What is the science behind audiophile fuses?

@lalitk I don't think anyone is now working on a version that fits into the fuse holder.  I was the most interested in that and I've moved on.  Like I pointed out, every IEC fuse holder is different so very hard to make one that works on every amp.

@mitch2  can you share what make and model magnetic breaker you are using?  thanks.

Fuses have to heat up and blow to protect the downstream equipment.  So they have to have a significant resistance (to heat up) and as current goes up, they heat up, resistance goes up (a property of all metals) and they heat more and blow.  This isn't a problem for electric motors or household equipment.  but a high end amplifier can have dynamic changes in power requirements over a very short time which can be limited by the fuse.  If this happens to your air conditioner, it will still cool.  If it happens to your amp, it will still make music, it just won't be as dynamic. Bass will suffer as well.  

An audiophile fuse supposedly has less resistance and limits current less.  I have never bought one and don't plan to.

I replace fuses with slugs.  an overcurrent situation in an amp is very unlikely and when it does happen it is usually caused by user error.  There is a very audible difference in most amps replacing the mains fuse.  This is especially true of tube amps.   Also if your amp has fuses on the rectifiers they should be replaced.  

No your amp won't burst into glorious flames but if you can't get this image out of your head, keep your fuses.

I have tested the Swiss Digital Fuse Box that replaces the fuse with a magnetic current sensor and a relay, thus there are no heated components in the power circuit.  My opinion of this piece was that it was better than any fuse but not quite as good as a slug.  It is also cheaper than an audiophile fuse.

Jerry

@tksteingraber Slugs are solid copper jumpers that replace the fuses.  No protection.  --Jerry

@tksteingraber realize that the fuse replacement is just a short piece of conductor adjacent to the power cable.  I don't think you'll ever hear a significant effect fro different coppers on such a short piece of conductor, just so it is heavy (not thinwalled tube).  Now often the fuse holder is not great--it can't be soft copper or it will relax and not clamp the fuse.  Often they are .....clears throat....whispers....steel.  so a good fuse holder would be where to focus your interest. 

That said, I'm as audiophile geek as anybody so I buy high conductivity copper 5mm bar from McMaster car, cut it into fuse lengths on my lathe, and polish with scotchbrite.  I'll be glad to send you one if you want one.

Jerry

@thyname thanks for the shout out as the original "we don't need no stinking fuses" guy.

I have tested the Swiss Digital Fuse Box and recommend it over any fuse.

My impression was that it wasn't as good as the "large gauge piece of metal" (high conductivity copper) but not a lot of difference.  If you feel you need/want electrical protection, I recommend the SDFB.

I think some people are confused about the configuration of the SDFB.  It provides better protection than a fuse.  Generally a magnetic current monitoring circuit will trip much faster than a slow blo fuse.

Of course we've all had experience where a compoent failed and the fuse didn't protect it.  that's just the nature of electronics  the fuse protects against upstream disturbances more than downstream failures.

Jerry

People overestimate the engineering and design behind the fues the OEM puts on their amp.  First fuses can't protect everything inside your amp, otherwise, the fuse would be practically the only thing that fails.  but in my life I've seen a lot of equipment fail and almost never does the fuse blow.  the latest example is the DRO (Digital ReadOut) on my milling machine.  It died 3 weeks ago. Opened it up to find a burned circuit board, and a fully intact fuse.  I just finished installing a new one  BTW, it was the Cadillac brand of DROs, similar to PASS for a power amp, not a boutique like some of the even more expensive amps.  

Input fuses are required by law (but not always) and expected by consumers.  I'm sure many engineers add the fuse last, look at the max expected current, add some margin via "engineering judgement" or "rule of thumb", and put the fuse size on the drawing.  If during development and testing the fuse blows, they increase the size of the fuse.

Now sometimes fuses are added to protect specfic components.  for example sometimes tube amps have a fuse to protect the output transformers from some specific failure--likely a failure that they observed during testing.  and of course they have incentive to protect from this failure tor reputation but even more so to protect from expensive warranty repairs.  Fuses in the signal path are a horrible compromise and I wouldn't buy and amp with one.  OTOH, some will have fuses on the output of the rectifier.  I have tested these fuses with slugs and found very little if any difference.  These fuses may be extrememely oversized.  for example, if you have .001 amp normal current but 10 amp fault current, you can put a 1 amp fuse in.  It is 1000 times larger than normal current and doesn't limit current but small enough to blow on a fault.

So I just want poeople to understand that fuses aren't a magical component that keeps your compenent from ever failing or that it is a carefully engineering precision device.  

I've also speculated that audiophile fuses are more carefully designed to blow at the extreme top end of the range.  suppose you have a 2 amp fuse with 10% accuracy.  The off the shelf fuse may blow at 1.8 amp, the audiophile fuse may blow and 2.2 amps.  this extra margin will come with some current carrying capability that could sound better. 

I encourage anyone contemplating an expensive fuse to do a 60 minute test (on a good weather day) with a copper slug replacing the fuse.  The slug is the best that can be achieved, no fuse at all.  You'll get an idea what improvements are possible.  and when you get your audiophile fuse installed you'll know if it's closer to the original fuse or the slug.  Now some components don't benefit from a slug/upgraded fuse since their power supply architecture results in a circuit that is not limited by the fuse.

