Physical explanation of amp's break in?

Sean has pointed out that the change which occurs with initial use is a DETERIORATION, and he needs to readjust circuitry to make it work right. Tuned, adjustable circuits (which appear to be what he refers to) can be shifted away from optimum adjustment by the small changes of component electrical characteristics. This is not the same thing as saying that a power amplifier circuit improves with use.

The original posted question sought to find a scientific explanation for "breakin" improvement, but somehow the thread has degenerated into a debate as to whether such a thing happens. Frankly, I remain to be convinced, but my comments have been directed to pointing out that some of the theories put forward are, from an engineering perspective, obviously wrong, and detract, rather than add, to the pro-breakin point of view.

Sheesh... As the components shift to their natural point of settling, the sound or performance of a circuit typically improves as the circuit itself reaches its' natural "plateau" of operation. In other words, the circuitry finds its' own "groove" and settles there. Since the device is now running at a point that it has reached via normal use and is no longer changing values during normal operation, the presentation tends to sound more natural and relaxed due to increased circuit stability. Everything is done shifting and is now working together. This is kind of like "neighbors" that have had time to become fully familiar with one another and know what to expect out of each other. If the relationship between any given components are pushed beyond the point of initial settling, deterioration and / or "re-settling" takes place but this is usually not without good reason. If pushed to an extreme, damage occurs and the circuit is no longer usable as is. Sean
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By the way, the brand new units that come back in for "re-alignment" after a few months typically work better than they did when i took them out of the box and aligned them the first time. I am not talking about small incremental improvements in selected areas of performance, but "better" in most every aspect once they've been "dialed in" after "breaking in". Sean
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Eldartford, It is really very simple.

1. a prototype is built
2. it is allowed to burn in for an extended period of time
3. the sound is evaluated
4. adjustments are made
5. it is burned in, evaluated, adjusted
6. it is burned in, evaluated, adjusted
7. etc. until the design is finalized

The final design is based on components that are burned in.

A new unit has not been burned in for this extended period. It does not sound like the one that was the final design until it has been.

Once again, I believe there *is* such a thing as "break in." I believe I have heard amplifiers change over the first few weeks
and they also sound better if you leave them on, never turning them off. But, I also believe manufacturers have become hip to the fact that buyers are often stressed by a new purchase and that, not only does the component "break in" but the buyer's ears return to
normal after a period of acceptance. And, this is just another good
reason to tell buyers to give the unit 300 hours to "break in."