Yes, Bob, as far as MY circuits go, that are NOT class A. Still, with preamps, I have found that no Global feedback is best. That might hold for power amps, but I personally have taken a commercial design far enough to make a successful power amp completely open loop. Charles Hansen HAS done so, and he has a Class A rating, just like me, AND one former JC-1 customer turned in his super JC-1's (Bob Crump's personal amps) for the new AYRE power amp. This tells me that I have to try a zero feedback, just to be sure.
No, I will NOT be boxed into a compromised or conflicted position on this, by anyone.
No, I will NOT be boxed into a compromised or conflicted position on this, by anyone.
Matti Otala continued to maintain that a 20KHz open loop bandwidth was a very good thing. I think that it is PIM distortion reduction that is intrinsic with high open loop bandwidth, all else being equal, is the reason. Where have you been? Has this not been put forth at least 100 times?
janneman said:
Jan, let me cite myself:
Wavebourn said:
It does not matter which stage is slower, but pushed out-of-limits will be the stage that precedes the slowest one. If it is an input stage, it will be the weakest chain, especially when points for closing the loop and for the input signal are different. In such case if an input signal is not over a slew rate yet, clipping would definitely make that speed causing still the same effect. So, an inverting connection, where an input signal goes to the point inside of the feedback loop, is the way to eliminate distortions caused by limited slew rate, but in case when the 1'st stage is the weakest point in chain, especially if to use "standard" for today Miller compensation in the 2'nd stage.
But no matter how you try, you can't avoid increase of distortions caused by slew rate limit absolutely, since for the stability you need to have stages with different frequency characteristic. That means, if to go round following feedback path you will always find the weakest part of the chain: the stage that precedes the slowest one.
What is possible, to shift poles way above frequency band, and use input filter to avoid overdrive by errors.
homemodder,
I hold to the principle of keeping the number of stages at a minimum, especially when GNF is present, where the "problems" escalate explosively with the number of stages,
I hold to the principle of keeping the number of stages at a minimum, especially when GNF is present, where the "problems" escalate explosively with the number of stages,
What we are working on, at this time. is bandwidth differences vs PIM. Bob didn't find much, but we are still hopeful. I don't understand why I have to answer the same questions and challenges, over and over. Let's close up a little and not ask the same question, over and over.
WHAT IS IMPORTANT. Matti Otala continued to maintain that 'slew rate' was not the only factor in why amps sound different. He maintained that the high open loop bandwidth was still important, EVEN THOUGH WE COULD NOT UNDERSTAND WHY, AT FIRST!
This is his legacy, I would have given up. PIM is the key, at least the first key to open the next lock in optimum audio reproduction. This I believe, and sooner or later it will become obvious to each and every one of you. This I predict from listening, not measurement.
This is his legacy, I would have given up. PIM is the key, at least the first key to open the next lock in optimum audio reproduction. This I believe, and sooner or later it will become obvious to each and every one of you. This I predict from listening, not measurement.
john curl said:
Perhaps because Otala and yourself were flat wrong then and today as well? I think Bob and others proved this beyond any doubt.
If there is any kind of (or way to) proof that you would accept in this particular matter, name it, I'll try to provide it. So far, you got everything from phenomenologic descriptions (Bob, Jan) to advanced math (Andy) to measurements (Bob), to simulations (Bob, jcx and others).
Ovidiu,
Jan wrote: Well, if you look around you with your eyes open for more than a few seconds it becomes abundantly clear that reality and nature is a lot of things, but not black and white.
Jan wrote: Well, if you look around you with your eyes open for more than a few seconds it becomes abundantly clear that reality and nature is a lot of things, but not black and white.
dimitri said:
Dimitri,
Have you mentioned the same quote to your friend?
Otherwise, speaking about black and white, I would appreciate a qualified opinion from your team about where and how were Otala and John Curl incorrect in this matter.
Nobody is denying Otala's contribution to the PIM theory and practice. What is under fire is the NFB correlation with PIM (and many other three letters acronyms).
I don't understand what are you asking for; I can probably discuss where and how did Otala and John Curl overestimate smth...
dimitri said:
I think you understand perfectly. But you must have very strong reasons to defend the undefendable.
Otherwise I agree that this discussion goes nowhere, therefore I'm over and out, unless:
Jan,
I doubt such a rapid course of events can be measured reliably
I'm sorry to inform you that low open-loop gain and wide bandwidth are unconditionally essential to lower dynamic (and other) distortions. Inaccuracy in time and transients cause GNF to passingly (but frequently) lose control over the close-loop gain and the output signal.
I doubt such a rapid course of events can be measured reliably
Maybe we should do that on a beautiful day.
Look, I`m not asking you (or anyone else) to agree with me, just to understand what I`m trying to say. I stated quite recently that the need for GNF depends on the open-loop characteristic, which is decisive for the perceived sound. If the sound does not live up to expectations, a suitable amount of GNF will make it less unbearable, otherwise it would be unfortunate to apply GNF.
john curl said:
Come on John, are you saying that listening to amps tells you PIM is an issue??
I really don't understand your stance on this. Several people have made a quite good case with math, reasoning, measurements, that PIM is no longer an issue. You yourself have never even measured it. You have not been able to even make a small dent in the offered evidence. There's nothing to support your position other than what Matti said 40 years ago and that since has been shown to be not quite as he said.
Is it so difficult to embrace new information and learn something new once in a while?
Earlier you complained that you have to 'explain this 100 times'. Well, if you bring this up again and again, people will refute it again and again. If you want to break that cycle, either come with new evidence or don't bring it up.
It's really easy.
Jan Didden
Lumba Ogir said:
I'm sorry to inform you that this is not true for a competently designed amp. And of course, these are the only ones we consider!
Lumba Ogir said:
Sounds like a good idea!😉
Jan Didden