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Old 4th January 2013, 08:27 AM   #7941
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I thought a nanosecond was shorter than a microsecond?
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Old 4th January 2013, 08:48 AM   #7942
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My worry about class D is that it is a new toy . A toy which might put people off of trying to learn . My friend who has PA equipment says the sound of class D is fine and the weight advantages critical . We are talking 3000 W sometimes . As he says 40 or 25 Kg is a big deal . He has a slight preference for AB excluding the weight . Some of the class D story is a myth . 78.5% verses 95% is not such a big deal . Class H is not as complex as D and for real music makes it a narrow margin of difference . I noticed Philips state crest factors of 10 in the application notes . Obviously this expects the average TV to be shacking to pieces long before the heat-sink becomes an issue . In old fashioned class B in vinyl days a crest factor of 6 was advised and 3 for PA . In my work crest factors of 0.5 are wise ( reactive loads ) . Thus what Philips recommend and I can use are miles apart . The problem I have is I can not shift the heat from such a small area albeit less than if class AB. My brother had a simple rule , always use TO3 . now the big plastic packages compete . Class D , fools gold ?
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Old 4th January 2013, 09:11 AM   #7943
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Hi Nigel,

I would just like to point out that class AB only has 78.5% efficiency when driven to max output. In normal situations the efficiency is much lower, usually around 30 - 40%. Class D does much better in this regard. But as always there are choices to be made, you can tune class D amps for maximum performance or maximum efficiency, (idling time, gate drive). The Hypex nCore white paper is an interesting read about state of the art class D amps: http://www.hypex.nl/docs/papers/ncore%20wp.pdf
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Old 4th January 2013, 09:26 AM   #7944
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Mark you are absolutely right . It is the industrial applications that need stressing as in my book if something says it is 100 watts I expect it to offer 5 years continuously at 100 watts ( 18 months is an undisclosed industry standard in things friends do , contracts exchanged on that basis , modules replaced each year when critical ) . When is a watt not a watt ? When it is VA or music . Like red-lines on engines to me it matters most , this is the same . I seek very high reliability in what I build . As simply put as I can the die area of any device is where my quest begins .
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Old 4th January 2013, 11:23 AM   #7945
dvv is offline dvv  Serbia
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Quote:
Originally Posted by john dozier View Post
I thought a nanosecond was shorter than a microsecond?
Yeah, I meant to say picoseconds, but it came out wrong.
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Old 4th January 2013, 11:53 AM   #7946
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I think class D is like GM food . Logical but ..... ? In normal plant research GM ideas have been used . Not GM but much faster research times using ideas common to both GM and standard . My objection to GM and class D is it transfers power of choice away from me . On the farm where I worked as a boy we saved seeds from broad beans , now it is illegal unless a club and not for profit .
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Old 4th January 2013, 03:16 PM   #7947
JMFahey is offline JMFahey  Argentina
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Quote:
On the farm where I worked as a boy we saved seeds from broad beans , now it is illegal unless a club and not for profit .
Weird, care to elaborate?
I think what you grow is yours
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Old 4th January 2013, 04:04 PM   #7948
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Well it is simple . The broad beans is how life was for thousands of years . Sensible farmers kept the best to grow on , silly ones grew the less good ones . From this we learned selection . Brother Mendel went on to show how this would be made into a science ( peas ) . Now some rightly or wrongly move to outlaw what was common practice for years . One has to ask why ? The parallel is if we loose the skills to make the internal parts of things we built how long before we become just consumers ? Metaphors , the world was full of them once . Time will come when no one remembers them or how to use them ?

Is saving seeds Illegal? - Yahoo! Answers
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Old 4th January 2013, 04:19 PM   #7949
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dvv,

LOL, I used the terminology that applies to woofers (long throw) without realizing it.
you are right about the engines. I'm familiar with motorcycle engines which are different in enough ways and I extrapolated from there, my mistake. the current tendency with motorbikes is to use oversquare engines though. I think it has a lot to do with the higher rpm's reached (my bike has a 12000 rpm redline and it's not even a new engine design, it's basically a pre-90's oil-cooiled engine with some upgrades) and the larger forces the conrod sees at stroke ends, with today's motorcycles rpm's of 16000 are not uncommon and I'm referring to common production models. may also have something to do with geometry which is more restrictive with bikes?

anyway, back to D amps.
well yes, at least some manufacturers seem to design by measurement. but a 50k$ Mark Levinson? am I missing something? a 50k$ amp does not address exactly to the same public that buys a $50 DVD player based on the number of formats it can read or number of different inputs or outputs. or the 20k TAD or even the "cheap" Devialet? these are respected manufacturers with a long history, what would make them employ a paradigm shift?

(this is all assuming that these amps are indeed somehow inferior to their linear counterparts which is not a given but speculation based on reviews)
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Old 5th January 2013, 06:29 PM   #7950
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Mr PP and others . Is there a class D amp which can be built " dead bug " and is > 90 % efficient and < 1% THD . It would be great to have something to work on . I always suspected a NE555 and some FET's should be able to get us somewhere . Hypex is too much like a cake mix for me ( look mummy I made a cake ) .

Google tells me this site is a risk ( Trojan horse or the like , policeman sign says " get me out of here " ) . hope me being here is sensible ? Other than that we are a threat to world order and we are being censored , great !
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