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Old 1st March 2004, 05:44 PM   #101
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Yes, Peak power will occur between 3-4 ohms. I am thinking towards my future speakers which will be in the +/-4 ohm range. With my current speakers (8ohm), this amount of bias shouldn't hurt either as I am assured to reach voltage limit before I reach current limit. 100Watts is more than enough. Finally, my basement is cold!!!!

P.S. Nelson said that increasing the bias increases the sonic performance, up to a point. I'm not sure where that point is but would like to find it.
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Old 1st March 2004, 05:45 PM   #102
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This photo shows the monoblocks in a more finished state minus the faceplate and electronics close to their new home.

Regards
Scott
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Old 1st March 2004, 06:04 PM   #103
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Quote:
Originally posted by SGregory
This photo shows the monoblocks in a more finished state minus the faceplate and electronics close to their new home.

Regards
Scott
Where do you store the Tow Motor?



Anthony
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Old 1st March 2004, 06:13 PM   #104
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Funny you should ask, My wife said the same thing.
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Old 1st March 2004, 06:15 PM   #105
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Aren't those heatsinks designed for active cooling (with a fan ???), if not where did you get them.
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Old 1st March 2004, 06:28 PM   #106
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The sinks are greatly enhanced by fans, but not required if they are large enough. Hense the need for a tow motor.

I designed these based on my old text books from college. With natural convection they should remove over 500 watts per side with 30 degree C rise. I derrated them 50% considering there has to be good thermal contact between the plates and the spacer. I will use thermal grease when I final assemble it.

I did a test with my wifes iron,(I thought it was a good idea until my wife saw it) and I was amazed at how well it kept 1200W. After two hours I could still hold my hand on the base plate. I understand that it is not a "scientific or quantitative test"

The sinks are made by 1/4" base plate, 1/2x1/2 spacer, 1/8" plate, spacer, 1/8 plate, etc. Size is 8" by 24".

If it doesn't work in real life I'll get a fan.

Scott
P.S. I now know that it is not proper to respond to the wifes question "What re you doing with my iron" is NOT "I'm just borrowing it, beside you never use it anyway"
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Old 1st March 2004, 07:29 PM   #107
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Quote:
Originally posted by promitheus
What would be the lowest voltage that could be used without having to sacrifice quality?
I have no idea but a few things come to mind. The voltage should be high enough to make the mosfets operate in their most linear region. Datasheets can be handy here.
Look at the graph in the spreadsheet. Changing voltage and current have a tremendous influence on the output power vs. impedance of the load. Choose appropriate values for your speakers.
Finally, as Nelson says: Burn heat as much as your heatsinks can take.

/Hugo
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Old 1st March 2004, 07:34 PM   #108
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Default I think you're in for it now!

At least with answers like that. Maybe something along the lines of "Just making sure this ol' thing still works right. They are on sale over at ?????'s you know." But that could bring even more problems!

Anyway, I'm guessing you are going to be asked again and again about the heatsinks, so I'll shoot first.

I understand the general construction of laminated plates with 1/2" spacers in between. My question is how many spacers? Are they located right at the mounting points of each Mosfet?

Overall, it does seem like a smart way of assembling a clean looking heatsink. The downfall of so many junctions to be smooth and thermally greased does seem real, but your de-rating seems conservative, which may just be fine. With a size like that, though, I'd guess you would want wider or more spacers. Just a guess.

Can you provide a sketch or something of your arrangement.

Regardless, good thinking. I hope upon completion your are sonically satisfied and have adequate cooling.

Sandy.
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Old 1st March 2004, 11:11 PM   #109
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Default heat sinks and better compound

Those are cool looking heatsinks, but the idea of using that much thermal grease gives me the willies. Try Digi-Key #HS243-ND instead. That is Aavid Ultrastick Thermal Compound. It is non-greasy, waxy material with better heat transfer characteristics than silicone grease, and is removable. Best of all, it doesn't "travel" or spread oily crap everywhere. It undergoes a phase change at 130 or 140 or so (use your wife's oven, since you already burned up the iron). It expands at that point to fill all available space.

I used it to bond built up sections of my A-75 heatsinks; u-channel to base plate, base plate to finned sections. It works great. Downside: it costs $17.13 per stick. But stick is good for 1000 sq. inches used correctly. I'll try to attach a photo, but might exceed bandwidth.

Larry Wright
Seattle area
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Old 1st March 2004, 11:13 PM   #110
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Rats! I didn't mean to use the word "bond", because this stuff is not an adhesive; it is just a thermally transmitting compound. To bond sections, I used screws.

Larry Wright
Seattle area
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