No. A valve amp can have sufficiently low output impedance to get good speaker damping. Not all valve amps are designed this way, though.udok said:
Feedback at 60kHz is only of interest to bats. I don't know if bats listen to music.Waly said:
Yes. Putzeys mentions a valve amp that he did as a stunt (more or less) that had lots of feedback and achieved low output Z and low distortion, and had people agreeing that it sounded fine (this in the Linear Audio "F-Word" piece). The problem was that the tube characteristics changed rapidly enough that it was difficult to maintain stability. I think Jan has posted a link to that article, for those who didn't buy the issue.
Sy
Pure utopia ,too good to be truth ,🙂
apart from Bruno`s primary nice wishes & interest even his product is not ideal to ,and can not be pure unconditionally accurate amplifier which only amplify ,but on some degree it become just another effect box ,as any other power amp is .
Sorry but that`s reality .
OK, you are not making the claim that in the 'power paradigm' there is a different meaning to output impedance than in the 'voltage paradigm'; you are merely reporting what others say, and you disagree with them as you know they are wrong?atmasphere said:
I have come across people who spent 3 years getting their degree, then 3 more years getting their PhD, then even more years before getting a tenured university post - yet still they misunderstand the science (in this case, of compact antennas and hence all antennas).
OK, you were simply reporting stuff you know is wrong in a way which seemed to dim people like me to imply that you actually agreed with it. My apologies. So you agree that there are not two paradigms, only one way to define output impedance, many ways to calculate and measure it but they must all give the same result.
I was attacking an idea, not a person. I attach even less importance to being in the business for 40 years than being a student for 4 years. Those who claim that the 'power paradigm' means that output impedance must be measured in a different way are clearly violating the laws of physics, as I am sure you will agree.
So it was all a terrible misunderstanding.
Is that so?
Is that so?
You seem to be implying that an SS Thevenin equivalent is somehow different from a tube Thevenin equivalent. This can't be what you are saying, because that might mean that you are quoting the 'power paradigm' people again (while still disagreeing with them). Just to help us all, could you use a different font when you are reporting something which other people wrongly believe so we don't get it mixed up with your own opinion?
I have no experience with Bruno's amps, so I assume that before asserting that they audibly distort their input, you have data to back up that assertion? Preferably a well controlled listening test? Or measurements showing distortion or frequency response errors above known thresholds?
The input to the second stage is either too big or not, whether or not this comes from a smaller intermediate signal or a bigger intermediate signal reduced by second stage feedback. This is because to get a particular output the second stage needs to see (open-loop) a particular input. This particular input is either too big or OK, irrespective of how it got there.bwaslo said:
Anyway, my point is that feedback is feedback is feedback. There is nothing new with global feedback. The theory is exactly the same. The thing which makies global feedback sometimes harder to apply is not that it is global, but that it is applied over so many stages - this brings stability problems. They are not 'global fb' problems but '3-stage fb' problems.
I am not attacking your intelligence but all this proves is that you are good at school.
I have seen George W Bush get awards. Wait wasn't he even the president or something?
Nicely put.
I learned this the hard way when making a valve power amplifier. It originally had 30db "global" feedback and it had stability issues. Phase shifts can cause positive feedback within the loop in turn causing instability. I learned how to compensate for these but I also lowered open loop gain and lowered the amount of feedback to 20db. They sound great now. I wouldn't want to design global feedback around an interstage transformer.
I think his argument is a bit more nuanced...He is claiming that since distortion is unavoidable, then there is a "preferred distortion pattern" or type of distortion that sounds most natural, based on research, and that amps that produce distortion products that differ from these "natural" or "more acceptable" types of distortion, sound poor in comparison to those amps which do, which he claims are mostly no GNF (because it produces spectral growth and an "unnatural to the ear" distortion pattern) and class A tubes....So he is basically saying that any amp which produces distortion different from that shown by research to be "natural" is crap.
Whoa. Stop right there. Audible distortion is unavoidable? Data to support that remarkable claim?
Here I don't agree with you Jan, as there are a lot of good recorded music, classical or jazz with good recording mike setups, quite close to live play. Not, of course, Rock concerts with powerful PA systems, and for years I don't go on that kind.
To compare to other amps is also not so good idea, if perfect amp existed it will kill all the joy of building amps, perfect company will build all perfect amps, no place for hobby there.
All audio shows I visited I was mostly disappointed, all to loud in non adequate rooms, nothing to compare with.
So I am back to square one, enjoy the live Classical or Jazz concerts and to come close to that with home amplification. I enjoy in all other kind of music (no rap please) but I have no footprint to compare.
This is my goal, and to get there technical knowledge is essential, but with my poor practical experience(I did build some amps but not so many) I just try to get the best I could from different circuitry.
Damir
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So, you just like horsing around and see where you end up, right. And I don't mean that derogatory - I've done the same. What mostly happens when you operate like that is that you turn around in circles and never get done. But it can be a lot of fun.
