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Pass ACA Class A Power Amplifier Review

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amirm

amirm

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I think some people would dismiss my experience as delusional, based only on measurements.
Measurements? No. We primarily know that from many blind tests where such differences disappear like the proverbial fart in the wind where we rely on ears and ears alone. :) Measurements tell us whether there is enough deviation from such research as to indicate audibility.

The research is so clear that if you demonstrate what you have said in blind testing, you will make significant news! Such test would need to be repeated to achieve statistical significance by the way. One AB test is not enough. We have to know you are not just luckily guessing.

Here is an example of such research (summary paper): https://www.aes.org/e-lib/browse.cfm?elib=5549

AES E-LIBRARY
Ten years of A/B/X Testing

Experience from many years of double-blind listening tests of audio equipment is summarized. The results are generally consistent with threshold estimates from psychoacoustic literature, that is, listeners often fail to prove they can hear a difference after non-controlled listening suggested that there was one. However, the fantasy of audible differences continues despite the fact of audibility thresholds.

1617585294130.png


I should note that there is one test that has shown amps to sound different. One of the authors of that test though confided there the one amp had audible glitches in pre-testing. If true, then the record remains unbroken.

So by all means, allocate some time to test your hypothesis. Match two amps by level and do an AB test blind with a video camera running so that we can see if you can pass such tests with your ears alone. No instrumentation. No measurements. Just your ears.
 

BDWoody

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I get your point. Chefs can do their jobs better if ovens all work the same, every time. But there are many kinds of ovens, each of which is designed to impart a different flavor to the food. For instance, have you ever eaten pizza cooked in a wood-fired oven, or hamburgers grilled over charcoal? Those ovens do add flavoring to the food. LOL, nothing is simple.

Those are tools of the chef, like a high distortion amp to an electric guitarist. You are illustrating my point.

My microwave is there to heat up someone else's (or my prior) creation, not alter it to some third person's taste.
A DAC or amp is not part of the artistic chain...at least not while pretending to be hi-fi(delity).
 
D

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In the end, my only purpose was to defend the ACA and Nelson Pass against what I thought was, in some posts, overzealous criticism.

Excuse me, but what investment do you have in these matters? Why do you see your purpose as being the defense of the ACA or Nelson Pass?

In the first place, Mr. Pass is perfectly capable of defending himself, should he see fit to do so, against overzealous criticism or any other kind of criticism. He doesn't need anyone else to do that for him.

As for the Amp Camp Amp, you have stated that it gives you enjoyment. That's fine. Enjoy it. If you love it and others denigrate it, what is that to you? No one is stopping you from enjoying it. Not everyone agrees with you, and not everyone is subtle about it. Obviously, you don't agree with everyone else, either. That's life.

If the fact that there are other people who denigrate the amp bothers you personally, then you have a problem that has nothing at all to do with the amp.

Jim
 
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amirm

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Here is a remarkable example of knowledge of reality doesn't change what you perceive. I was doing this speaker test the other day: https://www.audiosciencereview.com/...e-esprit-antal-ez-review-tower-speaker.22080/

index.php


After playing the Triangle speaker (in white) for a while, we switched to Revel Salon 2 to its left. What was remarkable was that you constantly, and I mean constantly, had to remind yourself it was NOT the triangle that was playing! Every bone in your body would say it was generating sound, not the Revel next to it. I think its expose drivers and white color may have caused that. Or the fact that we were playing it before. But the experience was uncanny.

So next time you say "trust your ears," remember this example. Your eyes override your ears every day of the week and twice on Sunday!
 

peng

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Very curious. Why isn't there any mention of intermodulation distortion? Don't HD and IMD go together? Why hide the IMD? The term "IMD" puts people off?

He did talk about it. Nobody hide it, Amir measured it...

One other thing, if THD is very low, IMD would likely be low too.
 

RichB

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D

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Measurements? No. We primarily know that from many blind tests where such differences disappear like the proverbial fart in the wind where we rely on ears and ears alone. :) Measurements tell us whether there is enough deviation from such research as to indicate audibility.

I'm not sure what your argument is. The claim, "All amplifiers that measure well enough sound the same," is the null hypothesis. It cannot be proven scientifically. On the other hand, it's scientifically valid to state, "No evidence was found that audible differences exist between amplifiers that measure well." It's an important distinction, to a scientist.

