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Old 17th May 2020, 2:15 pm   #1501
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Default Re: The Audiophoolery Thread.

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Originally Posted by stevehertz View Post
I sometimes (well, often actually) think we look too much into the science of 'effects' and much less to whether or not such possible nano effects are actually audible. Always keep in mind the relatively massive distortion levels of transducers such as microphones and loudspeakers. One of the basic mistakes of audiophoolery; drilling thousands of miles down for oil that isn't there apart from maybe a spoonful or two.
The key is that these people believe that there is no limit to the discrimination of their hearing (or maybe that of their gurus) and consequently any effect which could possibly occur is therefore significant... irrespective of magnitude.

They put the onus on the rest of us to prove that something cannot possibly happen at any level other than absolute zero. This is impossible, of course, and therefore the subjectivists must be right!

All it needs is the complete suspension of any sense of scale or proportion, and they've got that covered.

Audio homeopathy?

David
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Old 17th May 2020, 2:16 pm   #1502
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Default Re: The Audiophoolery Thread.

The only thing that class A (and class D for that matter) is no crossover distortion. But efficiency for class A is dire. For 100W into 8 ohms pure class A needs a standing current of 2.5A. With +/-45V rails that is a standing power dissipation of 225W per channel. So on a programme average level of 2W (which is typical) the Self 1% efficiency is about right. On programme peaks and transients of course the power will be much higher.

Self's position on subjectivism is well known. I have all his books, because there is a lot of sense in them. And Self in his role as design consultant has produced some landmark designs. But he does bang on a bit in the first chapter. Let's not forget that he was historically vocally against capacitors degrading sound quality, until he measured the distortion introduced by polyester capacitors, that they "ran in" with distortion reducing over time and remembered the running in behaviour.

At least he has the good grace to admit when he was wrong.

Of course most of the original material for the Blameless principle in the Power Amplifiers book, he originally published in eight articles in Wireless World in late '93 to early '94. So 26 years ago, including the term "blameless".

He has refined the Blameless class B designs a bit since '94, but not by a massive amount.

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Old 17th May 2020, 4:30 pm   #1503
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Default Re: The Audiophoolery Thread.

Let me think that through...

+/- 45 v rails 2.5A quiescent current is 90*2.5 = 225W

For class A, we aren't forced to have a resistor or even a constant current source opposing an output device, we can modulate the current source with the opposite of the signal.

So for peak positive output, we swing to +45v and the top device passes 2*2.5A =5A
The bottom device has linearly diminished to 0 Amps as we got there. Power consumption is 5A*45v on one rail and nothing on the other = 225W still

For peak negative output the top device has diminished to 0 Amps, and the bottom device is working hard now at 5A. Still 225W, but now on the other rail.

We've lost the constant current drain effect on the power supply usually associated with class A, but we still have constant total power drain, it just moves betweem + and - rails.

So what's the output power?

We swing between +/-45v applied to the load. And we swing between +/-5A into the load.

So the optimum load impedance is 45/5 Ohms = 9 Ohms close enough for government work, as minimum voltage drops haven't been accounted for.

So 45V peak is 31.8VRMS
And 5A peak is 3.535A RMS

So that gives an output of 112.5W absolute max in a perfect class A amplifier where all devices conduct over 100% of the cycle (definition of class A) and are always in linear mode. 112.5/225 means 50% efficiency under full power conditions. Reduce power and the efficiency slides proportionately right down to zero.

2W output and the input power is still 225W which remains constant is indeed 0.89% efficiency which is right and indeed dire.

However, by having the both top and bottom transistors in the output configuration being active participants in this way, we have a 100W ampligfier, making some allowances for losses. Yes, Self's arithmetic is fine. No surprise there!

But, if you look at some of the class A designs around, one direction of the output stage is sometimes set up as a fixed current source and this halves the efficiency of the above because it reduces the output power and therefore you need to scale the amplifier up to get back to the 100W design intent.

Having a single output transistor working against a pullup resistor would be unbelievably inefficient. But there have been designs!

