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Class A vs AB -- Do They Really Sound Different?

pma

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You need to check transition point calculated from idle current and load impedance. This is the level where to seek for crossover distortion, not at the zero crossing. More later.
 

MrPeabody

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See a recurring spike at the zero crossing? No? Then there's no crossover distortion.

That much is manifest. But I'm a little confused, because that certainly does not address every aspect of the question I raised, and you made it seem that it does.
 

SIY

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That much is manifest. But I'm a little confused, because that certainly does not address every aspect of the question I raised, and you made it seem that it does.

If your question was about crossover distortion, yes, it does. If there are any other touted advantages of Class A, they do not seem to show up in measurements, other than temperature if your room needs heating.

Again, look at Self's writing about this.
 

DonH56

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dualazmak

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Hello SIY and MrPeabody,

The thread title is "Class A vs AB -- Do They Really Sound Different?", and I would like to hear also your debate and discussion on difference in "phase rotation up to the ultra-high range" between Class-A, -AB and -D, even though I am afraid that I would not be able to fully follow and understand your technical and engineering details.

When I recently "subjectively" carefully compared Calss-A Accuphase A-36, Class-AB Accuhpase E-460 and Class-D TEAC AP-505 driving Beryllium tweeters plus horn super tweeters at above ca. 6,000 Hz in my multichannel multi-amplfier project, I "felt" I could hear the difference, and for my ears and brain, A-36 gave most comforable and stable "phase impression". Maybe, that was just a placebo effect, or due to any other factor(s) independent from "nature of phase rotation"??

Other than the possible use of REW with one measurement micorophone (ECM8000), I have no in-depth knowledge nor tool to objectively measure and compare the nature of "phase rotation" in high to ultara-high range.
 
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dualazmak

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For those who have not designed amps or read Douglas Self, this post has a very simple picture showing what crossover distortion might look like: https://www.audiosciencereview.com/...f-benchmark-ahb2-amp.7628/page-93#post-422631
HTH - Don

Thanks a lot. I sometimes mis-understand and confuse between "EQ/DSP crossover filter's distortion" and "zero-cross crossover distortion". :)

And, Oh, the post you kindly indicated;
https://www.audiosciencereview.com/...f-benchmark-ahb2-amp.7628/page-93#post-422631
is answering to a question for Accuphase pure Class-A amp!

Just conincidentally, I am also asking in above post about Class-A Accuphase A-36 regarding "phase rotation in high range"...
 
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SIY

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difference in "phase rotation up to the ultra-high range" between Class-A, -AB and -D, even though I am afraid that I would not be able to fully follow and understand your technical and enginnering details.

Marketing.
 

Wombat

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I trust my ears. Being a human, I realize my brain lies constantly so my perceptions need to be checked. :D

How do your ears bypass your brain? :facepalm:
 

dualazmak

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Hello DonH56 and friends,

Regarding the zero-cross distortion,,,

Although this is not directly related to the thread title, let me ask just one more here.

I my current multichannel multi-amplfier project, I very carefully removed attenuators for Beryllium squawkers (Be-SQ), Berullium tweeters (BE-TW) as well as for horn super tweeters (ST), and I inserted 20-25 Ohm audio-grade resistors in parallel with the SP drivers. Please refer to this post and this for details.

Can "the subjectively favorable effect of these 20-25 Ohm pararell resistors" (a small constant and extra power load to amps) be explained and/or justified in terms of the zerro-cross distotions in the amps? I myself am very questionable about this since almost all the modern Hi-Fi solid-state amps has no or neglegible audible zero-cross distortions...
 
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dualazmak

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Marketing.

You are always so subjective! And you are not answering my cordial inquiry... OK, now please just forget again about my specific inquiry..

(I am an end user audio enthusiast and I have no conflict of interest at all with any of the manufacturers, import companies, distributors and audio shops relevant to my posts in ASR.)
 
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pma

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You need to check transition point calculated from idle current and load impedance. This is the level where to seek for crossover distortion, not at the zero crossing. More later.

