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Class D Switching Power Amplifiers and Power D/A conversion

Quantifying class A quality.
Quantifying class A quality.
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Old 11th February 2019, 07:11 PM   #21
Oneminde is offline Oneminde
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Quote:
Originally Posted by doctormord View Post
This is IMD, so nothing is wrong about that. If not, what plot are you refering to?
You are right and I stand corrected, no THD was shown.
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Old 11th February 2019, 07:18 PM   #22
Oneminde is offline Oneminde
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Originally Posted by ViennaTom View Post
BTW I don' think that the easy explanation of THD and how much can be decteted says it all. There is also IMD (that sounds MUCH worse than pure THD!). Plus: IMD is related to THD and there are many ways to measure it so you can produce the number you want to see :-)
For sure. IMD sounds way worse than just THD.

This is a great video - for anyone - who is interested, these things are always fun to watch and there is always something to take home.

RMAF15: What The Specs Donít Tell YouÖ And Why
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Old 11th February 2019, 07:28 PM   #23
Windforce85 is offline Windforce85  Poland
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Originally Posted by Oneminde View Post
For sure. IMD sounds way worse than just THD.

This is a great video - for anyone - who is interested, these things are always fun to watch and there is always something to take home.

RMAF15: What The Specs Don’t Tell You… And Why

IMD is the same thing as THD but with different expression. IMD can reflect nonlinear harmonic distortion at the frequency where single-tone measurement (like 1kHz) would produce out-of band distortion products. IMD values measured at 10-19 kHz range usually look worse than 1kHz THD becouse of finite gain bandwidth products of every amplifier device with drop of available gain for correction by means of negative feedback loop. Yes, ugly feedback from hell. Without feedback, there would be not possible to fly F-16 aircraft or space shuttle, there would be no robotics and even people would nor be able to walk or eat. Feedback is a nature of our world. I'm sorry.

Last edited by Windforce85; 11th February 2019 at 07:31 PM.
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Old 11th February 2019, 07:34 PM   #24
Oneminde is offline Oneminde
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Feedback is How am I doing. Like with humans, if there is no feedback we would have killed this planet eons ago
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Old 11th February 2019, 07:43 PM   #25
Windforce85 is offline Windforce85  Poland
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Okay but you've wrote such a thing in post #16. Maybe it is me that I didn't understood your sentence.


The problems with negative feedback arose from the fact that people's habit was to apply too little feedback loop gain for mediocre amplifier's hoping that it magically cure all the problems but it just brought more harm than benefits in that form of application..
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Old 11th February 2019, 08:01 PM   #26
Oneminde is offline Oneminde
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What I mean was that feedback is error correction, meaning the system is unstable unless it is informed of how it is doing, and I am for a system that is stable without feedback, that is all. As a side not on that I know nearly enough since feedback is a huge topic.
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Old 12th February 2019, 05:23 PM   #27
Oneminde is offline Oneminde
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Is the consensus that THD / THD+N, S/N Ratio, Chn Separation, Damping Factor and IMD in the end matters more in terms of quality rather than which class is used ?

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Old 12th February 2019, 08:52 PM   #28
bwaslo is offline bwaslo  United States
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Quantifying class A quality.
You don't listen at the 'spec' THD of ANYTHING. Audio signals, bar continuous sinusoid waves, vary in level over a very wide range. Amp THD specs are given at some level, that spec doesn't apply for every instant you are listening. Often it is given at the 1W 8 ohm (2.83Vrms) level, sometimes where they want to "rate" the power output. In the old days, THD was mostly used as a way of leveling the field when giving power ratings -- to keep sneakier manufacturers from stating the power level an amp can under heavy clipping making a near-square wave (now being done again by a lot of SET amps, by the way!), or power drawn from the AC plug, or the like -- reputable manufacturers would say something like "50W at less than 0.5% total harmonic distortion". The salient part of that spec wasn't so much the %distortion, but the power level/amplitude the amp was capable of.

You don't listen to "0.03% THD" unless and only unless you are listening to a continuous sinusoid wave, and at the level where that much distortion is generated.

IOW, there's no such thing as listening to "Dark Side of the Moon" at 0.05% THD or IMD, that would make no sense. Distortion measurements like THD or IMD are not very relevant to listening situations.
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Last edited by bwaslo; 12th February 2019 at 08:56 PM.
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Old 12th February 2019, 09:02 PM   #29
Khron is offline Khron  Finland
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Technically, you kinda-sorta COULD listen to the "THD", if you wanted to.

Pad down the output signal to the level of the input one, flip its polarity, and you're left with the difference

YouTube

And on the subject of phase shift...

YouTube
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Old 12th February 2019, 09:24 PM   #30
Oneminde is offline Oneminde
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Originally Posted by bwaslo View Post
You don't listen at the 'spec' THD of ANYTHING.
I think I know that much, distortion change depending on freq. and power level. But wait, there is more, there is crossover distortion, clipping distortion etc.

If anything at all, quantifying - class or not - quality from an objective perspective amounts to more or less: Less is more and while that can be a good guideline it contains few if no quantifying remarks. A matter of fact that no one can give an objective statement such as - okay - good - outstanding - levels of performance. Everyone cannot be correct or have the best opinion, every method can neither be the best way - at some point, we arrive at a junction where two distinct paths appear.

Its like comparing a 1990 Volvo 245 station wagon and 2018 McClaren F1 and saying both stand a chance at performing equally under the same condition and on the same track.

There are contradicting "facts" floating around on the net and in forums. On one side you have individuals that rank class A as the style which can give the overall best performance closely followed by class AB and lastly we have class D. Then comes along opinions that express concepts such that the class does not matter, only distortion numbers, but that is neither the leading opinion because we end up at distortion is only half of the story ... and yeah, good luck.

The same **** took place when I wanted to learn about loudspeakers, no one can quantify low vs high quality, it all depend on the mood that day, what you had from breakfast and the last time you got laid ... LOL

Last edited by Oneminde; 12th February 2019 at 09:29 PM.
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