26th Jan 2020, 3:27 pm | #1261 |
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Re: The Audiophoolery Thread.
One of the trickiest things to get right with an AB amp is induction distortion. Because the power rails take half cycle currents, they can couple easily into low level circuits. That means that at low frequency the distortion is low - which is why most amp manufacturers selectively quote distortion at 1kHz. However induction distortion is frequency dependent, and leads to anomalously high distortion at upper audio frequencies.
This is not a problem with class A (because the power supply current follows the audio signal) or class D because of its operating principle. But Halcro and Benchmark have clearly found solutions to that problem; I'd like to see inside Benchmark's case if only to look at their power supply routing! Craig |
26th Jan 2020, 3:32 pm | #1262 | |||
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Re: The Audiophoolery Thread.
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26th Jan 2020, 3:34 pm | #1263 |
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Re: The Audiophoolery Thread.
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26th Jan 2020, 3:41 pm | #1264 | |
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Re: The Audiophoolery Thread.
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26th Jan 2020, 3:43 pm | #1265 | |||
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Re: The Audiophoolery Thread.
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26th Jan 2020, 3:55 pm | #1266 | |
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Re: The Audiophoolery Thread.
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Inductive coupling is a two-part affair. Careful layout of the high-current source of the unwanted stuff can minimise the effective loop area and hence the field strength. Careful layout of the victim region can minimise its effective loop area or arrange net cancellation, reducing the induced voltage still further. Like any screening/interference job, it's wise to win whatever advantage you can get wherever the opportunity arises. So don't look only at the power current loops, look also at input signal loops. They're just as important. David
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26th Jan 2020, 4:03 pm | #1267 |
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Re: The Audiophoolery Thread.
Absolutely agree David. I'm just saying that it is one of the toughest things to eliminate.
I've been looking at the Benchmark specs with a more critical eye - and sure enough they only quote at 1kHz, with either a 20kHz or 80kHz bandwidth. On the main page the do say that 3ppm is met from 20Hz to 20kHz for the following table of output conditions, but don't quote the measurement bandwidth. And in the manual, the AP plots of distortion vs output level are at an unspecified frequency and measurement bandwidth. So even they are very carefully stepping around some of the real world issues and being economical with the numbers. But is it a bargain for USD3000? Indeed it is. Quoting our friends from across the pond, it is a lot of bang for the buck. Craig |
26th Jan 2020, 4:05 pm | #1268 | |
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27th Jan 2020, 6:39 pm | #1269 |
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Re: The Audiophoolery Thread.
When did the world of hifi amplification take a major step forwards in being able to produce another octave of bass? Probably back in the 1920s?..
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27th Jan 2020, 6:45 pm | #1270 |
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Re: The Audiophoolery Thread.
But surely, it's not just a question of being able to hear 1% or even 0.01% distortion (whatever), it's the ability of an amp to exhibit clarity in complex passages? That can be affected by distortion levels that may not manifest themselves as 'pure distortion', but make for a subtle muddling of clarity.
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27th Jan 2020, 6:49 pm | #1271 |
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Re: The Audiophoolery Thread.
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27th Jan 2020, 6:58 pm | #1272 |
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Re: The Audiophoolery Thread.
Easy to do an amplifier right down to DC = 0Hz
How many octaves down is that? well, theoretically infinity! Realistically it depends on how long it's been turned on for and the listener's life expectancy. Suitable speakers might be a bit of a problem. David
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27th Jan 2020, 7:02 pm | #1273 | |
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27th Jan 2020, 7:03 pm | #1274 | |
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Re: The Audiophoolery Thread.
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Distortion (if you also include noise) is, at its root, any difference between an amp's output signal and its input signal other than the obvious one resulting from the amp's gain. If the distortion is low then, well, the output signal is the input signal, only louder. I can't see how the 'clarity' can be compromised in this case. When distortion percentage is quoted it commonly refers to harmonic distortion measured with a single-frequency sine input. Sometimes a percentage figure for intermodulation distortion, measured with two simultaneous input frequencies, is also given. It is theoretically possible for an amp to have low levels of these two types of distortion but still to misbehave when it's fed music, with its very broad range of frequencies and occasional rapid transients. But it's rare I think, isn't it ? Cheers, GJ
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27th Jan 2020, 7:05 pm | #1275 |
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27th Jan 2020, 7:06 pm | #1276 | |
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28th Jan 2020, 9:07 am | #1277 |
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Re: The Audiophoolery Thread.
I wonder, if all the energy that has been put into this debate were used to amplify a musical signal, just how much louder would be the output?
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28th Jan 2020, 9:45 am | #1278 |
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28th Jan 2020, 10:33 am | #1279 |
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Re: The Audiophoolery Thread.
My favourite Fourier amusement is entirely encapsulated in the phrase "Fast bass" it always makes me smile. Trying to explain Fourier transforms and the Q of a resonance to anyone who would use that phrase might make your reluctant 2nd years look easy
David
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28th Jan 2020, 10:53 am | #1280 |
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Re: The Audiophoolery Thread.
As applied to any half way decent electronics, "fast bass" is of course nonsense.
As applied to loudspeakers, it is much more meaningful. In particular bass reflex and ABR speakers can indeed sound bloated and muddy at the bottom end. However, even there it is subject to analysis, as Richard Small and Neville Thiele showed in their seminal papers on low frequency speakers in the early 70's. |