The imperfect amp: Pass or Ayre?

Every amp is imperfect.

An amp that shows distortion on the fundamental will always sound better than the one that doesn't.
Pass is correct.

I suspect anyone wanting either of these expensive amp would listen carefully  and choose the one they prefer and not worry  about specs.

sure I have heard both and while I chose to own an Ayre VX-R in both the initial and then Twenty ( Diamond ) design, I think you might be missing the point a BIT...compared to many other components in the chain, amps are VERY low in distortion...OF course both Nelson and Charlie gifted genius designers with KEEN ears. I did own many Threshold products and think highly of his current work. I think listening to the product in a system with similar design principles and objectives might be more illuminating than a point comparison. For example the effects of negative feedback on a temporally accurate transducer....or not...
have fun, enjoy the music...
Jim

From Nelson Pass, "I have numerous designs using ZGNFB"

This is zero "global" negative feedback, just like Ayre is trying to make you believe by shortening it and saying Zero Feedback.
Both will then have to be using a "local feedback loop" around the front end of the amp.
It’s advertising BS by Ayre to say "no Feedback!" on a solid state amp.
Any difference in amps sound will be because of other factors if they both have either global or local feed backs.

This thread seem again to be fishing for Pass bashing ammo yet again.
You give no tech reason behind wanting to denigrate it, just hoping that fishing for a reason, someone will present one for you.

And BTW bashing "God" (NP) is blasphemous.

Cheers George

Yes we know you don't like Pass Labs.  Is this thread just another  to validate your opinion or another attempt to be controversial?

I am beginning to see a pattern.....I have a question, which maybe, this one, you can answer ? With all of the threads started by you, Mr. Eric, when do you have time to listen to, and enjoy, music. ........And I suppose, you thought I was alone.....

Weird how my own preferences cause so many people to act so butt hurt. Actually, gentlemen, if I am allowed to use the term, my question is more about WHY.


Both Pass and Ayre are two amps which eschew technical perfection.


Both Ayre and Pass stand in contrast to say, the Halcro amplifiers, which were famous for their absolute dominance in technical terms.  Ayre and Pass however have ended with different followers.


Compared to an ideal SS amp, both Pass and Ayre are absolute failures, with different followings. Aren't you curious why?


I am.

So yes, I am asking the same question in different ways. No, I don't intend to prove a brand is better than another, that's for the buyer. I don't care. I truly do not. I do care more about why. What kind of imperfections are we drawn to?

mrdecibel - You may pay for my answer with meaningful contributions and not selling cables.

When you have done so, I'll bother.

@three_easy_pieces
You are not wrong, but what I meant was that these two amps have given up on the measurably ideal, straight wire with gain.

Much more so than other solid state amps, not to mention, they are pretty expensive.

So, the relatively high distortion, and high price makes them interesting to pit against each other as we try to figure out what it is that makes an audiophile.

well in general, the question what kind of distortion are you attracted to is certainly valid and reaches into the realm of the psycho acoustic, a rich vein as yet not fully mined....so few audiophiles own an SPL meter yet claim to understand the origin of the loudness button..... probably a different thread...

I do dabble is semi serious listening while writing and reading....like a heavy deep dive of Linda R while reading her book Simple Dreams...

peace

jim

Of course, Halcro is gone, but Pass and Ayre both are apparent financial successes.


Why?


If we discuss that, we are discussing the very heart of what it is to be an audiophile.

well in general, the question what kind of distortion are you attracted to is certainly valid and reaches into the realm of the psycho acoustic, a rich vein as yet not fully mined.

Exactly!! Lets mine!!

sure I have heard both and while I chose to own an Ayre VX-R in both the initial and then Twenty ( Diamond ) design, I think you might be missing the point a BIT...compared to many other components in the chain, amps are VERY low in distortion...

Hi @tomic601 
I'm not a scholar of either brand, but I thought they were relatively HIGH distortion?

