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Class A?  Really?
Class A?  Really?
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Old 16th September 2021, 06:26 AM   #91
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Berlusconi View Post
This finding is absolutely correct but it is utterly wrong to apply it directly, without further considerations, to any kind of amplifier because complexity of the actual physical system is simply too large to be represented by such a simple model. (Yes, Fourier transform is complex, yet too simple.)
This does not hold water. If I measure the weight of an item, that weight does not depend on the complexity of the item.

FFT simply tells you what a signal consists of. If you are concerned about the complexity of a signal, you can do a multitone test with 30 different simultaneous tones and look at the distortion, intermodulation and noise in the presence of signals, using FFT techniques. The actual complexity of the amp doesn't figure in that, ONLY how it treats a signal.

FFT doesn't tell you how something sounds. neither does 'class A' or '200W' tell you how something sounds. But FFT techniques can tell you how much an amp adds or subtracts from a clean signal, and we generally want that to be as low as possible. Of course, if you prefer warm, muddy sound, you don't want a clean amp! It's all about personal preference, there is no definition of 'best sound', it varies from person to person.

Jan
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Old 16th September 2021, 06:38 AM   #92
andyr is offline andyr  Australia
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Originally Posted by jan.didden View Post
But FFT techniques can tell you how much an amp adds or subtracts from a clean signal, and we generally want that to be as low as possible. Of course, if you prefer warm, muddy sound, you don't want a clean amp!

Jan
OK, Jan ... perhaps you can explain how FFT techniques will explain what is going on when 2 different amps produce the following results - using the same source and into the same pair of spkrs. The amps are:

1. a Purify 452 (I think the model is) stereo amp.
2. A pair of Audio Research 250SE tube monoblocs.

#2 produced a deep soundstage, from the plane of the spkrs to waaay back.
#1 had a flat soundstage.

This difference was easy to hear ... I'm curious to know what measurements would explain the difference we heard.

Andy
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Old 16th September 2021, 07:12 AM   #93
mocenigo is offline mocenigo  Germany
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Originally Posted by andyr View Post
If you are saying that good AB - and particularly D - measure much better than Class A ... then I agree with you.
Note that I said "good" AB and D (and I would now add B). Low THD, IMD, and SID (slew rate induced distortion) also contribute to a more faithful signal - cheap (or old) AB and D amps lack in this respect, sometimes egregiously so.

Class A can also measure spectacularly well, and it is not even particularly expensive to achieve that, by the way.

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But grunf, below, has hit the nail on the head!


I recently finished building two Class A amps (Hugh Dean's "Alpha Nirvana" - there's a thread in this section). Unfortunately, with a bias current of 3a, they do have a high heat output - hence I will need to use my Class AB amps in the summer months.

There is a biiiig difference in the sonic pleasure delivered by the Class A amps, compared to the Class AB. In particular - a much deeper soundstage!
And here I disagree. We are now talking about both subjective and sighted comparisons. This automatically invalidates any attempt to draw any qualitative evaluation from them. And if these Class A amps have moderate amount of distortion, esp second order (so they must be single ended, or have a single ended driver to a push pull stage), then they may sound subjectively more pleasing I know this from experience but it does not mean that they are "better'. One may like them more, of course.

There can be a lack of dynamics in AB amps that use simple feedback loops it is not the feedback per se that is bad, but the simplistic approach to it, which can be detrimental to dynamics.

And there is the "scarrafone" effect: what one builds oneself always sound better ("scarrafone" means "cockroach" in the Italian dialect of Neaples. They have a saying "Ogne scarrafone bell' a mamma soja" - which translated to "Each cockroach is a beauty in its mom's eyes"). My Class D amp (with a Neurochrome buffer) is of course the best sounding amplifier on the planet!
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Old 16th September 2021, 07:24 AM   #94
andyr is offline andyr  Australia
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Originally Posted by mocenigo View Post
And if these Class A amps have moderate amount of distortion, esp second order (so they must be single ended, or have a single ended driver to a push pull stage), then they may sound subjectively more pleasing I know this from experience but it does not mean that they are "better'. One may like them more, of course.
The Class A amps that I built have +/-22v DC rails - so not 'SE'.

My definition of "better" ... is that they deliver more sonic pleasure.

Quote:
Originally Posted by mocenigo View Post
And there is the "scarrafone" effect: what one builds oneself always sound better ("scarrafone" means "cockroach" in the Italian dialect of Naples. They have a saying "Ogne scarrafone bell' a mamma soja" - which translated to "Each cockroach is a beauty in its mom's eyes").
Haha - I like that ... and it is very true!

But in my case - the Class AB amps that I am using in summer ... were also built by me; so they are both 'scarrafones'.

