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Old 8th November 2004, 10:52 PM   #521
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Sorry for asking, but this thread is way to long
Can someone tell me where is located the Aleph-X calculator for the transfo voltage, power needed, etc...

I think I saw it somewhere but couldn't find it again.

Thanks in advance...

SB

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Old 9th November 2004, 08:44 AM   #522
Taco is offline Taco  Netherlands
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You can find it in the Wiki http://www.diyaudio.com/wiki/index.php?page=Aleph-X

and here is a direct link:
NEW Aleph-X calculation sheet: AXE-1
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Old 2nd December 2004, 07:36 PM   #523
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Default Do the output FET's need to be thermal matched?

HI,

I was considering an AlephX design of one FET per heatsink. I know most people are grouping each side of a mono channel to one heatsink each.

I'm looking at using 12 smaller heatsinks, one per output FET. After running the numbers on the AlephX spreadsheet each FET would dissipate 20 watts each for a single channel 100 watt amp. The heatsink thermal resistance is .08 per FET using 12 sinks.

From what I was able to read this seems OK, but let me know if I'm making a mistake.

Thanks!

-David
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Old 2nd December 2004, 08:54 PM   #524
byteboy is offline byteboy  Netherlands
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Default I think you are making a mistake

0.08 K/W seems a little too good for a single heatsink for one single FET dissipating only 20 Watts.........

At 0.08 K/W you could easily dissipate 100 ++ Watts per sink and it would be rather big in size.

Is this value correct?

Check this value for your heatsink or post its dimensions or a picture of it if you already have the sink.

It would be easy for people here to give an estimate of it's K/W value.
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Old 2nd December 2004, 08:58 PM   #525
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Thanks Byteboy,

Here's a link to the heatsink: http://www.aavidthermalloy.com/bin/e...LengthUnits=in

At four inches the heatsink has thermal resistance value of .97. I should have been more clear, the .08 value was .97/12=.08 as per cell B64 for the Rth value in the AlephX spreadsheet.

Thank you,

-David
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Old 2nd December 2004, 10:49 PM   #526
byteboy is offline byteboy  Netherlands
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Default Thats cool!!

OK David, I think you are OK with that value, I got you wrong there!

At a total K/W of 0.08 for 12 heatsinks of 0.97 K/W each, you should be pretty much on the safe side!

For 100 Watts @ 8 Ohm, @ 0.08 K/W total @ abt. 21C/70F ambient temperature, you will have abt. 40C/100F heatsink temperature.

Thats cool!!

With 12 of such heatsinks it will be a BIG amp though....

But that's cool too!!!!!
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Old 3rd December 2004, 01:29 AM   #527
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Yea, it will be fairly large. I estimate each amp will be 22Wx18Dx8H in inches or for our metric friends.. 559Wx457Dx203H in mm going with this approach. I really struggled with the fact that these amps run hot and opted to perhaps over heatsink them.

Does anyone know if there is a downside to not having the output FETs thermally coupled?


Thanks!

-David
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Old 5th December 2004, 07:28 AM   #528
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Default Fet choice

Hi i am a newby in this forum and the thread is very long so here a few questions.

Are the PCB's still available anywhere?

I have a lot of Fairchild 75345p laying around (bought 150 of them for 15$) can i use them instead of the irfp044.
Specs are about the same only slightly lower voltage (55 instead of 60) but higher current (75A) and much dissipation.
I also have some irfp450's laying around but not so much so matching would be more difficult.Which would be the better option?
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Old 5th December 2004, 05:03 PM   #529
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Default Re: Fet choice

Quote:
Originally posted by kro5998
Hi i am a newby in this forum and the thread is very long so here a few questions.

Are the PCB's still available anywhere?
Yesterday I saw a PCB group buy, now I can't find it anymore. Maybe I was mistaken.
I live less then 15 minutes away from you, if you are going to build the amp, maybe we can order parts together to get some discount.

Also check this page:
http://www.diyaudio.com/wiki/index.php?page=Aleph-X
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Old 5th December 2004, 05:03 PM   #530
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I'm very sorry, but I can't edit the post above. Here is the groupbuy:
http://www.diyaudio.com/wiki/index.php?page=AX
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