This is incorrect. Wheter you use Cdom to increase the fb around the Vas transistor, or whether you use resistive Vas loading to extend the olbw, in both cases there's the same fb available to the output stage at the top of the freq range.
jan didden
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I'd heartily disagree that criticism might be merited; engineering courses at most schools tend to be products of their time. Often a tendency to teach the known, and the graduates seem a bit more rigid (encased in a wall of certitude as it were) than might be best. One reason why engineers often become obsolete so quickly.
Fif.. err, some years on, the Physics degree, a science degree, should still be useful, as it should have included the methods and philosophy of research, the tools for continued learning, scientific method, perhaps experiment design; (how do you know you know, and why does it matter?) and all that.
And the engineering degree from that long ago is apt to be long irrelevant.
I beg to differ. What you have learned about methods and philosophy of research, the tools for continued learning, scientific method, perhaps experiment design, will never become obsolete.
jan didden
@ Charles Hansen
When you're taking about amplifiers without NFB please clarify
1. wihtout overall/global NFB - from output to input
2. without local NFB - no feedback at the amplifier stage as well
Thanks
When you're taking about amplifiers without NFB please clarify
1. wihtout overall/global NFB - from output to input
2. without local NFB - no feedback at the amplifier stage as well
Thanks
...
Some sort of misunderstanding Jan, that's what I thought I was saying. I believe that we're in complete agreement.
To try to clarify, those tools are usually not included in the engineering curriculum to the same degree (if at all) as in a science degree, at least in this country. (With exceptions, Terman being perhaps most notable.)
PS. Enjoyed Volume 0; I hope there will be more.
Some sort of misunderstanding Jan, that's what I thought I was saying. I believe that we're in complete agreement.
To try to clarify, those tools are usually not included in the engineering curriculum to the same degree (if at all) as in a science degree, at least in this country. (With exceptions, Terman being perhaps most notable.)
PS. Enjoyed Volume 0; I hope there will be more.
the only downside to the left example plot are the highish levels of 5th and 7th.
I suspect that making these lower, even at the expense of raising 2nd to 4th would sound better.
Is there a way to achieve that without bringing back the >8th harmonics?
"Is there a way to achieve that without bringing back the >8th harmonics?"
Yes, there is. This is the same circuit, 25W/4ohm (as before), close to clipping. If we go down to 100mW, distortion is same, but only 2nd and 3rd.
Attachments
Video is way different - there is less margin between typical transistor ft and Video frequencies than in audio amplification - the orders of magnitude larger ratio of device bandwidth to "working bandwidth" makes feedback hugely more effective at audio frequency
analog video signals are encoding a ~3 dimensional signal (2-d visual plane position + intensity), audio is very much 1:1 Voltage to sound pressure
human optic nerve devotes >1,000,000 nerve fibers to the "information channel" - audio ~ 30,000
the above make video signal sensitivity to PIM or AM to FM conversion in video amplifier references dubiously relevant to the audio amp designer
to accept the premise that the "unknown it" in audio amplification is PIM/FM distortion we need psychoacoustic demonstrations that PIM/FM is way more objectionable than “AM” distortion – by several orders of magnitude to justify using flat feedback factor over the audio bandwidth
I unaware of any such evidence in peer reviewed audio/acoustics journals - not that I'm very well read in the latter - but you would think someone would have searched out any that exist just for these discussions
and I get the impression that some people don't appreciate the fact that PIM/FM IMD products do show up in ordinary distortion spectra - it is just that the usual amplitude only display doesn't allow separating the "AM" from the "FM" at any particular IMD product frequency - but the combined amplitude is there - "FM" distortions do not totally "escape conventional measurements" if you include multitone IMD tests
analog video signals are encoding a ~3 dimensional signal (2-d visual plane position + intensity), audio is very much 1:1 Voltage to sound pressure
human optic nerve devotes >1,000,000 nerve fibers to the "information channel" - audio ~ 30,000
the above make video signal sensitivity to PIM or AM to FM conversion in video amplifier references dubiously relevant to the audio amp designer
to accept the premise that the "unknown it" in audio amplification is PIM/FM distortion we need psychoacoustic demonstrations that PIM/FM is way more objectionable than “AM” distortion – by several orders of magnitude to justify using flat feedback factor over the audio bandwidth
I unaware of any such evidence in peer reviewed audio/acoustics journals - not that I'm very well read in the latter - but you would think someone would have searched out any that exist just for these discussions
and I get the impression that some people don't appreciate the fact that PIM/FM IMD products do show up in ordinary distortion spectra - it is just that the usual amplitude only display doesn't allow separating the "AM" from the "FM" at any particular IMD product frequency - but the combined amplitude is there - "FM" distortions do not totally "escape conventional measurements" if you include multitone IMD tests
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I think it is far more complicated than that. But, I am *hardly* an expert or even 84 dB below that.
This guy probably is:
Homepage of Greg Berns
An aside
Hi jcx,
I find what you contribute to be good, however, the statement:
needs further clarification. If we are speaking of the sound pressure in a listening environment as it relates to the electrical drive signal at the transducer, the actual instantaneous sound pressure is more directly related to the instantaneous delta(I) / delta(T) in the loudspeaker itself. The relationship between the drive voltage and actual SPL is extremely complicated and different from speaker to speaker.
