Burn in question and evaluation before burn in


We all experienced sound transformation before and after a new equipment or cable is burned in, however, I am wondering if there is a general rule as to which direction any burn in would be heading? Specifically, I am interested to know would sound generally go smoother/darker or brighter/more transparent after burn in? I am thinking if there is such a rule, it would be valuable to know for evaluating products.
wenrhuang
Generally for me they sound bright first,but some electronics I remember my Thor Audio Electronics had actually 3 different phases of burn in ...From bright to dark and then to perfect.......I would assume it could go either way..
We all experienced sound transformation before and after a new equipment or cable is burned in

Your question is excellent - I see absolutely no reason to assume that gear should be better with burn in. Why can't it get worse too? How do you know when it should finally sound good or correct?

I tend to avoid the type of gear that changes audibly. Manufacturers can design gear to be dramatically less affected by burn-in by simply designing it in such a way that it less sensitive to the things that do drift with use (capacitors, driver compliance for example).
I am wondering if there is a general rule as to which direction any burn in would be heading

Seems to me to be pretty logical that the answer would be no. Obviously it would be dependent on the type of component (amp, cd player, preamp, speaker, interconnect cable, speaker cable, etc. etc.); and on the technology used (tube, solid state, dynamic speaker, electrostatic speaker, cone driver, dome driver, ribbon driver, electrostatic membrane, etc. etc.); the specific design of the particular example of the component type and technology, etc., etc.

I agree with Shadorne's comments as well.

Regards,
-- Al
I tend to avoid the type of gear that changes audibly. Manufacturers can design gear to be dramatically less affected by burn-in by simply designing it in such a way that it less sensitive to the things that do drift with use (capacitors, driver compliance for example).

Why don't you contact me via Audiogon. I see your comments here frequently and you seem to think caps and break in are a bad thing.

I can give you the name of the designer/ manufacturer that builds ALL the current hot caps that are on the market, sold under a dozen different names.

He will tell you break in is not only real but important. YES, it effects the sound greatly and if you think you can design around this, you are missing most of the great equipment on the market today.
Right on the money Albert! And any good designer will voice his equipment with the presentation of the components AFTER stabilization in mind. Hopefully- transparency will be their goal.
Albert,

I never said break in was not real. I just prefer components that are engineered to be precise and that do not drift dramatically with time. It is a simple design choice to place a capacitor in the signal path or not. It is a simple design choice to either place a capacitor in a passive crossover (where it adds distortion) or use a line level x-over filter. One can also design circuits so that they drift less with age and temperature through careful selection of components and design. I could go on about driver design as well -many drivers change dramatically with use due to thermal compression - every track the speaker may perform differently in some typical poor designs.

My point was to simply challenge the idea that burn-in that sounds greatly different is a good thing . It often implies overly simplistic designs that are commensurate with a goal of "purest signal path". Unfortunately, the engineering reality is quite the opposite - through added design complexity one can dramatically increase precision and robustness of product performance from changes in temperature, ground loops, cables, interconnects, power, noise, component aging etc.
Thanks for the responses. Shadorne, your point is well taken, actually, what prompted me to ask the question was that I was frustrated that my new solid state preamp sounded good at first install, but became too bright, and strangely, the tight bass was gone too after a week. I know I had only like about 30 hours playing time on it, so it is not fully burned in yet, but I wish I can be assured that further play time would kind of reverse the initial burn in direction, if that is at all possible.
Just curious if you bought your equipment without an audition. I would think that if you bought this new and auditioned a completely burned in one at a dealer, you would have an idea of how it will eventually sound. In my experience cables are a different animal, but usually there is even some information as to the burn in process and the overall sound qualities that can be expected when it's completely burned in. I don't have Thor electronics, but most of my experiences are the same as Thorman's, but I am pretty certain that others have had different experiences. Shandorne raises a question that I thnik we all are a bit fearful about and that is that the results of the burn in procees do not meet our expectations.
Mr W- I've had passive and active components that went through 4 or 5 changes in presentation before reaching stabilization. Some sounded ridiculous at times. Be patient(at least 200 hrs) before listening critically, and deciding whether you like the component's presentation or not. The best capacitors and cables use high grade dielectrics(ie: polypropylene/polystyrene/Teflon) that don't absorb/discharge energy as quickly. That means "burn-in" takes longer too. (http://www.national.com/rap/Application/0,1570,28,00.html) Also look at the paragraph about Dielectric Absorption here: (http://www.sbelectronics.com/application_notes/cterminology.htm)
I never said break in was not real. I just prefer components that are engineered to be precise and that do not drift dramatically with time. It is a simple design choice to place a capacitor in the signal path or not.