Here's an example:
https://www.stereophile.com/content/pass-laboratories-xa25-power-amplifier-measurements
Interesting that the distortion profile gets higher above 2k. The Ayre actually seems higher in distortion, though it is flatter:

https://www.stereophile.com/content/ayre-acoustics-ax-5-integrated-amplifier-measurements

higher in distortion compared to a driver that makes 90 db per. wattt with a great deal of the output out of phase ( non pistonic inn the pass band. ).... is the point...diitto for other transducers...

well also look at  the measure.  vs. listen switch on an AYRE DAC for a Phd in. why measurement might not matter , especially if the specification standard does not properly reflect the real world, phase angle being IMO a perfect example for amps and speakers...

Sorry, @tomic601 -

Not sure i understood your point. Do you mean that, compared to actual moving parts, the distortion of both of these amplifiers is so small to be insignificant??
If not, please correct my misunderstanding.


Best,
E

Eric....selling cables ? you must have me confused with someone else, which is not a surprise. 

I get Eric's point as it is amazing that people nearly unanimously think those ridiculous Pass and Ayre amps sound great. Why? From listening to them? BALDERDASH I say...it's all about esoteric measurements that, even if most music fans don't understand those things, matter so much!...You could waste hours or years enjoying something that's actually inferior in some way and has some form of distortion that fools you into thinking you're enjoying it, and do you get those years back? No you don't!..sure, Nelson Pass says a little even ordered distortion seems to make people like the sound of an amp, and even built little gizmos that generate that and gave them away to some DIY people! A CHEAP TRICK...I like tubes because they look cool and make me think I'm slightly hipper somehow, but although I enjoy the sound of 'em, I'm no dummy! Straight wire with gain is what I need man...I'm likely not worthy though, and I'll sadly continue to suffer along somehow...*sniff*...by the way...I have an eight thousand dollar acoustic guitar and if I pick it too hard it distorts! What a piece of junk...

@wolf_garcia : lol
Nonetheless, measurements do have merit—but, as usual, there are caveats and diyers’ old mantra often applies:
"if somethings sounds good & measures well, it is good; if it sounds good and measures bad, you’re measuring the wrong thing!

Based upon the Stereophile measurement both the Ayre and Pass are low distortion amplifiers.  Neither amp works well into low impedance loads.  Their distortion fingerprints are different, but from the measurements it is doubtful a listener will hear much of a difference when driving appropriate loudspeaker loads.  That's how I read the data.

IMO THD measurements are among the most useless of specs, and I would by no means consider amps having relatively high THD numbers, compared to competitive products, to be ones that "from a technical perspective, don’t do very well" (quoting from the OP).

It’s pretty well established that while large amounts of feedback can reduce THD to very small amounts, that usually comes with two significant side-effects:

1) Increased amounts of Transient Intermodulation Distortion, which is not normally measured, and which as far as I am aware does not even have a standardized basis for measurement. That despite the fact that its significance was recognized as far back as the 1970s, when Dr. Matti Otala famously authored several papers on the subject, this being one example:

https://pdfs.semanticscholar.org/b3c0/a892a982ebde91f83f228905dac30186f827.pdf

2) Increases in some higher order odd harmonic distortion components, which occur even though Total Harmonic Distortion is reduced. As Ralph (Atmasphere) has pointed out many times, our hearing mechanisms are extraordinarily sensitive to certain higher order distortion components.

As Gregm aptly quoted above:

If something sounds good & measures well, it is good; if it sounds good and measures bad, you’re measuring the wrong thing!

I believe, btw, that was originally stated ca. 1960 by Daniel von Recklinghausen when he was the chief engineer of the original H. H. Scott company. He later worked for KLH, among other firms, and served for a while as president of the Audio Engineering Society.

Wolf_Garcia, LOL! Thanks for another example of your inimitable humor.

Regards,
-- Al

It’s advertising BS by Ayre to say "no Feedback!" on a solid state amp.

This statement is false. Although there are not many examples, it is possible if build a solid state amp that lacks any sort of feedback whatsoever.

