I hope to aid in the understanding of break-in and what it does.
During my research into distortion, I was forced to include the break-in phenomenon.
Mostly because the tiny distortion I was going after was very similar to the size of the distortion reduced or removed by allowing sufficient “break-in” time. This component behavior is something I am very familiar with. There is no mystery as to how break-in affects sound reproduction. To understand how the sound changes, you need to know exactly what happens during that time.
There are those that have sought guidance from A-B tests done on capacitors from various manufacturers. An attempt is made to ensure that it is a “fair” test. Capacitors are swapped out under the same physical conditions (leads are held by screw terminal type connections). While it seems fair on the surface – it is not the way to determine which capacitors are better than others.
If you want it to be fair – you take the ten samples and build them into ten copies of the same circuit.
Then after listening tests that include early (fresh) and late (3 weeks) comparisons you will have your answer. Two capacitors from the same manufacturer can sound different depending on where it is used in the circuit. You have to know some history of the component even though it may be new stock. Depending on how it is tested before shipping will affect the length of time forming process will take.
In a nutshell: The capacitor will initially behave as having non-symmetrical impedance. It is not exactly the same as having a non-linear component. Current drawn by the charging cycle will not match the current given up by the discharge cycle. This is due to the instantaneous state of the dielectric. Therefore the impedance will be slightly higher in one direction and lower in the other direction (until it is formed). We are not talking about a big difference – in fact it is not measurable.
How then would I know that this is true? I have worked with distortion products that are at or below the noise floor. Once you reduce distortion down to extremely low levels (to where they don’t show up on test gear) it then relies purely on theoretical analysis to go any further.
Since I was already down there – the break-in phenomenon was right in my wheelhouse.
The mismatch in charge/discharge current causes the timing of the positive and negative wave-fronts to be askew. This detracts from the feeling of "live" that we naturally get when listening through air.
In fact if you want to see the difference just the break-in can make, I received 2 reviews for the same gear by the same person whose comments in the second (follow-up review) describe how the equipment has morphed into a different experience. When the circuitry has very low or no distortion, the break-in changes are much more noticeable because their distortion product is larger in size than the circuit’s own distortion. Once the forming is complete, a now clear path is recognized through the entire product. You begin to hear the true purity of just the circuit.
Roger