So Self's 1% is a good figure, calculated by legitimate means.... but it actually represents the best, and some designs are a lot worse than that.

Things go really wrong when people eschew mathematics and 'design' things on religious principles.

Given transistor amplifier's overdrive characteristics (irrespective of class) 100W/Channel is a good output rating so clipped peaks are not too common. For a stereo pair, we're looking at 450W of heat into the room, plus power supply losses.

OK in winter, I suppose.

David
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Old 17th May 2020, 4:42 pm   #1504
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Default Re: The Audiophoolery Thread.

Granted, Self hasn't always been right - he's in good company there - but he does document his mistakes as part of the explanation of something better. I have to admit I smiled on seeing in the 6th edition that he had measured a specifically "audio" capacitor as doing a better job than a cooking example when coupling an amplifier output to the load, the midband distortion being substantially reduced. Said capacitor (Cerafine) is physically larger than the general run of devices of that value and voltage rating, so presumably something in the construction is more generously proportioned.

I think much of audiophoolery stems from two main causes. Firstly, the confusion between a hi fi system and an electronic instrument. One you play and produce a sound, the other you want ideally to listen through to somebody else's performance. In one case, anything goes whch changes the sound to your liking; in the other, preservation of what is already there is paramount.

The second cause is the demise of the LP, or near-demise. When pickups were the key to hi fi (must be a book in there...) there were so many variables involved that evaluation had a large and unavoidable subjective element. This sold newsprint, undoubtedly, and whilst "pure perfect sound forever" was a simplistic over-statement, undeniably CD both raised the bar for performance and narrowed the differences between products. Simple evaluation of features and measured performance did not require gurus, so they set about inventing differences they could argue about.

It is interesting to note that John Crabbe, who, as editor of Hi Fi News for fifteen years, was in the vanguard of the quest for better pickups, abandoned LP without regret as soon as the music he wanted was avaolable on CD.

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Old 17th May 2020, 4:51 pm   #1505
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Default Re: The Audiophoolery Thread.

I have to 'fess up. I had such an amplifier for a few years - a Krell KSA100. This was dual mono in a common chassis. Two massive toroids etc, and two fan cooled heatsink chimneys with four pairs of TO3 can output devices on each.

It was a hernia inducing monster that chucked out 500W of heat.

And because of the stresses on the output devices it blew up spectacularly twice. Once after I had sold it, and the buyer was in transit from Kent to collect it.

If you are remotely interested in my audio insanity when in my 30's, this is what they look like

https://www.lfgss.com/conversations/324270/

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Old 17th May 2020, 5:02 pm   #1506
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Default Re: The Audiophoolery Thread.

Self set out his stall on subjectivism in a long and detailed article here https://www.americanradiohistory.com...ld-1988-07.pdf

32 years ago. AFAIK nothing much has changed other than methods of removing cash from punters has proliferated. Quantum morphic etc.
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Old 17th May 2020, 7:23 pm   #1507
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Default Re: The Audiophoolery Thread.

I remember Doug Self and Ben Duncan slugging it out month after month in the WW letters page. Self was backing up his arguments with SPICE simulations, but Duncan won that particular skirmish because IIRC the SPICE MOSFET models did not accurately model the obscure second order effects being argued over.
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Old 17th May 2020, 7:46 pm   #1508
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Default Re: The Audiophoolery Thread.

The next time I look at anything in old WW letters pages, I'm going to hear sound effects... someone hitting cabbages with bits of 2x2 plus sundry grunting and the occasional scream. "Take that you rotter! There is a quintic term, and it's non-zero!" THWAP!!!

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Old 18th May 2020, 8:32 am   #1509
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Default Re: The Audiophoolery Thread.

Back in University days, we hosted a Quantum Electronics conference. There was a theory session that cleared most of the people out of the conference hall. Those that remained dozed or did a crossword.

But it was worth paying attention for a guy at the podium wading though viewgraphs densely populated with things like Green's functions (which I never understood). All of a sudden a voice piped up from one of the few people who understood this stuff:

"Excuse me - what about Grad's thirteen moment theorem?"

