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Putzey's doesn't get it...

160.62.7.250
Posted on August 7, 2015 at 01:59:13
morricab
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 "Hi-fi review is a complete shambles. The few magazines that do measure are capable of reprinting
the most frightening distortion spectra from amplifiers and actually call them good. "Objectivity"
got downgraded from "independent of who's doing the observing" to "not favouring particular
brands". For me personally the affair hit rock bottom when in 2009 two reviewers, one Dutch, one
British, independently remarked of the same amplifier (a reasonably priced product with exemplary
performance) that it sounded surprisingly musical for an amp with such low distortion. In the 21st
century audio engineers build equipment while actively avoiding two of the most powerful tools
available to the whole of science and engineering: measurement and error control. The damage to
the audio industry and its reputation in the wider engineering world will remain immeasurable until
we decide to take control."

This tells me that Putzey's is either not aware of or is disregrding what has been found out about human perception and distortion. That the kind of distortion and its PATTERN is far more important than its level. Naturally above a certain level it is coloring the sound but when the pattern is wrong it also colors the sound even if it is THOUGHT that it should not.

Geddes found no significant correlation between THD and IMD and sound quality (in fact it was slightly negative but did not meet 95% confidence).

What he doesn't realize is that the small residual from amps with tons of feedback WILL color the sound in ways that much higher levels of harmonically correct distortion will not. Must be frustrating to him to be fighting with nature that doesn't conform to his "We make it perfect so it must sound perfect and why can't people hear that...dammit!"

 

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Have Geddes finding been pier-reviewed and duplicated?, posted on August 7, 2015 at 07:07:22
Feanor
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 Just asking.

If so, please provide a good set of references.

Personally I don't doubt that (1) NFB causes high-order distortion products, and (2) high-order HD is unpleasant sounding. However I'm not sure, (based on my listening experience, not as extensive as Morricab's), that there isn't some low lever of HOHD that isn't inaudible.

Also I'm not sure that some people react differently to various levels or frequencies of HOHD.


Dmitri Shostakovich

 

No doubt large amounts of feedback with an amp with high open loop distortion, posted on August 7, 2015 at 07:13:53
kuribo
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 produces something called "spectral growth", or higher amounts of higher order distortion.

The two key variables are, however, the open loop distortion and the level of the added distortion. If the open loop distortion is low (which Bruno claims it is), then the level of the added HD products is said to be inconsequential.

Whether or not it is inconsequential can be called into question. But the fact that many have raved about the ncore means either it is inconsequential or that large numbers of people find it to be benign. Or perhaps even preferable. It wouldn't be the first time people were found to like distortion. See: tube amps.

 

RE: Have Geddes finding been pier-reviewed and duplicated?, posted on August 7, 2015 at 07:26:17
morricab
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 They are AES convention papers but I do not know for sure if that means they are peer reviewed. I know that for the presentations I give at conferences it is now standard to have peer review before acceptance. Since these seem to be proper publications (not just abstracts) and are for AES journal I would assume peer review.

http://www.gedlee.com/downloads/Distortion_AES_I.pdf
http://www.gedlee.com/downloads/Distortion_AES_II.pdf
http://www.gedlee.com/downloads/THD_.pdf
http://www.gedlee.com/downloads/comments%20on%20howard.pdf
http://www.gedlee.com/downloads/AES06Gedlee_ll.pdf

 

And he advocates using a cheap Pioneer receiver as an amp..., posted on August 7, 2015 at 07:42:28
kuribo
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 So how can he possibly know what good sound is, right?

He also has said the speaker and room are more important because:

"very inexpensive and readily available electronics place the electronics into the "insiginificant errors" category."

 

RE: And he advocates using a cheap Pioneer receiver as an amp..., posted on August 7, 2015 at 08:04:56
morricab
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 We all have our beliefs...even if they fly in the face of one's own research...no one said humans were rational. He comes from an era where the engineering orthodoxy ruled audio.

Do you side with his assessment of electronics and their importance to the overall sound quality of a system??

 

Since you can't answer him..., posted on August 7, 2015 at 14:46:01
mkuller
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 >"very inexpensive and readily available electronics place the electronics into the "insiginificant errors" category.">

Do you buy this?

Measurable errors no doubt - he isn't talking about listening.

I agree that the speakers and the room are most important.

Next I would say matching the right amp to the speaker.

More than insignificant, IMO, but it requires listening since they all sound different.

 

Well, one wonders how one can believe the results of his distortion studies, which were made, posted on August 7, 2015 at 15:37:03
kuribo
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 with his Pioneer gear to the best of my knowledge, and yet believe Pioneer gear is flawed and unnatural because it uses feedback and doesn't meet the distortion "criteria" we are told is necessary for "correct" sound, there would seem to be a bit of a problem there, don't you think?

It is clear that speaker and room effect distortions are magnitudes in excess of those produced by well designed amplifiers. I have said many times that amps are part of a system, which includes the room, listener, and source material. Expecting one size to fit all, given the range of variables and interactions, is clearly flawed. As I have also said, if one amp topology was truly and absolutely supreme, we wouldn't have the variety or numbers of satisfied users across all types.

