Jeff, i think that there have been quite a bit of advances in terms of the materials used in both passive and active parts. Resistors are no longer resistors, capacitors are no longer capacitors, wire is no longer wire, etc...
By this, i mean that we have come to the point that one can measurably demonstrate differences from brand to brand of passive components. In fact, John Curl recently posted that he was able to drop distortion in his recent amplifier project by one one full MAGNITUDE simply by changing one passive component. He simply substituted a Brand A resistor for a Brand Z resistor of the same value and tolerance. By a magnitude, i am talking about a figure of .0X to .00X THD. His findings in this area were important enough to halt production of this product. They did this so that the manufacturer could incorporate these changes into production models before they hit the streets.
Needless to say, John was overjoyed with these findings and that is why he posted this information. He went so far as to comment that people that believed that "resistors are resistors" and that there were no differences between brands couldn't be further from the truth. Given Curl's credentials and previous design efforts for the last 30 years or so, i'd have to take his comments with a LOT more than a grain of salt. Especially given the fact that he was somewhat of an "unbeliever" in this phenomena himself not that long ago. Just ask his business partner, Bob Crump.
Obviously, there is something going on within the resistors chemical make-up that causes a difference in actual circuit use between these two brands. Even though they may measure nearly identical in terms of parts value in stand alone tests, they are performing differently when combined with other factors within this specific circuit. If one were to say that a Brand A non-inductive resistor of 1K ohm and 1% tolerance would measure and sound differently than a Brand Z non-inductive resistor of 1K ohm and 1% tolerance 20 years ago, they would have been laughed out of the engineering society. Yet such findings are now becoming more and more common place. The same can be said for capacitors, diodes, types of metals, etc...
Not only do some of these parts work differently within the same circuitry, they will have different "lifestyles" or operating curves within their lifespan. Due to metal migration in semiconductors, their gain curves, internal impedances, etc... can vary drastically with age. This is part of the phenomena that has been tagged "break in" or "settling". Not only do components initially "change" when first being used, they do so over their entire life span. Some may be more gradual, some may have sharp knee's in their operating curves, some may remain consistent until their point of demise, etc... Shoot, even solder conductivity changes with age. This varies depending on the metals used during its' initial manufacture and how well it bonded when applied to the connection. With that in mind, how much technology do you think goes into a solder formulation as compared to an actual part that has gain and internal impedance considerations ???
As we've had more time to experiment and chart these differences and reactions, the engineers have made quite a bit of progress in terms of incorporating this information and other findings into building better passive and active parts. As such, similar circuitry built 20 - 30 years ago might sound / perform / measure notably different than the same circuit using current technology and "high grade" parts.
As such, many products have simply re-invented the wheel using better materials and implimenting the knowledge that comes along with technological breakthroughs and studies done over a wide period of time. The end result: a "wheel" that lasts longer, is more reliable, produces a more comfortable ride with less "road noise", one that handles better under extreme conditions, etc... Yes, it is still a wheel, but it is one helluva wheel : ) Sean
>