NOTE:  if you do the test, recognize that you have no protection during the 60 minutes with the slug, but the chance of a failure in the 60 minute test is infinitesimally small.  that said, don't do stupid things with the slug installed.  Have the amp set up and playing, make no changes other than replace the fuse.  Don't even uplug and replug any cables.  

Jerry

An accountant can calculate the net present value (cost) of replacing your fuse with a slug.

Lets do an example:

Your amp costs $10,000.

the catastrophic failure rate on your amp is 1/100 years (I think it is really much lower than that, although in lightning areas it may be higher).

Lets say the likelihood that the fuse will save your amp is 50/50. I think it is less.

So the cost per year to put in a slug is $10,000 x 1/100 x .5 = $50.

Now that is statistically what the cost is per year. However, if you happen to have a bad roll of the die, then you’ll have to pay the full $10,000. For many of us that would not be a problem. For many of us that would be a hardship. And even for many of those would could spend $10,000 without any hardship, the worry would not let them sleep.

So some people can replace their fuses with a slug, and some can’t even consider it.

Jerry

PS  Notice I assumed the fuse will save your amp 50% of the time.  The other 50% of the time you amp will fry, even though you have a fuse in it.  so it cost $50/yr to operate your amp with  a fuse and $100/yr with a slug.

@mitch2 I have disassebled and inspected the SDFB.  It is the equivalent of a magnetic breaker.   It sounds like you understand the difference between a magnetic and a thermal breaker.  a thermal breaker has a resistive heater that may be worse than a fuse for sound quality.  

So before the SWFB, I tried very hard to find a suitable magnetic breaker that I could adapt to replace the fuse and I couldn't find one.  So SDFB, designed and built one and did a very nice job. 

Jerry

That is certainly possible. eliminate the fuse holder is always a gain.  the fuse holders have to be a metal that has spring so they are often a poor conductor. 

Jerry

@pproctor You are correct.  the fuse is indeed the biggest resistor in the entire line.  (there is some voltage drop over the long lines).  so that is why we want to repace or eliminate it.  

The best option is to find something that provides protection but isn't a resistor--thus the SDFB.  

I like on many components that I don't expect to fail, to just raw dog it with no protection and replace the fuse with a slug (some think this is crazy, they are entitled to their opinion). 

and finally, there are expensive boutiques fuses that try to protect your gear with less negative effects, with limited results.  

Jerry

@mitch2 I've trusted copper.  I make my own slugs from high conductivity copper I buy from Mcmaster.  It isn't very expensive.  I haven't bothered with silver or graphene slugs.  I know people trying slugs made of worse conductors like brass or even steel alloys.  these are much worse conductors than copper but much better than a fuse (becasue of the cross sectional area).  So I know there are lots of opinions here but I stick with copper.

Jerry

@devinplombier I agree with most of your thoughts above. I assume by "variable" resistor, you mean that it changes depending on what current rating it is.  

I will explain that the SDFB is basicly a relay with a magnetic current switch to open it (thus, the same as a magnaetic breaker).  So when closed, it is just a pair of contacts in line with the power. So if a good relay, with high power handling and good contacts with essentially zero resistance is chosen, it should be just about like a straight wire.

If you can find a magnetic breaker to put in the line I'd like to see it.  I couldn't find one that would work.

Jerry

@tksteingraber I have taken mine apart many times. I know the design inside and out.

@devinplombier I worked to develop a way to adapt the SDFB without an extra power cord and it isn't hard to do for a specific amp.  but every amp uses a different IEC receptacle on the back and every receptacle has a slightly different fuse configuration.  

So if you adapt the SDFB to plug into the fuse compartment on one amp, it likely won't fit onto another amp.  Just too much work to make it custom for every amp. 

Add to that the fact that there there is no performance improvement.  I was attempting it solely becasue there are a very large number of audiophiles with zero electrical knowledge and they can't get it through their head that the way SDFB is delivered provides the same, or better, protection.  They think putting the slug in the fuse location is heresy.

Jerry

@thecarpathian I don't think so.  but I'll give it more thought.

The breakers in your panel are a combination of thermal and magnetic.  The thermal component doesn't cause much problem because it is rated much higher so it doesn't act as a current limiter at low currents.  Lowering it to the level of your fuse would make it cause the same negative effects of limiting bass and dynamics. 

6.3A is a pretty big fuse.  You must have a big amp. If you have a big amp, with big copper coils and lots of stored energy, you may not benefit much from fuse changes or elimination.

Jerry

@mitch2 I totally respect the value of intellectual property. that is why I asked it how I did. I didn’t realize you are working with SMc.

It is tempting to buy one of the amazon breakers and take it apart. but if inside I find a thermal overload (which I have found in most of the breakers I’ve disassembled), we won’t really know if it is the same breaker you have.

I toyed with installation of that style breaker designed to fit into a rack designed to accomodat it and it isn't easy to do it without quite a bit of construction.  Easy to hook up but you need to cover all conductors for safety.  

Best of luck,

Jerry

@mitch2 beautiful clean install.  When i do something like that, the more work it is, the more rewarding it is afterward.  If those breakers really are purely magnetic, they are better than any fuse.

Great job.

Jerry