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Old 20th July 2012, 10:25 AM   #6821
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Originally Posted by a.wayne View Post
Distortion spectra, which starts out low , in the miliwatt range and then go high as power increases seems to fair better than those which starts out high then lowers as power is increased, in subjective listening test ..


I had touched on this many moons back any additional thoughts ... ?
That needs saying . One of my recent amps is very low distortion below 1 watt and 10 % where there is still useful power . Correcting the 10 % has lost some of the magic . Unlike most people I don't tell myself I prefer that type of distortion as with great experience I can say absolutely not so . Where it gets interesting is to say correcting it spoils that amplifier . The amplifier which I like equally has so close to zero distortion as to be almost a high grade op amp . Both allow me to be lost in the music . Both annoy me when loud . The 10% one as it becomes obvious we have rejoined the 1950's the other for it's lack of camouflage . Up to 5 watts it is hard to say one is better than the other .

I said the other day I was almost tearful at the simplicity of the mathematical description of feedback . Having seen those patterns many times it is helpful to say it is that simple . For example I was told the best description of a suspension bridge shape is a catenary . My friend said no because the chain suspends a load ( the bridge , a parabola ) . Galileo apparently got it wrong when mistaking a catenary for a parabola . These " shapes " are important .

To say negative feedback is the same as local feedback is in the simplest sense correct . If I degenerate an amp using global feedback with a little bit of local feedback it is not obvious anything has changed . The amplifier has to be reduced to a state of obvious dysfunction to yield trends . This tells me two things . First it is a good amplifier and secondly global is probably the optimum feedback for that amplifier . Another amp might show nasty harmonics using global that the local feedback does not . That amp is the " Chaotic pendulum " . Now just as a chaotic pendulum is a fake ( I feel it is although understand how that might not be true ) the feedback amp is not chaotic . Understanding it might be close to understanding chaos . By that I would refer back to Michael Gerzon and filters . It is worth saying the global amp when far from dysfunction does not sound exactly the same when trading local feedback . It looks so similar on an analyses as to be an identical twin . Having known identical twin girls they are not the same . I choose the wrong one I can tell you .

It is said in engineering that which is impossible should be made irrelevant . I wondered would it be better to make a power amplifier into an active filter ? I have done this at lower frequency for re-generators using Chebishev curves . The formulea are well known and simple to apply . Bessel ,Butterworth , Gaussian ,Linear phase , you name it . Here is the conjecture ( informed guess as Michael says ) . Apply a filter curve of sensible generosity of bandwidth to an amp . Does it sound better or worse than usual . This amp will have to be very fast to be useful . I suspect many of us have unwittingly have been doing this for years now ? Doubtless someone will tell us this is obvious or well known . Perhaps . I don't remember it said this way ? Instinctively I feel this to be a very bad idea . However .....?

Many shapes I see in everyday life I understand without resorting to reminding myself of the mathematical formula . The cone , cylinder , parabola . I passed my job interview by reciting Papas Guildinus theorem ( no big deal ) . The boss to be got me drunk at the interview then asked that . One could say geometrical maths is never boring to me . My mentor says we lost something when science was removed from the "Arts " . He makes a nice income from being an opera singer . His PHD is in electrical engineering .

Last edited by nigel pearson; 20th July 2012 at 10:49 AM.
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Old 20th July 2012, 12:25 PM   #6822
DF96 is offline DF96  England
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Originally Posted by Wavebourn
I even designed a "harmonizer" with a knob to add tube distortions, but nobody likes it.
But did you label the knob "distortion" or "musicality"?
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Old 20th July 2012, 12:31 PM   #6823
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I noticed TubeCad has a width control . Why not ? SSL mixing desks do have these circuits . Getting them to work is not easy . They mimic other desks one could say . The work of David Mate .
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Old 20th July 2012, 10:42 PM   #6824
a.wayne is offline a.wayne  United States
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Courtesy of STphile , a few contenders ....
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Old 21st July 2012, 05:57 AM   #6825
dvv is offline dvv  Serbia
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Contenders for what?
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Old 21st July 2012, 09:49 AM   #6826
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The Goldmund is so surprising as it is a very simple circuit ( an assumption as I may not know this specific circuit ) . I know those curves from others which are generically similar ( even the HH 1200 ) . Even people who work in PA wouldn't think of HH as anything special . I wonder with better speakers if it would shine ? I have never measured one so can only say is starts with what should get it there as a circuit

Last edited by nigel pearson; 21st July 2012 at 09:57 AM.
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Old 21st July 2012, 09:32 PM   #6827
a.wayne is offline a.wayne  United States
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Contenders for what?
MIcro watt -1 watt THD ...
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Old 21st July 2012, 09:40 PM   #6828
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Quote:
Originally Posted by a.wayne View Post
MIcro watt -1 watt THD ...
Not enough... More critical, what kind of HD, and how spectrum changes with power. Also, some other illnesses play the role. Like IMD between high frequencies with their difference below 20 Hz can show other symptoms of common modern amps with astonishingly low THD.

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Last edited by Wavebourn; 21st July 2012 at 09:43 PM.
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Old 21st July 2012, 10:17 PM   #6829
a.wayne is offline a.wayne  United States
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I can provide, too much to list for all of them , pick an eg from the list ....I like the Goldmund .
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Old 21st July 2012, 11:19 PM   #6830
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Originally Posted by a.wayne View Post
I can provide, too much to list for all of them , pick an eg from the list ....I like the Goldmund .
Not enough to judge. But some aspects, yes. Gooldmud and VTL both can be better than the rest pf amps. But can be worse. An amp with 140 dB open loop gain at 10 Hz can demonstrate nice THD/Power curves, but sound dirty.
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