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Old 5th October 2006, 01:48 PM   #11
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Quote:
Originally posted by dfdye
For the LM3886 based amps that I have built, Slot A CPU heat sinks have worked great for me simply because I don't really crank on the amps that hard. I have an aux. fan to cool the sinks if they need it, but I have never had it kick in.

The point is that in addition to th other parameters, I would keep in the back of my mind how loud I plan on listening to music. The amp I built for my lab (which has to play hard out to crank over noise from fume hoods and other equipment) is in a more robust package than the amp I have for my office since the latter doesn't ever play that loud.

Of course this is just anecdotal and can't really be modeled well, but it is just a little experience I have had with different design parameters.

Good Luck!
David
-- all you need is a four-function calculator -- even if you don't crank the amp it should still draw a decent chunk of milliamperes at idle -- dependent upon the rail voltage.

and as you crank up the rail voltage the distortion of the amplifier is reduced. the figures in National's datasheets were probably done with the rail voltage just below the max -- you can see this with a THD analyzer and a variac controlling the power supply. whether it makes for better listening is anyone else's guess, however.
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Old 5th October 2006, 02:05 PM   #12
dfdye is offline dfdye  United States
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Quote:
Originally posted by jackinnj
-- all you need is a four-function calculator -- even if you don't crank the amp it should still draw a decent chunk of milliamperes at idle -- dependent upon the rail voltage.
Sure. I'm not saying it takes much to model, just that from my experience, my little office amp runs cool and my lab amp runs hotter.
Quote:
and as you crank up the rail voltage . . . you can see this with a THD analyzer and a variac controlling the power supply.
Sure, but I am with you as to whether you would be able to have a better "experience" with the differing rails. I personally have had rail voltages dictated based on what transformers I could get my hands on!

Either way, thanks for the tips concerning modeling heat sinks. Rod Elliot had an article on his web page that I haven't seen mentioned yet, but as always, more info = better building in the future.
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