And it's a simple choice to provide the finest capacitor available in the best equipment and that means IF you have a cap, it's a VERY high quality cap, it will take a VERY long time to break in.

It is a simple design choice to either place a capacitor in a passive crossover (where it adds distortion) or use a line level x-over filter.

I use an active crossover with my speakers but they were designed that way from the start. To say it's a simple design misses some very important points. To execute an active crossover properly you need a separate amp for each frequency. I agree that's the best, but to call it simple is inaccurate. Such a design generally requires a lot more parts, amps, cables and space. Not every designer (or every customer) is willing to do this.

That leaves us with caps inside the crossover, a design that represents most of the speakers out there, yours and mine perhaps the exception. Regardless if the caps are inside (my) active crossover or in a passive design, they play an enormous role in performance and ALL great quality caps take forever to reach 100% performance.

There is no design exception to this unless you have system with no caps.

My point was to simply challenge the idea that burn-in that sounds greatly different is a good thing . It often implies overly simplistic designs that are commensurate with a goal of "purest signal path". Unfortunately, the engineering reality is quite the opposite - through added design complexity one can dramatically increase precision and robustness of product performance from changes in temperature, ground loops, cables, interconnects, power, noise, component aging etc.

I think every designer in the business would agree with that and most would say they worked to achieve that goal and provided same for their customer, within the limits of budget given for the project.
Rodman99999, thanks for the link.

Maybe designers will provide enough data over time that "tech" minded audiophiles will accept the fact that with current technology it's impossible to design caps that don't have "sound."

Caps used in critical positions in high end audio combined with a careful listener means the effect is huge. Most high end manufacturers have upgraded caps steadily and frequently over this last decade. It's a technology that's literally exploded with innovation and improvements.
Exactly!! =8^)
I think we are in full agreement about capacitors - see what Douglas Self has to say;

....well-known capacitor shortcomings such as dielectric absorption and series resistance, and perhaps the vulnerability of the dielectric film in electrolytics to reverse-biasing. No-one has yet shown how these imperfections could cause capacitor audibility in properly designed equipment.

The last sentence is a key one - "in properly designed equipment".

I think we also agree that it is not safe to assume that everything out there is designed properly and burn-in is necessary for many designs.
Cyclonicman,

My preamp was freshly installed with new upgraded board, it is supposedly better than the old version, but no, I have no idea how it will eventually sound.
Demo gear fully broken in and then decide if you like it. If you like it buy it...maybe even try it at home:)
what prompted me to ask the question was that I was frustrated that my new solid state preamp sounded good at first install, but became too bright, and strangely, the tight bass was gone too after a week.

Something is not right, IMHO. Check your interconnects and speaker wires. Any chance you got phase reversed - or did you flip the balanced/unbalanced switch or change the input volume offset by accident? Remote controls can be tricky - I have had weird things happen when I sat on one !
I think we also agree that it is not safe to assume that everything out there is designed properly and burn-in is necessary for many designs.

If that single criteria were used to assign quality to high end audio components, most or all of the best available would be termed "improperly designed," by that Douglas Self proclamation.

I'm excited by the improvements of the last few years from Dynaudio, Aesthetix, Audio Research, CAT, BAT and other companies that have embraced the latest high tech cap design. Many of the newest and finest pieces contain caps made by a guy that's a friend in the business. These caps are sold under a dozen names, made to different performance standards depending on budget.

I know of no contributions from Mr. Self that rival these designs, In fact he's probably one of those that think Radio Shack, Cardas and Nordost wire all sound the same with no audible effect on a high end system and the music it produces.

Wenrhuang, regarding break in process and what to expect. There are no set in stone results available where performance can be spelled out. Too much variation in parts and systems.

IF I had to guess (and this is a guess), considering the type of upgrade and the fact it's a transistor based design, I imagine right out of the box the sound was OK, but perhaps a bit compressed with slightly sloppy bass.

The music turned to shrill with poor bass after perhaps 20 to 50 hours and if it does prove to be superior to the original status (before your upgrade) it will not completely smooth out until about 450 to 600 hours.

