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Originally Posted by PhilS /img/forum/go_quote.gif
I'm more than happy to have both comments deleted. Why don't you report the threads and ask the mods to edit it.
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Because I'm happy to let the last word on your side, and the off-topic has been short enough not to disturb the discussion.
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Originally Posted by PhilS /img/forum/go_quote.gif
It's not inconsistent at all. It's only inconsistent if you feel compelled to advance a particular point of view,
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That's quite right : if there is burn-in, a proof can be given without discussing the existence of the phenomenon first, but in the other case, no proof can be given.
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Originally Posted by PhilS /img/forum/go_quote.gif
Go back and read the other threads like this in the past. Here's what you find:
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Too true... but two differences may appear in this thread. First, the rescriction to scientific explanations rules out the influence of Shakti stones, Langevin's heavy ions, Manta and other Hallographs.
Second, in the caricatural example that you gave, the "objectivist" side was not willing to explain at all.
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Originally Posted by plonter /img/forum/go_quote.gif
now,i want to make clear that although i am a "believer" i am also a thinking human being and willing to hear some comments about "burn-in" not true, not just comments that "Burn in" is true.
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Actually, the burn-in problem is masked by another, more important problem, that is the sound of amplifiers.
Currently, it is admitted that a perfect amplifier is possible, exists, and that its street price should be around 200 or 400 euros for less than 100 watts stereo. Some candidates models : Behringer A500, InterM M300. I don't know measurments performed on them, but they have been compared to high-end audiophile amplifiers in good conditions, and showed similar sonic qualities.
The problem is that if an amplifier is perfect, how can it burn-in ? It is already quite difficult to distinguish between the sound of two different models, let alone the sound of the same model before and after burn-in.
The usual answer is that differences between amplifiers exist and are easily audible (except in ABX). Ok, but these differences can't be
explained !
How can we expect to explain the différence between a burned-in amplifier and a brand new one, while we currently cannot explain why two
different amplifiers sound different (except tube) ? We must begin with the easy questions before going on with the difficult ones.
Here are three aspects of the problem with amplifier sound :
First, the measured performances. Often enough, noise, output power, frequency response, phase response, harmonic distorsion, and intermodulation distorsion are all below the audible threshold. And it is very difficult to imagine any other kind of distorsion. The most probable that I can see would be intermodulation distorsion at frequencies different than the ones used in the usual tests. But they are sometimes performed without interesting results.
Any other measurment, like square wave or impulse response, should be perfect if the above are all perfect.
Second, the cancellation test. Douglas Self talks about it in his article about amplifiers (
Douglas Self Site ).
Here is how it works : we use an attenuator in order to decrease the output of the amplifier, until its level is the same as the input signal. Then this signal's polarity is inverted, and it is summed with a copy of the input signal.
This way, the output is substracted from the input, and we can see what's left. According to D Self : zero !
This measurment encompasses any possible characteristics of the sound. The complete musical signal is compared to the original in real time, and the experiment shows that it consists in a strictly identical copy of it, with a bigger amplitude, even while speakers are connected to the output.
That's what Douglas Self says. But in another discussion, (here :
diyAudio Forums - Blind Listening Tests & Amplifiers - Page 1 ) a forumer gives more accurate figures. Actually, the result of the substraction is not null. Its amplitude is 60 dB below the original with cheap amplifiers (250 $), and 70 dB below with better amplifiers.
We must also note that these kind of measurments should be extremely difficult, because if the cable lenght of the original signal is not exactly the same as all the paths that takes the amplified one into the amplifier, at the speed of electricity (about 200 000 km/s), a difference of one meter would be enough to explain the -70 dB noise, because the two copies of the signal would not arrive exactly at the same time.
The third approach is blind testing. It is well known (is it ?) that tube amplifiers can be distinguished from transistor ones in ABX tests because of their high output impedance, that adds a coloration to the sound.
Example :
http://www.soundandvisionmag.com/ass...rInterface.pdf
But between transistor amplifiers, ABX usually fail. Recently in France, a small group of forumers called the Kangourous (Kangaroos) began investigating the sound of amplifiers. There have been 5 meetings so far (I was at the first one). Here are all the links :
homecinema-fr.com • Voir le sujet - Kangourou : Les liens, les produits écoutés.
Currently, some interesting points have been found :
-Not even listening blind, a very cheap InterM M300 pro amplifier (around 150 euros) seemed to deliver the same sonic quality as a Mimetism 15.2 amplifier (4500 euros), on high end speakers ( JMR Euterpe or JMR Concorde Signature, I don't remember at what moment we switched).
In the same comparison, we noticed a bigger difference with another high end amplifier, the Atoll In100, than with the cheap InterM, that sounded closer to the Mimetism.
The blind test between the Atoll and the mimetism failed (actually, the listener scored 12/15, which gives a probability of false success of 1.8 %, but we agreed before the test that 14/15 was a minimum).
However, the distorsion was obvious for two other listeners. We did not have the time to repeat the test with them, nor to measure the distorsion, that was plainly audible on a 1 kHz sine. We think that a success is possible.
Second interesting point, while it seems confirmed that "any properly designed amplifers sound the same", it seems on the other hand that finding a "properly designed amplifier" is not easy at all !
In our first test, an expensive audiophile and a cheap pro one seemed to fit in that category, but not the other expensive audiophile one.
In further tests, they found that some AV receivers have conception problems. One of them did not shut down the low frequency management for subwoofer when setup accordingly ! Which resulted in a completely wrong bass response.
GrandX, the person who launched the idea, now follows the same path as Mike here : he wants to refine the blind protocol until he finds why he can hear some differences in usual conditions, and not anymore in ABX. Many improvement have been suggested for the next listening sessions :
-letting the listened adjust the volume with a CD player that has a variable output.
-testing in XY instead of ABX (an idea that would please Wavoman !).
-performing no more than one comparison in a day.
-Performing usual comparisons (not blind) with volume and balance equalized within 0.1 dB.
-Looking for correlations in subjective comments of different listeners instead of yes/no answers, and for this purpose, let the listeners agre on a limited list of adjectives before the test.
As we can see, we know little about real-world amplifiers because manufacturers don't publish measurments anymore, because scientific studies never cite any brand or model and use to work on abstract "well-designed" amplifiers, and because blind tests are extremely difficult to perform (just think about equalizing the volumes, that must be done with speakers working (because they suck current and this might change the volume), and while plugging anything in the amplifier output may cause it to burn instantly).
In these conditions, we can see what it is that seriously studying the burn-in of amplifiers !
Oh, and about the variations of the capacity in capacitors, I've read from some DIYers that in "well designed" (again ! ) circuits, small variations of the values of capacitors have no effect on the output signal of the amplifier.