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Old 1st March 2007, 02:26 AM   #1
Arx is offline Arx  Canada
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Default Heatsinking/transformer for big chipamp?

I'm looking at building myself a bigger amp. I'm going to be running my crossover digitally, so am building the amp with 6 channels (tweeter, woofer, and subwoofer).

My current one is an audiosector.com kit, which I built into a simple chassis made from some aluminum 1/8" thick 2" wide angle, and some scrap blocks for the ends .

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I'm running on some pretty light rails though, at around 20V each. It runs super cool.

now, what I'm wondering is whether a similar case design would cool well enough when using a 25-0-25 transformer. I'll be scaling the length of it considerably to fit 6 chips of course. Basicly I guess I'm looking for a rough estimate on how much temperature difference I'm going to see due to the change in rail voltage. Anyone run 25vac transformers using 1/8" aluminum for a heatsink? if so, how much metal per chip?

Also, the transformer is 600VA, which I would assume is plenty to run 6 chips, 2 of which are only hooked to tweeters. If I hooked the subwoofer channels as bridged/parallel, would it be enough?

How about just bridged. I think my voltage is going to be a bit high for an apparent 4 ohm load, but has anyone tried it? What kind of heatsinks did you use?

-Nick
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Old 1st March 2007, 02:38 AM   #2
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You can test the thermal resistance of the heatsink/case by bolting a power resistor to it and applying a known voltage. Leave it sit for a while and measure the temperature rise in the vicinity of the resistor.
Calculate the power being burned up by the resistor as V^2/R.

Thermal resistance is temperature rise/power (that's why the units are degrees per watt).

Check the data sheet for the recommended heatsink thermal resistance for the chip you will use.

I_F
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Old 1st March 2007, 02:53 AM   #3
Arx is offline Arx  Canada
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Yeah, I know the physics. Just hoping someone who's built similar can give me a gut feeling and save me some time. Does it sound sane?

I'll probably just build the power supply ahead of time, and give it a trial by fire on my current amp. Play some Bjork really loud or something to see how it does temperature wise.

I'm not worried so much about heat at continuous full output, since I don't really ever drive it that hard.

-Nick
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Old 1st March 2007, 08:05 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
4ohm load impedance and 25-0-25Vac does not sound sane.

That higher voltage transformer takes 8ohm loading to the limit.
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Old 3rd March 2007, 07:25 AM   #5
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Why risk it? Bid on this and bolt them to the back or the top.

--
Mike
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Old 3rd March 2007, 08:20 AM   #6
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by mike_steinert
Why risk it? Bid on this and bolt them to the back or the top.
baseplate is too thin for a single device. use at least 4 devices to spread the heat more evenly.
Not suitable for the high dissipation requirements of a chipamp.
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