You can accelerate the process by turning the preamp on and feeding it signal ( FM, CD, or whatever) 24 hours a day for a couple of weeks. That should be close to 400 hours by then.

The amps and speakers need not be on and no requirement to listen to music during this time unless you want to. I would love to hear a report if you choose to do this experiment. The electricity used will be less than the shipping cost to return the preamp and you might learn something.
Thanks guys! I did checked all wiring, connections, phase switches, etc., my conclusion was that the preamp has been and is still going through stages of burn in, or that my ears were playing tricks on me.

Actually, the sound from my system seems to be going the positive direction in the last 24 hour, that's good news.

From past experience, I know I should not make judgment on my preamp before it is fully burn in. However, the reason I posted the original question was that I would really like to find out if there are some general "burn in" knowledge could be learned. Like how tube, capacitor, silver wire, copper wire, etc. would behave during burn in process. I am also curious that is it, and how is it possible for a burn in to go in opposite direction in different stages? That is, for instance, for system to becoming brighter at one stage, and then become darker at another stage?
Wenrhuang,

Please read my post, the one above yours. Also, regarding:
I am also curious that is it, and how is it possible for a burn in to go in opposite direction in different stages? That is, for instance, for system to becoming brighter at one stage, and then become darker at another stage?

This is not uncommon and not far off what I posted before you said the system seemed to be headed in a more positive direction.

Unless you have a lot of hours, be prepared for it to go wrong again before it gets right. I know this seems improbable, but mirrors my experience in many situations.
Albertporter,

Your guess seems to be spot on, at least so far. When I first put my newly upgraded Linn Klimax Kontrol preamp back in my system, it sounded polite but precise, very musical actually; however, after about 30 hours playing, it turned to shrill with very little bass as you have guessed for a transistor based design. It became not enjoyable at all to listen to, and I thought something was wrong with my system. Only after another 10 hours playing today, I began to feel the music is slowly coming back a bit. I hope that my preamp would really smooth out and shine after 450 to 600 hours as you predicted may happen, again, for a transistor based design.

The preamp I have been using for the last two years is a Linn Klimax Kontrol. Linn just recently offered an upgrade kit---mostly new board(s)---and I went for it because I believe Linn would not offer it if not for real sonic improvement. I would of course rest my judgment until my upgraded preamp is fully burned in---(the kit and the preamp are not returnable anyway). And I will report back to you.

Anyway, my original post was mostly out of my curiosity about burn in, it seems to be a black art. But if your prediction is true, it means although a system or a whole equipment burn in maybe generally too complex to predict, there is still some basic component burn in rules to go by.

The kind of knowledge and experience you had is exactly what I am hoping to learn out of my original post.
I know of no contributions from Mr. Self that rival these
designs, In fact he's probably one of those that think Radio Shack, Cardas and
Nordost wire all sound the same with no audible effect on a high end system
and the music it produces.

Fair enough. Here is another comment from the
[url=http://www.theaudiocritic.com/downloads/article_1.pdf]Radio shack
camp[/url].

As far as I am concerned, I don't agree with Peter but I do suspect that too much
audio gear is based on inappropriate designs for the kind of precision needed to
avoid burn-in. (Examples are "no negative feedback",
"amplifiers with monster damping factors", "amplifiers with
incredible (and useless) flat bandwidth to several hundred KHz", designs
with "capacitors in the signal path" and so on and so forth...)
One thing I've learned over 40+ years is that initial impressions can tell you alot about a system and or it's componentry. If it sucks from cold, it may get less sucky, but it will not be transformed during the breakin process. If a system "WOWS YOU" in the gut from new, you are on the right track. Most aplogies and breakin stories come from people who have chosen poorly and can't deal with the awful truth (I've been there myself).
Most aplogies and breakin stories come from people who have chosen poorly and can't deal with the awful truth (I've been there myself).

Dave, are you saying break in is not real?

I have a break in story, my Dali Megaline speakers were so bad when I first got them that members of my group said I could not "fix them."

Now they say I have the best sound they have ever heard. It did take over 800 hours before they stopped changing. Bass was NON existent in the beginning and I mean absolutely non existent.
Very rare is the story such as yours Albert, and no I do not deny breakin at all! What I have experienced is that great gear sounds great to a certain degree, right out of the box. Time, self-delusion and tweaking will make us feel better for awhile, but in the end reality bites.
If my story is rare, lightning strikes multiple times. Audiogon member and good friend Louis (Logenn) experienced the identical thing with his Karma Exquisite Enigma's.