Of course at a certain level (undoubtedly this level is not universal), distortion is audible, and it is well known some types are less objectionable than others, to some people. It is also well known that some types of distortion are even preferred to no distortion by some, but not all.

So, before we make generalizations about distortion being "good" or "bad", we need to have conclusive evidence that it is in fact even audible when poo-pooing certain equipment. Especially when the levels are so low that they become buried in the noise floor. Considered in light of Gedde's comments about speaker and room effects being dominant, it seems all the more likely that for many well designed amps, regardless of whether or not they are class a, ab, or d, levels of distortion even out of the noise floor, at some minimal level, are insignificant. Reality would tend to agree with this...

There seem to be those who prefer a wire with gain, which is where I would place Bruno Putzeys, and those who prefer what is called on diyaudio, effects boxes. The fact that there are indeed these two camps should be proof enough that not everyone interprets what they hear the same way, nor does everyone agree on what "sounds best"....

We should also question claims that certain equipment is "better" because it more "accurately" recreates the live event. With all the equipment in between the performance and the playback, it requires a major suspension of belief to think that the minimal amounts of any distortion produced by well designed amps is going to trump all the other distortions produced along the way from the recording to the listening chair. Also, what exactly is the "live experience"? The sound is different in different venues, different spots within the venue, etc. There is no established standard for exactly what constitutes "real sound" as the same performance measured/recorded in different locations is well, different. We are all listening to recordings, which by their very nature are less than perfect copies of but one possible soundscape out of an innumerable number of possible soundscapes.




 

RE: And he advocates using a cheap Pioneer receiver as an amp..., posted on August 7, 2015 at 17:17:05
Don Reid
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 Does he also praise the antichrist and wear white shoes after Labor Day?
I dream of an America where a chicken can cross the road without having it's motives questioned.

 

LOL...some may think so....nt, posted on August 7, 2015 at 17:23:32
kuribo
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 nt

 

Just what I should have expected..., posted on August 7, 2015 at 17:59:25
mkuller
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 >..it seems all the more likely that for many well designed amps, regardless of whether or not they are class a, ab, or d, levels of distortion even out of the noise floor, at some minimal level, are insignificant. Reality would tend to agree with this...>

Perhaps this is your personal view of reality, but it's not mine and many others.

If it measures good and sounds bad, you're measuring the wrong thing.

"Accuracy" is in the ear of the listener.

 

Not sure I understand what appears to be a contradiction...., posted on August 7, 2015 at 18:41:07
kuribo
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 "If it measures good and sounds bad, you're measuring the wrong thing."

""Accuracy" is in the ear of the listener."

These two statements seem at odds.....Which is it?

I think one needs to clarify their perceived purpose for an amplifier: straight wire with gain, or effects box.

Some people seem to prefer distortion. Some amps measure badly but some people like them regardless. We see this often.

If it measures well but seems to sound bad, doesn't mean necessarily you are measuring the wrong thing, it may mean you prefer certain distortions.

If you believe an amp should simply add gain and nothing else, then if it measures badly, it's bad.

If you think an amp should simply make pleasing sound and don't care if that sound contains signal not in the source, then you prefer an effects box.

For distortion products: Bill Waslo's Sousa test as well as Geddes's suggest a threshold greater than -80dB for anything remotely resembling the distortions of real, physical amplifiers.

To each his own.

 

Speaking of contradictions...., posted on August 8, 2015 at 09:43:23
mkuller
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 >If it measures well but seems to sound bad, doesn't mean necessarily you are measuring the wrong thing, it may mean you prefer certain distortions.>

If it measures well according to you, it has little or no distortion.

Since no amp is distortion free, some may prefer one type of distortion over another, say 2nd harmonic over 7th harmonic, for example.

 

Distortions perhaps caused by amp/speaker interactions, etc..., posted on August 8, 2015 at 09:51:02
kuribo
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 Geddes and others have shown that distortion below 80dB is inaudible. Many modern, well designed amps usually not only meet this criteria but exceed it. Of course there are other sources, many times greater, in a system. Some prefer amps that preserve the input signal, others...prefer tube amps with audible distortion. That's fine too....

 

RE: Distortion?, posted on August 8, 2015 at 10:12:02
mkuller
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 ...when you talk about distortion, what specifically do mean?

Specific harmonic distortion?

Total harmonic distortion?

Transient intermodulation distortion?

Frequency response distortion?

Switching distortion?

Amplitude distortion?

Phase distortion?

Group delay distortion?

Other distortions?

 

RE: Distortion?, posted on August 8, 2015 at 10:13:49
kuribo
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 Any and all of the above. Deviations in the output from the input. That is the standard definition I believe...

While all amps produce distortion of some sort, you need to ask yourself if all amps produce AUDIBLE distortion...

You really should read the thread on global feedback on diyaudio....

