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Old 10th October 2011, 01:16 PM   #481
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About the highs... I've seen claims that class D amps have very large amounts of higher order distortion products at high frequencies, say for 10 kHz there are distortion products up in the 200 kHz range. I just cant believe those claims.... but it would be interesting to see an FFT of 10 kHz taken at a very high sample rate to see what is happening in the range up to 200 kHz or so. Can you do that?
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Old 10th October 2011, 01:23 PM   #482
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People will claim just anything to justify their belief that class D can't be good. These people are fighting a rear-guard battle. I don't think I shall join the fray. I simply haven't got the time for it.
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Old 10th October 2011, 01:51 PM   #483
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But you agree that those claims I referred to are complete nonsense, dont you?
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Old 10th October 2011, 02:18 PM   #484
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They are nonsense. I know the game. Someone has a case to make (e.g. for the existence of supernatural beings, telepathy, etc) and they try to prove this by pointing at evidence which perchance hasn't been collected yet but which will surely vindicate their beliefs when provided. And when you say "bollocks" they'll then proceed to challenge you to disprove them, thereby suggesting that by default their theory holds. And by accepting to play their game you accept their terms. Well, before doing so, be aware of what follows: you do the hard work to do the experiment of which they claim to know the answer without bothering to try. You provide evidence which flatly refutes their claim. What happens? Instead of saying "you're right and I was wrong" they'll just invent another story for you to disprove. That tactic is called "moving the goalposts". It is one of a range of techniques nitwits use to give the impression that they are in a position to take on actual experts. I haven't the foggiest whose claims you are referring to but I'm imagining some forum discussion where someone says "oh THD is nothing, it's IMD that matters" and someone else says "go and check out the IMD plot then, it's all there" followed by the first speaker replying "yes but their plot stops at 20kHz and beyond that be dragons". It just keeps going, there's no telling what they'll come up with next.

Now, to answer your question technically. Ncore's loop gain is plotted in the white paper. Unlike linear amplifiers, open loop distortion is fully independent of frequency so the distribution of various harmonics is the same for all frequencies. You can take that as a given. You can read the distortion spectrum either from the 30W plot I posted earlier or you can glean a good indication from the IMD plot done at even higher output powers. So you look up how much lower loop gain is at various harmonics of 10kHz, you look up the amplitude of the matching harmonics from a known spectrum and from there you can work out what the HD would be at 10kHz. Since loop gain includes the output filter, be sure to scale the calculated HD back down 40dB/dec after 35kHz.

In short, the information is already there. Querulants often rely on their inability to read in order to make a point
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Old 10th October 2011, 02:22 PM   #485
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Thanks!

I'll go to an other forum and swing my axe. Some heads are about to roll.
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Old 10th October 2011, 02:27 PM   #486
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Ah the Viking spirit awakens
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Old 10th October 2011, 02:36 PM   #487
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I have nothing against opinions of course, but when people start to spread lies, then my Viking blood starts to boil...
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Old 11th October 2011, 08:24 AM   #488
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Quote:
Originally Posted by StigErik View Post
I have nothing against opinions of course, but when people start to spread lies, then my Viking blood starts to boil...
people who strongly believe that WAVs sound intrinsically (as opposed to incidentally) better than FLACs do exist. they would testify to it.
whether or not you bring arguments against the higher order distortion is of no use, because they can always resort to some other argument, no matter how scientifically incorrect or downright illogical. in their view it's still a valid argument. and when all arguments (valid or not) end there is the "i don't care how it measures, my ears know better" one. in the end there is the knowledgeable one wasting time and the dogmatic one still feeling superior.
is it only me who sees the futility?
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Old 11th October 2011, 08:50 AM   #489
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is it only me who sees the futility?
Not at all - you're not alone. For practical reasons you've got to let people have their opinions but I don't have to treat those as valuable unless there's knowledge behind it. When people think they can teach me about designing amplifiers I just ask them where their design spreadsheets and their hardware are. If none are forthcoming I can do without their ideas as well.

That was what I hated about working for some Japanese companies. I was just the lowly slob who took care of the menial task of making the product work and they had the unfathomable magic genius to make it sound good. Right. Mind you, when people just have opinions about how something sounds without proffering technical advice I do listen because they might very well have an actual listening experience to report that I haven't had.

On another note and entirely off topic. In a local Italian restaurant there's a sign saying "Le opinioni sono como le palle, ognuno ha le sue". On the internet the quote is widely attributed to Clint Eastwood, except that I can only find it in Italian...
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Last edited by Bruno Putzeys; 11th October 2011 at 09:07 AM.
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Old 11th October 2011, 09:24 AM   #490
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