Andy
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Old 16th September 2021, 07:26 AM   #95
mocenigo is offline mocenigo  Germany
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Originally Posted by phase View Post
With the advent of modern dsp, ie Dolby Atmos, there may be a future for class D for critical listening.
The future for class D for critical listening is now. In fact, it has been that future for a few years now.
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Old 16th September 2021, 07:42 AM   #96
mocenigo is offline mocenigo  Germany
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Originally Posted by andyr View Post
The Class A amps that I built have +/-22v DC rails - so not 'SE'.
So they are balanced? push pull?

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My definition of "better" ... is that they deliver more sonic pleasure.
Perfect.

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[The scarrafone effect] Haha - I like that ... and it is very true!

But in my case - the Class AB amps that I am using in summer ... were also built by me; so they are both 'scarrafones'.
It may be that you are better at building Class A amps than AB amps ;-) In fact, getting the latter to work properly is not easy at all. You could try to use a trick used also by Cambridge Audio: add a bit of DC to the signal before the amplification and them remove it at the end (you can do that in a fixed way instead of using a DC servo at the end, since you know your gain). This should reduce the influence of crossover distortion on the signal by orders of magnitude.
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Old 16th September 2021, 08:22 AM   #97
Berlusconi is offline Berlusconi
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Originally Posted by jan.didden View Post
This does not hold water. If I measure the weight of an item, that weight does not depend on the complexity of the item.
But of course, my statement absolutely holds water and you can not view this complex phenomena in terms of simple weighting a kilo of potatoes. Just look at the complexity of events at the cross-over region (observe the difference: I am not talking about the "point", instead I use proper word "region"). There is a plethora of possible outcomes and functions representing the underlying phenomena are rather complex, or should I say "fuzzy". There are discontinuities, overlapping trends, functions aren't differentiable, function can abruptly drop to zero and suddenly emerge from nowhere. How that can be presented as an infinite sum of "harmonics"?

On the other hand a kilo of potatoes is in front of you, it doesn't move and you can read its weight correctly, as a simple value representing it's mass. By the way, are you sure that a kilo is really a kilo. It is much more complex. Consult Albert.

When you measure in "frequency domain", you in reality measure voltage as a function of time. The magic hidden inside your instrument uses an algorithm to present the measurement results as a function of frequency. But remember, the algorithm "assumes" that the input signal is a finite sum of harmonics. Is that true? Honestly.

Now, human reasoning tends to accept the measurements as scientifically correct beyond any doubt. I was actively involved in scientific measurements for decades and I perfectly understand that all circumstances and especially assumptions must be carefully evaluated during interpretation of the results. Remember, we are talking about values that are beyond human perception. Hence, we use instruments to extend our perception to the "invisible", in contrast to obvious variables like the weight of an object.

Furthermore, human mind rejects complexity and rather decides for simplicity of a single absolute parameter: THD.

Take all these THD measurements with a grain of salt. And think what is really happening behind the scene. Otherwise you will place fog and mirrors in front of your own reason.

No offense meant, whatsoever.

Cheers
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Old 16th September 2021, 08:46 AM   #98
andyr is offline andyr  Australia
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Originally Posted by mocenigo View Post
So they are balanced?
No, they do not have a balanced topology - RCA inputs.

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Originally Posted by mocenigo View Post
push pull?
I am afraid I am no expert; I know they are 'Class A' (so the NPN and PNP Mosfets never turn off) - but whether this is defined as 'push pull' ... I have no idea.

Andy
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Old 16th September 2021, 08:50 AM   #99
andyr is offline andyr  Australia
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Originally Posted by mocenigo View Post
It may be that you are better at building Class A amps than AB amps ;-) In fact, getting the latter to work properly is not easy at all. You could try to use a trick used also by Cambridge Audio: add a bit of DC to the signal before the amplification and them remove it at the end (you can do that in a fixed way instead of using a DC servo at the end, since you know your gain). This should reduce the influence of crossover distortion on the signal by orders of magnitude.
I said I "built" both amps; what you are suggesting, seems to me to be part of the design stage?

I don't design - merely construct.

Andy
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Old 16th September 2021, 11:16 AM   #100
jan.didden is offline jan.didden  Europe
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Originally Posted by andyr View Post
OK, Jan ... perhaps you can explain how FFT techniques will explain what is going on when 2 different amps produce the following results - using the same source and into the same pair of spkrs. The amps are:

1. a Purify 452 (I think the model is) stereo amp.
2. A pair of Audio Research 250SE tube monoblocs.

#2 produced a deep soundstage, from the plane of the spkrs to waaay back.
#1 had a flat soundstage.

This difference was easy to hear ... I'm curious to know what measurements would explain the difference we heard.

Andy
I don't know of any measurement that measures sound stage width in amplifiers. But the deeper question is: was this your personal impression, or was this concluded from a controlled test?
I'm sure as an experienced audio person, you are well aware of the impact of personal opinion and convictions upon audio perception.

Jan
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