As with my system, multiple people (about 20 in our group) visited both homes and listened and reported on outcome multiple times.

Some of these visitors listen only once every two or three months, some once a month and some once a week or more often. Considering the huge difference in equipment, solid state, tubes, electrostatics and cones among this group, to have everyone agree about the changes that happen with break in is pretty conclusive in my book.

Similar things with electronics, especially things that have big power supply and or high end caps.

I agree that some people change the personality of their system repeatedly by tweaking this and that. Entertainment value is about all that's good for. My goal is to try and remember every variation possible so I can correct things that are wrong with the system as I slowly upgrade over time.

A typical thing that requires adjustment is my new improved crossover, the Air Tight Supreme over the PC-1 and the Aesthetix Eclipse replacing my Signature models.

All these new items have potential to be better out of the box (as you state) but unfortunately they are not 100% right away. All the high quality moving coil cartridges I've had experience with require 40 to 150 hours before they sound their best.

I'm told by Aesthetix that the new Io Eclipse must be burned for over 100 hours before they can trim the RIAA accurately. Since that's done with an oscilloscope that should qualify as a true indicator of how much caps move after signal is passed through them.
Albert, I agree breakin occurs in most cases within a certain degree of subjective/objective criteria. I have found that gear which sounds off/not right/bad etc.., will not change enough over time to make it acceptable. All of this is very personal and predicated upon ones expectations and degree of discrimination. My best systems sounded pretty damn special right out of the box(es).
I have found that gear which sounds off/not right/bad etc.., will not change enough over time to make it acceptable.

All I can do is refer to the examples I've already given. If you don't accept my experience as believable, that's OK. It obviously differs from the path you've chosen.
I was a believer of burn in before, much more so now than before. When I started the thread two days ago, I noticed my new preamp turned from good sounding to intolerable after about 30 hours of playing. I played several my most familiar music, the treble was so bright and thin, and the bass was absent, that I had to check all my set up and connection to see if anything wrong; I found nothing and concluded the change in sound was most likely due to a certain burn in stage, I was not sure though, and hence posted my thread out of my curiosity.

After reading Albertporter's posts, and especially his prediction on burn in stages on transistor based design, I was more assured of that what I heard was not just my ears playing tricks on me.

After another 20 hours of play time since my first post, sure enough, the bass came back, and the treble became more focused and detailed. Actually, I found the bass is now actually a bit too much, I am hoping it would become slightly better controlled. Anyway, those are dramatic sonic changes in the last few days. I would easily dismissed the preamp if I only heard it during its worse burn in period.

Come to think of it, I seldom owned brand new equipment, and maybe that was one of the reason I did not experienced such dramatic burn in change before. Also, although the preamp was not totally new, the main board was replaced with brand new one, and that the unit I purchased came with brand new Linn silver interconnects and power cables, which I also put into use at the same time, all would attribute to more burn in changes.

If my current experience about burn in is jusitified, I would not judge a brand new equipment just because it does not sound good right out of box.

Maybe I'm not being clear? I agree wholeheartedly in burn in being significant overall. All I'm saying is that a sow seldom transforms itself into a goddess.
If my current experience about burn in is jusitified, I
would not judge a brand new equipment just because it does not sound good
right out of box.

That is exactly what the manufacturer and salesman would say. Just be patient -
eventually it will sound right. I prefer gear that sounds good from the "get go"
and barely changes with use - "robust" would be the right word or - perhaps -
"radio shack".
Burn in could certainly be conveniently used as an excuse by salesman or manufacturer when facing complaint about their product.

Re design with or without components with significant burn in drift, I do not have sufficient technical knowledge to decide which way is better, I am sure it is arguable. However, I think it would be very helpful for manufacturer to educate sales and the consumer how its products would change sonically after burn in. So for example, if I know a product would eventually be sounding brighter/darker than when it is brand new,then I have some fact to rely on in deciding if this equipment would be good for my system without keeping it forever, or well past the allowable return period.

