Burn in question and evaluation before burn in

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

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.).