The thing is there is proof, just ask Bob Cordell which is a member here, he has a paper on the exact topic, prove him wrong. Scott Wurcer is here too, ask his opnion
On the other hand you only got incorrect info from 35 years back, no one ever wrote anything besides and after it because they know they are wrong.
The only people you find agreeing to it are owners of some hifi companies and there designers, they have to have some selling point but not all are fooled.
You got to have your facts straight, youre even wrong about the XX and its suposed mythical properties. No myth for those in the art of electronics.
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No, a few people here are more than enough for me.
I NEVER stated anywhere that Otala was right and everybody else was wrong; I stated that I think Otala was right, you people pushed in the rest.
Consequently, your first sentence is meaningless because it's untrue. My beliefs are just that, mine alone, no general truth and certainly nothing carved in stone from Mount Sinai. Nevertheless, it's odd that they have functioned so well for over 20 years, given how wrong you seem to think they are (just a musing).
I never play the blame game. And I don't really trust any reasoning until it is proved in a live model on my test bench. I can still reliably judge what I can do and what I cannot, so some convoluted designs are a moot point with me, I have neither the time or money to play around with them for the hell of it.
I have said so before, and I repeat - over the years, I have heard some amps from both camps, so to speak. There were some good and bad ones from both camps. The low global NFB camp seemed to produce more good ones, and in terms of absolute number, they simply seemed to statistically show that they have a better chance of sounding good TO ME (<-N.B. me, not everybody).
My personal collection of amps (I kind of collect them) contains 3 amps with low global NFB and 3 amps with a high global NFB. I like them both, but I repeat, all my own designs (not counted in my collection) use around 20 dB of global NFB. Of note is only that the 3 low NFB types are all by Harman/Kardon, using 20, 17 and 12 dB of global NFB respectively. They are all the grandsons of the work Otala did at H/K in the late 70ies.
So telling me Otala was all wrong is truly wasting your time. Deeds speak louder than words.
"The F-word - or, why there is no such thing as too much feedback"
That should rebut Matti sufficiently.
jan
That should rebut Matti sufficiently.
jan
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We almost agree on something for once.
The issue has nothing to do with being technically correct per se, it's about highlighting this signal-masking issue in general and the consequences of this sluggishness, and derogatory affects on the audio signal (or any other signal) etc.
Various designers of op amps and discrete circuitry then subsequently went on to do measurements on the slew rate of Vinyl and so forth. Others come to the view that a 10:1 margin in power amps is adequate.
He definately influenced this, and is probably the most important mind/influence in power amp design in the last 30-40 years.....
Cordells THD20k/IMD/phase measurements and the slew rate wars anyone ?
Mikeks, please wake up will you pal...
Prof Otala etc
Gentlemen,
Is there any point discussing Prof Otala's theories?
At my first AES conference, Hamburg 81, one of his students did an excellent paper which showed conclusively the zillion V/us slews Matti postulated simply NEVER occurred (even with MC cartridges & mistracking).
JC was pontificating on zillion V/us slew on another thread and posted as 'proof', a letter he'd sent to one of the HiFi comics. It's a pity he didn't actually read his own letter first cos it only confirmed Kogan et al of Shure's seminal paper on recorded & playback levels.
More personally, I tried to drink Matti under the table, a foolish endeavour for a young Chinaman Just before we both slid to the floor, he blearily confided to me that the next big thing in amps would be PIM.
And like Doug, I also have experience of his JAES design. It was awful. In particular, it was unstable on certain speakers on certain (music) signals .. all dependent on the overload, signal & thermal history. Bob mentions this can happen on certain amps and I can confirm many (most?) High End amps do this.
______________
But I really wanted to say something about Geoffrey Horn who I'm sad to hear passed on while I was in the bush.
He's one of the best ears I've put through a Double Blind Listening Test. For others, buy John Atkinson (no slouch himself in a Blind Listening Test) several drinks and ask him for his opinion of the ears of the old guard like Horn & John Borwick.
