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Old 24th September 2001, 03:14 PM   #1
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I have basically decided on a 25-30W SOZ amp ( if its too quiet i'll just build find some more efficient speakers ) and now i just thinking about parts and cooling.

other there any good performng but cheaper avaliable resistors i could use , raheter than forking out for dales ?? as they are quite expensive and i would rather build the amp first using mid-range resistors and then upgrade them later when finances are better
The main ones are the 250W 8ohm one and the 50W 1ohm.

PASS says that the mosfets need to be4 kept at 50C or so but what is the thermal requirement for the resistors ?

When can i find a good 1KVA toroid ?

cooling cooling cooling.

Water Cooling ( via water jacket ) - too messy and risky
Water Cooling ( Immersion ) - messier and still risky
Liquid Nitrogen - umm silly

Big heatsinks. I am thinking of some custom heatsinks to make up the sides of the amp ( i have a friend who makes custom heatsinks )

Or Tunnel heatsinks with fan forced convection.
The rating on these things is awesome 0.3C/W
I'm just worried whether the fans wouls add noise to the amp ? Maybe a ducting system to keep the fan a bit further away and shielding enclosure ?

any help would be appreciated






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Old 25th September 2001, 01:24 AM   #2
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FBLEAGH,
Resistors can run quite hot indeed, but it would be best if you were to check the specifications for the resistors you choose. I'm not aware of any good alternatives to the Dale resistors.
One possibility for a 1kVA toroid is: http://www.plitron.com
I believe Avel-Lindberg has transformers in the 1kVA range, too: http://www.avellindberg.com
My Aleph has been water-cooled for six months or so, and hasn't made a mess yet. I would not recommend water immersion cooling. Liquid nitrogen...hmmm...now that's something I hadn't considered.

Grey
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Old 25th September 2001, 03:13 AM   #3
PassFan is offline PassFan  United States
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There is more info in a post titled "Interpreting Electronic Schematics" in the general forum . Some sources for dale resistors and other things. I just recieved a 625va transformer from plitron. Nice transformer but you have to wait. It took them about 4 weeks on mine because they build them when you order. Their price is right so its worth the wait. You might also check out the gallery at passlabs for some ideas on the SOZ(lots of pix). Always ask for help,were always here
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Old 25th September 2001, 03:25 AM   #4
Super is offline Super  United States
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If you can get custom made heatsinks, then you can save yourself some serious cash. However, these buggers are going to be big. If you can tolerate the slight noise coming from a PC fan, then you can save yourself some space. From what I've read of Grey's experiences with water cooling, its not as complicated/risky as it sounds. There should be a topic regarding it somewhere around the SS forum. And as PassFan said, check the "Interpreting Electronics Schematics" section. I too was planning a SOZ, and there are several links to sources and questions answered. The SOZ article on the Pass website should also be able to tell you how to calculate how much heat you're going to have to compensate for, so you can get an idea of just how much heat sinking you should need. Good luck.
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Old 25th September 2001, 12:36 PM   #5
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Default Crazy people wanting to build large wattage SoZ

I hope you're only building a total of 25 - 30 watts SoZ? I will say a 1KVA transformer is NOT enough juice for a 25w x 2 (50w total) SoZ. If you're looking for 250 watt 8 ohm resistors.. then i'm assuming you are building a 25w x 2 amp? Better get a larger transformer!

For my SoZ i had a custom made toroidal and worked out to be even cheaper than Plitron (however, New Zealand labour is much lower than in Canada). I will add, anything custom made usually means MORE $$$. So I hope your friend can cast aluminum heatsinks at a reasonable price.

I personally will never consider using fans because of the dust buildup on the fan blades and the noise they produce over time. However, it all depends on how much money you want to spend. Fans are normally a cheaper route over heatsinks. Forget water cooling unless you have the money to build a 100% sealed water enclosure - not to mention what if bacteria/algae forms after it's all enclosed.

The heatsinked resistors can run safely at a much higher termperature than the mosfets. So I wouldn't be too paranoid. On my SoZ, I find the 4 mosfets dissipates just as much or more heat than the resistor do. So it's a good idea to heatsink those FETs heavily!

High wattage resistors (audio friendly ones) are not cheap. There's not many brands to pick from and also have never seen cheaper high wattage ceramics used in the SoZ. Most common are wirewounds - brand like Arcol & Huntington. If someone has built a SoZ using Caddock resistors please let me know.

If you're on a budget.. stick with a 5 or 10 watt version SoZ. The more watts you want.. the more cost grows exponentially.
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Old 25th September 2001, 05:28 PM   #6
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http://www.audioreview.com/reviews/A...uct_3295.shtml

This fellow built a 30watt SOZ and he used a 1.5KV transformer from Plitron and you might want to check out his comments regarding parts melting etc.

Also I think there is some information on water cooling by Hugh Dean at http://www.printedelectronics.com.


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Old 25th September 2001, 07:04 PM   #7
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I will state again that while the SOZ can be scaled to
50 watts, the dissipation is a scary proposition for
most, and I recommend that any first effort be in the
10 watt range or so.
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Old 26th September 2001, 02:47 AM   #8
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Cool soz resistors etc

hi guys!

I have buildt no less than 5 versions of the SoZ, and may have som useful information.

I have tried both ceramic (witrohm) and thick film (caddock), and a friend of mine (Chris) uses the arcol wirewounds.

currently I am using caddock mp 930 (2*4ohm).

My version is a 2*8W stereo (22V rails, draws app. 400W), and I am using a 600VA toroid (well cooled). I know I am stressing the toroid, but it will have to do until the mk VI monoblocks are finished (project for the winter).

The mp 930's are really nice, but the sad thing is that they have only a 2000 hours full load life (found out after I ordered them). And they can't take as much punishment as wirewounds (only 150 'C, where the arcols can take 220'C!)
My next versions are going to be made up of several arcol NH 50's in paralell. I think heatsink-mounted wirewounds are the best way to go in all repects (sound, cost, durability, handling etc)

Nelsons tip about building a small (10w) version first is a relly good idea.

PS! my first version with air-cooled ceramics (just wanted to hear it run) worked just fine! This is the el-cheapo way, and involves some clever solutions to be made with repect to mounting etc., but it sounds good!

PPS! I am using my this amp to drive a pair of 8ohm, 87dB/1W speakers, and it works really nice in a 20m2 room, a long as you don't need to scare the neighbours..
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Old 26th September 2001, 10:13 PM   #9
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A very good idea for fans is too use 2 fans at half voltage (110VAC for Europe or 50-60VAC for USA). You connect them in series so they work at a lower speed but at the correct voltage. The advantage is that you have very low noise and only a percentage less cooling.
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