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Old 7th Sep 2020, 8:57 am   #1841
Craig Sawyers
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Default Re: The Audiophoolery Thread.

Did you read the measurement of this massive set of chassis? It is specced at 150W. But at 100W the distortion was well in excess of 10%. The frequency response is laughable - a 9dB hump between 80Hz and 160Hz. 3% IMD at 2.5W into 8 ohms.

Yeesh and yuck

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Old 7th Sep 2020, 9:01 am   #1842
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Default Re: The Audiophoolery Thread.

Of course you could synthesize this performance digitally, and play it through a very low distortion semiconductor amp.

I wonder how seductive that would be if reviewed? How about a blind audition?

Craig
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Old 7th Sep 2020, 10:37 am   #1843
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Default Re: The Audiophoolery Thread.

Quote:
Originally Posted by knobtwiddler View Post
NB - I hope you snuck around to the bins and rescued the SP10
No, I didn't - I only found out about it weeks later
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Old 7th Sep 2020, 11:08 am   #1844
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Default Re: The Audiophoolery Thread.

Quote:
Originally Posted by Craig Sawyers View Post
Did you read the measurement of this massive set of chassis? It is specced at 150W. But at 100W the distortion was well in excess of 10%. The frequency response is laughable - a 9dB hump between 80Hz and 160Hz. 3% IMD at 2.5W into 8 ohms.

Yeesh and yuck

Craig
No, I missed that. When I got to the foot of page 3 and tons of adverts squiffed into view, I thought that was it. Only 3 pages were liisted. Now I see that the lower words were hyperlinks and I clicked on 'measurements' and then I read and read.

Brilliant!

Real measurements and honest conclusions. I'm much cheered! and he's independent about it, not in anyway fazed by all the eloquence printed ahead of him.

Well, you can see the transformer resonances dominating everything above 30kHz so the manufacturer's mention of 100kHz is complete crap.

The jump in the audible region is probably what gives it presence.

Anyone who wants an amplifier to produce this much distortion and to have such a shaped frequency response could save themselves an awful lot of money.

Basically, its a piece of art, designed solely to appeal to the eye.

The subjective review with all those specified recordings is just made funnier.

David
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Old 7th Sep 2020, 12:24 pm   #1845
Craig Sawyers
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Default Re: The Audiophoolery Thread.

John Atkinson stepped down as Editor of Stereophile last year, alas. But when he moved from HiFi News to Stereophile it was on the basis that he bought into the company. He sold it to a publishing company in 1998, and probably made a bunch of money.

But he was 71 when he retired, so you can understand why he decided to go. His objective reviews were a high point though. https://www.stereophile.com/content/next-generation

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Old 7th Sep 2020, 1:16 pm   #1846
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Default Re: The Audiophoolery Thread.

There is a great interview with Atkinson on Youtube, concerning the importance of measurements. We really need younger people to step into his shoes. I thought he was staying on as a technical consultant?
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Old 7th Sep 2020, 1:37 pm   #1847
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Default Re: The Audiophoolery Thread.

The trouble is doing measurements takes time and expertise. It's cheaper just to do the subjective review and results like the above "sounds great, measures crap" leave average readers in the "measurements don't matter" camp.
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Old 7th Sep 2020, 6:08 pm   #1848
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Default Re: The Audiophoolery Thread.

Unfortunately during Atkinson's tenure at HiFi News, it became a measurements only magazine. There were few if any listening tests for quite a long time.

The only audio magazine I now subscribe to is HiFi Critic. That has no advertisements, or advertising revenue. So the reviews are without favour, and are a good mix of listening tests and in depth measurements. The only problem is that the gear reviewed is always expensive, and not affordable by mere mortals (like me). But fun to look at and read the reviews. And since it is only quarterly you don't drown in nonsense from the monthly comics.

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Old 7th Sep 2020, 8:15 pm   #1849
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Default Re: The Audiophoolery Thread.

Quote:
Unfortunately during Atkinson's tenure at HiFi News, it became a measurements only magazine. There were few if any listening tests for quite a long time.
Why do you say 'unfortunately'? Everybody's room acoustic, hearing (especially at different times / moods etc), as well as personal taste is different. An analyser will give the same results pretty much anywhere at any time. I would argue that we would be living in a far better world if people made choices based solely on objective data as well as their own taste, than have their decisions biased by those who often have an agenda, and even when not, are relying on a mechanism as prone to plasticity as the human auditory mechanism. If audio weren't such a subjective field, we wouldn't have £100K cables, and people could do something useful with the money as opposed to giving it to those with scant evidence that their goods perform as advertised.
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Old 7th Sep 2020, 8:19 pm   #1850
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Default Re: The Audiophoolery Thread.

