john curl said:
Hi John,
Why don't you then elaborate on the point, rather than just throwing out generalizations.
Why would not such a terrible mess of behavior as described by Franklin not be easily measurable?
Is it the point that Scott Franklin's language is just a great over-exaggeration of what he is trying to describe?
Thanks,
Bob
SY said:
Very good point, SY. Sorry I missed that. The substance still strikes me as gobbledy-gook.
I guess the "subtlety" that JC asserts I don't get is the old argument by Otala et al that NFB causes or exacerbates Interface Intermodulation Distortion. That is an eminently measurable phenomenon. It was also long ago shown that NFB did not cause or exacerbate IIM.
Otala's work on IIM was not without value. It helped put the spotlight on the need for high-current output capability in power amplifiers. This is analogous to his flawed TIM work; it was not without value - it put the spotlight on the need for high slew rate and very good high-frequency nonlinearity.
Cheers,
Bob
I thought the Scott Frankland interview was pretty good. It seemed at first that he was going to launch into a set of Cheever-like claims, but that didn't happen. I got the impression that most of what he said that might seem dubious to engineers was just his way of getting the point across to the lay person. He mentions that high feedback is good, provided the open-loop amplifier is sufficiently linear, but also recognizes that high feedback isn't really feasible in tube power amps. He made the distinction that in the THD wars of the 1970s, only THD at 1 kHz was normally mentioned. That's a key element in an argument that comes up pretty often, and I'm glad he mentioned it. I didn't see anything controversial in the interview at all.
It seems that KBK's post really had little or noting to do with what Scott Frankland was saying in the interview, but I do appreciate the pointer to the interview nonetheless.
It seems that KBK's post really had little or noting to do with what Scott Frankland was saying in the interview, but I do appreciate the pointer to the interview nonetheless.
andy_c said:
Hi Andy,
Thanks for pointing this out. I'll go read the interview itself.
You are so very right about THD-1 being abused and giving THD measurement in general an undeserved bad rap. It's not the be-all and end-all, but THD-20 is quite useful, for example (especially when the content of the distortion spectra is looked at).
Thanks,
Bob
PH104 said:
Yes, the M39003 is the MIL spec number, and the "09" is the so-called "slash sheet" number. So these would be M39003/09. The remainder of the part number is the so-called "dash number" Here is the Vishay data sheet PDF.
For example, in Joshua's first link, the part number would be M39003/09-0085J. So it's solid tantalum, 50V, 22uF (by doing a search of "0085" in the Vishay data sheet above.
Poor Dr. Otala, he could never get anything right, that is why Bob took over back in 1980, in order to straighten the rest of us out. Well, we published our response to Bob in a 15 page rebuttal, signed by Dr. Otala, Dr. Marshal Leach, Walt Jung and me, in order to get him to see things our way a bit more. I guess that he hasn't learned much from us at this point.
For the record, Bob Cordell has systematically attacked Dr. Otala and his work on TIM, PIM and IIM, and has tried to make it his own. We don't appreciate that.
For the record, Bob Cordell has systematically attacked Dr. Otala and his work on TIM, PIM and IIM, and has tried to make it his own. We don't appreciate that.
andy_c said:
True enough. I only read the first half before I posted. I just finished reading the rest.
When only the transient is required to come through cleanly than feedback is 'chasing the unreachable dragon's tail', with little real workable effect that the ear can use--beyond a measurement bench.
Rather simplistically overstated, but I'm trying to get that point across. If I understate it, no-one notes it or makes the effort. Sometimes it's best to use a gaudy baseball bat to get the point across. Depends, as usual.
My post has to do with how chasing around the completely un-complimentary resonant/elastic motor that a loudspeaker driver -IS-....will naturally drive a high NFB amplifier totally nuts, and yes, I hear it every time I listen to one on a loudspeaker system. I recognize the component of colouration that it brings to the sonics-for what it is. Turn the volume up an hair and the natural dynamic envelope is blown to bits and false detail is dropped in - instead of the actual detail. Micro-detail is destroyed by the corrective signal and the stressing of the overall system,and the more gross high delta components are exaggerated via the point of their temporal (in-time placement, ie, slewed) separation from the bulk of the given harmonic structure. (This last sentence...this is how the ear hears it. A critical point!!! Don't ever forget it. Not for one second!!!)
Negative feedback is a nice engineering bit of handjob-glad handing and it can make for happy engineers with note in their lab books that have lots of zeros in the distortion measurements but it is not always useful for making a real sounding amplifier, IMO. As I said, overstated, but getting folks attention sometimes requires clubbing them.
If you don't actually look at the harmonic transient structure as peaks, and as an isolated component (ie, 100% of the signal intelligence) and then compare that to the bulk of the signal with respects it's internal components appearing in time and value....correctly..and then that as connected to the rest of the bulk of the signal, once again as a compared group in value and in time..you are not going to make the connection.
I'd gather that any engineer here who knows his way around an amplifier does not really need to do the measurement- he knows this point is absolutely screwy.
If you don not understand what I said, I do apologize, but you should also consider enlarging you mind and vocabulary instead of harping on me. I do keep trying, and this isn't the first time. The problem is..that it is clear enough, if you already know what I mean!
I'll try again:
What component of the signal out of the DUT represents the distortion? It may be less than 0.01% of the total as measured on the bench. But what is the part of the signal itself...that is distorting?
