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Old 22nd November 2008, 05:32 PM   #11
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Hi Paul,

Apply an ambient room temp correction factor of 1.4 to the c/w rating of .21 for a real world c/w of .295.

Several members here, including myself, run these MF350x151.5 heat sinks at 100 watt of dissipated power. The real world temp for me at 100 watts is 135 to 155 degrees. They easily pass Nelson's DIY heatsink temp test with flying colors. I have a handful of friends and neighbors hold their hand on the top of the heatsinks for an average of 5-15 seconds before feeling unconfortable. Nelson's benchmark is 5 seconds.

A stereo Aleph30 or mono bloc Aleph60 is a "no brainer" for these heat sinks. It's almost as if Conrad made this model heat sink for these Alephs.

Let us know what you decide.

-David
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Old 22nd November 2008, 05:35 PM   #12
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Paul forgot to mention, the above post was refering to 2 MF350x151.5's per chassis for the stereo A30 or mono A60.

-David
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Old 22nd November 2008, 06:17 PM   #13
john65b is offline john65b  United States
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I have the exact same speakers - Maggie MGIIIa - and love them. I have had many friends offer much more than what they go for on Agon (~$600 - $800) after hearing them. The wife even likes them - she said they have an Eames look to them. I guess a nice Eames Loungechair would look slick in front of maggies, but an original would be well over $3000. I'd rather spend it on audio stuff...

I currently have them driven by a Pinkmouse Krell Clone KSA-50 using Stuart's Chassis in his pic (the bigger of the three - many thanks Stuart!).

Anyway, the chassis has four monster sinks bolted together to drop, what I calculate, 235 watts per channel (Re - .65 ohm, +/-39VDC rails, 1 amp/device bias, 3 pairs of 2SA1943, 2SC5200). Tranny is a 1250VA and total of four 56,000uf power supply caps.

With these parameters, I am calculating around 72wpc @4ohms. The heat sinks get warm, but even in the summer months in my basement in Utah only really got to 45C - 48C (115F - 120F), and two of the heatsinks do not have output devices bolted onto them - but they do conduct from the adjoining hot sinks...

I always thought the more power the better, but these sound just as powerful at 72 wpc than my UCD400, which is 400 wpc @4 ohm. It could be the over sized tranny and PS cap that make it feel much more powerful.

I am building a Aleph 60 to see what they can do on the maggies. I only have a 600VA tranny for the Aleph 60 tho...

There is also a Heatsink simulator on Rods ESP website that you can enter various dimensions and it will spit out a estimated C/W rating.

I also use Nelson's rule - if you can touch it for over 5 seconds its under 60C....
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Old 22nd November 2008, 06:20 PM   #14
john65b is offline john65b  United States
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Now wouldn't this look cool between the MGIIIas??

As soon as the stock market turns, I am all over it.
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Old 22nd November 2008, 06:33 PM   #15
john65b is offline john65b  United States
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Aha, I found that heatsink simulator...hope its ok to post it -
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Old 24th November 2008, 02:23 PM   #16
pdrie is offline pdrie  United States
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Thanks for the reply. I would love to be sitting in that chair between the maggies! I have finalized my heatsink plans. I'm going to use three forced convection tunnels on each monoblock. Each tunnel will consist of two heatsinks with fins face-to-face, with each individual sink rated at .11 C/w at 27 cfm. I'll be using one 17 dba 80 cfm fan on each tunnel. I'm planning on mounting 2 mosfets on each heatsink (4 per tunnel). As long as the fans aren't intrusive, I expect that there shouldn't be a heat problem. Given the amps probable location, I think that the noise will be OK.

I am still working on the front end. The Aleph 2 seems a little more forgiving, but I am pouring over the Aleph-X threads, as well. If I go with the X, I'd probably use 2x18 800VA toroids that I have on the shelf. I'm a little concerned about the rails being closer to 27V than the 22V I usually see for an X, but I could probably drop it, if need be.

Thanks again for all of your replies. I hope that I can return the favor as I gain more knowlegde and experience with solid state.

Paul
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Old 24th November 2008, 03:20 PM   #17
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Hi Paul,

The Aleph-X is not the best choice for any Maggie. The AX design, as seen here, does not do well into high current heavy loads. The AX.5 commercial amps include a follower circuit that helps with heavy loads like the Maggies.

Something to consider anyway.

-David
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Old 24th November 2008, 03:37 PM   #18
pdrie is offline pdrie  United States
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Thanks for the insights on the X and the Maggies. The Aleph is simpler circuit and probably a better choice for me to tackle, anyway. I have my mosfets on the way. Now that I have settled on the circuit, I need to start aquiring the rest and making the boards.

Thanks again.

Paul
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Old 24th November 2008, 03:56 PM   #19
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Make sure you dampen the fans to decouple mechanical vibrations to the heatsinks.
Forced convection cooling has been given a bad rap, partly because electronic engineers are, euh...electronic engineers.
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Old 24th November 2008, 05:01 PM   #20
moe29 is offline moe29  United States
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Aleph heat sinks - rule of thumb:

take what you think is good enough, then DOUBLE it.

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