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The trouble is doing measurements takes time and expertise. It's cheaper just to do the subjective review and results like the above "sounds great, measures crap" leave average readers in the "measurements don't matter" camp.
I think you make a profound point here. You could argue that we'd be better off separating objective reviews and subjective completely. I think the fact that a $350k amp which has poor performance even by budget standards, yet is praised subjectively, proves my point about how unreliable subjective appraisals are.
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Old 7th Sep 2020, 10:02 pm   #1851
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Default Re: The Audiophoolery Thread.

There was a time, a goodly number of years ago when measurements done on audio amplifiers were a bit, well, simplistic.

Around the same time amplifiers had some failings that these simple measurements didn't pick up, so some people were saying a model of amplifier tested well, and others were saying it sounded crap. And the ears were right this time.

Since then this has been used by a variety of people to argue that measurements are crap and therefore all measurements are crap and that many things which can be heard can't be measured.

This is of course, nonsense. Once the issue was understood, amplifiers could be and were designed to circumvent that problem, and measurements were evolved that could verify its successful eradication.

However, the legend of measurement versus ears lives on as tribal folk-memory and has been repeated often enough to be accepted fact.
Yes, the subjective listeners were right but that was then and this is now. Designers have actually learned things in the intervening period.
Emboldened by this, some subjective people have flown off on wild flights of fancy about imagined characteristics.

So you should always question measurements... have the appropriate things all been measured? Accurately? Thoroughly? and the results explained well? Any vested interests. Big advertisers?

You should always question subjective opinions. What planet is the guy on? Any vested interests? Is he writing to show himself off, or is it reallly about the equipment?

Good measurements and good subjective reports are complementary.

David
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Old 7th Sep 2020, 11:40 pm   #1852
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Default Re: The Audiophoolery Thread.

Yes to all that David. The latest house mortgage price Audio Precision test set can do much more than just test amplifiers. But it does test amplifiers exceptionally well.

As an indication of what it can do in characterising an amplifier's performance, Neurochrome have some pretty impressive measurements with just such kit

For example the performance graphs here:
https://neurochrome.com/products/modulus-686
https://neurochrome.com/products/universal-buffer

By way of background, Audio Precision was founded and run by Bruce Hofer. In a previous existence he designed 7000-series plugins, the AA501 distortion analyzer and the partnering SG505 ultralow distortion sine generator, and digitizer products while at Tektronix.

https://engineering.oregonstate.edu/...ring-hall-fame

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Old 8th Sep 2020, 9:59 am   #1853
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Default Re: The Audiophoolery Thread.

Quote:
Originally Posted by Radio Wrangler View Post
There was a time, a goodly number of years ago when measurements done on audio amplifiers were a bit, well, simplistic.

Around the same time amplifiers had some failings that these simple measurements didn't pick up, so some people were saying a model of amplifier tested well, and others were saying it sounded crap. And the ears were right this time.

Since then this has been used by a variety of people to argue that measurements are crap and therefore all measurements are crap and that many things which can be heard can't be measured.

This is of course, nonsense. Once the issue was understood, amplifiers could be and were designed to circumvent that problem, and measurements were evolved that could verify its successful eradication.

However, the legend of measurement versus ears lives on as tribal folk-memory and has been repeated often enough to be accepted fact.
Yes, the subjective listeners were right but that was then and this is now. Designers have actually learned things in the intervening period.
Emboldened by this, some subjective people have flown off on wild flights of fancy about imagined characteristics.

So you should always question measurements... have the appropriate things all been measured? Accurately? Thoroughly? and the results explained well? Any vested interests. Big advertisers?

You should always question subjective opinions. What planet is the guy on? Any vested interests? Is he writing to show himself off, or is it reallly about the equipment?

Good measurements and good subjective reports are complementary.

David
Interesting. What era was this? Early transistor? I used to have a friend who worked at Leak, and he claimed he could tell whether they were playing a transistor or valve amp from his room down the corridor...much to the annoyance of Mr Leak. What parameters were they not measuring? IMD while driving a very low impedance? Overload recovery? My understanding is that studies over the years have shown that people cannot accurately discern level change below 0.3dB, nor THD below 0.3%, but my info might be somewhat out of date. Personally, if I can see unintended artefact on the FFT when the circuit's working hard, even it's below -100dbV, I will try and eradicate it. This is more due to technical pride than because I think it will be heard. I also think that unexplained artefact, however low in nature, can signify something that might affect reliability long term or get worse in other environments (as many here will know, something that seems ok, but is on the threshold of stability can show low level quirks that hint it's not as stable as you'd like). I've always believed in better specs for the same reason Mr Atkinson outlines in his Youtube interview. It's not whether you can hear they've shaved a handful of dB off the noise floor, but more a question of showing that the OEM is striving to achieve the best, as a matter of integrity.

NB - I'd be surprised if it hasn't been posted before, but this is a fun link for those who haven't seen it - Visit to Leak circa 1968:

http://44bx.com/leak/1968.html

(I might have first found link here..not sure where I found it. Apologies if it's been posted and I've parroted it here)

edit - and another thing: if reviewers are going to publish subjective impressions, they ought to publish a plot of their listening room...it might be illuminating. It would show that even mastering rooms have vastly more deviation than any half-decent circuit in terms of FR.