Science has not and cannot prove that all "good" amplifiers sound the same. But so far it has failed to prove they sound different. Audiophiles who say they hear such differences in uncontrolled tests are not speaking scientifically. They have not met the burden of proof to support their claims scientifically. Possibly their claims are valid in some other faith-based thought system, I dunno.

But I don't know why you're bringing this up in this thread. It's almost like you're putting words in my mouth. The ACA is an amplifier that measures badly, and people claim it sounds different. So far, so good. Your measurements confirmed the claimed (bad) specs. You tried a "listening test" (why?) but made no effort to match the amp to a suitable speaker. Nor, apparently, did you even try to find a source strong enough to drive the amp to full output. You thought it sounded bad, but that's not a scientific assertion.

Your complaint seems to be that some people say the amp sounds "good" or even -- more galling -- that it has qualities superior to other amps. This is Audio Science Review. Do you have some scientific evidence that those claims are false? Are you saying they're wrong, that they actually hate their Amp Camp Amps and are lying about it?

Forgive me. This is getting very confusing.
 
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amirm

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I'm not sure what your argument is.
I thought I was very clear. You said we were relying on measurements to be incredulous of your personal experience as far as differences between amps. I pointed out that our reluctance to believe you is not due to measurements, but countless blind tests that show experiences like yours never materialize when we are only using your ears to judge.

The ACA is an amplifier that measures badly, and people claim it sounds different.
Such claims need to be verified in blind tests. I am confident that the "good distortion" people think they are hearing, indeed is not audible to them.

Your measurements confirmed the claimed (bad) specs. You tried a "listening test" (why?) but made no effort to match the amp to a suitable speaker.
I performed a test and its lack of power was enough reason for me to dismiss it as a proper amplifier. I explained how a cheaper amplifier ran circles around it. Now, you want to go and light your house with a candle, you go right ahead. I am not one to bend to the needs of the amplifier and buy speakers that it likes.
 
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amirm

amirm

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Your complaint seems to be that some people say the amp sounds "good" or even -- more galling -- that it has qualities superior to other amps. This is Audio Science Review. Do you have some scientific evidence that those claims are false? Are you saying they're wrong, that they actually hate their Amp Camp Amps and are lying about it?
Not at all. I know they believe what they believe as much as you do about your experience.

As I just noted, I think these audiophiles are oblivious to the flaws in this amp. The positives are therefore manufactured in their mind, not reality of the speaker. This comes from testing literally hundreds of audiophiles in controlled blind tests to see how good they are about hearing non-linear impairments. Sadly, audiophiles tend to be the same as general public in lacking such abilities. Indeed, if they had good hearing, they would run away from such amps! So many companies produce flawed audio products because their customers can't hear their flaws.

Clever marketing though, has turned the above upside down. The customer is told that the flaws are actually good for them! "We don't use feedback and that is what makes our amps sound so good!" Lack of feedback sharply increases distortion but as long as you are convincing enough to a lay audiophile, you can "sell the bug as a feature!"

The problem with imagined benefits is that such imagination wears out over time. The user then chases other myths. Oh, let me upgrade the power supply! How about them caps? Oh yeah baby, it sounds even better now! Speaker cables? Yes, that is what I upgraded and the sound is really fantastic now. It goes on and on.

Watch this video I produced for a detailed proof and logic of why audiophile sound observations is so faulty:


The day you stop self-scoring your exam, is the day you get enlightenment in audio. There is no way around it.
 

rdenney

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Thank you. That's very interesting, especially the description of how traffic studies have improved with technology.

We can all agree there's an enormous amount of bullshit in hi-fi. I believe in subjectivism because at the end of the day it's the sound I listen to. I don't believe in sighted, uncontrolled subjectivism. And I definitely don't believe in snake oil. I just happen to think the interface between subjective performance and technical performance is complex and murky and not as pat-and-dry as this forum makes it seem sometimes.

Henry, you make a good point. We’ve got the terminology screwed up. Preference testing is by definition subjective testing, but when done right it controls for sighted bias to find out 1.) the ability to distinguish what cannot be seen, and 2.) a resulting preference for one or the other.

Without the first, the second has no meaning. And without both, there is no basis for recommending one’s experience as being instructive to another. The control against sighted biases does not make preference testing any less subjective. I try to use terms like “controlled testing” when taking about preferences.

