Nelson Pass said:The analysis to which you refer is without reference to circuit
bandwidth or delay.
You may assume the bandwidth to be infinite, and toward that end
you may also assume a continuum of voltages.
The seven test tones are simply ratios, as given previously. You
may assign any arbitrary frequency to the lowest of the test tones.
Any discussion you want to get into with reference to time lags or
bandwidth would be on top of the results presented.
I went to a tektronix seminar for HD-SDI. The bandwidth is 1.485 Ghz. but with the quick transitions you need to have circuits that will handle a couple times that frequency.
I was thinking that maybe with multiple tones the transition were causing problems because of bandwidth. I wasn't assuming infinite bandwidth. My mistake.
Also is the power level of the seven tones making the amp go out of its linear range?
Grey, it all in the algorithms and software for forward error correction.
GRollins said:
GR, are you saying that a lower bandwith circuit has lower distortion, all other things being equal? I can understand that if you lower the *measuring* bandwith of the analyzer you measurer the higher harmonics lower, but of course they haven't changed in the output signal. You just turn a blind eye on them, so to say.
If, on the other hand, I lower my amp bandwith from, say, 150kHz to 50kHz, would that then lower the harmonics from a test signal? Probably not for a 1kHz test signal. What about a 20kHz test signal? At the very least I would think that it matters, for this issue, in which stage in the amp the distortion is predominantly generated, input, Vas, output.
Anybody has looked into this?
Jan Didden
Thank you, Nelson, for everything that you have provided in this latest article, past articles, and published amp designs. It is really great stuff and much appreciated. Summing it all up in the context of this distortion and negative feedback article, though, leads to the conclusion that we really want more from you -- isn't that always the case?
You've now made it unavoidably clear that IM distortion is at least as important as THD or THD+N. You've also provided us with a series of amp designs that minimize the number of gain stages (and thus should minimize IM) and that also show generally decreasing measured levels of THD+N, to the point where the F5 has some quite impressive THD+N measurements, single-tone harmonic spectrum measurements, slew rate and bandwidth measurements. The question now naturally arises: How do the various Pass amps compare in terms of IM?
Seeing and comparing seven-tone IM measurements for various Pass amps could be very enlightening. Any chance that you will be doing these measurements and letting us see the results?
You've now made it unavoidably clear that IM distortion is at least as important as THD or THD+N. You've also provided us with a series of amp designs that minimize the number of gain stages (and thus should minimize IM) and that also show generally decreasing measured levels of THD+N, to the point where the F5 has some quite impressive THD+N measurements, single-tone harmonic spectrum measurements, slew rate and bandwidth measurements. The question now naturally arises: How do the various Pass amps compare in terms of IM?
Seeing and comparing seven-tone IM measurements for various Pass amps could be very enlightening. Any chance that you will be doing these measurements and letting us see the results?
janneman said:
We are in agreement that it depends on where the distortion is generated. To a first approximation let's assume that a follower output stage (short of being driven into clipping) has minimal distortion excepting class B crossover stuff, and that's easily enough cured by biasing class A. Okay, so that leaves the front end as being the primary culprit. Even Douglas Self said as much in a paper I read a few months back. At this point, it's a trivial exercise to run small caps to ground after the VAS to limit the bandwidth and shunt the distortion products to ground in the process.
To accomplish much, you're going to have to limit the bandwidth more than I'd be happy doing. From my point of view, the cure is worse than the disease, but that's to be expected since I favor wide bandwidth. However, if someone else feels that wide bandwidth is overrated, then they're perfectly welcome to take a whack at it.
Yes, the above assumes open loop behavior. Otherwise, the feedback will do its dead level best to push the bandwidth back open. But since I've been doing non-feedback stuff, I tend to think in those terms. I regard it as a parlor trick, not something I'd pursue for my own purposes, but nonetheless it can be done.
Grey
I try to observe, boys, already this works for me.
This is an important thread here because I feel it in that manner.
Grey, since Nelson's plate is full,and you you have plenty of time anyway, you could mark some thoughts for my stony bonce, anyway, than the psychologist of the stones.
Regards,
Gyuri
This is an important thread here because I feel it in that manner.
Grey, since Nelson's plate is full,and you you have plenty of time anyway, you could mark some thoughts for my stony bonce, anyway, than the psychologist of the stones.
Regards,
Gyuri
Actually we should say thanks to Nelson. I had forgot about them until after reading Nelson's article.leapcat said:
Mr Fourier warned me about discontinuitiesGRollins said:
But amplifiers are more fun to discuss than math...
This is interesting. The question to follow is how much bandwidth is needed to achieve this?GRollins said:
If more is always better, we also open up the amplifier to be more sensitive to exernal noise which is bad.
Gyuri said:
I'm afraid I'm not following what you're saying.
(Me? Plenty of time?)
Audio_se said:
If some is good, and more is better, then too much is just enough...