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Old 8th Sep 2020, 10:42 am   #1854
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Default Re: The Audiophoolery Thread.

My memory is that it was with early transistor amps and that it might have been to do with missing crossover distortion at low audio levels, where it's rather audible, but I can't be certain about that.

The audibility of THD does depend on the particular harmonic spectrum. The higher-order components (above about 6th if I remember rightly) can be troublesome at quite low levels apparently. It was interesting that Quad specified the II amplifier's THD at 0.1% excluding 2nd harmonic. It's been reported that in blind tests people (on average) actually preferred the sound of music which had had a little 2nd harmonic added !

Cheers,

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Old 8th Sep 2020, 11:14 am   #1855
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Default Re: The Audiophoolery Thread.

If you read old copies of Hi-Fi news from the early 60s they occasionally mention something called 'transistor treble'. This was the subjective increase in treble level compared to a valve amp.

The early transistor amps could use hitherto unheard of levels of feedback due to the lack of an output transformer. This gave good measurements at high power levels
which was the headline they cared about. However, at lower levels (normal listening) you're relying on the feedback to massage crossover distortion if you've not engineered it properly. This was probably what people were hearing, especially with the high sensitivity speakers of the day. A second potential issue was how stable was the loop when hit with a transient and driving a real speaker?

Transistor amps only really hit maturity when the Quad 33/303 appeared. Radford showed a prototype transistor amp in about 1963, but it never went into production.
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Old 8th Sep 2020, 12:19 pm   #1856
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Default Re: The Audiophoolery Thread.

Is part of the problem that crossover distortion occurs at a point where both output devices are so close to cut-off that the amp transiently has almost no open-loop gain ? Without open-loop gain feedback struggles to do much good.

Cheers,

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Old 8th Sep 2020, 2:15 pm   #1857
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Default Re: The Audiophoolery Thread.

Self's book on power amplifiers has a comprehensive treatment of crossover distortion. A classic case of measurements not telling the whole story is Len Hulley's review of the Dynaco 120 amplifier in 1966. Having negotiated the saga of getting a sample which didn't blow up, he carried out listening tests against his own valve amplifier and a good commercial valve model. He identified a crspness to the treble with the 120 which was absent on the valve models, and spent some time with oscilloscope and generator trying to pin it down, eventually admitting defeat and giving the amplifier unstinted praise. As we now know, the 120 made a point of having no quiescent current in the output devices and consequently had substantial crossover distortion, which a spectrum analyser, for instance, would have shown up straight away.
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Old 8th Sep 2020, 2:54 pm   #1858
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Default Re: The Audiophoolery Thread.

Maybe it's not the type, but the price of the distortion?
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Old 8th Sep 2020, 5:18 pm   #1859
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Default Re: The Audiophoolery Thread.

Self is a fan of class B, rather than AB. When correctly biassed his "Blameless" class B designs achieve 6ppm harmonic distortion at 1kHz rising to 80ppm (0.008%) at 20kHz on an 80kHz bandwidth and 25W into 8 ohms. Of course those vanishingly small numbers include all crossover artefacts.

And the reason that modern designs are capable of such tiny distortion figures are (a) design understanding has improved and (b) device technology has improved.

Also the increase in distortion at high audio frequencies increases is related to beta droop in the output devices - so the drivers have to work harder. The net effect is that loop gain reduces at high frequencies.

Now you can do better than the high frequency increase in distortion is by using feedforward. There is at least one commercial power amplifier that uses this approach made by Halcro https://halcro.com/product/eclipse-mono/ . It is of course ridiculously expensive. Internally the bottom pod is two switched mode supplies. The first is a power factor corrected single rail unit. That is followed by a second switched mode supply that derives the DC rails for the amp, in the top pod. That is a MOSFET power amp with feedback and feedforward. Distortion is <1ppm over the audio bandwidth.

There is also a series of papers by Stoichino published in Linear Audio on feedforward power amps. Again massively complicated, and again achieving exceptionally low distortion.

The trick is to make a feedback/feedforward design stable.

Alternatively you (shock horror) can go Class D. The Hypex NC400 modules achieve less than 10ppm distortion flat over the audio band at 200W into 4 ohms.

Craig
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Old 8th Sep 2020, 7:05 pm   #1860
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Default Re: The Audiophoolery Thread.

There is also the Benchmark Media AHB2 which uses the THX-patented version of FF error correction. It achieves similar specs to the Halcro, but at a fraction of the price: https://www.stereophile.com/content/...r-measurements

It's almost in danger of being decent value for money. I ought not to post it in this thread!

FFEC has been around as a concept for decades. I haven't looked into what makes THX's implementation special enough to patent, though.
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