There followed what seemed an eternity of silence from the speaker, and then:

"You're absolutely right - this is actually total rubbish" picked up his viewgraphs and exited the stage.

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Old 18th May 2020, 8:42 am   #1510
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Default Re: The Audiophoolery Thread.

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Originally Posted by wd40addict View Post
I remember Doug Self and Ben Duncan slugging it out month after month in the WW letters page. Self was backing up his arguments with SPICE simulations, but Duncan won that particular skirmish because IIRC the SPICE MOSFET models did not accurately model the obscure second order effects being argued over.
I know Ben Duncan very well indeed. An interesting and entirely self taught zen master of audio. He uses Microcap as his spice modelling tool, and knows spice modelling backwards and forwards. In fact he has been getting Microcap free from their early days because he was a beta tester for them.

So it is not at all surprising that he won a spice battle with Doug Self.

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Old 18th May 2020, 8:51 am   #1511
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Default Re: The Audiophoolery Thread.

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Green's functions (which I never understood).
It has long been suspected that there is a book circulated amongst lecturers and kept secret from all others on pain of death.

No, I've not personally seen one, I have no solid evidence for its existence, but a group of us managed to deduce its existence from the effects of its application.

It contains numerous rules, laws, equivalences, theorems and identities which are absolutely guaranteed NOT to have been taught or explained at earlier stages in education.

Thus armed, the lecturer (who had signed in blood for his copy) can scrawl all over his blackboard and drop in an occasional one of these gems if he thinks someone in his audience is actually following him so far and needs to be thrown off the trail. Once done, the rest of the lecture can be absolute crap. So long as he doesn't do anything stupid like mentioning magic pixies, he's home and dry.

Without such defences at the ready, the embarrassing situation Craig just described could happen.

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Old 18th May 2020, 9:18 am   #1512
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Default Re: The Audiophoolery Thread.

Sometimes death by PowerPoint plays its part too. I was once at multi-day lecture series on semiconductor IC design held in London. Actual design of the silicon is not my field, but for various reasons I was there.

The American lecturer was a world authority on the subject and powered through his slides 19 to the dozen. I tried to keep up as best I could, but my lack of background meant it wasn't easy. A couple of days in he threw up an equation based on some of the previous stuff, I looked at it and thought it didn't look right. By the time I raised my hand he was another 5 slides on. I nervously asked "that equation 5 slides back, is it correct?".

He wound back to the slide in question and said something like "good grief I've been giving these lectures round the world for five years and no-one's noticed that before!"
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Old 18th May 2020, 9:54 am   #1513
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Default Re: The Audiophoolery Thread.

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Green's functions (which I never understood).
Some of our maths lectures were given by Professor Zienau, a total genius who considered undergraduates to be stupid. He was known for his squeaking shoes which signaled his impending arrival long before he came into sight. He gave lectures straight out of his head with no notes. On one occasion he started a lecture by writing a triple integral which extended over two blackboards. After looking at it for a few seconds he announced "and we can see by inspection that the solution is ...". One of us dared to admit that he couldn't see it by inspection and asked for a bit more explanation. After the obligatory "you are so stupid", Zienau spent the rest of the hour working out the solution step by step and eventually came up with the same answer. Long afterwards I saw that he studied under Wolfgang Pauli and would have undoubtedly been an interesting person to talk to.

Anyway, he taught us about Green's functions in a mini-lecture lasting all of five minutes which is probably why I never understood them either.
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Old 18th May 2020, 10:51 am   #1514
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Default Re: The Audiophoolery Thread.

I've just looked up Grad's thirteen moment theorem and Green functions.
It was a bit like Tony Hancock getting two words into Bertrand Russell and diving for the dictionary...
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Old 18th May 2020, 11:40 am   #1515
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Default Re: The Audiophoolery Thread.

I'm with Ted! However, I admire Craig's lecturer. If more people had the strength of character to admit when they're wrong things might be better in general. Pig-headedness is of no benefit in any field, except a piggery.
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Old 18th May 2020, 1:37 pm   #1516
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Default Re: The Audiophoolery Thread.

