"Burn in" in amps (and all other electrical parts) - Page 3

What are your thoughts on what Happy Camper posted regarding capacitors, oxidation, etc.?

there are sometimes measureable changes in electronic circuits/components with extended operation - just not obviously audible because of their tiny effect on audio frequency signal response:


the component ageing effects I am aware of are much smaller than the initial tolerance so even ABX with 2 amps could be difficult - you'd have to "blueprint" the amps to get the initial component matching better than the expected change on burn in

I've had problems with every new amp I've bought. It definitely sounded different thand the one I was used to, superior in certain aspects but also somewhat disharmonic over-all. That was again the case with the change from the Opera to the Symphony. I couldn't tell which I liked better, but they didn't sound the same.

I think this contradicts the purely psychological explanation from an objectivist point of view with the opinion that amps that measure the same sound the same: Given the different looks, the newness and the investment one would expect a positive impression.

After about 240 hours the Symphony was beginning to sound undisputedly better than the Opera. And these days (after more than a year of living with it) the case is absolutely clear.

Now it's easier to argue with the psychological effect of getting used to a new sonic characteristic (a possibility I don't absolutely exclude). But from the objectivist point of view there's a decision to be made: Either there is a difference in the first place – so there's a need for acclimatization –, or there's none, and every sonic difference is imagined. In the latter case it's not logical to hear a difference without a clear improvement based on high expectations (the motivation to buy a new amp); in the former case acclimatizing to an imagined alteration isn't a logical scenario.

Moreover there's the question of the allegedly limited acoustic memory. It's impractical or impossible to ABX two different headphone amps. So the capability of the acoustic memory to really remember the former characteristic can be disputed, and the pretension that it's all in the listener's mind sounds somewhat plausible. It's just that in the latter case there would be no need for acclimatization to a new characteristic.

There are a lot of inconsistencies in a strictly objectivist approach when it comes to amps and burn in. So in my book real differences and real burn-in effects are just as likely as placebo effects even or precisely from an open-minded objectivist perspective.

As to the OP's request: Unfortunately I'm not technically knowledgeable enough to give any useful information.
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I think it is unlikely that the mere flow of a signal changes the properties of those components.
Heat and oxidation are intriguing, however. These could very well change the materials. Whether the change is sufficient enough to alter the sound signature (enough to be audible) is another matter but I believe it is certainly possible, if unproven at present.
EDIT: It still leaves the question of how it is possible that the changes are always for the better unanswered.

Ahh... misread that, sorry.

What you're saying is true (a strictly 'objectivist' position is contradictory with mental acclimating) if and only if the two components are volume matched. This is almost never the case. If someone compares amps without any level balancing, they're likely to mistake a different volume level for a difference in detail, etc. Furthermore, most amplifiers' potentiometers work over different ranges and provide different levels of attenuation based on the specific amplifier's gain, so changing volume would also not be a constant affair. Finally, whatever mental predispositions the listener has can also change over time (similar changes happen with medical placebos) and even imagined details can seem more familiar over time. I don't think that the two positions (components not making an audible difference and the theory of mental acclimating) are contradictory at all, especially when taking into account the dozens of variables present in uncontrolled settings.

OP: by definition, a scientific explanation is a (scientific) theory. Those theories have to be backed by some form of empirical evidence in order to be called a scientific theory instead of mere speculation. Without empirical data that fits the theory, you just have a "Just-so story." That said, you probably would have better luck posting in the misc. cables thread.

I have my doubts on some claimed burn in issues as well, but with respect to your question above, I'd offer two thoughts, sort of playing devil's advocate given my own doubts on certain aspects of this issue:

1. I have seen several instances where people claimed, not that a component sound worse when it was finally "broken in," but that it did sound worse for a time and then got better. I'm not sure I accept that, but there are also instances where people claimed to be happy with an amp when they first got it, but after a time with it, they decided they didn't like it. Maybe they just didn't like it; OTOH, maybe the burn in had negative effects, but they did not attribute it to burn in.

2. I'm not sure it's totally illogical to conclude that an amp designer/manufacturer who is trying to achieve a certain sound would not be working primarily with components that are burned in. Hence, if things like capacitors do change over time (and assuming for the sake of argument it's audible), it would make some sense that the amp would sound better when it reaches the stage that mirrors what the amp designer was experiencing with his prototype.

Anyway, it would be interesting to hear what a guy like Ray Samuels would say on this subject. He always recommends substantial burn in time for his amps, and it would be interesting to see what his explanation would be.

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.

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.

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.

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.

Interesting. Could the same be said for placebo then?

Good points. I would think if that was the case the manufacturer would "pre-burn-in".

I would rather hear someone like Justin's opinion but yes, it would be interesting. Has it never been addressed by a manufacturer before as to the reasons for burn-in?


EDIT: Great frikkin post pio!!!

What do you mean?

I seem to recall that from time to time, some of the headphone amp manufacturers have offered some information on this, but it's usually in other types of threads (e.g., a thread pertaining to a particular amp). They tend to stay out of sound science-type discussions; they have more sense than a lot of us, I guess.

Burn-in is sometimes explained away as simply getting used to a new sound. But is that really what is happening? this involves not only what we are hearing, but how we are reacting to it.

i have never met anyone who liked their first taste of beer, and who didn't "get sick" to some degree or other from their first cigarette. lots of people drink beer and/or smoke cigarettes however. the question is -- do they taste different now than when they were first tried/ brand(s) aside?

how we judge things has a lot to do with our state of mind, and our past experience with comparable experiences. as a former teacher, i have run across students who had test anxiety, such that they could not give the correct aanswers under the pressure of the exam, but could answer them all in calmer settings. music is an emotion-inducing affective art form, and it is much harder to perceive subtle differences under pressure. Nor are all people's acuities equal. a proper test would use subjects with proven abilities to pick out differences-- whether any particular person can hear a differences has nothing to do with whether such differences actually exist.

food for thought. maybe burn-in is a form of warm-up. spec sheets certainly show performance differences relative to temperature. i think there is more to it than mere habituation-- not sure what it would take to prove it.

Just want to give the a semiconductor manufacturer's perspective. We do not like change after burn in. Predictable and deterministic behavior is key. What if after 100 hours of use certain parameter change and cause plane to crash and telecom equipment to malfunction.

To make sure things are consistent, there is a qulaification process. Devices are burn in for 1000 hours at 125 deg C junction temperature to see if there is any gross number of failure or deviation. If not, then the chip is deemed production worthy. If not, usually there is some design error or manufacturing process at fault.

Can't tell you must about capacitor, but crystal and LED go through the same testing.