Both Pass and Ayre are two amps which eschew technical perfection.


Both Ayre and Pass stand in contrast to say, the Halcro amplifiers, which were famous for their absolute dominance in technical terms. Ayre and Pass however have ended with different followers.

@erik_squires 
IMO/IME you've got this backwards. Ayre and Pass are great successes, because they sorted out what is important to the human ear and applied engineering to design a circuit that more closely obeyed the rules of human hearing/perception. This was done in the face of a test and measurement regime that ignores how the ear works and instead concentrates on measurements that have little to do with how the ear perceives sound.

Now if you are coming from the perspective of 'objective measurement' this will come off as a bit of heresy. But the simple fact of the matter is 'objective measurement' isn't objective; at best appears to be a mindset that just gets really riled up when things don't go its way. To this end if an amplifier circuit is designed to sound good to the human ear, it gets lambasted for 'high distortion' in the face of what we know at this time of how the ear perceives distortion. 

So a bit of a primer: lower orders (2nd, 3rd and 4th) are perceived as 'richness', 'bloom', 'warmth' etc. But they do more than that, but first its important to understand that the ear perceives the higher ordered harmonics as harshness and brightness- in particular the odd orders. Now the ear also has a masking principle- how a louder sound masks the presence of a quieter sound. In the case of distortion, the lower orders are useful in masking the higher orders. This is important as the ear uses higher ordered harmonics to sense sound pressure (which is very easy to demonstrate with simple test equipment).

So imagine what happens when feedback suppresses the lower orders (and for that matter, the higher orders too) but in the process **adds distortion of its own** through a process called 'bifurcation' (which, not by coincidence, is a common term to those familiar with Chaos Theory). Also not coincidental is the fact that some basic Chaotic systems have mathematical formulae that are strikingly similar to the feedback formula!

So in an amplifier that employs feedback and thus has low THD, the remaining THD that is *does* have is mostly there from the operation of the feedback itself (again this phenomena is well-known; see the writings of Norman Crowhurst from 60 years ago for more). So this distortion, while low, has nothing to mask it (the lower orders are suppressed) and so easily stands out to the human ear as brightness and harshness. Some people describe it as 'crisp'.


Put another way, an amp that has higher levels of higher ordered harmonic distortion will sound smoother and not as bright **if** it also has lower orders (in particular the 2nd or 3rd) to mask the higher orders. This is why tube amps have higher overall distortion across the entire spectrum yet sound smoother and not as bright; this having nothing at all to do with bandwidth, since the ear is converting that distortion into a tonality. In a sense the tubes are very good at obeying human hearing perceptual rules- that is why they are still around.


So neither Nelson or Charlie were/are going for a tube sound so much as they are going for a **natural** sound. The problem is simple to any pragmatic designer: its impossible to build a circuit with zero distortion! So next best isn't to make an amp that is as low distortion as possible, the next best is to make an amplifier that has the lowest possible **perceived** distortion, which is something very different. Since the ear is relatively insensitive to the lower orders. such a design makes use of that fact and the masking principle to create an amplifier that actually sounds neutral (IOW, more like real music).


Something peculiar here is that amps with a prominent 2nd or 3rd harmonic also are perceived as more detailed with a more palpable sound stage- better center-fill. Why this is so isn't well understood and might be an excellent topic of inquiry.


So you've singled out the two most commercially successful solid state amps that address these issues!. They aren't failures!- instead they are **leaders** which will be historically recognized as such when the rest of the industry sorts the above facts about human hearing. But I'm not holding my breath on that because the spec sheets are some of the best advertising any inferior amp manufacturer has at their disposal; 'see?- very low distortion- it has to be great!'; an excellent example of the Emperor's New Clothes. If things were otherwise we could simply look at the spec sheet and know how the amp sounds and we wouldn't have to audition it in our systems to know it would work. In a nutshell, the industry has been lying for at least the last 60 years- and we've all grown up with that so don't see it as weird that despite the spec sheets we still have to do an audition.