BTW I agree that small-venue jazz or club concerts can probably be reproduced the most realistic in a living room.
Jan
I don`t found in these NC1200 charts nothing special , which is characteristic of one ` ideal amplifier which only amplify ` , just look at first chart , top left ,small signal test , Freq.response @ 8,4 & 2 ohm .
At 10Khz Freq.Response start to fall gradually ending almost -5db @ 50Khz , than again climbing to -2db @ 70 Khz , hm .....
http://www.hypex.nl/docs/nc1200 folder web.pdf
I think that I understand where Atmasphere is coming from: In the early days, before we had lots of loop feedback in amplifiers, designers had to make do with what they had available, and I recall learning in electrical engineering about maximum transfer of power with matching. I can imagine that a 800 ohm speaker would have to work that way. OR, what was the damping factor of the hi Z speaker directly driven by vacuum tubes?
It is known that horns are much more forgiving of damping factor, because they have a separate damping mechanism, and virtually all serious early designs were horn loaded.
When the direct radiator speaker was designed by Rice and Kellog (sp) in about 1925, a LOW drive impedance became necessary to meet the conditions for a flat response, even with a widely varying load impedance. This is not an EFFICIENT power transfer, just a practical way to make a loudspeaker in a cabinet work reasonably well. We have forgotten its origin and nature over the decades.
It is known that horns are much more forgiving of damping factor, because they have a separate damping mechanism, and virtually all serious early designs were horn loaded.
When the direct radiator speaker was designed by Rice and Kellog (sp) in about 1925, a LOW drive impedance became necessary to meet the conditions for a flat response, even with a widely varying load impedance. This is not an EFFICIENT power transfer, just a practical way to make a loudspeaker in a cabinet work reasonably well. We have forgotten its origin and nature over the decades.
Guys, this has progressed into 'I said what I said and that's how it is' territory.
I read the last 7 pages or so and in fact there is truth in almost everyone's claim with exaggerations of parts where they seemingly differ. I am quite a bit surprised to read these kinds of posts from people who I carefully follow and value their opinion.
Here's an example, SY 'translating' a posd where on contributor mentions that one wants harmonic levels falling in intensity with rising order, as 'wanting harmonics'. Honestly this sort of dishonest grasping at semantics is to be expected from pulp 'journalists' where a statement is so 'simplified' that it's stripped of of it's intended meaning.
NO, no one wants harmonics, but hey, they DO happen and that's a fact. And once they do, one certainly wants a distribution that is less offensive to the ear.
Now, there can be a lot of discussion what is and is not offensive, and at what level the mere criterion of offensiveness falls short of the criterion of accuracy. Which is why accuracy has failed to be described bz a composite single figure such as THD, for instance. Once again, what is MATHEMATICALLY more linear, is not PERCIEVED as more linear - mathematical criteria did not form the human ear-brain system, evolution did.
For those who want to experiment, it's not extremely difficult to generate some common THD spectra using files converted into the frequency domain (adding frequency scaled FFT and then doing IFFT). There is a wealth of research into panic and danger perception in animals and humans which relate, such as the basic whz screaming will provoke an alertness and flight/flight effect while an equally loud tone containing little higher harmonics will not. Closer to home, why an amp with rapidly falling OLG creates 'unnatural' harmonic distribution (such as strongly suppressed low but less suppressed or even rising high order harmonics) and sounds unnatural unless all harmonics are suppresed well below the noise floor.
Also, using words such as we have that are closest but not exactly with the right meaning, such as paradigm. I think Scott got what Carsten was saying, designong loudspeakers for a perfect voltage source drive is not the only way to design them. Before work by Thiele and Small, there were a lot of ideas how to best match the amp with the speaker, and they were not voltage drive. In fact, anyone who has spent some serious time designing speakers and has designed passive crossovers, may recognise that some of that is still relevant - it is in fact rare that any driver except the woofer approaches anything close to voltage drive, and one has to adjust for that, or indeed discover that some units will not give satisfying results with higher drive impedances. While one could call today's drivers 'based on the voltage drive paradigm' I would hesitate to call ones before that 'based on a power (drive?) paradigm' and certainly do not agree it's cpnstant power as such, but approaching that in a band of sensible speaker impedances - ones that the designer has to design for, mind you.
But getting back to the actual topic.
Saying GNFB is a huge benefit for audio brings us again to the problem of simplifying a statement to the point where it looses any semblance of accuracy. This is not curch and dogma, this is engineering. NOTHING is universally good or bad, so it's actually silly to pose a statement or question essentially taking one side in something that has no sides. One could just as well have asked is the wheel a huge benefit for humanity, like everything is improved if it has wheels on.
GNFB is a huge benefit if you use it as the right tool for the right job, so it's all in the application - and I am sure all of the contributors in this thread can name instances where it wasn't well applied. It's not an universal benefit, just like there is no universal spice that makes every food even better, or an universal amplification element that automatically makes a perfect audio amplifier, for that matter.
By the same token, it is certainly not an universal evil or something that should be avoided.