Nearly 2 decades of doing Blind Listening Tests suggests that present day High End reviewers (with notable exceptions like JA) do considerably worse than the man (or especially the woman) in the street.
But dem oldies weren't deaf They were gentlemen and not prone to dissing others in public. But its remarkable what a pint o two of Tetley's biitter will reveal.
_______________
Now can we go back and discuss something REALLY useful like why VAS should be called TIS?
[deleted: my slim 150 pg monograph on the subject]
Gentlemen,
Is there any point discussing Prof Otala's theories?
At my first AES conference, Hamburg 81, one of his students did an excellent paper which showed conclusively the zillion V/us slews Matti postulated simply NEVER occurred (even with MC cartridges & mistracking).
JC was pontificating on zillion V/us slew on another thread and posted as 'proof', a letter he'd sent to one of the HiFi comics. It's a pity he didn't actually read his own letter first cos it only confirmed Kogan et al of Shure's seminal paper on recorded & playback levels.
More personally, I tried to drink Matti under the table, a foolish endeavour for a young Chinaman
Just before we both slid to the floor, he blearily confided to me that the next big thing in amps would be PIM.And like Doug, I also have experience of his JAES design. It was awful. In particular, it was unstable on certain speakers on certain (music) signals .. all dependent on the overload, signal & thermal history. Bob mentions this can happen on certain amps and I can confirm many (most?) High End amps do this.
______________
But I really wanted to say something about Geoffrey Horn who I'm sad to hear passed on while I was in the bush.
He's one of the best ears I've put through a Double Blind Listening Test. For others, buy John Atkinson (no slouch himself in a Blind Listening Test) several drinks and ask him for his opinion of the ears of the old guard like Horn & John Borwick.
Nearly 2 decades of doing Blind Listening Tests suggests that present day High End reviewers (with notable exceptions like JA) do considerably worse than the man (or especially the woman) in the street.
But dem oldies weren't deaf They were gentlemen and not prone to dissing others in public. But its remarkable what a pint o two of Tetley's biitter will reveal.
_______________
Now can we go back and discuss something REALLY useful like why VAS should be called TIS?
[deleted: my slim 150 pg monograph on the subject]
Michael K's designs
Mr. Didden, I'm pleased to see you here.
May we ask a favour? Would you allow Michael Kiwanuka to post the complete circuit and .ASC of his working 'real life' high performance amp that I believe you intend to publish in Linear Audio.
That would silence some of his critics but more importantly, whet our appetites for the next issue of your excellent publication.
_________________
Mr. Wurcer, I'm not sure the requirement for Power Bandwidth exceeding audio freqs. ie low distortion full power @ 40kHz which I believe is what you like ...
.. is the same as Otala's contention that Open Loop bandwidth should exceed 20kHz.
Excuse my lack of faciltity with English as she is spoken.
Mr. Didden, I'm pleased to see you here.
May we ask a favour? Would you allow Michael Kiwanuka to post the complete circuit and .ASC of his working 'real life' high performance amp that I believe you intend to publish in Linear Audio.
That would silence some of his critics but more importantly, whet our appetites for the next issue of your excellent publication.
_________________
Mr. Wurcer, I'm not sure the requirement for Power Bandwidth exceeding audio freqs. ie low distortion full power @ 40kHz which I believe is what you like ...
.. is the same as Otala's contention that Open Loop bandwidth should exceed 20kHz.
Excuse my lack of faciltity with English as she is spoken.
Nowadays, all Airbus pilots are trained on a flight simulator. The Air France pilots are the worst, they even haven't learned how to recover from a stall. So, maybe your sun is even a better pilot than his French 'colleagues'.
Cheers, E.
Hi Edmond,
Although I am not a conspiracy theory kind of guy, I do not believe that AF 447 went down because of pilot error.
