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Old 6th January 2012, 03:55 PM   #611
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Quote:
Originally Posted by DF96 View Post
Yes, my mistake.

In the Geddes/Lee paper they use 'transfer function' with the same meaning that I did, so at least I have company! Sorry for causing confusion.
Actually, I was confused the same way, thinking in terms of a transfer function.
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Old 6th January 2012, 04:13 PM   #612
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Hi,

Quote:
Originally Posted by DF96 View Post
In the Geddes/Lee paper they use 'transfer function' with the same meaning that I did, so at least I have company! Sorry for causing confusion.
You can translate the "transfer function" of any Amp output stage into a "wingspread diagram".

If there is (for example) a smooth gain falloff (or rise) towards the extremes, we may call the system producing the graph monotonic, if the transfer function is not monotonic we can see discontinuities and up/down undulations... It may be worth looking at those for Class AB Amp's...

Ciao T
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Old 6th January 2012, 04:31 PM   #613
DF96 is offline DF96  England
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Do you mean the sort of diagram which Doug Self uses, showing gain vs. instantaneous signal voltage? They do look like wings, and can have alarming wiggles in the middle. As the differential of what I was speaking of, the condition for monotonicity is that it stays positive.
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Old 6th January 2012, 10:07 PM   #614
Pano is offline Pano  United States
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DF96. Your proposal in post 610 is an interesting one and certainly should go a long way toward a decent SQ metric. My audio mentor, Mr. Hiraga, often pointed out that good amps not only have a favorable harmonic structure, but can maintain it a different power levels and into complex loads.

It does not take much measuring to see that the distortion spectrum changes with power levels. It takes a bit more to see that the harmonic fingerprint also changes with frequency and into complex loads. I've seen amps where one harmonic changes depending on load while the the other harmonics don't. Certainly something like that is important.

As some others have stated in this thread, it would be nice to boil down SQ into a few easy numbers. Getting there won't be easy, tho.
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Old 7th January 2012, 08:24 AM   #615
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A lot of discussion on thermal modification of transistors, has anyone considered the various issues in caps? They are variable with respect to capacitance, DF, esr and leakage due to voltage, temperature, and humidity. Various film types are more stable than say, z5u or x7r multilayer monolithic, but none the less very imperfect devices. If I remember, inductance is pretty stable.
It was actually Walt Jung's Audio article in the 70's that led me to solve many issues back in my lab days. Of course the seminal paper on z5u's was done in the FA lab at Goddard after a shuttle launch failure that tied the earlier Japanese humidity problem together with the low voltage carbon track issue. Combined with the mechanical termination problems of axial glass packaging, we assumed over 5% defective caps installed on our digital boards. With logic voltages dropping from 5 down to 1.5, I wonder how the low voltage carbon migration was solved?
Back when I was current, polystyrene was the hot ticket for audio, but they were big, expensive and fragile, so we settled for mylar. There were debates over the self healing features of deposited film vs foil and the termination issues. Manufacturing improvements march on, so I don.t know the current thinking.
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Old 7th January 2012, 12:47 PM   #616
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If it seems to be preferable to have less global feedback and more local stage, then it would make some sense why the chip-amp club is quite limited as this is fixed by the original designers giving the application integrator no leeway. Where the opportunity in a chip to use many more transistors and means of compensation to produce amazing new op-amps, unless they choose to change their design concept the chip amps are limited. Reasonable extraction?
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Old 7th January 2012, 03:24 PM   #617
jcx is offline jcx  United States
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audio power chip amps don't have many external design degrees of freedom, and not too many options - discrete or hybrid design certainly still makes sense

for small signal applications you can't buy, effectively apply discrete Q of the quality/speed of the last decade's advanced analog IC semi fab capabilities used in recent op amps
the internal design of op amps has advanced by a discontinuous step up from the huge investment by big companies with already deep institutional knowledge in the competition for medical imaging, telcom A/DSL markets demanding low distortion at 100 kHz thru low MHz - in circuits using global feedback

Curl's favorite examples, "proving" global feedback is "bad" use comparisons with 30 year old monolithic op amps - right up to Ron Quan's 2010 paper - he didn't even test a TL07x - he used the low power TL06x part instead in order to (be able to) measure phase modulation errors

for home audio small signal applications only phono preamps require lower noise parts than are available in monolithic op amps

Last edited by jcx; 7th January 2012 at 03:29 PM.
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Old 7th January 2012, 04:58 PM   #618
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This is unfortunate. While it is true that my 'examples' were derived from past work from as long as 35 years ago, and that Ron Quan's 'examples' were rather dated as well, it should be understood that we both test modern IC's as well. It is just that they are not such OBVIOUS 'examples' of the problems with op amp design and use. When we design, or even write a paper, often, REASONABLE WORST CASE is what we normally use, because that is what other engineers will probably try to get away with, for cost and convenience reasons, if they are not shown the problems generated by doing so.

As far as 'listening' and trying IC's, we get many of the latest products and invariably hope that we find the 'perfect' solution to our needs. Sometimes, they work well enough, like in my latest JC-3 phonostage, so that I get the 'phonostage of the year' in the Jan 1012 TAS, and I breathe a sigh of relief. Sometimes they are initially designed into my products and have to be 'ripped out' or replaced, after reviewers reject my design effort.

Yet, in both cases, it would be difficult to MEASURE the reason for the acceptance or rejection of the IC in its location, in my designs.
Therefore I hope to promote all-out efforts in audio design to show what CAN be possible, rather than just, 'good enough' and I have a customer base that supports it. Then, later, the successful approaches can be made in more 'cost effective' form for the rest of us.
It is a little like Honda making racing engines first and then putting the technology learned into a Honda Civic, for example.
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Old 7th January 2012, 08:05 PM   #619
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John, you got some props today. I stopped by about the only stereo store left within a 100 miles after getting my wallet cleaned out at the woodworking show. Anyway, this shop still has a nitty-gritty machine in the window, so that should be a hint. I said I was looking for a small integrated with remote for my guest room. He said, "well, if you need Phono, you want one designed by John Curl."

Then he went on trying to convince me tubes don't generate distortion and I needed some $5000 KT88 unit. I just smiled and nodded my head, checked on what else they carried, thanked him and went on my merry way.

My parts to refurb my DH-20 came, so off the to the workbench!
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Old 7th January 2012, 08:33 PM   #620
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I have a 'Nitty-Gritty in my closet. Never used it after 15 years. I'm lazy.
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