 

LOL! Of course..., posted on August 8, 2015 at 10:21:14
mkuller
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 ...here's a quote from Ayre designer Charles Hansen from an article posted on General:

"We've probably got $100,000 worth of state-of-the-art test equipment at Ayre, but I have not found any single measurement that correlates with what you hear, not one. If you were going to measure something, I would say there's only one thing to measure that makes any sense, and that's the brain activity of the listener."

 

And I can post counterpoint comments and studies that show, posted on August 8, 2015 at 10:27:18
kuribo
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 once amps perform at a certain level, other factors become dominant. Like Geddes, the stereophile article I linked to, and comments and info in the feedback thread I mentioned.

It's all personal preference. Some prefer an amp that is true to the source, others prefer certain distortions. Whatever makes you happy...

 

Of course you can..., posted on August 8, 2015 at 10:35:04
mkuller
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 ...there is no such thing as a straight wire with gain.

All amplifiers have distortions.

Some prefer one type over the other but there is no such thing as an amp with no distortion.

It is all personal preference.

Thanks for playing.

 

I didn't say there are amps with no distortion. I said there are amps with no audible distortion...nt, posted on August 8, 2015 at 10:50:11
kuribo
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 nt

 

More to the point..., posted on August 8, 2015 at 10:54:03
kuribo
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>10% THD will always sound awful and <0.001% THD will always be inaudible regardless of the distribution of the spectrum non-linear distortion products. 0.001% is -100dB so if you are listening at anything below 100dB SPL all the distortion products are below the threshold of audibility. It's not hard to design an amplifier which has inaudible distortion for a practical power output range.

We do know that amps sound differently but assuming those differences are due to distortions below the audible range, instead of other factors, is not only a logical fallacy but is also completely unsubstantiated.

 

RE: Of course you can..., posted on August 8, 2015 at 14:53:07
morricab
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 Cheever demonstrated that if the distortion, at all levels, follows the pattern laid down by nature (i.e. what he calls the ear's self-distortion the "Aural Harmonics") then the distortion is effectively masked and invisible to the listener. Violate this pattern and you will have some that sounds to one degree or another distorted or more subtly colored. Obviously this won't satisfy all listeners but the majority of people should prefer something that follows this pattern.

Keith Howard demonstrated that by adding harmonic distortion to a recording ANY distortion was worse than the original unadulterated file. However, he also found that a pattern that mimics what Hiraga felt was the best pattern (similar to CHeever's "Aural harmonics") was better sounding than other patterns. Given that the base case (completely unadulterated) doesn't exist with amplifiers then we have to go with nature.

Those who think we can get distortion low enough by the standard engineering bag of tricks to be inaudible are missing the obvious fact that people STILL hear big differences between almost perfectly measuring amplifiers.

 

RE: Why ....? , posted on August 9, 2015 at 05:05:41
A.Wayne
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 Morri ,

This is very unbecoming , I 'm sure we can discus distortion , amp topology and the benefits or not of NFB without tearing down Bruno Putzeys like this , pretty sad Bro....,


 

Amen..We should also be able to discuss without a non sequitur as the basis for criticism. nt, posted on August 9, 2015 at 08:13:40
kuribo
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 nt

 

Some designers focus on..., posted on August 9, 2015 at 10:47:59
E-Stat
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 Measurable errors no doubt - he isn't talking about listening.

the "maths" while others focus on the music.

 

And some are clever enough to pay attention to both....nt, posted on August 9, 2015 at 12:13:19
kuribo
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 nt

 

RE: Why ....? , posted on August 9, 2015 at 14:07:32
morricab
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 Didn't even mention his name in the post you are responding to. I believe i mentioned CHeever and Keith Howard, oh and Jean Hiraga and I was discussing aural harmonics and audibility. So, not sure what you mean...Bro.

 

RE: Why ....? Lol , posted on August 9, 2015 at 14:29:27
A.Wayne
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 Morri , look at your OP ....

 

RE: Why ....? Lol , posted on August 9, 2015 at 15:43:00
morricab
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 so you bury a comment down here about my OP?? Seriously, ease of the drink there Bro...

I have every right to comment about a designers ideas and concepts and what I think is right or wrong with them. I have not said anything about BP personally...for all I know he is a really cool dude.

 

RE: Why ....? Lol , seems fair , posted on August 9, 2015 at 15:45:00
A.Wayne
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 Ok ,

I will over look the Putzeys doesnt get it comment in your OP, what was i thinking ... :)

 

RE: Why ....? Lol , seems fair , posted on August 9, 2015 at 23:24:21
morricab
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 Again, that is a comment on his professional work, not personal.

 

RE: Why ....? Lol , seems fair , posted on August 10, 2015 at 10:07:28
A.Wayne
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What about these . good /bad ......

 

RE: Why ....? Lol , seems fair , posted on August 10, 2015 at 10:08:13
A.Wayne
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ahhh:


 

RE: Why ....? Lol , seems fair , posted on August 10, 2015 at 10:08:45
A.Wayne
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NFB is really bad

 

RE: Why ....? Lol , seems fair , posted on August 10, 2015 at 10:09:40
A.Wayne
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Well at least one looks good , if running below 1 watt .....

