What is "break in" and what difference does it make? In amps? Preamps? Speakers? More?

Its the period of time that the dealer does not want to see you and hopes you dont bring the item back within 30 days. 

+1 djones51, +1 davekayc

I’ve posted these before but give these two links from GR Research a read.
Myths Busted!
http://gr-research.com/myths.htm
http://gr-research.com/burnin.htm

I had the same question as you hilde45 since I put in all new components this past Spring. For instance Magico told me it would take 400 or so hours to break in their speakers.

I have noticed with my Magico A3 speakers lately the bass content has become noticeably tighter and well focused. Any improvement seems to creep up on you gradually though, so it's hard to notice improvement on a day to day basis. I don't know if it's only the speakers breaking in or a combination of all the new components at the same time that caused this improvement in bass response, but there's no mistaking it.

The sound stage on the other hand has remained fairly constant from about Day Two on when it suddenly and oddly popped into focus that day when I was playing a Grateful Dead album and wondering about how this system was supposed to sound after breaking in, or if it would actually break in at all.

Overall I think everything sounds much better now, but maybe I'm just more acclimated to what I'm hearing. It's hard to say. I couldn't recognize all that much difference between my old system and the new at first, but after eight months or so my new system sounds so much better than the old, perhaps due to all the components breaking in or who knows what other factors like familiarity. Anyway, it's a good question you posed for us newbies even if some of the regulars have heard it before. Good to see another newbie aboard. Welcome.

Mike

I've been through my share of gear over the years and yes, for whatever reason, I've found that the majority of components do sound better after they've been played for a while. Agreed, some of it might just be your ears coming to terms with what the new components are feeding you but that's only a part of things.  I've always found that edginess trims downward, bass becomes more integrated with the rest of the sound, and timbres of instruments become easier to distinguish.  Phono cartridges get more limber. My only components that did not suffer/benefit through break-in time were my long-departed Celestion SL600's and my even longer-departed Quicksilver Mono Amps.  On the other hand, my new Mytek Brooklyn Bridge has improved markedly in the few months I've had it.  As for my now ancient, much repaired/upgraded SOTA turntable & Alphason arm, who the heck knows?