Physical explanation of amp's break in?

Sean is right, as a piece ages, the components inside it change value. Resitors changes value, electrolytic caps start to dry out and ALL of them will eventually fail if used long enough, substances such as plastics used as dielectrics change especially when they get hot, and it is indisputable that tubes change as they are used.

I have rebuilt numerous tube guitar amps over the years and the change in sound is quite amazing when the carbon resistors that have risen in value and the old, dried out electrolytics are replaced.

Electronic components have a rated lifetime but they don't have an instantaneous change in value at the end of their life. They change gradually over a period time until finally they are stressed past the point they can withstand or the circuit they are in no longer functions properly.

Solder joints are a very good example. There have been numerous studies about this and volumes of data that support the fact that these joints change over time.

Whether you want to call this "breaking in" or not is up to you. Whatever you call it it is very real.

Eldartford, your logic is flawed. Even though it is true that components are rated at some value plus/minus some percentage, it does not follow that a different value will sound the same even though it is within the rated specification. For example, if you built a crossover with all caps that are + 20% and another with all caps that are minus 20%, they would have decidely different cutoff frequencies and they would sound different.

As to the original weaker bass, stronger bass question, this could have something to do with the capacitors in the amp. The dielectric does change over time as voltage is applied to it. This affects the capacitance as well as the effective series resistance. I have no idea what the topology of this amp is or what type of caps are used, but I would not rule this out. Sean has given sound scientific explanations for his response, Bomarc, I would be curious to hear the reasoning behind your "nope."

Missile guidance systems ???????????? Are you seriously comparing the performance of missile guidance systems to that of audio circuits? If you insist on taking your experience in controlling the flight of giant bullets and using it to explain the function of audio circuits, then I fully understand your inability to grasp these concepts.

If I had known we were discussing two entirely different worlds, I would never have refuted your original position.

I too am "over and out" on this one :>)

Eldartford, you are correct. Components are ignorant, but designers are not. They listen to their creations after everything has settled in, if it sounds worse than when they began they attempt to find out why. This is the same reason amps, etc. sound better when they are warmed up, that is how the designers listened to it when they finalized the design.

And yes, the circuits are sensitive to the value of componenets. Maybe not "exact" values, but there has to be some point at which the change is audible. Otherwise there would only be one value of resistor, capacitor, etc. Why does Levinson use laser trimmed resistors in some of their circuits? Because they believe that the exact value at that point in the circuit is critical.

Dmitrydr, I am not a capacitor engineer so I don't speak with great authority on how capacitors change over time, but I don't find it unreasonable to assume that if one was to apply a certain signal to a certain material that it's reaction would be predictable. So I would say yes to your question.

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.

Aball, back to an earlier question: when you say that capacitors drift, for a given type of capacitor, do they always drift in the same direction?