Neither did AA 589. We know that AA 589 went down because its vertical stabilizer fell off, and they blamed the pilots for steering too agressively in the wake of a 747. I believe it likely that AF447 lost its vertical stabilizer due to stress in the strom and autopilot rudder corrections for yaw (it was recovered in one piece miles away from the wreckage - yes I know about ocean currents).
Three pilots on AF 447 had 38,000 feet and 4 minutes to figure out how to right a plane at a lower altitude where the flight envelope is as big as a barn door. All three would have had to be extremely bad. If not lacking a vertical stabilizer, I suspect there was something that made the plane essentially un-flyable, quite possibly software off in the grass in the avionics.
As a retired Continental pilot friend of mine used to say, "if its not Boeing, I'm not going". Of course, I know that this rant of mine is not making me any friends in the EU
.Cheers,
Bob
Matti Otala did some things right, and amplifier designers learned a lot from having to work hard to rebut the theories about negative feedback and open loop bandwidth that were wrong. I think he ended up misleading a whole generation of audio engineers about negative feedback.
This is NOT to say that power amplifiers without negative feedback are bad. My friend Charles Hansen at Ayre make superb amplifiers that do not use negative feedback.
A remnant of the TIM fray can be found here CordellAudio.com - Another View of TIM.
Cheers,
Bob
This is NOT to say that power amplifiers without negative feedback are bad. My friend Charles Hansen at Ayre make superb amplifiers that do not use negative feedback.
A remnant of the TIM fray can be found here CordellAudio.com - Another View of TIM.
Cheers,
Bob
Where did you get the idea that I intend to publish in the undoubtedly excellent Linear Audio?
Where did you get the idea that I intend to publish in the undoubtedly excellent Linear Audio?
Indeed, we have no such agreement - or even discussion - at all. Not that I wouldn't entertain the thought
jan
_________________
Mr. Wurcer, I'm not sure the requirement for Power Bandwidth exceeding audio freqs. ie low distortion full power @ 40kHz which I believe is what you like ...
.. is the same as Otala's contention that Open Loop bandwidth should exceed 20kHz.
Excuse my lack of faciltity with English as she is spoken.
No, I refer to the obvious bare minimum slew rate requirement for an undistorted sine wave even for an amplifier with a perfectly linear gm at the input. There is no logic that leads from there to the open loop BW requirement. My main complaint remains, they restated and renamed known effects as something new and threw in a little obfuscation for good measure. The fact that some folks still think the unlabeled spurs on that graph are some yet unknown effect causing non-harmonically related frequencies shows just how confused they are.
/OT Flight AF 447
Hi Bob,
Indeed, it was flight AF 447 which I had in mind when I was fulminating on the training of French pilots.
I think it's unlikely that (in this case) failure/lost of the vertical stabilizer was the cause of the accident. Besides, this rudder controls the direction (left/right), thus not the height of the plane (as for the latter, the elevator, together with the amount of thrust, are used for this). Anyhow, please read this story and it becomes clear what has happened. In the meantime the procedures for how to recover from a stall has been changed. I've discussed this accident with several friends (who are pilots) and they not only blame faulty input from the instrument and software, but also the crew who, contrarily to old school pilots, can't handle such nasty situation any longer. The only thing they have learned today is how to push buttons (their words, not mine).
Cheers, E.
PS1: Did you have received my email about DTMC? edit: yes.
PS2: Last week, one of my flights back to Holland was in a Airbus. As you can see, I'm still alive.
PS3: Sorry guys for being so off-topic.
Hi Edmond,
Although I am not a conspiracy theory kind of guy, I do not believe that AF 447 went down because of pilot error.
Neither did AA 589. We know that AA 589 went down because its vertical stabilizer fell off, and they blamed the pilots for steering too agressively in the wake of a 747. I believe it likely that AF447 lost its vertical stabilizer due to stress in the strom and autopilot rudder corrections for yaw (it was recovered in one piece miles away from the wreckage - yes I know about ocean currents).