 

RE: Why ....? Lol , seems fair , posted on August 10, 2015 at 10:10:41
A.Wayne
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Love the stability of a good 300B , I guess a 1K squarewave is an issue thou..

 

RE: Airtight , posted on August 10, 2015 at 10:16:31
A.Wayne
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Toobs , lovely toobs ... obviously some feedback looking at squarewave

 

RE: Airtight , posted on August 10, 2015 at 10:17:07
A.Wayne
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Airtight

 

RE: Airtight , posted on August 10, 2015 at 10:18:09
A.Wayne
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Fig.11 Air Tight ATM-1S, HF intermodulation spectrum, DC-30kHz, 19+20kHz at 5W peak into 8 ohms (linear frequency scale).

 

For comparison...., posted on August 10, 2015 at 17:09:00
kuribo
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Check this out:

Note it is at 200 watts, not 5!

 

Further comparison..., posted on August 10, 2015 at 17:37:47
kuribo
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Hmmm, notice any differences?

 

RE: Airtight , posted on August 11, 2015 at 00:26:37
morricab
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 Good tube amps measure much better than the ones you have cherry picked. Look at the Lamm ML2.2 for example. Not that most of what is shown really matters because the powers used for the measurements is likely well above what would be normally used so the distortion is being exaggerated. When an amp is clearly less linear at high power than low power then 2 measurements should be made, one towards the normal power output and one near the "knee" in the distortion curve.

Martin Colloms review of the Jadis Defy 7mkII illustrates this. At low power (1 watt) the amp is VERY pure. At higher powers it gets considerably dirtier. I have heard this amp and it is one of the best PP tube amps I have ever heard (better than Jadis's larger amps). Check it out in STereophile.

 

RE: Airtight , posted on August 11, 2015 at 00:28:15
morricab
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 STudy some more, there doesn't have to be feedback to give a good squarewave...just a wide bandwidth output transformer, which is expensive.

 

RE: Airtight , posted on August 11, 2015 at 06:36:50
A.Wayne
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 The airtight is obviously running more feedback Morri ...

 

RE: Airtight , posted on August 11, 2015 at 11:54:14
morricab
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 And I wasn't referring to the Airtight, Wayni.

 

RE: Airtight , posted on August 11, 2015 at 12:06:20
A.Wayne
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OK Morris ....... LOL


not good ...

 

RE: Airtight VS VTL , posted on August 11, 2015 at 12:17:45
A.Wayne
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WELL

 

RE: Airtight , posted on August 12, 2015 at 01:01:36
morricab
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 And what is this?

 

RE: Airtight VS VTL , posted on August 12, 2015 at 02:11:24
morricab
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 And? I fail to see where you are trying to go with this wonderful parade of graphs.

Do you want to imply that SS measurements are so much better? It is pointless to argue this if you do not accept that sonics can only be partially determined by looking at these graphs. Also, if you do not accept that the pattern of distortion is more important than the amount (up to a limit of course) then we cannot have a meaningful discussion about the measurements.

You have to remember that mostly the measurements are made with the amp stressed to some degree (JA runs that IMD close to clipping usually).

Read the Jadis Defy 7MkII review in Stereophile. Note the differerence between stressed measurements and unstressed. Unstressed the amp measures superbly in terms of harmonic and IMD distortion. It sounds that way too in real life, having heard it now a couple of times it is probably the best amp Jadis ever made.

http://www.stereophile.com/content/jadis-defy-7-mkii-power-amplifier-measurements#2GdXtJa2p0X5DrbH.97

See Figures 3 and 5



The Lamm ML2.2 is a superb measuring amp in terms of the right harmonics, although you might claim it has too high absolute distortion, listening to it makes it clear it sounds very UNdistorted thus demonstrating the what over the how much.

http://www.stereophile.com/content/lamm-ml22-monoblock-power-amplifier-measurements#VgDqZxgwFjEDH3FL.97


Note particularly the THD vs. frequency, which is nearly flat even in the bass, indicating a sufficiently sized output transformer that is not saturating...a rarity to be sure. Also, note that even in the bass (where most tube amps will have lots of distortion) the harmonics are nice and monotonic. Finally, the IMD, while a bit noisy has very few harmonic lines even at 15 watts, near clipping.

"Yes, the ML2.2 has a bent transfer function, which means that it produces higher-than-usual levels of second-harmonic distortion—but this is not accompanied by high levels of high-order intermodulation. And you have that low output impedance and very wide bandwidth!"


http://www.stereophile.com/content/allnic-audio-5000-dht-monoblock-power-amplifier-measurements#PuJaHwm1qd9G2osv.97

This amp needs an easy speaker, but when you give it one it will have very nice performance indeed.

