is very good cooling inside the cabinet, lots of clearance around the chassis, and with the bottom of the heat sinks a couple of inches above the shelf/resting surface. For example, ventilation holes along the bottom of the chassis and a rather open top. A low speed box fan is also a good idea. There are a number of very good quite box fans that if run a a lower voltage are extremely quite.

A thermal cut off switch on each heat sink is always a good idea.

-David

[gl]

I have found that the Aleph-X is very sensitive to air moving over the front end circuitry and particularly the input diff pair. This causes significant drifting and shifting of the absolute DC offsets. I would be cautious too, of uneven heating of the output heatsinks.

So any use of a fan requires special attention to fan location and air flow patterns. The only fan cooling that I could see as having minimal issues would be the use of a tunnel type heatsink arrangement for the output section. I would also pay attention as to how the output transistors are arranged on the sink so that cooling is even for all transistors of all four quadrants.

Regards,
Graeme

[hifimaker]

Graeme is correct in his advice regarding air circulation. If your AlephX does not exceed 100w dissipation per heatsink, then you're in fat city and no additional cooling fan is needed.

My prior thought on adding a fan was to keep the other components like the capacitors from cooking, and not so much to provide additional cooling for the heat sinks.

Also the orientation of the heat sinks is critical. Heat sinks designed for horizontal mounting that are mounted vertical can reduce thermal efficiency by 10% or more.

-David

[gl]

I look forward to seeing you at BAF again this year Dave.

Graeme

[hifimaker]

Hi Graeme, Same here! Frequently while watching cable financial news you come to mind. See you at BAF.

-David