That is the part you have to fix. The rest if it is nearly immaterial and not relevant to the ear. A slight exaggeration-but not by much. For those who go strictly by the numbers, this can open a real can of worms for their intellect to chew on, but if they actually want to make better sounding amplifiers, this is one of those key points.
KBK said:
True enough. I only read the first half before I posted. I just finished reading the rest.
When only the transient is required to come through cleanly than feedback is 'chasing the unreachable dragon's tail', with little real workable effect that the ear can use--beyond a measurement bench.
Rather simplistically overstated, but I'm trying to get that point across. If I understate it, no-one notes it or makes the effort. Sometimes it's best to use a gaudy baseball bat to get the point across. Depends, as usual.
My post has to do with how chasing around the completely un-complimentary resonant/elastic motor that a loudspeaker driver -IS-....will naturally drive a high NFB amplifier totally nuts, and yes, I hear it every time I listen to one on a loudspeaker system. I recognize the component of colouration that it brings to the sonics-for what it is. Turn the volume up an hair and the natural dynamic envelope is blown to bits and false detail is dropped in - instead of the actual detail. Micro-detail is destroyed by the corrective signal and the stressing of the overall system,and the more gross high delta components are exaggerated via the point of their temporal (in-time placement, ie, slewed) separation from the bulk of the given harmonic structure. (This last sentence...this is how the ear hears it. A critical point!!! Don't ever forget it. Not for one second!!!)
Negative feedback is a nice engineering bit of handjob-glad handing and it can make for happy engineers with note in their lab books that have lots of zeros in the distortion measurements but it is not always useful for making a real sounding amplifier, IMO. As I said, overstated, but getting folks attention sometimes requires clubbing them.
If you don't actually look at the harmonic transient structure as peaks, and as an isolated component (ie, 100% of the signal intelligence) and then compare that to the bulk of the signal with respects it's internal components appearing in time and value....correctly..and then that as connected to the rest of the bulk of the signal, once again as a compared group in value and in time..you are not going to make the connection.
I'd gather that any engineer here who knows his way around an amplifier does not really need to do the measurement- he knows this point is absolutely screwy.
If you don not understand what I said, I do apologize, but you should also consider enlarging you mind and vocabulary instead of harping on me. I do keep trying, and this isn't the first time. The problem is..that it is clear enough, if you already know what I mean!
I'll try again:
What component of the signal out of the DUT represents the distortion? It may be less than 0.01% of the total as measured on the bench. But what is the part of the signal itself...that is distorting?
That is the part you have to fix. The rest if it is nearly immaterial and not relevant to the ear. A slight exaggeration-but not by much. For those who go strictly by the numbers, this can open a real can of worms for their intellect to chew on, but if they actually want to make better sounding amplifiers, this is one of those key points.
Thank you – this is most instructive.
Also – many thanks to all who commented about the capacitors I linked.
john curl said:
John,
This is complete baloney.
First of all, awhile back, your "rebuttal" and my response to it were made available to anyone who wanted them. and your "rebuttal" was shown for what it was and was not. You should not keep bringing that up, because it is an embarrassment to you. This is such a broken record from one who is obviously living in the past.
I will be happy to provide both letters to anyone who wants to evaluate it for themselves. Maybe I should just post it right here.
As I have said time and again, Otala got a number of things right, for which I have given him credit. Indeed, he was kind enough to invent objective tests for TIM, IIM and PIM. It was those very tests which I carried out on real amplifiers that showed that his assertions about the role of negative feedback in these distortions was wrong.
You yourself subsequently admitted that Otala was stubborn.
I did not try to "take over" anything. I was certainly not alone in legitimate criticisms of Otala's work. Many other highly regarded audio people weighed in, including Dr. Cherry and Rich Cabot (founder of Audio Precision).
This whole thing got started with a simple article I wrote in Audio, originally entitled "Understanding TIM" and unfortuantely later changed by the editor to "Another View of TIM". Anyone who wants to can read the very reasonable explanations I gave in that article on my web site at www.cordellaudio.com.
You should be cautious about using "we" too much in what you assert to be the present tense. You are the only one of that group still carrying the torch for that flawed work. I'm sure Marshall and Walt cringe whenever you mention their name in this context. They've moved on, you have not.
Why don't you just say "I don't appreciate it", then everyone will not be misled.
Cheers,
Bob
john curl said:Please be careful with what you post, KBK. I don't like cleaning up afterward.
OK. Sorry John.
The dead giveaway is in that when the clock in CD player has reduced Jitter, the bass and drums are noted as being more 'solid'. This is due to the fact that the drums have the biggest bandwidth (lower treble to subsonic in the one note) and all components of the note structure MUST be correctly placed and valued in the temporal domain as a whole group for it to sound more 'correct' to the ear.
High feedback generally makes people think that the amplifer has more solid bass, or more bass 'air' and bass 'definition'.
No.
It's high feedback exacerbating the tiny transient components and slewing them out of sync with the rest of the complex note structure, making them appear more distinct to the ear.
False detail.
andy_c said:
I've collected several hundred editions of old Austrailan publications ETI, EA and AEM, chock full of audio reviews. Full power THD at 1kHz and 6.3kHz (but never any higher) seems to have been some kind of established standard, mandatory measurement.
Where did 6.3kHz come from?
Cheers,
Glen
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