"Given the A-5000 DHT's single-ended topology, the presence of relatively high levels of second-order distortion in its output is inevitable. But the wide frequency response, excellent squarewave reproduction, and low output impedances, even from the 16 ohm output tap, are all commendable for such a design. One caution remains: If this amplifier is not to run out of steam, it must be used with speakers having an impedance equal to or greater than that of its nominal output transformer's tap"

 

RE: Airtight VS VTL , posted on August 12, 2015 at 05:33:40
A.Wayne
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 The graphs are all toob amplifiers , looking at the VTL 450 vs the airtight is what is being put forward for discussion , no SS graphs were included, they would be vastly superior and devoid of such high order artifacts and Since we are aware measurements mean nothing unless drawn to support a particular position , i had decided to take a look at three different toobs amplfiers , seeing how you have stated on many occasions the all important distortion spectra of each is what tells the tale ....


Pretty Euphonic , huh ... The VTL does have alot of high order harmonics ...

 

I guess the argument is "my distortion is better than your distortion" but , posted on August 12, 2015 at 06:35:58
kuribo
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 I prefer an amp like ncore which doesn't produce audible distortion. I prefer to add my seasoning in a different and more controllable manner.

 

RE: Airtight , posted on August 12, 2015 at 07:34:00
Inmate51
 "the powers used for the measurements is likely well above"

One of the things which bother me about audiophiles is that they always couch/hedge their dogma with words like "likely", "possible", "to my ears", etc., and don't provide any evidence of their claim. This is why I store such comments in the "one person's thoughts" section of my brain, rather than in the "here's proof" section.

:)

 

RE: Airtight VS VTL , posted on August 12, 2015 at 08:33:28
morricab
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 "VTL 450 vs the airtight is what is being put forward for discussion "

By whom? Not me. Why these two as they are completely different? One is low power EL34 and the other is high power 6550.

"no SS graphs were included, they would be vastly superior and devoid of such high order artifacts "

LOL...you can't be serious, can you?? They can and do have and often without the correct pattern of having higher low orders. That said, you chose poor examples for tube amps from a measurement perspective.

"Since we are aware measurements mean nothing unless drawn to support a particular position "

Also a ridiculous comment. There is only one position, what sounds best to the listener and studies show that it isn't the engineering wet dream of minimal THD no matter how it is achieved.

"i had decided to take a look at three different toobs amplfiers , seeing how you have stated on many occasions the all important distortion spectra of each is what tells the tale .... "

I guessed you missed the memo that it is not inherently tube amplifiers but how they are designed and (probably more importantly) executed?? Tube amps with undersized output iron...a big no no (and most commit this sin). Tube amps with negative feedback...causes a lot of the same problems in Tubes as it does in SS but perhaps a bit less severe...and more sounds worse (of course you can't get to the "Magicland" of feedback with tubes). Push/Pull amps (regardless of tubes or SS) have inherent pattern flaw due to cancellation of even order harmonics leading to an odd order dominated pattern.

Still, some quite good examples exist like the CAT JL2 signature MK2 (see link).

"http://www.soundstagenetwork.com/measurements/amplifiers/cat_jl2_signature_mk2/"

At least at lower powers bass saturation is minimal and the harmonic content at 10 watts is quite good with nothing above 7th harmonic and both 6th and 7th are low. The noise floor is also low.

I have first hand experience with this amp driving LARGE Apogees (we were driving Apogee Grands, passively with a Diva Crossover while he electronics were being repaired) and it was very good but still NOT as good as a NAT Se2Se, which actually bench tested over 100 watts (friend had it tested in Germany) of parallel SET (Class A2). For a comparable class of amp, I have found SET trumps PP every time, especially for naturalness of tone.

However, I am quite sure the JL2 will eat nearly every other PP tube amp for breakfast. Maybe the Lamm ML1.1 would be competitive in the PP tube amp arena or VAC PHi 70 monos or one of VACs newer amps. Both the Lamm and the VAC are true triode amps (but not their newer ones).


"Pretty Euphonic , huh ... The VTL does have alot of high order harmonics "

Not at all. This whole concept of "euphonic" harmonics is a myth. There are audibly iritating and not iritating harmonics but not euphonic because you NEVER get just 2nd order in isolation. If you inject just 2nd order into a signal at a high enough level (probably need at least 3% 2nd order to be audible...and that is with a pure sine wave) you might get a warming "euphony". In real amplifiers any AUDIBLE distortion will be negative on the listening experience.

Keith Howard looked at this with software to add harmonic patterns to a music track. See here: http://www.stereophile.com/reference/406howard/index.html#h2MsxQ2ZbUQM8yTP.97

"The most important finding was that none of the different patterns of nonlinearity sounded in any way preferable to the undistorted reference. They all sounded worse, albeit in different ways."

We can take the undistorted reference to be the theoretical "straight wire with gain" that simply utterly doesn't exist. Now for something more realistic.

"Pattern 1 added a distinct "dirtiness" to the sound that was not unpleasant but did change the instrumental timbre and diminish the sound's sense of fidelity—there was something clouding the sound. Pattern 2 was much better, with the closest sound to the undistorted reference. But I thought I could also detect it just beginning to muddy the presentation. Pattern 3 was unpleasant, adding an edge to the sound that would surely become fatiguing over extended listening. Pattern 4 wasn't as bad, but there was still something unnatural about it. Although Patterns 3 and 4 both introduce less distortion than Pattern 1, it was Pattern 1 that proved less subjectively annoying. While I could hear its effect, it did not threaten to send me screaming from the room after 10 minutes' listening."