But lots of the preference studies have been done already, and with amps above a rather low threshold, the first hypothesis—that there is a difference—often can’t be demonstrated. Which makes the second hypothesis void. The limitation is operating amps in their linear range, which is a problem with amps of very low power like this one.

If we are sure we can experience a phenomenon repeatably, by all means let’s construct a controlled test. If we can detect a difference, then we can explore what measurements will explain it. But it usually goes the other way, objective measurements vary by greater amounts than we expect given that we can’t tell the difference in controlled subjective testing.

Example: the Directivity Index resulted from Spinorama speaker testing and is the product of trying to explain controlled subjective preference results. That testing explained why speakers that were flat on-axis didn’t always perform well in a real room, and that it wasn’t always the room’s fault (or the amp’s). Objective and controlled subjective testing worked synergistically to improve products.

With amps, though, the only feature that I think marks the good from the great is quiescent output, and that is masked when music is playing. The very best amps are silent even with an ear to the speaker. Amps that are indistinguishable in preference testing but have a slight hiss when quiescent may call attention to themselves in a sensitive system and quiet room. My B&K Reference 125.2 amps hiss when I’m within a foot or two—maybe 80 or 90 dB down and inaudible at any normal listening distance. A similarly powered modern Benchmark AHB2 won’t hiss like that.

In fact, the amp of this thread was very quiet in that dimension. It’s problem wasn’t noise floor but rather distortion, and the low power requires pushing it to the limit. It might be unable to achieve 30 dB RMS above the noise floor a normal listening environment would require without pushing the peaks past lineari. Testing with very sensitive speakers would answer that. And that may be why many like the thing in spite of itself.

But we both know that if it was a Rick Denney kit, threads full of people here and elsewhere would be laughing at it rather than praising and defending it. Are these people trusting their ears? Doesn’t seem so.

Rick “distinguishing between subjective opinion and controlled subjective testing” Denney
 
D

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I thought I was very clear. You said we were relying on measurements to be incredulous of your personal experience as far as differences between amps. I pointed out that our reluctance to believe you is not due to measurements, but countless blind tests that show experiences like yours never materialize when we are only using your ears to judge.

You would have a point if I had said the Aleph 3 sounded better than other amps. But I didn't. I just said it sounded good to me. Other amps sound good to me, too. The measured performance of the Aleph 3 is ok, but not great. I think you probably wouldn't recommend it on that basis if you tested it. I was guessing, but TBH have no evidence, that people might tell me I was deluded for liking the sound of the Aleph 3, just because it isn't a low-distortion amp. I may have gotten ahead of myself there, sorry. If anything, my listening test is consistent with your philosophy, that all amps sound the same.

Such claims need to be verified in blind tests. I am confident that the "good distortion" people think they are hearing, indeed is not audible to them.

Quite true. But not pertinent to my anecdote. There was no perceived difference to disprove. Just a positive listening impression of the one amp.

I performed a test and its lack of power was enough reason for me to dismiss it as a proper amplifier. I explained how a cheaper amplifier ran circles around it. Now, you want to go and light your house with a candle, you go right ahead. I am not one to bend to the needs of the amplifier and buy speakers that it likes.

Anyone who buys an ACA intending to use it with 86dB/W speakers is likely to be disappointed, for sure. I don't know what the gain of the ACA is (too lazy to look it up) but I wonder if the issue here was that you didn't give it enough drive voltage. I'm not sure, don't have enough information.

To answer someone else's question, I have no vested interest in the ACA and don't own one, nor have I ever listened to one. As I said before, I just thought some of the hating on this amp, people who build it and like it, and Nelson Pass, was inappropriate.

Begging your pardon, but I think I've beaten this to death. I understand I'm not doing a great job of making friends here. That's ok. I think the community as a whole benefits from an occasional difference of opinion, provided it's polite. Have a good evening.
 
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amirm

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If anything, my listening test is consistent with your philosophy, that all amps sound the same.
This is not my philosophy. People build some really awful things where their distortions can be audible. In a bad way that is.

The problem is that typical audiophile is so wrong in his assessment that we don't consider their views of this and that amp differing is of no probative value. Show that you can hear a difference strictly with your ears and we do believe you. We will then proceed to analyze the situation and figure out why.
 
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amirm

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Something that I just find myself wanting to say is that no one with honorable intentions would show up here and write something like: "The hand wringing evident in this thread on ASR is not a good look." You came here looking for a fight. Why?
Probably because I'm a dirty, rotten scoundrel? Sorry, gotta go. Have a good night!
 

