Has anybody built an Aleph-x to this spec??? - Page 3 - diyAudio
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Old 29th April 2004, 09:47 PM   #21
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I don't know whether it would qualify as a "solution," but it's something I thought about trying. Still haven't gotten around to doing it, as I'm not set up to machine metal, just wood. Aluminum, copper, silver, gold, whatever you've got sitting around going to waste.
To date, all my Aleph-X variants have either had free-standing MOSFETs or back-to-back. Yes, the free-standing ones tend to drift. The problem can be reduced if you mount the MOSFETs against the circuit board.
I have at least two more variations on the Aleph-X theme that I intend to try, maybe three. It'll all depend on time and money.
(Would you believe that the heat pump problem is still dragging on? I've now gone to the BBB, and intend to start in with the Department of Consumer Affairs if someone doesn't say something pretty astounding by next Monday. I would advise against going with Trane heat pumps...)

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Old 30th April 2004, 02:02 PM   #22
D3 is offline D3  England
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Thanks for the reply Mr Rollins

My guess is that you want to avoid a heatsink with cooling fins.....I would imagine a simple 4 or 6mm alloy shim more less the size of transistor would suffice...................

When ready I will try this and report back!!

Meanwhile I will check out other peoples findings ... cheers
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Old 30th April 2004, 02:47 PM   #23
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You could conceivably get to the point where you'd need a heatsink if you raise the rails enough. Nelson likes to run things hot; he probably doesn't worry until the MOSFETs glow cherry red. I tend to start thinking in terms of heatsinks when I see a TO-220 package at .5 to 1W Pd. It's just two views of the same thing. You can choose either endpoint, or somewhere in between.
Given that the rails for an Aleph-X are about half that of an equivalent Aleph for the same power, you're not likely to reach the point where the MOSFETs get really warm unless you're building a pretty large amp.

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Old 1st May 2004, 11:07 AM   #24
D3 is offline D3  England
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Default My proposed amp design!!!

Hi....hope you can take a look at this......my amp will be running with 8a bias and 23v rails and 16 fets(current proposal) this will push out nearly 400w of heat!!!!

I have done some calcs based on Conrad Heatsink MF35-151
this is 350x151x40mm rated at 0.21C/W..........each side of amp will need to dissapate 200w........I am proposing to increase cooling by integrating the heatsink into the prerimeter casework increasing emmitance area....by at least 30%. The idea is to make the amp thermally stable at around say 65degC (total asuming 25deg room temp)......this is to ensure the thing does not go splat. To make matters friendly for all the components...I am proposing very mild air cooling using 4 high quality brush less 125mm fans running at around 5v............this should bring temps down to arround 45-50deg....please take a carefull look at the design.....here!!!! I would like as many people to chip in and advise and crit this compact design (wife friendly!)

nb here are my calcs............

R(80degC)=0.21C/W
Temp orrection factor for 25deg K(25degC)=1.42
R25(degC)=1.42x0.21=.2982C/W
Power Dissapation @ 40degC rise above ambient P(40degC)=40/.2982=134.13Watts
Power Dissapation to allow for 200w = 200x0.2982 = 59.64deg above ambient!
Therefore bare sink temp = 59.64+25 = 84.64 Say 85 deg.

Mild air assistance will give 0.17C/W (very conservative) gives 0.2414
0.2414x200 = 48.28 = final sink temp of 73.28

However my design increases thermal radiating area by at least 30% (conservative)
Therefore 30% off 0.17C/W = 0.119
0.119 x200 = 23.8 above ambient giving a final figure of 48.8deg (bingo)
Attached Files
File Type: zip my aleph-x chassis.zip (37.1 KB, 163 views)
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Old 1st May 2004, 01:16 PM   #25
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I honestly don't understand how you calculated that your case will increase the dissipative area of your heat sink by 30%. I will address that later. I had a look at your specs and this is what I come up with. Each heat sink will dissipate one half of the total dissipation of 352 watts as taken from the AXE-1 spreadsheet for your proposed 23 volt rail and 8 amp bias. if you divide that in two each heatsink will need to dissipate 176 watts. With your proposed heatsinks that have a thermal resistance of .21C/watt you can expect a rise above ambient of 36.96C. If I am correct your heatsinks will run at about 57C or for those here in the States 123F. It appears from your drawing as if you are going to sandwich your chassis side panels between the heat sinks and your transistors in hope that you get more surface area to dissapate heat. If this is your intent (I can't really tell from your drawing), I think you will have some problems in that you will rob your transistors of good thermal contact with the component that will dissipate the most heat, the heatsinks. Your chassis will be dissipating most of the heat. I do however like your idea of using copper as a heat spreader. What I would do, because you plan on using some fans anyway, is to get the transistors on a piece of copper plate much larger than you propose to spread the heat over a much wider area and bolt that directly to the heatsink with some thermal goo between the copper and heatsink. With the fans and that setup, I think you will doing just fine. BTW, I really like your chassis design. It is very professional and extremely well thought out. Just my suggestion, I hope it helps.
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Old 1st May 2004, 01:58 PM   #26
D3 is offline D3  England
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Default My Amp..............

Dear Kilo..............thanks for the comments...........I am in the process of sourcing copper bus bar!!!
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Old 9th May 2004, 01:33 PM   #27
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Lightbulb My amp changes!!!!

I have been looking at the heat dissapation figures for my amp....
I am going to change the design................

I going to double the heatsinks..............this will keep things to a max of around 55-60degc ........... without fan assistance.

I suggest that other people in the forum.......check out their dissapation ... taking into account the Trafo/rectifier and any resistors....if you have a CRC setup.....

I have been informed that running computer fans at low speed can be very unreliable............is this the case......or have others in this forum found otherwise?????

Because I am changing the design.......I am ordering 4 more Conrad Heatsinks in about a months time...........is anybody else interested in extra heatsinking from Conrad???

I am also going to be using copper bus bars to mount the fets directly.........I have been informed that this assists in reducing the all critical fet junction temp......again I can let you know who my supplier is.....they work out at approx 10 per 250x50x12mm
bus bar....

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Old 10th May 2004, 08:38 PM   #28
Phill is offline Phill  France
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D3

Have you references for fan ?

good post !
Phill
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Old 12th May 2004, 07:58 AM   #29
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Default Fans for Aleph

Hi I was recommended to use panaflo fans which are very quiet.....I have attached a link....hope it works.....

http://homepage.ntlworld.com/dorothy...ry/panaflo.htm
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Old 12th May 2004, 10:48 PM   #30
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Default high powered Aleph X

This maybe a little redundant but has any one built the Aleph X high power version, oh 130 watt or more. I am looking to start my project but have not been keeping up with the threads. It seems that some values with the current sources should be changed and of course the biasing circuit resistors. So does any one have an high powered X that is up and working and info to share.

Thanks
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