Pattern 3 would be the ideal push/pull amplifier and Pattern 4 basically doesn't exist (I have yet to see an all even order harmonic pattern). Pattern 1 would be a somewhat poor SET design and Pattern 2 would be a good SET design but neither would quite follow the steepness of Cheever's "aural harmonics", which indicates something like a 20db drop from 2nd to 3rd harmonic and at least 10db after that.

"As already described, it has long been known that THD is a poor indicator of nonlinear distortion's subjective impact, and so it proved once again here. Shorter's n-squared weighting regime didn't correlate well either. The GedLee metric was a much better indicator, although my listening suggested that it underestimates the relative subjective annoyance of Pattern 4."

This is the crux of the argument. Pattern matters. If you employ a pattern as suggested by Cheever in his thesis it sounds almost indistinguishable from the undistorted reference...I know I have used Keith's software to try this out. I also took patterns from real amps and they are all wrong in one way or another but some are clearly better than others.

One thing I wish Keith had tried would be to have higher odds than evens in a pattern that is more like a real world Push/pull amp because they never perfectly cancel the evens. Maybe it sounds a bit better and it is only lucky (somewhat poor) design to get some evens leftover?

I think the point Hiraga was TRYING to make is that in the real world a Cheever like monotonic pattern of even and odd will be the best sounding. Get it out of balance and it is worse.

Also interesting is that the one that sounded the worst, Pattern 3, is how most amps in this world are made. Now, add feedback and even higher multiples of even and odd orders in the wrong balance and you are talking trouble.

 

RE: Airtight , posted on August 12, 2015 at 15:12:06
morricab
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 WHat is the problem with having conditional statements? Most things are not absolute and full of exceptions. That is the real world...no dogma here. Would you prefer a dogmatic statement that you can then attack?

I used the word likely because in many cases it is so but not in all. So I avoided an absolute statement that would be wrong. It can actually be evaluated on an amp by amp case by looking at the THD vs. power and then at what power the harmonic or IMD spectra were taken. It would be interesting if there was another, much lower powered spectrum for comparison...something in the normal range of the amp rather than near clipping.

What would you like to see as "proof"? You realize the variability in human perception, no? What level of correlation do you need between data and hearing to be convinced that it is true? What confidence interval?

Since you post quite a lot on this forum I would have assumed you are an audiophile...is that not so?

 

RE: Airtight , posted on August 13, 2015 at 05:33:00
A.Wayne
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 Morri,

This stuff is being put up for discussion , no need to feel anyone is being attacked , you had mentioned what you see in the measurements of class -D , that , IYO makes them wrong , now did you not notice the high order distortion from the graphs above , we both agree anything out to and past the 7th is nasty , yet all but the SET amp ( below 1 watt) in the first set of graphs have high odd order distortion. Maybe this is one of the reasons why most toobies prefer SET's ..


I will look again , i dont think any of the others were done near clipping ...


Regards

 

RE: Airtight , posted on August 13, 2015 at 08:37:07
morricab
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 Read his post again, there is a not so veiled comment about dogma and the implication I am trying to soften my dogma...except I don't have any dogma other than experiment and observe and then make hyptothesis, then experiment and observe and refine hypothesis, then experiment and observe and further refine hypothesis etc. BTW, that is scientific method...don't tell anyone. My only dogma is scientific method. This I will admit to.

If my scientific method had led me to conclude that high power, high feedback amps sound the best then I would be digging into why that is so. But it didn't and it still doesn't and if you look at the growing evidence it never will. It is kind of like saying that the theory of evolution, because everything follows it and not once in 150+ years has it been debunked is dogma. At this time it is a non-falsified theory but one that has been tested rather robustly.

"now did you not notice the high order distortion from the graphs above , we both agree anything out to and past the 7th is nasty , yet all but the SET amp ( below 1 watt) in the first set of graphs have high odd order distortion"

I did notice but you have to realize that it is not just the presence of harmonics it is the pattern that they make. A complete pattern of even and odd in decreasing intensity is less damaging (we can ignore the silly euphonic term I think) sonically than just evens and especially just odds. Sure any additional high order harmonics are bad though as they clearly don't happen in nature. But it is far worse when there is the absence of the low order ones. Patterns matter more. Also, Let's look at the Air Tight for a moment. Square waves look pretty good. Bit much power supply noise but seems a lot of amps have this. Something wrong with the left channel, maybe bad tube or bias was out. Right channel makes 20 watts at 1% and at 1Khz. Nice, even THD vs. frequency, which indicates minimal feedback and good output transformers. Spectra taken at 5 watts where THD is 0.7%. Decay is more or less monotonic up to 7th harmonic but doesn't decay further, which is not so good. Given that the distortion drops rapidly as the power drops, it is possible that these higher orders will disappear below the noise floor at 1 watt or so. If you use a efficient speaker then it could sound very good but if you push it probably it will harden up quickly.