This is a typical example of the amplifier with highly pronounced crossover distortion, 4ohm load. See the transition from class A to class AB at some 15mV. This behaviour may not be so much noticeable in better designs, however very often we are able to find the transition point. The crossover distortion at exact "zero crossing" as mentioned by @SIY happens only in class B (zero idle current).

One would not reveal this from typical review plots. They start about 0.1V output voltage and measure THD+N. A lot is buried in noise or the plot starts at too high level.

crossover_dist.png
 

SIY

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This is a typical example of the amplifier with highly pronounced crossover distortion, 4ohm load. See the transition from class A to class AB at some 15mV. This behaviour may not be so much noticeable in better designs, however very often we are able to find the transition point. The crossover distortion at exact "zero crossing" as mentioned by @SIY happens only in class B (zero idle current).

One would not reveal this from typical review plots. They start about 0.1V output voltage and measure THD+N. A lot is buried in noise or the plot starts at too high level.

View attachment 100447
What you see in the time domain (residual) plots will be a spike or non-sinusoidal bump that's correlated with the signal. At zero crossing is the classic Class B crossover distortion, but still, if the residual shows no periodic discontinuity correlating with signal, the crossover distortion is either zero or totally buried (and thus insignificant).

Moving to richer biasing, we then encounter a bigger issue with gain doubling, which will also show discontinuities correlating with signal when viewed in the time domain.

A deeper dive is shown here, with Section 5.3 being the relevant one. Self did a cool trick with the Cambridge amps, but that's a story for a different day.
 

SIY

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You are always so subjective! And you are not answering my cordial inquiry...

Your inquiry is about a marketing term in an advertisement. Unfortunately, I'm not a marketing guy, so I'm not competent to comment on it.
 

MakeMineVinyl

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What do you think you gain with a Class A Amp? I used one on the tweaters of a tri amp system and then one summer tried a Neurochtome amp to save on AC and besides being cooler , smaller, and quieter I could not tell any difference so I stuck with the AB amp.
Since the horns I drive it with have a efficiency of 107dB/1w, there is a virtual magnifying glass on the low level behavior of the amp. I heard crossover distortion artifacts with the previous amp, so I wanted to eliminate all potential for this type of distortion. Since the horns/compression drivers are so efficient, I only needed very low power, so the fact that this amp only has 2.5 watts is more than enough. Also, since it has such low power, there is a safety factor for the diaphragms of the compression driver, and the amp emits little heat due to the low power.
 
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MakeMineVinyl

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Strange. If you didn't want anyone to ask you to prove the claim, why did you come here and wave it in everyone's face?
Its called sarcasm. Sometimes people do that. :oops:
 

pma

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Unfortunately very few here have any deeper understanding of amplifier circuit design and analysis. The debate then goes in ridiculous extremes and attempts of jokes, without any basis.
 

levimax

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Since the horns I drive it with have a efficiency of 107dB/1w, there is a virtual magnifying glass on the low level behavior of the amp. I heard crossover distortion artifacts with the previous amp, so I wanted to eliminate all potential for this type of distortion. Since the horns/compression drivers are so efficient, I only needed very low power, so the fact that this amp only has 2.5 watts is more than enough. Also, since it has such low power, there is a safety factor for the diaphragms of the compression driver, and the amp emits little heat due to the low power.
Ok makes sense. The Neurochrome amps have something like 220 dB of gain and 200 dB of feedback, exact opposite approach but both work.... Part of what makes this hobby interesting.
 

dualazmak

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Since the horns I drive it with have a efficiency of 107dB/1w, there is a virtual magnifying glass on the low level behavior of the amp. I heard crossover distortion artifacts with the previous amp, so I wanted to eliminate all potential for this type of distortion. Since the horns/compression drivers are so efficient, I only needed very low power, so the fact that this amp only has 2.5 watts is more than enough. Also, since it has such low power, there is a safety factor for the diaphragms of the compression driver, and the amp emits little heat due to the low power.

Thank you, I am in the same direction in my multichannel multi-amplifier project...
 
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