On second thought, it is probably too much too hopeful for any manufacturer to do so. There is just so many variables, and there is no financial incentive.
For those of you wondering about the effects of both better caps AND burn-in, I propose a simple and low cost test:

1) Buy an inexpensive but decent quality tube amp in its stock configuration. My example will be the Almarro A205A. Low power but very nice sound, even stock.

2) Listen to your reference recordings and get the amps strengths and weaknesses firmly in your auditory mind, as best you can.

2) Change the cheap output caps for something nicer. I put in Sonicap Platinums; lots of people use V-Caps, sometimes Mundorf, pick your flavor. Make no other modifications to the amp. Doing this yourself is usually pretty easy and keeps the cost down.

3) Put the amp back in your system and fire it up, no prep, no burn-in.

4) Put your reference recordings back on and listen to them again, once again noting the strengths and weaknesses.

5) Listen to the reference recordings again at 50, 100, 200 and 400 hours. Feel free to accelerate the burn-in by leaving the equipment on 24/7 until it reaches the hour checkpoints.

I predict that during 4) you'll hear immediate and noticeable improvement in many areas. This often the case even with far more expensive amps, because so many use parts that aren't very good. This has little to with good design or bad design; it's mostly about hitting a price point. If that isn't convincing that better caps are generally an improvement, I'm not sure what else will.

I further predict that at the checkpoints in 5) you'll hear noticeable differences, some that will be improvements, some that won't be, but that at all the checkpoints the sound will be converging on what you hear at 400 hours. The total number of hours to "settle in" will, of course, vary with the equipment and the caps, but you get the picture.

At 400 (or whatever your "settled in" point is), I predict you'll think the sound is improved, possibly greatly improved, from what you heard immediately after the upgrade. If that isn't convincing that burn-in is real and generally an improvement, I'm not sure what else will.

If you only bought the amp for the experiment and not to keep, chances are good you'll be able to re-sell it for $50-100 more than you paid for it, because lots of people believe doing such upgrades makes a difference and are will to pay for a piece where they're already done and burnt-in. At worst, you'll sell it for what you paid for it and the only cost of the experiment will be the caps and maybe some shipping.

I was skeptical about both better caps and burn-in effects until I did the above experiment. I am no longer a skeptic.

David
Thank you David, very well stated.
My example will be the Almarro A205A. Low power but
very nice sound, even stock.

The total number of hours to "settle in" will,
of course, vary with the equipment and the caps, but you get the picture.

Exactly! I completely agree. Those tubes and that coupling capacitor on the
Almarro will almost certainly yield audible changes with a re-cap or burn-in - I
can see that simply from a circuit diagram. This is exactly the kind of design
that I was referring too - one that will indeed change audibly pretty much over
its entire useful life - although there should be a period of 1000 hours or so
where it is fairly stable.
Shadorne,

I'm glad we agree. :-)

I think the question then becomes, is it even possible to build an amp that is unaffected by component burn-in? My experience, and not just with the Almarro, leads me to believe that it's difficult, maybe impossible. Do you own such a piece, or have an example you know of? Do you think such pieces inherently sound better than ones that experience burn-in, or do they just drive you less crazy because they don't change?

David
The discussion is veering towards the absurd. Are people seriously arguing that they can accurately compare the changes in the sound of high quality systems when separated by hundreds of hours of actual listening time? It can't be done. Memory is not that reliable. If a component takes 400 hours to fully settle in, that translates to 2 or 3 calendar months (assuming 3 or 4 hours/day of listening). There are too many variables involved for any reliable comparative conclusions to be drawn over such a time span.
There are too many variables involved for any reliable comparative conclusions to be drawn over such a time span.

I agree, unless the differences in the particular case are very great, AND extreme care is taken to rule out extraneous variables. A few possible extraneous variables which come to mind include the following; there are undoubtedly many others as well:

Ongoing aging or burn-in of OTHER system components; seasonally-related temperature changes in the room affecting component performance; changes (also possibly seasonally-related) in line voltage, or in noise levels on the ac line; if records are used, subtle wear in record grooves due to repeated playings; and last but certainly not least, improved perception by the listener of subtle details in the music, due to repeated listening.

Regards,
-- Al
Onhwy61,

That's a totally valid point, but it cuts both ways. If it's impossible for us burn-in believers to ascertain differences from 0 hours to 400, then it's also impossible for burn-in denyers (or those with a preference for equipment that doesn't burn-in, like Shadorne) to ascertain whether a piece sounds the same after 400 hours.

