What is the science behind audiophile fuses?

In the entire power chain, from nuclear reactor through to your component, the piece with the greatest resistance to flow is the fuse, at least among the pieces you have any control over. It would logically follow that assuming input power had any effect (a whole other topic!) it would be the fuse that has the greatest effect.

@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

@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

When my amps were finished in 2020, SMc Audio had begun doing away with power switches (mine have none) but it wasn’t until a year or two later that they found magnetic breakers that they were comfortable with using to replace fuses.  Apparently they ruled out more than a few manufacturers/models that didn’t sound so good, until they found one they liked.  The magnetic switches they use, like in my SMc DAC-2, serve three roles:

1. Over-current protection for the equipment
2. On/off switch (although less conveniently located on the back)
3. Delay to resist blowing due to in-rush current upon power-up

Their source is proprietary but I am going to receive two of them (10A) that I plan to use for a solution external to the amp chassis, but that will not require an extra power cord like the SDFB.

My experience using Sluggo’s is that they are similar to tubes or cables. Each metal has it’s own sound signature. Copper warmer, silver more detailed and revealing, silver/rhodium hollow in between. But the graphene/copper slug was another “Oh My” moment and made the biggest improvement in SQ. Sluggos take many hours to break in and as crazy as this sounds some sound different if you switch their direction after break in. I am somewhat in Carlsbad2 camp where I only use the SDFB for my tube components with rectifiers. All other components with power input fuses I use sluggs without protection. I feel the very low risk of failure and the cost to repair the component is cheaper than buying more SDFB’s. I have never had a power input fuse blow just internal fuses protecting rectifier failures. Some are connecting a single SDFB to a splitter or outlet box and plug in multiple components with the same amp rating to avoid buying a SDFB’s for each component. Not sure of the science to it all but Sluggos do make a noticeable difference in SQ.

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).

Reading through this thread leaves me open to the possibility that line fuses, being essentially variable resistors, may have a discernable effect on sound quality. If so, the difference is likely to be confined to fuse vs. no fuse, such that replacing a Bussmann fuse with an "audiophile" fuse is likely to be of no import since the latter is still a variable resistor. So I would have to agree with @carlsbad2 's quote above.

The best way to achieve this, though, is not to install slugs of various metals that can’t possibly make any audible difference, insofar as they are cradled in uber-cheap fuse holders made of common steel. Desoldering and tossing that 10 cent fuse holder and jumpering a length of appropriate gauge wire in its place, thus essentially hardwiring your power cord to your equipment's PCB as @mitch2 suggested, seems the sensible way to go.

As far as the Swiss Digital Fuse Box, it answers the safety question, but it seems highly unlikely that any device sitting inline with your power cord AND needing a 2nd power cord in order to function would not impart its own sound signature onto your system, just like power cords themselves have their own sound signatures.

Can the Swiss Digital Fuse Box be truly neutral sounding, or is swapping it for a fuse a case of robbing Peter to pay Paul, so to speak?

How about magnetic breakers, can they be free of effects on sound quality?

It is of course easy to take the fuse thing to absurd extremes that attract scorn and ridicule, but there is a sound case to be made for eliminating them - in a way that ensures safeguards remain intact of course, or are even improved. Fuses are not that good at doing their jobs anyway, so it is interesting to read about what can be done to improve upon the current situation.

@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

@carlsbad2 

We are on the same page. Electrically, a closed relay is definitely equivalent to a straight wire.

So are power cords, but folks still heatedly argue about them.

If we accept that power cords - the essence of a straight wire - can have a sound signature, whether based on brand or copper purity or braiding style, it seems fair to assume that a more complex device inline with a power cord might also introduce its own sound signature.

Re magnetic breakers, I was just following along with @mitch2 's comment:

I am going to receive two of them (10A) that I plan to use for a solution external to the amp chassis, but that will not require an extra power cord like the SDFB.

I for one am curious to find out how his experiment turns out

Let's assume for a moment that we know what the "filler" is in an Audiomagic M2 fuse. Some rumor that it is graphene loaded beeswax.

Can anyone here scientifically speculate about the effects thereof? I know how the fuse sounds, but how would it be achieving that sound and why would that sound be different from a bare fuse wire?

@devinplombier 

I for one am curious to find out how his experiment turns out

I will be happy to share how my installation of the breakers turns out, but I probably wouldn't categorize this as an "experiment" since SMc Audio are currently and successfully using these breakers in the amplifiers they construct and also in the amps that they upgrade.  In fact, I have the same type of breaker (in a lower 1A rating) in my SMc DAC-2, that I received from them last year.  Pics posted on my system page.

