Why does it take so many hours to brea in arc preamps and amps?

"Let’s play with the "burn in" crews heads.

If you think about it, all the optimum adjustments are made at the factory after the amps been on for a while, maybe an hr if your lucky.
If thing change after 600hrs then those optimum factory adjustments have just gone out the window and need to be redone again.

So it’s either out of adjustment because of aging, and therefore not optimum, or the factory needs to have them on for 600hrs before they are adjusted and sent out to the shops. 
Either way if things change they would be out of the original optimum adjustment. "

Cheers George 
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In response to this, "burn in" and "being out of adjustment" are not the same. When a unit reaches burn in doesn't make it out of adjustment and requiring new setup from a technician. The components may be aging but this is a good thing. Everything reaches its optimal state of age and for most electronics it takes a long time to consider them not good. Generally I think under 100 hours is the most you should expect to break in a large variety of components. The amount of "current" can play a role as well. 

In fact how a unit sounds after break in is a planned part of prototyping to final design. All electrical parameters are set to reach this "break in sound". 

During break in an electrical effect happens, the flow of the electrons across all of the components causes micro surface arcing and tends to smooth and create a shortest route pathway. There is also a small magnetic field that develops around all paths which affects signal flow and interaction between materials.

To give you a visual idea, all this happens over time like water flowing through a pipe that had very fine sand in it. The effect smooths and polishes the edges and surface of the pipe, to electrons at an atomic level it also aids in flow. The flow of electrons can be a violent one, if they "carve" themselves the optimal pathway noise decreases and more of the original signal is heard. 

In response to this, "burn in" and "being out of adjustment" are not the same.

If you know better convince Nelson Pass of this below, in case you missed it.

Nelson Pass:

"We burn products in for two reasons -

1. We want to see if anything fails.

2. We want to readjust the amplifier against any drift in performance that comes with a burn-in."

Nelson Pass on "Burn In"
"It's pretty clear that any such long term behavior is going to be
obscured by the burn-in of the listener. People come to new
audio components carrying the experience of the previous
equipment, and may experience some dissonance with the new
sonic character, even if they like it overall. Over time they often
get used to it and grow to like it.
There are plenty of cases where they initially like it, but the sound
becomes irritating over time. That is called burn-out."

Cheers George

In response to this, "burn in" and "being out of adjustment" are not the same.

If you know better convince Nelson Pass of this below, in case you missed it.

Nelson Pass:

"We burn products in for two reasons -

1. We want to see if anything fails.

2. We want to readjust the amplifier against any drift in performance that comes with a burn-in."

__________________________________________________

Yes of course these are factors in any piece of gear, but where do most manufacturers draw the line? Nelson Pass is an exceptional designer of both consumer and professional gear, but this isn't explaining what burn in is? 

He is also doing this because he knows that on occasion a small percentage of parts "drift" from their values quickly and are by their standard out of spec, not necessarily anyone elses spec. 

I have built and repaired many pieces of gear and always take readings of the values of for example capacitors and resistors, they can be so close to spec for dozens or even hundreds in a row and then all of the sudden so far from spec. This is why all good manufacturers burn in their products and do a final analysis of specs.
They know from experience the parts failure, drift and burn in time rate that is expected. 

Quoting Nelson Pass doesn't make your description any more accurate than you previously stated, that is his procedure for meticulous production standards which are seldomly done by any in the field because final costs of products get pretty high. 

Nelson has set the bar pretty high for himself and can't be caught with his pants down so going to those lengths of "burn in" is beyond what is burn in. It really making sure his product has satisfied his standards to not get back a piece of gear for component failure within the warranty period or even much longer. This is so far above most others ethically alone that it is a personal over financial gain that few choose to go to.

Think about what "burn in" really is again in the real world in everyday use products.

DM 
 

I think the notion, differences and understanding of "burn in" are pretty misunderstood form reading many descriptions.

If everyone realised that "burn in" has so many factors involved that it should be broken into sub categories of "break in" rather than "burn in",  perhaps getting a better idea of what is expected from it might be easier to answer? 

I know when I buy a new piece of gear or replace a capacitor I call it "break in". A new piece of gear that has been used for some time is "broken in" but also well "burned in". 

A new piece of gear that has been broken in and burned in for some time and needs say a few new capacitors because of failure is still burned in but needs to be re-burned in again because the new capacitors will take about anywhere from 10-100 hours to break in and reach their final burned in sound. The gear as a whole is still burned in just the capacitors will keep changing sound until they get to a certain point. Break in generally refers to getting a part or gear to certain point of aged reliability through a controlled break in of parts. Not all parts can go to 100 percent full on from new and have to be slowly broke in or premature damage could result from over heating or sudden stress. Metallic parts are heat treatable so too fast of or hard of break in can actually change the way a part ages or takes to being able to predictably get past the final "burned in" point. 

There is a point where different electrical parts take longer than others to get to their "optimal state" from new. And then from that point they are degrading slowly and steadily. The sound may change for better or for worse. It is a combination of experience and parts that dictate this.  

One good example of this is Cables. A cable only has the variables of the wire and dielectric. A little more straight forward from a "burn in" point of view. 

Most speaker, power, interconnect, etc... are not "broken in" because they have a near zero failure rate, have no electrical parts and ultra high consistency in sound out of the box. They are just used to transfer electricity or the source signal. So here we can refer to where I believe many confuse the two, "break in" and "burn in".
They similar but different as the burn in is only really changing the surface and magnetic field of the wire and dielectric. So because these attributes change the the conductor so does the sound for the reasons I stated in the original post I made. 

So hopefully this makes as much sense to you as it does to me? ;)

DM

Georgelofi wrote,

In response to this, "burn in" and "being out of adjustment" are not the same.

If you know better convince Nelson Pass of this below, in case you missed it.

Nelson Pass:

"We burn products in for two reasons -

1. We want to see if anything fails.

2. We want to readjust the amplifier against any drift in performance that comes with a burn-in."

Nelson Pass on "Burn In"
"It’s pretty clear that any such long term behavior is going to be
obscured by the burn-in of the listener. People come to new
audio components carrying the experience of the previous
equipment, and may experience some dissonance with the new
sonic character, even if they like it overall. Over time they often
get used to it and grow to like it.
There are plenty of cases where they initially like it, but the sound
becomes irritating over time. That is called burn-out."

Classic case of Appeal to Authority. I.e., just because someone deemed to be an authority offers an opinion on something doesn’t necessarily mean it’s true. One actually doesn’t have to look too far to find a designer of audiophile amplifiers or whatever who has stated he has some sort of issue with break-in/burn-in of amplifiers, cables, capacitors, wiring, fuses, wire/fuse/cable directionality, polarity, or anything else related to audio. In fact, if I may be so bold, amplifier designers might be the most dogmatic of the bunch. No offense to Mr. Pass or anyone else.