Looking from a different standpoint, again, this is engineering, i.e. the art of the possible. In real life design goals are to be met at a price, and in many cases GNFB may be the only way to even get there. And, again, I am sure all here will agree, often once you have, you may already come up with a better way to do it and a doyen others were there only more time, money, or availability of a different component etc. And then, there are more and less competent designers, who are more or less competent in using the tools at their disposal, one of which is the use of GNFB. Again, many here will agree, I am sure, that given the same basic design goals and target price, different people may come up with different designs which can vary substantially in performance, one common thing being, that dogma such as NFB bad or measurement not useful, WILL fail at some point, just as any unwillingness to learn to use all the tools at ones disposal eventually will.
I read the last 7 pages or so and in fact there is truth in almost everyone's claim with exaggerations of parts where they seemingly differ. I am quite a bit surprised to read these kinds of posts from people who I carefully follow and value their opinion.
Here's an example, SY 'translating' a posd where on contributor mentions that one wants harmonic levels falling in intensity with rising order, as 'wanting harmonics'. Honestly this sort of dishonest grasping at semantics is to be expected from pulp 'journalists' where a statement is so 'simplified' that it's stripped of of it's intended meaning.
NO, no one wants harmonics, but hey, they DO happen and that's a fact. And once they do, one certainly wants a distribution that is less offensive to the ear.
Now, there can be a lot of discussion what is and is not offensive, and at what level the mere criterion of offensiveness falls short of the criterion of accuracy. Which is why accuracy has failed to be described bz a composite single figure such as THD, for instance. Once again, what is MATHEMATICALLY more linear, is not PERCIEVED as more linear - mathematical criteria did not form the human ear-brain system, evolution did.
For those who want to experiment, it's not extremely difficult to generate some common THD spectra using files converted into the frequency domain (adding frequency scaled FFT and then doing IFFT). There is a wealth of research into panic and danger perception in animals and humans which relate, such as the basic whz screaming will provoke an alertness and flight/flight effect while an equally loud tone containing little higher harmonics will not. Closer to home, why an amp with rapidly falling OLG creates 'unnatural' harmonic distribution (such as strongly suppressed low but less suppressed or even rising high order harmonics) and sounds unnatural unless all harmonics are suppresed well below the noise floor.
Also, using words such as we have that are closest but not exactly with the right meaning, such as paradigm. I think Scott got what Carsten was saying, designong loudspeakers for a perfect voltage source drive is not the only way to design them. Before work by Thiele and Small, there were a lot of ideas how to best match the amp with the speaker, and they were not voltage drive. In fact, anyone who has spent some serious time designing speakers and has designed passive crossovers, may recognise that some of that is still relevant - it is in fact rare that any driver except the woofer approaches anything close to voltage drive, and one has to adjust for that, or indeed discover that some units will not give satisfying results with higher drive impedances. While one could call today's drivers 'based on the voltage drive paradigm' I would hesitate to call ones before that 'based on a power (drive?) paradigm' and certainly do not agree it's cpnstant power as such, but approaching that in a band of sensible speaker impedances - ones that the designer has to design for, mind you.
But getting back to the actual topic.
Saying GNFB is a huge benefit for audio brings us again to the problem of simplifying a statement to the point where it looses any semblance of accuracy. This is not curch and dogma, this is engineering. NOTHING is universally good or bad, so it's actually silly to pose a statement or question essentially taking one side in something that has no sides. One could just as well have asked is the wheel a huge benefit for humanity, like everything is improved if it has wheels on.
GNFB is a huge benefit if you use it as the right tool for the right job, so it's all in the application - and I am sure all of the contributors in this thread can name instances where it wasn't well applied. It's not an universal benefit, just like there is no universal spice that makes every food even better, or an universal amplification element that automatically makes a perfect audio amplifier, for that matter.
By the same token, it is certainly not an universal evil or something that should be avoided.
Looking from a different standpoint, again, this is engineering, i.e. the art of the possible. In real life design goals are to be met at a price, and in many cases GNFB may be the only way to even get there. And, again, I am sure all here will agree, often once you have, you may already come up with a better way to do it and a doyen others were there only more time, money, or availability of a different component etc. And then, there are more and less competent designers, who are more or less competent in using the tools at their disposal, one of which is the use of GNFB. Again, many here will agree, I am sure, that given the same basic design goals and target price, different people may come up with different designs which can vary substantially in performance, one common thing being, that dogma such as NFB bad or measurement not useful, WILL fail at some point, just as any unwillingness to learn to use all the tools at ones disposal eventually will.
The idea is that you can adapt the individual distortion coefficients and hear what the effect is.
The amplifier transfer function is:
y = A1 * x + A2 * x^2 + A3 * x^3 + A4 * x^4 ...
with A1 = Gain, and A2 ... An are the higher order coefficients.
You can choose the Ai and hear the effect for your favorite song.
But meantime i have the impression that most people here are not interested in serious work but are nursing preconceptions...