@atmasphere

Thanks for that *very* informative post! I think it's a telling anecdote that Halcro is no longer a thing (THE BEST AMPLIFIER EVER! - lol).

How many other pursuits in life are people so obsessed with measurements in a realm where the ultimate goal is to engage in something pleasing to our senses? I won't possibly like the way this tastes because of the absence of sugar or salt? This artwork doesn't move me because it contains too much in the blue-green spectrum?  If it sounds good enjoy.  Why sabotage your happiness by questioning whether you truly like it while critically assessing measurements that perhaps don't seem to quantitatively equal perfect sound?

My power amp, one of Dennis Had's SEP High Output tubsters (10 to 17 WPC allegedly), is one that I hope nobody ever measures for anything as that could harsh my mellow.

So in my system with Vandersteen 5A Carbons, my Pass XA 60.8s do an admirable job, checking almost all of the boxes of the sonic attributes I’m looking for. Then comes along an opportunity recently to demo a pair of Vandersteen M5-HPA’s. Immediately I notice a couple of things 1) there’s a better image center fill, a quality that Ralph (atmasphere) mentioned, and something I noticed about the Ayre KX-5 twenty preamp that I demoed a couple of years ago and 2) instruments sound more natural. The sax on The Girl from Ipanema sounds more like live, with an almost tangible weightiness to it as well. Massed strings are smoother as well.  Now the Pass is no slouch, but theses amps take it to another level IMO. There’s a small amount of upper midrange glare that I hear sometimes which has been alleviated. RV told me that his time and phase accurate speakers need a no feedback design (specifically no global?) to sound their best. Is it the push push design that makes the main difference I wonder? How much is due to the low parts count for in the signal path? I know the Stereophile review is coming which should be interesting.

If recordings captured performances perfectly we would want a perfect amplifier.  They don't so we choose amps that allow us to enjoy imperfect recordings.

Ralph a tour de force post and recognition of the true scientist engineers that also LISTEN

Eric two points of clarification; Yes the relative distortion levels between components is massive, especially when comparing transducers to gain devices. AND look at the Ayre QSB DAC white paper for a Phd in filters that measure well but sound worse...hence the measure/listen switch, 

Wolf - harshing the mellow love it....what low distortion strings are ya using on the eight thousand dollar wonder ?

@earthtones  Welcome to the unfair advantage of Vandersteen powered bass and finally an amplifier PURPOSE designed to exploit that advantage. The M7- HPA replaced the Ayre in my system, not a fair fight for a lot of reasons. yes Vandersteen had very specific goals to hit for odd order harmonic distortion in the M7 and M5. Really a towering achievement IMO and little understood : just 5 parts in audio signal path, liquid cooling for bias set point and device stability, no emiter resistors, analog temp control ( no RF trash near audio ), built in HRS suspended truss isolation, 128 V DBS....cyclotronic circuit....the list goes on, but of. course the music and the listening are the gig....

@tomic601 , 
How I envy you...

I hate to sidetrack, and, I probably should just PM you, but I'm here...
You mentioned you had both a non-Twenty and Twenty version of an Ayre amp. Could you describe the differences between the two versions?
I keep wondering if I should upgrade.
Bob

I use Elixer Nanoweb lights.

Good components or gears are the ones that provide us with musical enjoyments. We can never judge hifi audio components with bunch of numbers (measurements). We all have to listen, listen, listen. What I look for in amps and other components or gears is musical involvement and engagement if it's used for stereo music application. 
I won't look for their distortion measurements, etc, etc. 

We can never judge hifi audio components with bunch of numbers (measurements).

It’s what all "good" designers use to make their components, yes they also listen at the end and change those "numbers/measurements" to suit.
There is no voodoo involved!
And if you have components that were built not doing this, then you most certainly have a pile of junk!

Cheers George

Haters gonna hate!
Enjoy the music

Ralph / Al, 

Your posts are reasons why I still visit these these forums. Thank you. 