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Green's functions (which I never understood).
You are among friends!

George Green was born in 1793 and lived for most of his life in Sneinton on the outskirts of Nottingham. His father, also named George, was a baker who built and owned a brick windmill used to grind grain. The father died in 1841 and the mill fell into disuse and dereliction in 1860. In the early 1920s it became a factory manufacturing polish. I grew up in Loughborough Avenue, Sneinton and our house backed onto the field in which the Mill is sited. in 1947, when I was eight years old, the mill caught fire and the heat was so intense that we feared it might crack our windows. Once again, the mill became derelict and faced demolition, until it was acquired by Nottingham City Council in 1979.

Little was known locally of George Green until Nottingham University publicised his mathematical achievements. Funds were raised by the University in the mid 1980s enabling the mill to be fully refurbished. It was reopened in December 1986, is now a Grade 2 listed building, a working windmill and part of a science centre in honour of George Green, which is open to the public. No 3, Green's Gardens was also restored from near dereliction by Nottingham Buildings Preservations Trust as a residence for one of the Museum staff.

Green died in 1841 aged 47, and only came to prominence posthumously.

On a visit to Nottingham in 1930, Albert Einstein commented that Green had been 20 years ahead of his time. Westminster Abbey has a memorial stone for Green in the nave adjacent to the graves of Sir Isaac Newton and Lord Kelvin. His work and influence on applied physics had been largely forgotten until the publication of his biography by Mary Cannell in 1993. The George Green Library at the University of Nottingham is named after him, and houses the majority of the university's science and engineering collection. The George Green Institute for Electromagnetics Research - a research group in the University of Nottingham engineering department - is also named after him.

His achievements were quite astounding.

In his youth, Green was described as frail with a dislike for working in his father's bakery.

However, as was common at the time he worked daily to earn his living at the age of five. His life story and contribution to mathematics is all the more remarkable in that he was almost entirely self-taught. He received only one year of formal schooling as a child, between the ages of 8 and 9. His father recognised his above average intellect, and being well off due to his successful bakery, he enrolled him in March 1801 at Robert Goodacre's Academy in Nottingham, where the extent of his mathematical teachings was limited to algebra, trigonometry and logarithms. Thus, his later mathematical contributions, which exhibited knowledge of very modern developments in mathematics, could not have resulted from his time at the Academy. He stayed for only four terms and it's thought that he'd probably exhausted all that they had to teach.

When his father died, his legacy enabled Green junior to abandon milling and pursue his mathematical interests. Sir Edward Bromhead, with whom Green shared correspondence pressed Green go to Cambridge. In 1832, aged nearly forty, Green was admitted as an undergraduate at Gonville and Caius College, Cambridge. He graduated with a BA in 1838. A remarkable achievement given that he had only one year's formal education between the age of eight and nine. Sadly, he died three years after graduation. Who knows how much unrealised potential he took with him to the grave?

https://en.wikipedia.org/wiki/George...(mathematician)

The mill can be seen from the south of the river Trent from several miles away.

https://en.wikipedia.org/wiki/Green%27s_Mill,_Sneinton

When open again, the mill & science centre is well worth a visit if in the area:

https://www.greensmill.org.uk/about/...-the-windmill/

Nothing at all to do with 'audiophoolery' but hopefully given how the thread has drifted, I hope it's interesting enough to merit a mention.

(When I started this thread, I never imagined that it would be destined to have a longer run than 'The Mousetrap'!
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Old 18th May 2020, 3:03 pm   #1517
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Default Re: The Audiophoolery Thread.

That was fascinating David - thanks for that and for the links.

And to Ted who made me laugh out loud!

Craig
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Old 18th May 2020, 4:28 pm   #1518
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Default Re: The Audiophoolery Thread.

It's a useful principle but not often used by name.

White noise has an infinite spectrum, think of it as infinitesimally spaced components across a frequency range extending from zero to as high as you can manage. The interesting things are the overall amplitude template, and the pattern (if any) of the phases of all those components. White means the amplitudes are flat, and the phases are randomly scattered.

