Quantifying class A quality.

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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 Don’t Tell You… And Why
 
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.
 
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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..
 
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.
 
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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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
 
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Interesting. So you are saying that the benchmark is not the benchmark at all ? might it be then that class AB is because of its better efficiency ?

It says: the amp (which happen to be class D) can compete with the best amp (which happen to be class A).

Amp advancement has reach to a point where average ears wont be able to hear difference between good amps, whatever the class.

But I guess it is fair to think that crossover distortion is the major issue (in low quality level). Then there is high frequency garbage that somehow someway get into the audible frequency. Then the design itself affects sound quality, just like no two class A amps sound the same.
 
Thanks for clarifying. Are you referring to ultrasonic in the upper band of the filter causing IMD bellow 25kHz ?

Yes. though IMD can be just one of a few possibility. I can plug in my pc tablet power supply adapter to the same AC outlet of my amp and the amp sound quality is affected. Of course such switching adapter is raw and primitive but many class D amps are also primitive in its filtering.
 
A good amp shouldn't be affected by another device in such a way. I dunno, but sometimes its like who ever designed and approved the product have no clue ... its scary. Too much of "I need profit" going on and the product takes a huge hit. Which is very sad. But there is a cure, learn and become a good engineer. Anyway, that's why I got involved in studying class D. The diyaudio community have already established a fantastic platform for class AB so have nothing to add there really - yeah, thinking of the Honeybadger.
 
A good amp shouldn't be affected by another device in such a way. I dunno, but sometimes its like who ever designed and approved the product have no clue ... its scary. Too much of "I need profit" going on and the product takes a huge hit. Which is very sad. But there is a cure, learn and become a good engineer. Anyway, that's why I got involved in studying class D. The diyaudio community have already established a fantastic platform for class AB so have nothing to add there really - yeah, thinking of the Honeybadger.

Ground in our houses is never perfect and so are amplifiers' psrr. Turn off all electrical devices in our house and the sound becomes better.

To average ears, nothing to add because the hypex and the honeybadger will sound the same. That's the point here, right?
 
You could always build a AC conditioner by using a battery or capacitor operated PSU line for your audio stuff. AC-to-DC-to-AC. Some portions of the world have huge issues with dips and peaks which kill electronics or make them suffer, happily, I don't like in such a place. The voltage is very stable here.

Regarding Hypex and Honeybadger, not be "that guy" but the Honeybadger allow for the builder to chose components, meaning it can be built fairly cheap or fairly expensive, and that will dictate the outcome of the performance. So two of them might measure differently. Still, it should perform on par with other good AB amps. The Hypex or NAD M22 should perform the same every time.

If they in the end sound the same in a blind test, then class D win due to the much better efficiency and runs cooler. Electricity - typically - cost money and unless you don't care, stuff like that matter.
 
"Build an AC conditioner"? In the rest of the world, that's called a UPS ;) You're describing the "online / double-conversion" kind, which can get quite pricey, though.

That being said, i would imagine mains dips would affect mostly devices with linear (50Hz "big iron" transformer) power supplies; many switching power supplies nowadays are "wide range", 85-240V AC input.
 
:D they are indeed called UPS, but I like to be special .. LOL

Linear power supply can have a "wide range" AC/DC section and capacitor bank, mainly to act as a ripple rejection section and some do, that way the DC side have a steady supply from its reserve which would qualify as a tiny UPS or "AC conditioner" - the transistor voltage rail capacitor bank is another thing :). By "big iron" I assume you mean the classical EI Laminated core, and I can't understand why anyone would choose that in this day and age. A potted toroidal core, R-core or SMPS is the only type of power section an audio amplifier should use. Its not a law but I could never recommend an EI transformer for anything.
 
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