@gdnrbob OK a short comparison and context for the upgrade and eventual replacement. I bought the VX-R to run Vandersteen 5a after a lengthy evaluation of several other amplifiers, notably the ARC REF150 and the Aesthetix Atlas Stereo. All from competent designers certainly held in high regard by Vandersteen. All three had virtues, ultimately I chose the Ayre for its seamless one character top to bottom balance. I did audition at some length the MXR w Vandy 7 also. I very happlily ran the Ayre for a period of years and eventually landed on the 7 speakers. Leave the Ayre amps on a d they shine after 24 hours or so, before that they sounded just a hint metallic and etched on the very top end. So just leave it on !
the On Semiconductor output devices w thermal trac proved problematic and i lost a channel, Ayre stepped up w shipping both ways and the repair covered under warranty some 4 years on...I decided while it was back at factory to get it upgraded to Twenty series. In short the twenty sings twenty minutes out of standby and lacks any of the etched quality and IMO the midrange sounds more warm and lush, like the REF150. Neither amp has the low end of the Aesthetix. Per my other comments, before I invested in a better amp, I would go as far as I could with speakers...just my buck fifty...

I own a pass labs amp, I don’t care about stats, years ago stereophile did a blind test with the worst specs an amp ever had, the other amp had near perfect specs. Guess who won? The amp with the worst specs, by the way it was a tube amp. Specs don’t mean crap, it’s all in what you hear and like.

Some top amps in this thread.  Ralph's post is priceless as Jim pointed out.  

Bob, the difference for my system was night and day.  To my ears, it shares the fast Ayre traits, but the bass got tighter, the dynamics all showed huge gains.  Feel free to call if you want to.  

Specs don’t mean crap, it’s all in what you hear and like.

A lot of audiophiles feel that way. However as I see it specs (and measurements) can often provide a lot of value in two ways:

1) By allowing one to identify and RULE OUT from consideration candidates for purchase that would be poor matches to either the surrounding components or to the user’s requirements. An example of the latter would be how much power is needed to support desired peak volumes. Examples of the former would be incompatibilities due to impedance issues, gain and sensitivity mismatches, and various issues which can result in amplifier/speaker mismatches.

One way in which specs and measurements can sometimes serve that purpose is by providing insight into the priorities of the designer, and in doing so making it possible to identify misplaced priorities. Such as specs that may be TOO good and thus may signify undesirable design tradeoffs. A classic example of the latter would be an amplifier having unusually good Total Harmonic Distortion numbers relative to other comparable kinds of designs, which can signify heavy-handed application of feedback in the design, with the downsides that have been mentioned.

If specs are disregarded and/or are not properly understood the randomness of the process of assembling a satisfactory system, and the likelihood of expensive mistakes, are significantly increased IMO.

2) Specs and measurements are also often useful in troubleshooting problems and diagnosing sonic issues. I couldn’t begin to count the number of times I and many others have referred to John Atkinson’s measurements in Stereophile in addressing such issues in discussions here.

@Nrenter, thank you kindly for the nice words.

Regards,
-- Al

Very interesting and informative comments. The most pleasurable power amplifiers I have heard with my Vandersteen model 5A speakers are the Lafayette KT-550 tube amp, the refurbished old Luxkit power amp (sounds amazing) and the hybrid tube amps that I built.

Happy Listening. 

To add to @almarg 's comments above, specs *are* important; perhaps the one that can be the most counter-intuitive is THD, as a very low THD spec is often an amp that doesn't sound nearly as good as one with a higher THD spec. I've already explained why above.
But bandwidth is real, output impedance is important (which isn't to say that the lowest output impedance is the best). Some speakers **require** that the amp have a higher output impedance, such as ESLs, horns and single-driver full range loudspeakers. Or any speaker where the designer has sorted out that he doesn't like brightness and harshness and so has designed the speaker for amps designed with intention to not have these properties (and often that means no feedback, so a higher output impedance). For more on this topic see:http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
Now I discovered back in the 1970s that feedback wasn't all it was cracked up to be; that it could cause the amp to have a smaller soundstage (unlike the original recording; I know that from the use of master tapes) and be brighter than the actual recording as well. Since then I learned there is far more to it than just that simple concept- the use of feedback introduces about 7 different variables that the designer has to weigh out. FWIW the feedback formula doesn't offer a lot of guidance in that regard: in a nutshell most amps with feedback have a rather cursory application and ignore some factors (like RFI leaking into the amp via the speaker cables) entirely.


