1)Many of the purported explanations of the benefits that have been reported to be provided by expensive fuses amount to descriptions of their physical characteristics, and/or descriptions of how they were manufactured, but do not explain how those characteristics would affect the power supply circuitry and/or audio circuitry that is downstream of the fuse within the component, at least to an audibly significant degree and in a way that would be consistently beneficial.
2)Extensive sets of comparative measurements that have been provided in papers by HiFiTuning, that are sometimes cited as explanations, have been mostly debunked as explanations by me and others, such as noted amplifier designer Roger Modjeski. Generally that has been because the measured differences are far too small to account for the reported benefits, and/or are so small that they would be totally swamped by corresponding differences in the associated wiring and circuitry. (Although see item 2 below for a possible exception).
3)It is not unreasonable, IMO, to consider the high degree of consistency that has been reported for the reported benefits of SR and other expensive fuses, among components that perform completely different functions, that are completely different in design, that are used in completely different systems, that are powered by AC having very different voltage and noise characteristics, and that are used in both DC and AC applications, to simply be implausible.
4)Wolfie, as well as many of those who are on the opposite side of this issue, have earned considerable respect in my book as a result of his and their many posts here over the years.
Those are the reasons I consider Wolfie’s question to be legitimate, and to have been mostly unanswered in the past despite the lengthy discussions that have occurred, involving many of the same protagonists, in various fuse-related threads going back at least as far as the “Fuses That Matter” thread which began in 2012. At the same time, of course, I certainly recognize that many highly experienced, sincere, and knowledgeable audiophiles have reported significant benefit from these upgrades. While at least a few members having similarly high caliber audiophile credentials have tried some of these fuses and found them to provide little or no benefit, including at least one exceptionally experienced member I can think of whose system costs well north of $50K.
So from a technical standpoint what might account for the benefits that have been widely reported, and what might account for the absence of those benefits in some applications? I suspect that among the many different kinds of applications many different factors may be at play. Here is my shot at it:
1)I suspect that the effects of the small but rapid variations in fuse resistance that occur in applications in which the current through the fuse fluctuates widely are somehow affecting circuitry that is downstream of the fuse. Presumably the fluctuations in resistance differ significantly among different fuse types. I can’t explain exactly how those effects on downstream circuitry may result, though.
Circuit applications in which fuse currents fluctuate widely would include speaker fuses (even the late Peter Aczel of “The Audio Critic” recognized back in the 1980s that speaker fuses may have audible consequences), amplifier output fuses, DC rail fuses in most power amplifiers and the power amplifier sections of integrated amplifiers, and mains fuses in most power amplifiers and the power amplifier sections of integrated amplifiers, especially those not operating in class A.
2)I suspect that small differences in voltage drops resulting from small differences in resistance are probably marginally significant in at least **some** applications. For example, perhaps those differences result in audibly significant changes in the filament voltages supplied to some tubes, in designs in which those voltages are not internally regulated.
3)I would assume that the aging effects George has repeatedly referred to contribute to or are responsible for **some** of the reported benefits.
4)I would assume that improved contact integrity, scraping away of oxidation, etc., resulting from simply removing and replacing a fuse contributes to or is responsible for **some** of the reported benefits.
5)I would expect that the explanation Ralph (Atmasphere) has provided for the directionality effects that have been reported, namely reinsertion of the fuse with differing rotational orientation (rather than intrinsic directional properties), resulting in voltage drop differences which he has experimentally found to be both measurably and audibly significant (and which another member here has reported to be audibly significant), contributes to or is responsible for **some** of the reported benefits.
6)I would expect that unrecognized extraneous variables, for example differences in equipment warmup states, differences in AC voltage and noise characteristics, differences in room temperature or humidity (temperature is a fundamental parameter in the physics underlying the operation of semiconductors such as transistors, diodes, and integrated circuit chips), flushing of internal digital memory that occurs when power is cycled, etc., are responsible for **some** of the reported benefits.
Finally, given the many positive reactions to fuse upgrades that have been reported here in a multitude of diverse applications, by many (but certainly not all) of the members here who have tried them and for whom I have considerable respect, I would feel pretty certain that there are other explanations I am unaware of that are at play in some cases. Especially in the harder to explain applications in which the current being conducted by the fuse does not fluctuate significantly, and where excellent internal voltage regulation is incorporated in the design. But I have no further ideas as to what those additional explanations may be. Given though, that in the video that was recently linked to in this thread even Paul McGowan indicated that he can’t explain these benefits, I guess I’m in good company :-)
Finally, as far as my own interest or lack thereof in pursuing these things is concerned, taking into account the numerous experiences and opinions that have been reported on both sides of the issue, my own technical understanding of these matters, the numerous reports we have seen here of expensive fuses that have failed when they shouldn’t have (from at least eight different members here during the past two years), and my own general preference to devote most of my listening time to just listening to music rather than spending a lot of time trying to extract the last 10 or 20% or so of the performance my system may potentially be capable of, FWIW I personally have no plans to devote time to assessing fuse upgrades in my system in the foreseeable future. Best wishes to those who do, however.
Best regards,
-- Al