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Old 2nd May 2012, 09:18 PM   #4991
SY is offline SY  United States
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Quote:
Originally Posted by john curl View Post
Amplifier noise, then.
Yeah, I calculate a little under 0.2mV of noise would do it, and that's a pretty reasonable number for a power amp.
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Old 2nd May 2012, 09:19 PM   #4992
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It is impossible for a class A region to increase distortion at low levels.
To reassure yourself, look at the Ayre graph more carefully
It is SCALED to be read out in Watts. The voltage sensitivity therefore changes as to the rated load resistance. Note the noise increase with the scale magnification increases. In fact it should be approx. 3 dB per measurement, because it takes less volts out (and therefore in as well) to achieve 0.1W out, for example, with a lower resistance load.
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Old 2nd May 2012, 09:31 PM   #4993
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Quote:
Originally Posted by john curl View Post
To reassure yourself, look at the Ayre graph more carefully
It is SCALED to be read out in Watts. The voltage sensitivity therefore changes as to the rated load resistance. Note the noise increase with the scale magnification increases. In fact it should be approx. 3 dB per measurement, because it takes less volts out (and therefore in as well) to achieve 0.1W out, for example, with a lower resistance load.
Exactly. Thanks for saving me typing.
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Old 2nd May 2012, 09:38 PM   #4994
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Old 2nd May 2012, 09:43 PM   #4995
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Default Noise .

This might be general knowledge , however I have never seen discussion about this . A friend of mine was taught by Martin Hawksford . If I am correct Martin offered an explanation for people liking tube amplifiers . He said that tubes have a pink noise spectrum and transistors at best white ( blue ) . The suggestion was that reducing noise to the lowest possible levels produced a feeling that the warmth of the sound is better . If this is true it might explain why tube amps and transistor amps with similar distortion and general qualities still sound different .

How do people feel about null tests where a " blameless amplifier " acts as a buffer and mimics a preferred amp ? I was also told that the other form of null test useful where the distrotion residuals are listed to . Seems reasonable to me that it should relate to the sonic signature of the amp . Quad always maintained that a 405 would always sound identical to the amp it was coupled to with the proviso that phase was correct and load was sensible .

I don't know if this is Urban Myth . I was told Bob Carver met a challenge to modify one of his amps to sound exactly like any another by null cloning it ( feedback loop and bandwidth limiting ) . The test done in a hotel room with the tools and pieces he brought with him . The story continues that he won his test . If the next part is true he said what it might prove is that some had better ears than him .
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Old 2nd May 2012, 09:44 PM   #4996
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Quote:
Originally Posted by bcarso
Although if an amplifier has a stable and smooth set of nonlinearities in the vicinity of zero signal, the net distortion should fall off predictably with decreasing level, it's not inconceivable that the concatenation of stages of some sort might have an overall signature, a curve-of-growth, that actually produces net distortion that is non-monotonic with level.
I doubt it. I would expect that a cascade of stages, each with a smooth gain curve around zero-crossing, has a total gain curve which is also smooth although perhaps slightly less smooth. This assumes that there are no mathematicians' pathological functions lurking around.

I would not want to do a proof, but I expect that the product of a few rapidly-convergent smooth infinite series is itself a rapidly-convergent smooth infinite series. Distortion will then be monotonic with signal level, for sufficiently small signals.
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Old 2nd May 2012, 09:50 PM   #4997
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Quote:
Originally Posted by nigel pearson
This might be general knowledge , however I have never seen discussion about this . A friend of mine was taught by Martin Hawksford . If I am correct Martin offered an explanation for people liking tube amplifiers . He said that tubes have a pink noise spectrum and transistors at best white ( blue ) . The suggestion was that reducing noise to the lowest possible levels produced a feeling that the warmth of the sound is better . If this is true it might explain why tube amps and transistor amps with similar distortion and general qualities still sound different .
I assume you mean Malcolm Hawksford? I thought both valves and transistors had essentially white noise, apart from 1/f at lower frequencies. The circuits might have different noise spectra, due to different architecture.

BTW why the space before punctuation? It makes reading your posts more difficult.
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Old 2nd May 2012, 09:51 PM   #4998
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Originally Posted by nigel pearson View Post

I don't know if this is Urban Myth . I was told Bob Carver met a challenge to modify one of his amps to sound exactly like any another by null cloning it ( feedback loop and bandwidth limiting ) . The test done in a hotel room with the tools and pieces he brought with him . The story continues that he won his test . If the next part is true he said what it might prove is that some had better ears than him .
This experiment did happen and Carver was correct ....
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Old 2nd May 2012, 09:57 PM   #4999
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Quote:
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.........modify one of his amps to sound exactly like any another......
I just wonder what that means
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Old 2nd May 2012, 09:58 PM   #5000
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Some of us had a suspicion that Carver actually didn't do anything, or at most added a single resistor to the output of his amp to get the frequency responses equal.

Despite the amazing performance of many people in ears-only testing of things like frequency response, data compression, phase, level, and localization, when the tests don't support the marketing or a priori assumptions, they may safely be dismissed with a sneer.
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