What Exactly Does "Burn In" do for Electronics?

So it seems like we are in agreement, that to us "break in" for better or worse can occur with the mechanical devices such as speakers drivers, cartridges, and tubes, as you also said.
And you and I will not commit without skirting around the edges and state to "break in" periods of semiconductors or active components can get "better sounding" with said "break in" times of 100's of hours, unless some technical proof is brought forward, forgetting hearsay of friends and customers.
Cheers George

There is a certain semi-conductor I do believe undergoes burn in, but as an exception to the rule. And I seriously look forward to yours, George, and Al's comments on this. I've brought up the offset and bias trim pots which are variable resistors, on a couple of other threads but not in regards to this topic. I'm suggesting that because they are always adjusted after recap/refurb, that the perceived short term progressive improvement heard even with new gear is a result of the wiper contact on the pad of the trim pot 'seating' and thus improving it's contact point until optimal and it is this action that is being tracked sonically by the user. The change is real but simply mis-attributed to stationary components. I regularly experience this phenomenon. It's easily observable and you George may be able to relate to this as the same issue pertains to basic mechanical attenuators. The very issue your own product addresses. On a single turn trim pot where you have direct contact with the wiper against your screw driver, you can press on it at the point of correct adjustment and hear improvement. Leave it alone and it will slowly reach that same quality over the short term. I incidentally noticed this a long time ago as another position I hold on bias adjustment requires that I do that procedure while listening. Sq has always continued to improve for up to a month or so after I adjust offset/bias pots. I'm thinking this has to be some how measurable. Without knowing the specifics as I don't recall the text, volume pots have contact issues such that optimization is apparently next to impossible and I'm hoping George can speak on this.

I know this won't be good enough, but I'll try one last time.

This is directly out of the manual for my Ayre V-5.

"Break-In
100 to 500 hours of music
played through the system will
ensure full break-in.
Due to the manufacturing processes used for the
printed circuit boards, wires, and capacitors, a
break-in period is necessary for the amplifier to
reach its full performance potential."

Here's one from Pass Labs.

"Amplifiers
Do the amps need to break in. Yes. Most improvement comes in the first 24-36 hours, after which the amps will continue to improve as long as they are left on.

Preamplifiers

How long do the preamps need to break in?

That depends. The XP-10, XP-20 and XP-15 need about 24 hours to fully warm up. The XP-25 and XP-30 take closer to 36 hours. After initial warm up period the preamps will continue to improve as long as they are left on."

If you want more examples like this, there are thousands. All you have to do is look for them. If you read reviews from magazines like TAS and Stereophile, break in details are included in almost every equipment review they publish. (I haven't read reviews for about 10 years now. I'm assuming they still talk about break in.). You can also call a manufacturer directly. They are usually happy to answer any break in questions pertaining to their equipment.

Other that that, I don't know what more I can offer on this topic.

06-23-14: Georgelofi
So it seems like we are in agreement, that to us "break in" for better or worse can occur with the mechanical devices such as speakers drivers, cartridges, and tubes, as you also said.
And you and I will not commit without skirting around the edges and state to "break in" periods of semiconductors or active components can get "better sounding" with said "break in" times of 100's of hours, unless some technical proof is brought forward, forgetting hearsay of friends and customers.

George, that is not quite what I said. Note particularly item no. 2 in my previous post, which is entirely consistent with what is stated in the references ZD cited just above.

Peter (Csontos), the potentiometer-related effect you described certainly strikes me as being plausible, and a clever observation, but my suspicion is that it is just one of a great many effects that can occur.

Best regards,
-- Al

"ZD cited just above." Is again not a technical explaination. Could conscrewed as getting used to the sound so you don't take it back for refund.

As for trimpots Peter (Csontos), yes if they are left in one position for a while they do tend to loose contact between the wiper contact point (metalic), and track (carbon or conductive plastic) because of current flow between dissimilar materials.

Part of the same reason for the Lightspeed Attenuator, no contacts of dissimilar materials (diode effect). When ever I see this, I take out the single turn trimpots and replace with Bourns multiturn, they last a bit longer but still have the same problem after a while. Maybe we should use the Lightspeed system as bias pots as well, now you've given me another idea.

Cheers George