Three pilots on AF 447 had 38,000 feet and 4 minutes to figure out how to right a plane at a lower altitude where the flight envelope is as big as a barn door. All three would have had to be extremely bad. If not lacking a vertical stabilizer, I suspect there was something that made the plane essentially un-flyable, quite possibly software off in the grass in the avionics.
As a retired Continental pilot friend of mine used to say, "if its not Boeing, I'm not going". Of course, I know that this rant of mine is not making me any friends in the EU
Cheers,
Bob
Hi Bob,
Indeed, it was flight AF 447 which I had in mind when I was fulminating on the training of French pilots.
I think it's unlikely that (in this case) failure/lost of the vertical stabilizer was the cause of the accident. Besides, this rudder controls the direction (left/right), thus not the height of the plane (as for the latter, the elevator, together with the amount of thrust, are used for this). Anyhow, please read this story and it becomes clear what has happened. In the meantime the procedures for how to recover from a stall has been changed. I've discussed this accident with several friends (who are pilots) and they not only blame faulty input from the instrument and software, but also the crew who, contrarily to old school pilots, can't handle such nasty situation any longer. The only thing they have learned today is how to push buttons (their words, not mine).
Cheers, E.
PS1: Did you have received my email about DTMC? edit: yes.
PS2: Last week, one of my flights back to Holland was in a Airbus. As you can see, I'm still alive.
PS3: Sorry guys for being so off-topic.
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@ jan.didden
Thanks for this
http://www.linearaudio.net/images/onlinearticlesPDF/volume1bp.pdf
*
Slew Rate, or Slow Rate
I mentioned in another thread, that a wise man once told me that .5Vus per 1V out was optimum !
Funny thing though, consider ALL those kW power amps on the "Pro" market powering 100,000's of clubs around the world, & 1000's of concerts each year, that do NOT have high SR's. In spite of that, some high quality sounds are to be heard & enjoyed ! Naturally i'm taking into account that the rest of the gear is very good, which isn't always the case, so they are excluded.
Thanks for this
http://www.linearaudio.net/images/onlinearticlesPDF/volume1bp.pdf
*
Slew Rate, or Slow Rate
I mentioned in another thread, that a wise man once told me that .5Vus per 1V out was optimum !
Funny thing though, consider ALL those kW power amps on the "Pro" market powering 100,000's of clubs around the world, & 1000's of concerts each year, that do NOT have high SR's. In spite of that, some high quality sounds are to be heard & enjoyed ! Naturally i'm taking into account that the rest of the gear is very good, which isn't always the case, so they are excluded.
Michael K's designs
What august journal is this design going to appear in? We might be able to get a similar dispensation from the editor. I'm sure many of us here would like a glimpse of your working 'real life' amplifier with good performance ... even in .ASC form.
It would certainly generate interest & possibly sales.
My apologies Mr. Kiwanuka ... & Mr. Didden. Please excuse any misunderstanding due to my lack of facility with English as she is spokenWhere did you get the idea that I intend to publish in the undoubtedly excellent Linear Audio?
What august journal is this design going to appear in? We might be able to get a similar dispensation from the editor. I'm sure many of us here would like a glimpse of your working 'real life' amplifier with good performance ... even in .ASC form.
It would certainly generate interest & possibly sales.
I've personally found that there is not a need to have amplifers that do excellently in the conventional measuring sense to get worthwhile sound; my experiments in prodding "junk" electronics to do better than most people would expect of them indicates there are more significant issues than getting the last ounce of performance from design topologies, in order to produce sound which does the right thing in key areas ...
???
Please, consider feedback as a servo. There is two things that makes a servo machine able to mirror a movement: linearity and speed.
Speed limitation introduce a variable delay = distortion. And i see no way we can fix a speed limit, it is asymptotic. faster is better.
The rule is quite simple: the input signal has to be limited to never excess the slewrate of the amplifier.
In the old analog time, slew-rate and bandwidth where correlated. It is not necessary true with digital, where you can see terrific slew rates despite bandwidth is limited to 20Khz.
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