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Old 15th March 2004, 10:56 PM   #1
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Default quick heatsink question for 5w XSOZ

hey all_

i have all of the parts to construct a pair of XSOZ 5 watt monoblocks. i just wanted to know from someone else w/ the same opperating conditions what to expect (heat wise). i have purchased 2 of the following heatsinks, and was curious if that would be sufficient (mounting both resistors and mosfets on the same sink - one per channel). they are pretty big. 12lbs worth. (and dirt cheap).

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3079190191

also...i'm not sure if it matters, but i will be halving all of the power resistor values to use these amps w/ 4ohm speakers. i'm assuming this just doubles the current they will operate at. does that mean a significant increase in heat?

the rails are going to be ~ +/- 13-14V. i currently have IRFP240s for this. would the 044 be a better choice (because of the low rail voltage)? does the higher current make up for this?

sorry about the additional questions. new to the solid state end of things. i've been building tube amps for about 5 years though.

thanks!
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Old 16th March 2004, 06:03 AM   #2
Mad_K is offline Mad_K  Norway
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P=U*I

Double the current = double the power = double the heat = double the heatsinks...

It's a very good idea to have the mosfets and resistors on separate heatsinks.

Use the IRFP240 (you can always try IRFP044 later)
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Old 16th March 2004, 06:36 AM   #3
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Default thanks

thanks! i'll order two more...and proceed as planned. i had just gotten excited to start building, so i was gonna see if i could squeak by w/ just one per chassis. and i guess you're right about the mosfets. i always just want to put my best foot forward.

btw...i loved your 10w XSOZ. real nice job!! i see that you changed it up though (to an aleph)? running too hot, eh ;-) i'll try and avoid the same issues!
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Old 16th March 2004, 11:13 AM   #4
Magura is offline Magura  Denmark
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The rule of thumb for SOZ heatsinking:

Estimate how much you could need "worst case scenario", and multiply by 2.

Ive yet to see the first SOZ thats not running at its (or close to) upper temperature limit. Generous heatsinking pays off in many aspects....especially if you count in that its gonna be summer approximately half of the year

Magura
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Old 16th March 2004, 05:22 PM   #5
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ok...then i will try and be the first to rediculously over-build this beast. i want to have it to give to my grandkinds (well...if i were to have kids in the first place). but you get the point

thanks a lot for the help guys! i'll definitely be posting pics when i finally get around to finishing this thing. now i need to order 2 more sinks!!
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Old 21st March 2004, 12:04 PM   #6
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These are the heatsinks I used in my 5 watt "rackmount SoZ" They barely get hot.

http://www.geocities.com/super_bq/Hi...sinks/HS_3.JPG

Voltages are also higher around 22VDC after rectified.

BQ
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Old 21st March 2004, 04:33 PM   #7
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Default THAT'S what i like to hear!!

great...thanks for the info! i was *hoping* that these were seriously over-spec'd. unfortunately...the link you gave was down. mind posting a pic here, or referencing one in another thread on the board? i'd love to see it!

also...you only get 5 watts from 22v?! i thought that it should be closer to 8 or so. either way...i think that means i'll be fine! out of curiosity...did you just use 2 sinks (one per channel)? i ended up ordering one more, as i'm now building a stereo (dual mono) amp. all of the paralleled 8ohm resistors go on the center sink, and then the paralleled 1ohm and mosfets go on the other.

thanks again...
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Old 21st March 2004, 07:23 PM   #8
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Try this link

My Rackmount SoZ

22v is incorrect. I meant 18v. I use this amp almost everyday and it's been very reliable.
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