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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 20th August 2013, 03:08 AM   #42501
fas42 is offline fas42  Australia
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Yes, since we have been talking about digital audio I thought the context would have been fairly clear ...
 
Old 20th August 2013, 09:06 AM   #42502
marce is offline marce  United Kingdom
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Woops
 
Old 20th August 2013, 09:28 AM   #42503
marce is offline marce  United Kingdom
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Curious as to what you do consider is a perfect square wave?
Perfectly square edges are never going to be reproducible through any electronics.
I am at a bit of a loss here at what you are trying to achieve?
Enlighten me please Frank
 
Old 20th August 2013, 10:09 AM   #42504
fas42 is offline fas42  Australia
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The square wave, expressed in digital form, will never be truly thus, there must alway be at least one sample period between successive samples, from -ve max to +ve max - which obviously then determines what the corresponding analogue slew rate will need to be, to be a correct reconstruction. As you say, in the analogue world the rise time will always be some value greater than zero, so 'perfection' can never be achieved there either.

The confusion has arisen because I used the word "perfect" to describe the trivial exercise it is for software to generate an audio track which at first glance looks to be, exactly a square wave. Which it is not, of course - just passing it through software equalisation with flat response immediately exposes the intrinsic ripple component, that is 'hidden' at the initial software creation of the waveform.
 
Old 20th August 2013, 10:14 AM   #42505
marce is offline marce  United Kingdom
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Cheers Frank
 
Old 20th August 2013, 10:30 AM   #42506
fas42 is offline fas42  Australia
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Old 20th August 2013, 03:02 PM   #42507
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by simon7000 View Post
Scott,

In looking back on this thread there was an issue that we didn't quite settle on.

Attached is the picture of the setup. A current source of 1 amp was used and the voltage across the resistors was 7.32 and 7.31 volts. Both pieces are .125" 5052 aluminum 3' x 6" with the hole .125" centered. The finish was mill finish cleaned with a lye bath. Paint is Rustoleum Flat Black spray paint both sides. Temperatures measured using a bead thermistor in direct contact at the heatsink back just under the mounting bolt were 39 & 42 C.
Not a lot of difference IMO. I don't see 10-15% difference changing things enough considering a resonable overdesign margin.
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Old 20th August 2013, 03:15 PM   #42508
simon7000 is offline simon7000  United States
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Originally Posted by scott wurcer View Post
Not a lot of difference IMO. I don't see 10-15% difference changing things enough considering a resonable overdesign margin.
Let us look at the costs! One square inch of .125" aluminum costs me about $.04. The cost to anodize it black is around $.02. So for heatsinks running under about 50 C the advantage is clear. For those running above that the advantage goes to a fan. But if a fan is not acceptable for either noise or MTBF then the advantage goes dark.
 
Old 20th August 2013, 03:23 PM   #42509
Kindhornman is offline Kindhornman  United States
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John Curl's Blowtorch preamplifier part II
Simon,
If I am reading this correctly and not doing the math here it would appear that a small increase in surface area would be cheaper than the black coating for the small 10% differential you would get with the black. If space is at a premium then the black coating may be required but if not simply sizing the aluminum a bit large would make a greater differential. That does not mean we shouldn't use the black coating, just that surface area would seem to be the driving force here. Correct me if I am wrong, I could just do the math and answer my own question.
 
Old 20th August 2013, 03:30 PM   #42510
simon7000 is offline simon7000  United States
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Originally Posted by Kindhornman View Post
Simon,
If I am reading this correctly and not doing the math here it would appear that a small increase in surface area would be cheaper than the black coating for the small 10% differential you would get with the black. If space is at a premium then the black coating may be required but if not simply sizing the aluminum a bit large would make a greater differential. That does not mean we shouldn't use the black coating, just that surface area would seem to be the driving force here. Correct me if I am wrong, I could just do the math and answer my own question.
Metal cost $.04 To get 10% better $.044
Anodized cost $.06

However anodized radiates better as temperature goes up. So as a heatsink gets to temperatures that one should avoid any human contact anodized becomes price effective. But a fan will keep such a heatsink cool enough to be safe.

So when a heatsink size is limited and you cannot use a fan then anodized is a solution. The other reason to anodize is that it looks good.

Shown is my Class A "Butterfly" amplifier.
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