So of the specs that are suspect as to how much they contribute to good sound in an amplifier, IMO/IME the two top suspects appear to be THD and output impedance (IOW a better sounding amp might be one where these specs have higher rather than lower numbers).


Alternatively we also know that IMD is highly audible so low IMD specs are a very good sign but IMD is more pervasive than most audiophiles like to think about. In addition to the normal interactions between two tones, IMD also is a major issue in digital audio, but because the intermodulations are having to do with the scan frequency and the Nyquist Theorem, its called 'aliasing'. But as far as the ear is concerned, aliasing (the digital industry does not like to refer to it as a distortion, but that's exactly what it is) is an intermodulation (sometimes called 'inharmonic distortion' in the analog world) and so highly audible (the ear treats it as a brightness or 'crispness' and its still there if you turn down the treble, because the brightness is caused by distortion rather than frequency response). Of course if you look at the specs of a digital product, this form of distortion isn't listed. Again- the Emperor's New Clothes. Fortunately the digital world has been getting a better handle on this in later years; the more they do so the more natural digital is able to sound.

I think specs and measurements are for the most part stuck in the 1970s when it comes to amplifiers and electronics, despite better tools. Yes, we can measure THD 100x better and cheaper. But have we added any meaningful measurements? Anything new that helps describe a listener, room, speaker, amp interaction with a particular amp?


A lot of what I think I'm circling around is bemoaning that we don't have better.


While some speaker makers have gone to great lengths to connect measurements to listener preference, if amp makers are doing this, for the most part I haven't heard of them. Pass, to his credit, makes some of what he's trying to do transparent.


It would be nice to me if I could go from my preferred amps to specs and go "aha! This is what I like!" and therefore, buy the cheapest that fits. :D :D :D

@almarg & @atmasphere Just to repeat, thanks so much for posting.  It's so good when education is made part of this site where so much is just opinion.

@erik_squires And depending on what design you're focused on, Pass doesn't just make some of what he does transparent, he makes all of it so. So many of his circuits are totally laid bare for people to read/analyze/copy/modify. His support of DIY makes the high end audio world a better place.

It would be nice to me if I could go from my preferred amps to specs and go "aha! This is what I like!" and therefore, buy the cheapest that fits. :D :D :D

@erik_squires 
What is needed (and entirely possible right now) is a weighting system for the various harmonic spectra. The 2nd and 3rd, since the ear is least sensitive to them having a weight of  'one', something like the 7th having a weight of 500 and the 11th or 13th maybe 1000. If we had a system like that we'd know what we're dealing with in a heartbeat, but don't hold your breath- the industry collectively would be really hating on something like that since its bad for business- what- a spec sheet that tells you how it sounds?? Yikes!!

@ctsooner 
@tomic601 ,

Thanks for the detailed answer.
I own the MX-R and KX-R. Both sound pretty amazing in their non-updated state. I had a chance to update the KX-R, but wanted to hear it first before I did anything. In fact, it bested my Atma MP-3. (So, Ralph is going to build me an MP-1😁, so I can do a closer comparison).
As it sounds so good now, I really needed your comments regarding the Twenty upgrade in order to get an idea of what kind of improvements there would be. (Looks like I will be waiting for the next Upgrade Special at Ayre).
Unfortunately, my Treo's are not up-gradable to CT status.-And, I really don't wish to buy another speaker.

@erik_squires 
Sorry for the digression.
Bob