Fuses that matter.

+1 to Metralla's comment.

Vance, I'm not certain that the Classe person you spoke to was giving you a precise answer. Breaking capacity (also referred to as "interrupting rating") has nothing to do with the likelihood that inrush current at turn-on will cause unnecessary fuse blows. Or, at least, there is no direct relation between the two.

Breaking capacity refers to the maximum amount of current occurring under fault conditions, when the fuse SHOULD blow, that the fuse can deal with without an explosion or other safety hazard occurring. That rating will be far greater than the current rating of the fuse.

The parameter that is most relevant to withstanding inrush current without blowing unnecessarily is what is called the "nominal melting" point of the fuse, which is usually specified as (amps squared) x (seconds).

Datasheets at the Littelfuse site provide very comprehensive technical data on their fuses. You might want to look up the specs for the particular fuse that is in your amplifier, and ask the manufacturer of the upgraded fuse you are considering if they can provide you with the nominal melting spec for their fuse (as well as its breaking capacity, which as I said is relevant to safety). Their response should be interesting.

Regards,
-- Al

Al,

I am no engineer, so I'm certain I poorly paraphrased the fellow at Classe' but he was quite concerned with the safety of using anything other than the Littelfuse fuse because of the extensively described measurements in the data sheet to which you are referring. I plan on forwarding the data sheet for the fuse in question to both Synergistic and Hifi Tuning. I agree that the response should be interesting. For anyone interested, the fuse is a 215 series 012 Littelfuse...12 amp slo blo 5x 22mm.

Thanks, Vance. Here is the datasheet. (I assume you meant 5 x 20 mm, not 5 x 22). Looks like the breaking capacity/interrupting rating (related, as I said, to assuring that blowing which occurs under fault conditions occurs in a safe manner) is spec'd as 1500 amps @ 250 volts, and the nominal melting spec (related to the likelihood of unnecessary blowing at turn-on) is 515.5 amps squared-seconds.

Regards,
-- Al

Al,

I really should refrain from posting after 11pm. My attention to detail declines markedly. Yes, I meant 5x20mm.

I'm just curious as to whether you think one should generally be concerned with the specs of after market fuses produced by reputable companies like Synergistic and Hifi Tuning? The Littelfuse for my amp costs a mere $1.67. Surely, we can't be talking about a product that is beyond Hifi and Synergistic's ability to re-produce, assuming there would be any profit in it for them.

Does the data sheet reveal anything to you that would indicate how it is "special" or "out of the ordinary?" I ask because you clearly know more about this technological data than I do.

Regards,

V.

Hi Vance,

I don't doubt that these companies COULD replicate the protection characteristics of the stock fuse. However, different designs of just about any electronic product differ in terms of their design goals and philosophies, and how the tradeoffs that inevitably must be made between many different parameters are prioritized.

As you've seen in the datasheet, even something as simple as a fuse has a great many different specifiable parameters. In addition, earlier in this thread links were provided to papers prepared by HiFiTuning which presented several pages of comparisons between various measurements of various makes of fuses. The data differed widely among the different fuses. (Although I commented that IMO none of the differences appeared likely to be quantitatively significant, and even if some of them were quantitatively significant in some applications, I saw no reason to expect the resulting sonic effects to be consistent among different component designs, and among different AC line voltages).

So given the many parameters that are involved, and the diversity of measured data for different fuses having similar current ratings, it seems to me that while the aftermarket fuse manufacturers COULD replicate the protection characteristics of this particular Littelfuse, I would have my doubts that they DO closely replicate them. But as we said earlier, it will be interesting to see what they provide in response to an inquiry asking for breaking capacity and nominal melting numbers.

Here's another thought, though, that is suggested by the numbers in the Littelfuse datasheet. On the first page, take a look at the numbers in the table of "opening times" (i.e., the amount of time required to blow) that are shown at the lower right. Note in the entries for 275%, 400%, and 1000% that the range of specified opening times for a given fuse and a given overload is huge. For example, for fuses rated between 8 and 20 amps, and overloaded to 400% of their rating, the blow time can be anywhere from 0.15 seconds to 5 seconds. That is a huge possible variation from fuse to fuse. Which suggests the likelihood that many other parameters, for which only a nominal value and not a range of possible values are specified, could also have wide fuse-to-fuse variations.

So it seems to me that a useful experiment may be to simply buy a bunch of fuses that are the same make and model as the stock Littelfuse, and compare sonics between them. Who knows, maybe you'll find significant sonic differences between them, and perhaps one or more of them will provide sonics comparable to what the aftermarket fuses would provide.

If you do that, btw, it might be best to split the order among multiple distributors (e.g., Digikey, Mouser, Newark, etc.), which may increase the likelihood that the fuses you try come from different production runs.

Regards,
-- Al