To do my above experiment really correctly, I guess you'd have to take two identical stock Almarros, modify one, let it burn in, and then compare it in an identical system and room to the stock one.

Of course, that would be the kind of scientific rigor that we audiophiles reject, because then we'd have nothing to argue about.

:-)

David
Onhwy61...yup!
Maybe veering off from the exact direction of this conversation, but the way I determine break in is to drive the component 24/7 and do sample listening sessions every few days.

This is easy to do because I'm self employed and my photo studio is connected to the room where my system is.

The break in period I refer to is obtainable in little more than 2 weeks. If you've owned a system for several years and cannot keep track of changes over two or three weeks, you should not be discussing this topic.

For the record, I keep a pad beside the stereo when changes are made and record time. Then I have people in my group listening at least once a week with no coaching from me.

I find this is not only a good way to learn about changes during break in, it's also effective in determining the character of NOS tubes and every kind of tweak that's ever been thrown into my system.

I've learned a lot by including as many others as possible.
I think the question then becomes, is it even possible to
build an amp that is unaffected by component burn-in? My experience, and not
just with the Almarro, leads me to believe that it's difficult, maybe impossible

Yes - It is possible to minimize the problem of burn in to the point that most
engineers would be quite comfortable that changes would be inaudible. It
requires careful design but it is not rocket science. Removing capacitors from
the direct signal path is the first step as these components are indeed non-
linear. Tubes are also well known to change response over time - although
negative feedback can be used to minimize this issue.
Amstrod, simultaneously comparing two identical components with different usage hours would be revealing. I actually believe it would show burn-in as real, especially for mechanical transducers (speakers, cartridges, mics, etc.).
Shadorne,

I'm not an engineer, but your suggestions about burn-in resistant designs certainly sound plausible. Are your Anthem and Bryston designed around those principles? If not, are you searching for amplification that is? What have you found that meets your criteria?

Onhwy61,

Now you've opened another whole field of inquiry. I too believe mechanical components break in (not burn!) and that the effects are very audible. I own Zu Druids, and was discussing break in with Sean Casey, and he said the whole reason they started running in the big drivers at the factory was because they had too many returns; people would set them up and hate the sound of the new stiff drivers and want to send them back, not being patient enough to wait the 200-400 hours they need to loosen up.

I was thinking about your earlier post:

Are people seriously arguing that they can accurately compare the changes in the sound of high quality systems when separated by hundreds of hours of actual listening time? It can't be done. Memory is not that reliable. If a component takes 400 hours to fully settle in, that translates to 2 or 3 calendar months (assuming 3 or 4 hours/day of listening). There are too many variables involved for any reliable comparative conclusions to be drawn over such a time span.

If all that is true, how do we ever make judgments about whether one component is better than another? What time span is short enough to be able to accurate compare differences in what we hear? I use Albert's method of taking some notes, and I have my wife listen and give me her opinion - she hears completely different things than I do. I also use a few recordings I know VERY well as a reference.

If we truly have such lousy auditory memories, it certainly explains why we sometimes seem to be chasing our tails on the upgrade path.

David
Armstrod, the approach you and Albertporter describe could actually be as good an approach as exist for determining overall system satisfaction, but it is not the only way and it certainly isn't foolproof. Short-term A/B listening is the best way to determine whether there's a difference between two audio signals. Longer term listening is probably much better at determining whether those differences are important to music reproduction. That's just my opinion based upon my listening experiences. As with anything, there will be people who are far better at doing something than I can, so I must admit to the possibility that those people can hear things and draw meaningful conclusion from data that I can't.
...our suggestions about burn-in resistant designs
certainly sound plausible. What have you found that meets your criteria?

Most modern SS designs are pretty robust. The "radio shack" type
designs, which are so frowned upon.

Frankly, IMHO - there at least three things going on;

1) User acclimatization to a new sound (true for all gear) - it takes time -
especially if you are well accustomed to your music collection. This change
will be slow as it will require you to go through your entire music collection a
few times to re-train your sonic memory.
2) User trying to hear things about their new toy - the extra effort and
expectation generally means you do hear something (or think you did) almost
every time you listen (at least for the first six months of a new expensive toy)
3) Real audible changes (mostly in the first 30 hours) on certain purist
designs that use very little feedback and valves with coupling caps and
transformers, and certain speaker designs.