All non-repetitive signals give spectra of infinitesimally spaced components. By choosing the template of the amplitudes of those components and the pattern of their phases, we can make any wave shape we can imagine. (Fourier)

If we make the waveform repetitive, then the spectrum simplifies, leaving only components at the repetition frequency and its harmonics. The amplitude template and phase pattern remains.

So the non-repetitive waveform case is just the repetitive one with the repetition frequency set to zero.

One interesting cousin of white noise happens if we keep the infinite number of infinitesimally spaced spectral components and order the phases into a regular pattern.

We wind up with a waveform which tends towards a zero width spike of infinite amplitude Mathematicians call this a Dirac Function

From an engineering point of view, Dirac functions are a bit of a problem. You hit something with an infinite force but for zero time? did it move? Angels, pinhead. pinhead, angels. So arbitrarily the amplitude-time product is assigned as 1 for a Dirac impulse.

Green's functions describe the behaviour of something described by differential equations (like most circuits, filters, transmission lines, control systems etc etc) if it gets hit by one of those Dirac spikes. You can play about with the results and get either the impulse response of the system, or the amplitude and phase versus frequency response.

Play the game backwards and you can take the frequency/phase response of a system and you can calculate its impulse response. This is great for finding the impulse response of something that would have been destroyed if you hit it with a real impulse.

And there's that white noise bit. You could feed noise into something and correlate it with the things response to that noise. This will give you the impulse response and you can trade that into the frequency response.

There's another relative to white noise and Dirac impulses, THe step function (Heaviside function, yes, him! he got around a bit.) this also has infinitesimally-spaced frequency components, but a different zero freq value and a different phase pattern) So you can play the same game with these as with the Dirac. Once you know the full frequency/phase response, you can calculate how your circuit or whatnot will behave when hit with a perfectly fast step of voltage.

If you want to test bridges, nuclear power stations and other things that would get in the papers if you wrecked them, you can apply gentle noise, measure the response and calculate what stresses would be created if you hit it with something more dramatic.

There is one small fly in the ointment:

It all assumes the system is linear. Which means that if you apply several signals at once (added together) the response will be the sum of all the responses to each of those signals individually. This is calles 'superposition'

The interchangeability of all these ways of looking at essentially the same thing is so common and so everyday that it's a crying shame Green doesn't get credited.

Never thought I'd explain that little lot in an audiophoolery thread. It's the very antithesis of audiophoolery saying that you can measure one thing and calculate everything else and invoke theoretical signals which are impossible in practice. It leaves nowhere for the golden eardrums to hide AND it's mathematically provable!

Thanks for the local knowledge, David. Somewhere I'd like to visit.

David
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Old 18th May 2020, 5:08 pm   #1519
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Default Re: The Audiophoolery Thread.

You can get around the infinite thump of a Dirac Delta by using a Kronecker Delta, which has unity amplitude at t=0 and is zero elsewhere.

It is though a bit academic since hitting any engineering system with a zero duration impulse is non-physical, and as David said the way around that (for a linear system) is by using low amplitude excitation and working backwards.

Craig

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Old 18th May 2020, 8:02 pm   #1520
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Default Re: The Audiophoolery Thread.

Interestingly, the discussion about lecturers and the such takes me back. I really struggled at Uni (Imperial) and then Poly (Lanchester). But realised that practically I understood how stuff worked. For example I was 'taught' twice how transistors worked, all being about voltage gain, with particular resistors. As soon as I was shown that actually they were essentially a current amplifier I got it.

But it also reminds me of a long lost friend who gave up on electronics because he didn't get transistors and how 'holes' transferred. He had been quite active previuosly having built a TV using a ministry scope, but got an upside down picture becuase of a misconnection, this in the days where transmission was still crystal palace. Later, but before transistors, he and a group of friends were also experimenting with recording video on swedish iron wire.

When he gave up after transistorisation, he got back into motorbikes, supprting his son in TT racing.

I still have some of his radio servicing books that he gave me 30+ years ago.
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