I immersed myself in this issue when designing current-mode active speaker systems in the early 90's. IMHO properly designed current-mode speaker systems are the most significant improvement I have experienced in sound reproduction (no offense intended to the fantastic equipment designed by some people in this thread). To implement current-mode speaker drive correctly requires a complete redesign and integration of both the amplifier and speaker, and cannot be implemented as individual components as some have tried, with unsatisfactory results. My own designs were implemented by several mobile amplifier manufacturers with limited success due to this requirement and the variable loading presented by the mobile speaker environment.
If any of you are interested in this subject further, Esa Meriläinen has recently written a book which for me substantiated and greatly expands upon my experience of years ago, and explains it in much more precise terms than I could:
Current-Driving of Loudspeakers
Other than the problems caused by high damping factors common in voltage-mode amplifier/speaker drive (high circulating back-EMF) and it's relationship to amplifier feedback, this is probably a subject for a different thread. I return you to the Blowtorch thread, and feedback wars, currently in progress...😉
Howard Hoyt
(where is that 'throwing gasoline on the fire' emoticon when you need it?)
Hi jcx,
I find what you contribute to be good, however, the statement:
needs further clarification. If we are speaking of the sound pressure in a listening environment as it relates to the electrical drive signal at the transducer, the actual instantaneous sound pressure is more directly related to the instantaneous delta(I) / delta(T) in the loudspeaker itself. The relationship between the drive voltage and actual SPL is extremely complicated and different from speaker to speaker.
I immersed myself in this issue when designing current-mode active speaker systems in the early 90's. IMHO properly designed current-mode speaker systems are the most significant improvement I have experienced in sound reproduction (no offense intended to the fantastic equipment designed by some people in this thread). To implement current-mode speaker drive correctly requires a complete redesign and integration of both the amplifier and speaker, and cannot be implemented as individual components as some have tried, with unsatisfactory results. My own designs were implemented by several mobile amplifier manufacturers with limited success due to this requirement and the variable loading presented by the mobile speaker environment.
If any of you are interested in this subject further, Esa Meriläinen has recently written a book which for me substantiated and greatly expands upon my experience of years ago, and explains it in much more precise terms than I could:
Current-Driving of Loudspeakers
Other than the problems caused by high damping factors common in voltage-mode amplifier/speaker drive (high circulating back-EMF) and it's relationship to amplifier feedback, this is probably a subject for a different thread. I return you to the Blowtorch thread, and feedback wars, currently in progress...😉
Howard Hoyt
(where is that 'throwing gasoline on the fire' emoticon when you need it?)
I did get a ride in his Lexus. Barrie loves opera and he knows what live music sounds like especially vocals.
jcx - I had to laugh about your Bruno comments. Barrie told me he honestly had no preference between our class D demo card and his "Classe" class A power amp until you clipped it.
Well, at least some interesting input on AM-PM conversion.
I would also like to state that I never design with distortion being a good ingredient in the mix. I ALWAYS design for lowest distortion, ESPECIALLY lowest HIGHER ORDER ODD distortion.
It was found, even before I was born, that people could live with significant amounts of lower order distortion and hardly, or not really notice it. This is 2nd, 3rd, and maybe 4th. 5'th is iffy, and 7th is 'death and destruction'. Just go back to the 1941 'Radiotron Designers Handbook' or some later copy and read it, yourself.
Audio component 'clarity' does not magically increase with significantly lower and lower measured static distortion. I have found this, myself, when comparing IC op amps with discrete op amps with lower feedback. It would be so easy if if did. However, we are looking for MORE than just lower IM or THD. We are looking for other subtle changes that the ear might key into, perhaps as a long forgotten survival tool. AM-PM might well be one of those important factors. Works for me, in practice, now maybe we can learn why it appears to be important.
I would also like to state that I never design with distortion being a good ingredient in the mix. I ALWAYS design for lowest distortion, ESPECIALLY lowest HIGHER ORDER ODD distortion.
It was found, even before I was born, that people could live with significant amounts of lower order distortion and hardly, or not really notice it. This is 2nd, 3rd, and maybe 4th. 5'th is iffy, and 7th is 'death and destruction'. Just go back to the 1941 'Radiotron Designers Handbook' or some later copy and read it, yourself.
Audio component 'clarity' does not magically increase with significantly lower and lower measured static distortion. I have found this, myself, when comparing IC op amps with discrete op amps with lower feedback. It would be so easy if if did. However, we are looking for MORE than just lower IM or THD. We are looking for other subtle changes that the ear might key into, perhaps as a long forgotten survival tool. AM-PM might well be one of those important factors. Works for me, in practice, now maybe we can learn why it appears to be important.
It seems to me that the main claim of interest here is not the fact that GNFB makes an amp worse. The main claim seems to be: "an amp with no GNFB will sound better than another with (high) GNFB even though they measure the same".
By "measure the same" it is usually meant that they have the same THD.
Personally I think it's an interesting idea which should be investigated scientifically.
In order for the claim above to be credible scientifically someone needs to give compelling arguments that support it, or, lacking that, someone needs to prove it by blind listening tests.
If no technical arguments are given and no experimental evidence is provided (by blind listening tests) then for a scientifically oriented person the claim is only an unverified hypothesis and cannot be considered "true".
I'm not trying to offend anyone by saying this. On the contrary, I'm eager to learn from the more experienced people that contribute here.
So my question is: what are the mechanisms that could explain the unsatisfying (to some) sound of the GNFB amps ? People have mentioned limited OLBW, intermodulation distortions, maybe even input-output delay.
A companion question is: what blind listening tests have shown conclusively that people can distinguish between highly performing (or "blameless") amps with high/no GNFB ?
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