Vuki

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Here is a remarkable example of knowledge of reality doesn't change what you perceive. I was doing this speaker test the other day: https://www.audiosciencereview.com/...e-esprit-antal-ez-review-tower-speaker.22080/

index.php


After playing the Triangle speaker (in white) for a while, we switched to Revel Salon 2 to its left. What was remarkable was that you constantly, and I mean constantly, had to remind yourself it was NOT the triangle that was playing! Every bone in your body would say it was generating sound, not the Revel next to it. I think its expose drivers and white color may have caused that. Or the fact that we were playing it before. But the experience was uncanny.

So next time you say "trust your ears," remember this example. Your eyes override your ears every day of the week and twice on Sunday!

Or Salons have somewhat narrow soundstage :D
 

peng

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As far as I can tell, I made no claims requiring proof. In the end, my only purpose was to defend the ACA and Nelson Pass against what I thought was, in some posts, overzealous criticism. And to encourage people to take a little broader view of the whole objectivist-subjectivist thing.

I read a lot of Nelson Pass's articles and never felt he needed anyone to defend him except/may be the way he talked about the negatives of negative feedback. Even on that, I believe he simply might have exaggerated it a little to make his points, not that he is against it. Surely he used it too, though perhaps more sparingly. On the topic of distortions, he's one of the few amp designer who actually elaborated on the warm, punch, cool kinds of sound signatures that people talked about and if anything he himself does not seem to buy a lot of those audiophile claims/arguments one way or another, other than less 0.1% is better than 5% sort of deal.

I bought and build the ACA amp and will do the F5 soon, but I don't do it for "sound quality". Mr. Pass never claimed the ACA amp would "sound better" than other amps that offer lower distortions, he posted the distortions vs output graph so we all know what to expect. He rated the amp 5 W into 8 Ohms and a little more if you use a larger PS and accept a little higher THD. So I have no idea what you are defending him for, specifically.
 
D

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So I have no idea what you are defending him for, specifically.

Thank you for your reply. With nothing to do all day, I may have allowed myself to go a little too far down the rabbit hole, relative to the greater needs of the community.

Maybe I was imprecise and should have said I felt the need to defend the idea of the ACA and Nelson Pass' design philosophy. As to why ideas need defense, well, that's something for philosophers to debate. Seems to me a lot of ASR members feel obliged to defend audio consumers from misleading manufacturers' claims. Did any of those consumers ask to be defended?

Seriously, though, arguing on the internet is like eating popcorn; it's salty and tasty and once you start it's hard to put down the bowl.

Thank you for a thought-provoking debate. I think I'm done for now.
 

scott wurcer

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Seems to me a lot of ASR members feel obliged to defend audio consumers from misleading manufacturers' claims. Did any of those consumers ask to be defended?

This statement does not follow from you previous posts. Nelson Pass makes no "misleading manufacturers' claims" that know of, his DIY and hobby projects are in his words for entertainment purposes and IME are things that a lot of folks will actually build. We had a running joke about hobby magazines (of all sorts) about things that no one else will ever build.

I'm more concerned with the pseudo-science like the box of dirt ground, super-luminal cables, scalar waves, etc. I can't get excited about someone liking 0.2% second harmonic in their mix whether they can do it in a DBT or not.
 
D

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This statement does not follow from you previous posts. Nelson Pass makes no "misleading manufacturers' claims" that know of, his DIY and hobby projects are in his words for entertainment purposes and IME are things that a lot of folks will actually build. We had a running joke about hobby magazines (of all sorts) about things that no one else will ever build.

I was trying to make the point, in response to a complaint from another member, that if I am out of line for defending Nelson Pass when has not asked to be defended, then maybe ASR members are out of line for trying to defend consumers from misleading manufacturers' claims, when they have not asked to be defended either.

I get the impression some people on ASR feel obliged to defend the public against misleading audio claims. It's interesting to ask, but the subject of another discussion I don't have time for right now, just how far it's appropriate for "elites" to go in protecting the "masses" from their own ignorance. And what the benefits and costs may be of mounting that defense.

You seem to have conflated my points and deduced (incorrectly) that I meant Nelson Pass makes misleading claims. I didn't say that and don't believe it. I hope this clears up any confusion.
 
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