I won't comment on the fact that apparently something was wrong with the amp so it may well be not representative.

VTL: The mighty Siegfried II; wide bandwidth, good square waves, low PSU noise (all below -95db), truly clips at 200 watts into 8 ohms (only 0.2% but takes a sharp bend at that point so clearly clipping), Not very nice THD vs. frequency (too much rise in the highs), unlike the Air Tight, which probably has nicer sounding higs as a result. Distortion spectrum at 50Hz not so bad but too much odd harmonic (It is push/pull afterall). Strangely the pattern from the Air Tight looked more like a SET. Poor HF IMD because of that rise in the highs. That is typical, BTW, for amps with feedback and not so good open loop linearity. All were done at 100 watts, which as we can see from the THD vs. power is about 3db below clipping and probably stressing the amp quite a bit. At 1 watt everything would be 10x lower in level.

The Lamm within its admittedly lower limits looks far better than both and most certainly will sound better with a sympathetic speaker.

 

Hey Morricab, posted on August 13, 2015 at 09:47:48
Inmate51
 I wasn't attacking you personally, and my use of the word "dogma" might have been a bit too strong in your case. So, please don't take it personally.

I could have made my point in another thread or after another comment somewhere else.

My point, which I hope/think you understand, was simply that audiophiles often make statements or pronunciations about this-or-that, but hedge their bets by using words which give them an "out" in case they're wrong or don't fully understand the topic. And, yes, "dogma" applies to some of them. (Can y'all say "tubes versus transitors"? lol)

With regard to evidence, this is an area which is sorely lacking in audiophile-land. I read post after post where someone says this or that, and they're just plain wrong and don't provide any evidence to support their claim. See what I'm sayin'?

Yes, my AA status is "audiophile", only because there isn't a category for "former industry professional/musician/recording engineer". It's a burden which I bear.

:)

 

RE: Hey Morricab, posted on August 13, 2015 at 15:11:35
Inmate51
 Bump.

:)

 

RE: Hey Morricab, posted on August 14, 2015 at 04:31:46
morricab
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 Maybe but you posted it under my post and made rather pointed comments.


FWIW, I try to back what I am saying with research papers that I find. Found another one recently that was complex but interesting and they concluded that a quadratic function distortion is less audible the a cubic function distortion...I will let you guess which one more applies to different types of amp topologies...

 

RE: Hey Morricab, posted on August 14, 2015 at 05:55:06
Inmate51
 Hahahaha!

"a quadratic function distortion is less audible the a cubic function distortion"

That's funny.

Next year, when I come to Switzerland again, if I have to fly into Zurich, I'll be sure to come and say hi. Although, I'd rather fly into Geneve - it's easier.

:)

 

RE: Hey Morricab, posted on August 14, 2015 at 12:12:57
A.Wayne
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 Well the top Horney speaker designers are now using SS amps to power their Horns, tells me, as i have experienced over the years, there is no clear winner, good sound is not mutually exclusive to toobs and most of what is known now, is just scratching the surface because of the complexities of what pleases the most complex of machines , the end user ...


Regards.

 

RE: Hey Morricab, posted on August 14, 2015 at 13:34:17
morricab
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 who would that be? Not at all what I saw in Munich... Only Avantgarde and Tone Audio...all other horns were running tubes

 

RE: Hey Morricab, posted on August 14, 2015 at 13:39:56
morricab
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 Interestingly, a MOSFET in Class A pretty much follows a quadratic function. A bipolar transistor something significantly more bent. Read the simulation paper by Boyk and Sussmann.

 

It also should be mentioned that any distortion which is below audibility matters not...so , posted on August 14, 2015 at 13:57:30
kuribo
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 who cares what the distortion pattern may be if it is inaudible?

 

RE: Hey Morricab, posted on August 14, 2015 at 17:32:25
A.Wayne
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 Magico is another i can readily recall , as most of my friends with their big custom Horns have switched to SS, Pass, etc ..

 

RE: Hey Morricab, posted on August 15, 2015 at 01:13:57
morricab
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 And all my friends switched away from SS to tubes or hybrids...all but one (the devialet guy). 4 of them switched to horns in that time (plus myself, which makes 5).

 

RE: Hey Morricab we are OK ...., posted on August 15, 2015 at 06:19:04
A.Wayne
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Its our friends who are strange .... rofl :)

 

RE: Hey Morricab, Charles Hansen weighs in , posted on August 15, 2015 at 17:17:12
A.Wayne
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 Tubes are also microphonic, says Hansen. "If you tap on a tube, especially in a phono stage, you will hear very loud noises coming through your speakers. I'm fairly convinced," he adds, "that much of the 'depth' from tubed gear is literally just the sound of the speakers vibrating the tubes and creating an acoustic feedback loop, much like reverb in a guitar amplifier. Pleasant? Yes. Accurate? Probably not." - Charles Hansen

Feel the same way myself ...

Regards

 

RE: Hey Morricab, Charles Hansen weighs in , posted on August 16, 2015 at 00:37:57
morricab
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 THen why do you get this effect regardless of volume level, bass content or other factors that would cause significant vibration? Also, not all tubes will make a noise if you tap them or even bonk them pretty good.

