I guess I would define "Mods" as changing parts values and brands, changing cables and wire types, and adding acoustic damping and such without making any significant improvements in the overall design topography or making the electrical engineering effort to determine the worst case problems in that particular unit. I am dubvious of this approach because everything we have learned over the years regarding electrical engineering suggests that almost always the worst case problems are the actual electronic circuit designs, either/and the actual design or the linearity of the active parts used in that circuit. I am suspect of any "mod" projects that does not have the engineering background to locate and fix worst case problems first. Of course some passive parts replacement can do a world of good, especially if the originals were a design blunder, such as using polarized capacitors in a coupling application where the audio signal swing can drive them into negative bias range, or simply under-rated power values causing parts to cook to death long term.
I do wish that "capacitor replacements", for example, would be done more carefully. This means measuring the real value of each part removed and replacing it with a matching part of the exact same value. Capacitors are not the value printed on them, they are the value they actually measure. The most important tool for an amateur trying do it your self mods is a precision capacitor meter. Since many capacitors are 20 percent tolerance or worse, randomly changing lots of them in a given circuit will randomly change the actual circuit operation, for better or for worse. If the actual values are not held as a constant, then any differences in sound (and there will be differences) cannot be reliably judged to be better or worse - - - just different (unless the original part was obviously defective).
When we offer a "rebuild" for an audio unit, we are offering a completely new audio circuit design that is engineered to fit in the place of the original circuits. For example, in the Insight 400 rebuild/upgrade of the old Dyna St-400 amplifier, the heat sink is stripped to bare metal, all the original Dynaco circuit boards and wiring are discarded, all are replaced by new modern AVA circuits. The only thing remaining is the power transformer and some of the mechanical bits that have no history of premature failure.
I would also suggest that "built down to a price point" is not a significant issue in any audiophile grade component. Precision metal film resistors are about 6 cents each in quantity. High reliability capacitors are available at 20 cents to 5 dollars each depending upon type. "Audiophile" grade passive parts are simply a giant scam in my book, preying on the folks with no EE background and no skills to separate fact from hogwash.
Regards,
Frank Van Alstine
P.S. We do not use "cheap Chinese vacuum tubes" although some arriving Chinese tubes are just fine. They are learning fast.