The only difference with the install for my amplifiers is that we decided it would be a cleaner and equally beneficial application for me to use the breakers outside of the amplifiers while replacing the fuses with slugs.  Even though I am fairly comfortable self-performing such things, installing the breaker internally is much better accomplished as part of a new amp build, or an upgrade (a process that involves SMc removing all the inside components anyway) than as a customer-installed retrofit.  After discussing what was involved with SMc, I decided not to fiddle around inside of the amp and especially if I can achieve pretty much the same result with an outside installation mounted in a box adjacent to my wall duplex. 

I will share here in advance that, unfortunately, the breakers used are proprietary as SMc Audio spent quite a bit of time figuring out which breakers worked well and sounded best with their equipment.  Therefore, I will not be sharing the manufacturer or model, although it is a 10A magnetic breaker.  I suspect a similar type of breaker is used inside of the SDFB, and it is probably not that much different from breakers that other manufacturers may use currently.  I remember my first experience with a breaker on/off switch was the thermal circuit breaker in the BPT 2.5 power conditioner I formerly owned.

@mitch2  I don’t know if you have seen the inside of a SDFB but I added a photo of one on my systems page to view. Thought it might be of interest to folks.  I have trouble posting pics on forum threads…😩

@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

Thanks @tksteingraber - the SDFB looks well made with heavy wire where necessary (except to the LED).  It appears to be a breaker with a small control board, likely for the automatic reset.

If I were to use one, I might hard wire a pig tail power cord to get rid of one IEC, but I make PCs so one more short cord is really no problem. 

@carlsbad2 ,    @mitch2 ,

You guys are light years ahead of me with this stuff and I have a question for you:

If you have a dedicated line to your amp, and your amp has say 6.3 amp fast blow fuses in it, would putting a low current 6 amp breaker in your panel do the same thing? 

@tksteingraber

Thanks for posting the picture of SDFB.

@carlsbad2

It sounds like you’ve put a lot of thought and effort into addressing a concern from some of us. I am ok with slugs but don’t want a pigtail in the signal path so let’s see if SDFB would make a version that can be plugged directly into a component IEC.

@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

@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.

If you have a dedicated line to your amp, and your amp has say 6.3 amp fast blow fuses in it, would putting a low current 6 amp breaker in your panel do the same thing?

Panel mount: The issue is that a magnetic breaker replacing a fuse needs to be dedicated to a single the component, just like a fuse protects the component. OTOH, the breakers in your panel protect the line - i.e., a 20A breaker breaks when current on the line exceeds 20A at which point a single component might already be fried.

Fuse holder mount: The magnetic breaker is quite a bit larger than a fuse holder. If you are asking about retrofitting existing equipment the easiest method would be to use something like the SDFB. In looking at retrofitting my SMc amps, it would have required cutting a hole in the back plate of the metal case and then rewiring the fuse holder and IEC, all of which I was comfortable doing myself. The problem was having to move the main board and disconnect several parts to make room to perform the work and at that point it became easier, less invasive, and less risky to incorporate a solution that was exterior to the amp. SMc uses the breaker to replace a fuse in their new equipment, and in their upgrade work. However, the breaker requires a larger hole in the case than a fuse holder. The breaker can also take the place of an on/off switch as it does in my SMc DAC-2.

Exterior box mount: I believe the easiest DIY opportunities for existing equipment are either a separate external box (like SDFB) or perhaps mounting the magnetic breaker in a gang box or separate small breaker box wired directly to the power line feeding the duplex where the equipment is connected, which is what I plan to do. The key is providing one breaker for each piece of gear so every outlet would need to have its own breaker. My two amps are fed from a single dedicated 30A line and each have a 10A fuse. I plan to mount the two 10A breakers just in front of the duplex, with each breaker feeding one of the two outlets in the duplex. Each outlet will have its own dedicated breaker. The outlets in my Furutech duplex will need to be separated from each other by cutting the tabs on the outlet and then each outlet will need to be individually wired. The breakers are basically an in-line switch wired on the hot side.

@mitch2   Krell was using magnetic breakers over 30 years ago. I have a 20a breaker in my Krell ksa 300s, seems to work fine.

@carlsbad2 

Perhaps @lalitk meant a SDFB dongle that would plug directly into the equipment's receptacle, eliminating the extra power cable the regular SDFB requires.

I wonder if this ABC-30-R fuse would be just as effective as a slug operationally and sonically?  This ceramic case fuse is 3x the capacity of the big 10A fuses in my amps and I suspect would be no more restrictive than the wiring connected to the IEC inside of the amp.