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Old 19th November 2008, 11:59 PM   #1
pdrie is offline pdrie  United States
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Default New mamber- Aleph 2 Heatsink Confusion

I am a new member, just recently returning to my beloved MG-IIIa speakers after their multi-year banishment due to a "disagreement" with my spouse over furniture placement. I am starting to collect parts for an Aleph 2 build. I have lots of experience building tube amps, but precious little with solid state. The major question at the moment is heatsink capacity. I have searched multiple threads and come away with the conclusion that I don't have a clue!

I have been looking at the 8.5" wide heatsinks offered on ebay by barredboss (Unfortunately, he has no data on the heat transfer properties of these heatsinks). It seems as if four of these on end would make an Aleph-like chassis, albeit smaller than the original. Since I have a transformer that will readily power multiple monoblocks (28-0-28 at 30 amps), I am planning an outboard supply feeding two amplifier chassis.

Other options that I have considered are M&M Metals (Too pricey at $485 plus shipping for a 6 foot section of extrusion), surplus (No luck, yet), and homemade, which is an option that I am still considering.

I would appreciate any suggestions that you might have regarding this approach, and any experience anyone may have had with these heatsinks.

Thanks in advance.

Paul
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Old 20th November 2008, 12:29 AM   #2
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Hi Paul,

You need truly massive heat sinks for this project. The factory Aleph 2 was 12x12x10.5" with all four sides with heatsinks. The amp even had corners that were heat sinks. The fins were also large and heavy gauge.

The amp dissipates something 300 watts of power. I have a friend with a pair and they heat the entire listening room. Sometimes in Winter he has to open the windows. Probably an extreme case, but it does happen. The point being the usual heat sinks seen on eBay like Barred Boss'es are way too small. I imagine enough of them in a cube might work.

Search the web for a picture of the Aleph 2 and take a look.

Not trying to scare you off, but you're looking at a serious investment in aluminum.

You might consider an Aleph60 which is a mono bloc. You'll get close to 90 watts into 4 ohms. Each Aleph60 needs a pair of Conrad 350x151.5mm heatsinks.

http://www.conradheatsinks.com/produ...at100_350.html


-David
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Old 20th November 2008, 01:26 AM   #3
pdrie is offline pdrie  United States
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David,

Thanks for the reply. I was looking at four of the 12" x 8.5" heatsinks on ebay, but the fins looked small for the amount of heat involved and I was afraid that they wouldn't be enough. I'm not totally dissuaded, yet, but the heatsinks may be the dealbreaker for me. I guess that DIY is still an option, likely the only affordable option. I used to own a Krell KSA-100 back in the day, and just want to recapture some of the magic that I remember.

Thanks again.

Paul
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Old 20th November 2008, 04:13 AM   #4
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Hi Paul,

I understand capturing the magic all too well. There's nothing like building and tuning your own hifi!

I have a pair of Maggie 1.6QR's under driven by an Aleph30 at the moment. The room is rather small (12x17'), but lively and the speakers sound very nice. A very good friend of mine has the same speakers driven by a commercial Aleph 5 which is 60 watts in 8 ohms, and they sound fantastic. His set up is what convinced me to buy the Maggie's and retire from box speakers.

Nelson has said may times Maggie's like and need tons of power. A distributor friend of mine said I should hear his setup - a pair of 1.6QR's and commercial Pass x-600. He said they really sing and better than the x150 previously used. I'm not sure how true the comparison actually is between the two amps in this setup, but they do like power. Still the sound from my little amp and my friends Aleph 5 sounds fantastic.

I'd encourage you to try the Aleph60 mono bloc, I bet you'll be happy. The heat sinks mentioned earlier from Conrad are perfect. The amp will work flawlessly without overheating for hours, given the usual amount of free space for ventilation that's standard with class A.

Here's a picture of my Aleph30, which could be an Aleph60 Mono bloc someday. I actually have an identical setup, but have not gotten around to building it since what I have sounds so good.

-David

Here's a pic of my amp with the Conrad heat sinks:

Click the image to open in full size.

Click the image to open in full size.

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Old 20th November 2008, 05:24 AM   #5
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Default My 2c...

Hi Paul,

I've been through the similar dilemma. Since you have a nice transformer, and a cost effective source of nice heatsinks, my advice is build the chassis you are thinking of, stuff the boards and a bunch of output devices into the chassis, then fire it up. You then adjust bias to get the temperature you can stand.

Fortunately the Aleph amps are eminently adjustable, I did this with 9"x11" plate heatsinks (fins 1.25"). I ended up with a set of Aleph 55 monoblocks, ~38v rails, 2A bias, 50% AC gain.

http://picasaweb.google.com/lh/photo...N2w0bsTuc17Kpw

HTH

Stuart
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Old 20th November 2008, 09:23 AM   #6
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Quote:
Originally posted by pdrie
their multi-year banishment due to a "disagreement" with my spouse over furniture placement.
Welcome to the club.

Quote:
Originally posted by pdrie
Krell KSA-100, recapture some of the magic
300W of dissipation per channel is a lot of heat to get rid of with natural convection heatsinks.
An alternative is fan forced cooling, KSA-100 style, with the right fan/heatsink combo you can visit bias levels where no man has gone before.
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Old 20th November 2008, 09:57 PM   #7
pdrie is offline pdrie  United States
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Thanks again for the replies. I hadn't considered forced cooling. Now I'm eyeing a Marston tunnel. I have possible source for a 5.9" high tunnel that would have a theoretical coefficient of about .32 with the fans that I have in mind. If I understand it correctly, if each of the four heatsinks is dissipating 75 watts, it looks like I'd be seeing about a 30-35 degree C rise over 25 C. That seems to be acceptable for the IRFP240s. There might even be enough margin to run them a little hotter. Does anyone see any holes in this line of thought?

Tahnks again.

Paul
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Old 20th November 2008, 10:47 PM   #8
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Paul,

Something else to consider. After spending all the time and money making a silent high resolution amp, the white noise of a fan in the background can become annoying. I'm sure there are a lot of successful forced air implementations, although they are not seen as often as convection.

You probably need 4 of these tunnels for an Aleph 2.

-David
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Old 20th November 2008, 11:13 PM   #9
Aengus is offline Aengus  Canada
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You might also want to read about Grey's water-cooled Aleph 2.

[edit] A search for "water cooled" will bring more information, not to mention a lot of speculation. Note that Grey's is a long-term working solution. [/edit]

Regards.

Aengus
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Old 22nd November 2008, 08:50 AM   #10
pdrie is offline pdrie  United States
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So, my transformer showed up today, my power supply caps are in the mail... I am rethinkng the Aleph 2, although it is difficult to let go of the dream. I've seen the water-cooled thread, but that is probably beyond what my wife would tolerate.

I thought about something like 4 Conrad M35-151.5s for each monoblock, arranged in pairs such that the fins are vertical and facing each other to form two tunnels. With 80 cfm of airflow through each pair and 3 IRFP240s on each heatsink, I think they would stay cool enough. It is a much cheaper alternative than two Marston towers in each amp. At a resistance of .21 C/w, each of these heatsinks should be able to dissipate 75 watts comfortably, even with a 50% derate and no forced convection.

Am I deluding myself to think that these heatsinks could handle this heat load?
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