 

RE: Hey Morricab we are OK ...., posted on August 16, 2015 at 00:41:52
morricab
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 I once heard a demo of the K29800 speakers with mark levinson gear and it was simply...fatiguing. FM Acoustics sure costs a lot... ;-)

 

RE: Hey Morricab, Charles Hansen weighs in , posted on August 16, 2015 at 02:50:09
Inmate51
 This is why all microphones need shock mounts. Have you ever tapped a mic stand and heard the sound coming through the speakers?

(I know, a little OT, but hey, you said microphonic.)

:)

 

RE: Why ....? , posted on August 16, 2015 at 03:34:48
Disbeliever
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 Morricab As for Keith Howard he has his own opinions ,they definately do not correlate with mine. Its about time he got himself a decent listening room. I still prefer well designed Class AB amplifiers over any other types,

 

RE: FM Acoustics is pretty Pricey , posted on August 16, 2015 at 05:54:16
A.Wayne
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 Yes and standing room only , good stuff, manny is on top now ...

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 18, 2015 at 05:10:19
A.Wayne
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He exchanged toobys for class-D ....

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 18, 2015 at 05:11:23
A.Wayne
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His new whip ...

With gain of 26 Db and DF of 2000 , i guess we can safely say , Feedback city , but yet sonic nirvana .. :)

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 18, 2015 at 05:56:27
morricab
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 Naturally...or rather unnaturally !!! ;-)

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 18, 2015 at 05:57:30
morricab
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 You mean Dave Wilson? Where is that published that he changed amps to Class D?

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 18, 2015 at 06:54:25
A.Wayne
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 Wilson , over on Big Wallet...


So far better everywhere, stage , life likeness, etc. I guess time will tell if he can live with such good sonics from feedback.


Ahhh, Humans :)

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 18, 2015 at 06:57:45
A.Wayne
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 Dave Wilson..? only if he switched to genesis Planers ... :)

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 19, 2015 at 04:19:01
morricab
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 Don't know and don't care...more money than ears most likely.

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 19, 2015 at 05:10:11
A.Wayne
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 So no possibility in this application it actually sounds better huh ? well , I'm intrigued and while i do favor monolithic sized amplifiers over matchbox size i should give one ago ...


Regards

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 19, 2015 at 13:38:42
morricab
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 If dropping some coin on an experiment doesn't bother you then yes, you should try one of the latest Class D wonders...you seem to be quite curious about the Devialet...having heard it I am no longer curious...or interested. Same for the mola molas. Heard them twice...it was enough I think so I don't need to purchase either of those rather expensive options.

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 19, 2015 at 23:26:05
Disbeliever
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 Hear Hear Class AB still the best IMO.

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 20, 2015 at 01:32:47
morricab
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 I know you just made a typo and really meant "Class A with no feedback", right? ;-)

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 20, 2015 at 02:45:57
A.Wayne
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 I guess " you " meant Class-A Toobs with no feedback ..... :)

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 20, 2015 at 03:14:34
Disbeliever
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 I would not use a hot Class A amp with or without feedback. Class AB still easily the best for me. No antique tubes, No Class AD, No Class D, No Class G. or Hybrid.

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 20, 2015 at 06:52:16
morricab
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 Hybrid also works sometimes ;-)

Still have to try a FirstWatt...just to be sure of course...

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 22, 2015 at 12:17:54
A.Wayne
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 First watt is good with speakers over 98db, I guess you are border line , so it should work ...

 

RE: Hey Morricab , Wilson doesn't get it , posted on August 22, 2015 at 14:51:25
morricab
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 My next, "have to try", will be SET OTL...possibly a Transcendent sound kit.

 

RE: Ever tried ...? , posted on August 24, 2015 at 13:50:55
A.Wayne
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 I think these were Originally Finals .....

 

RE: Ever tried ...? , posted on August 25, 2015 at 02:25:23
morricab
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 Never owned them but a friend had their older reference models (huge and power sucking). Weren't nearly as dynamic as my old Acoustats...still the best all-around estat I have heard and the only ones with real balls to the sound.

The purity of STAX ESL-F81s though will be burned on my mind forever though...

Audiostatic ES100s were in-between STAX and Acoustat for purity but had a pretty nasty venetian blind effect that was ultimately a deal breaker.

I would love to try electrostats "direct drive" with a high voltage OTL amp. That might very well be the ultimate.

 

RE: Ever tried ...? , posted on August 26, 2015 at 07:09:22
A.Wayne
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At 2K shipped, must be a hell of a steal unless crap.

 

May I Add..., posted on August 26, 2015 at 23:53:09
Inmate51
 Speakers and amplifiers are joined at the hip.

Edit: As are speakers and rooms.

Can y'all say "system"?

:)

 

RE: Ever tried ...? Mola Mola , posted on August 29, 2015 at 02:56:52
A.Wayne
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Posts: 2527
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Show me the Mola .....:)

 

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