Burn in question and evaluation before burn in

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).

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.

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.

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 !

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".

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...)

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.

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.

...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.