There's no question that you're playing with fire when you extend the bandwidth of a piece of equipment. The primary problem is that you could be opening the door to oscillation or RF. As I've detailed elsewhere, I live in a state that is practically Stone Aged in regards to technology. Add to that the fact that I live in a stone bowl and the few radio/TV stations in this neck of the woods don't give me any problems. A fellow I know who lives about six miles farther in towards town developed problems when a country music station erected an antenna near his house. He (and I) both despise country music, so it's insult added to injury. For the time being, I'm still in the clear.
In the meantime, I aim for 200-250kHz bandwidth and generally end up between there and about 500kHz. That's open loop, as I'm not currently using feedback.
Grey
Hola Y'all
As I do not have the math skills and the mental capacity to understand alot of the the stuff discussed here. I may be entering a GREY area, but as a musician i understand subsonics and overtones(harmonics ) as they affect the tones we hear. I feel that bandwidth as is resonable is a desirable thing to produce the most realistic musical reproduction and a certain amount of distortion is acceptable. People like Joe Grado and (forgive me for saying ) Doug Self all realize that the amplifier is the last link in the chain of musical reproduction and if the source band width is limited then everthing after is limited as well...
did i mention Mr. Rollins minored in computer science(blured by alcohol and time)
Oh I think that means we need to work on bandwidth of sources
(Thank you Mr.Pass).
My $0.02 worth
Regards, Elwood
As I do not have the math skills and the mental capacity to understand alot of the the stuff discussed here. I may be entering a GREY area, but as a musician i understand subsonics and overtones(harmonics ) as they affect the tones we hear. I feel that bandwidth as is resonable is a desirable thing to produce the most realistic musical reproduction and a certain amount of distortion is acceptable. People like Joe Grado and (forgive me for saying ) Doug Self all realize that the amplifier is the last link in the chain of musical reproduction and if the source band width is limited then everthing after is limited as well...
did i mention Mr. Rollins minored in computer science(blured by alcohol and time)
Oh I think that means we need to work on bandwidth of sources
(Thank you Mr.Pass).
My $0.02 worth
Regards, Elwood
Do not be looking for what there is not on the source!
I ask an apology, shows, how much narrowed down in a consciousness state I exist.
I took it to reason now only, that Elwood my friend, ( I hope for it I may summon you in this manner! ) is in a similar situation, than I:
Most important sounding with the words of the good source, Béla Bartók:
Only from a clear source.
I hope for it this does not call for an explanation, Elwood!
It was my favourite hobby horse always, that most in the interest of the achievement of the good tone quality the sound engineer and his devices may do.
Than against this.
Gyuri
PS:
Only interest: there is a double children song my record, the Hungarian record company's publication. It was indicated beside the pieces, in which studio the given sound recording was made.
I can guess it in big safety, which one prepared where.
I ask an apology, shows, how much narrowed down in a consciousness state I exist.
I took it to reason now only, that Elwood my friend, ( I hope for it I may summon you in this manner! ) is in a similar situation, than I:
I agree with the rest of his opinions resolutely however.
Most important sounding with the words of the good source, Béla Bartók:
Only from a clear source.
I hope for it this does not call for an explanation, Elwood!
It was my favourite hobby horse always, that most in the interest of the achievement of the good tone quality the sound engineer and his devices may do.
Than against this.
Gyuri
PS:
Only interest: there is a double children song my record, the Hungarian record company's publication. It was indicated beside the pieces, in which studio the given sound recording was made.
I can guess it in big safety, which one prepared where.
Now then what there is holy **** here?
Possible it, that I have a persecution complex only, but I feel it in this way,
the life stops there if I write something somewhere, and the air congeals.
This is very strong feeling.
I feel it hence, as if totally incomprehensible, or what I write would be uninteresting possibly.
Calmly calm, if this is accordingly really!
Gyuri
Possible it, that I have a persecution complex only, but I feel it in this way,
the life stops there if I write something somewhere, and the air congeals.
This is very strong feeling.
I feel it hence, as if totally incomprehensible, or what I write would be uninteresting possibly.
Calmly calm, if this is accordingly really!
Gyuri
Nelson Pass said:Flattery will get you anywhere. Sorry we didn't find the time
to yak at BAF, twice now.
Likewise (once for me), may be next year. I can't read this now but I'll look at it tonight. Have you ever seen Jerry Sussman and Jim Boyk's paper on distortion? It was only published on line I think. They cover this stuff from a heavily analytical angle.
janneman said:
Thanks Jan. I was remembering the wrong paper.
I do have an issue with their conclusions about degeneration in Fets, as my
own measurements with both Jfets and Mosfets do not show this behavior
with degeneration. I did not see enough information on the simulation they
did to decide if there is some other factor. I do think it's important to separate
out the effects due to Vgs/Ids versus Vds/Ids.
feedback and distortion
Well, I know it already, there is not feedback because I am negative and distorted. But may be, that I am because of that distorted because there is not feedback.
But it may be it that I expect too much of the peoples while what I can provide for them means nothing to them simply.
Gyuri
Well, I know it already, there is not feedback because I am negative and distorted. But may be, that I am because of that distorted because there is not feedback.
But it may be it that I expect too much of the peoples while what I can provide for them means nothing to them simply.
Gyuri