[Roger A. Modjeski]

I have received a response from the maker of tuning fuses. I asked the following questions as an owner of a tube amplifier.

Dear Mr. Ahne,

I have been reading your claims for Hi Fi Tuning Fuses and I have a few questions.

1. Are these fuses suitable for use as tube fuses? My amplifier uses several ceramic, high breaking 200 mA slow blow fuse.

2.Can you please explain this I read from various sellers of your fuses.   "HiFi Tuning SilverStar Fuses are made from ceramic bodies which are tuned for resonance control".

I received this reply.


Bestellung HiFi-Tuning
6:54 AM (1 hour ago)

to me
Yes,
all of our fuses got ceramic body.

I await replies from PF where I sent a message to editors, assistant editors and technical editors.

[watercourse]

Hi Roger,

Also try some domestic manufacturers. I'm sensing some translation difficulties.

Audio Horizons make tube gear, and their engineer has a respectable CV in the audio world. Located near Sacramento.

Synergistic Research is down in Irvine. Ask them as well.

I'm a fan of aftermarket fuses, but would still be interested in hearing about this.

[Roger A. Modjeski]

Hi Roger,

Also try some domestic manufacturers. I'm sensing some translation difficulties.

Audio Horizons make tube gear, and their engineer has a respectable CV in the audio world. Located near Sacramento.

Synergistic Research is down in Irvine. Ask them as well.

I'm a fan of aftermarket fuses, but would still be interested in hearing about this.

I don't think there is a language problem, especially at PF. Based on their reviews they have lots of words and use them freely, though often incorrectly when it gets technical.

However I have written the companies you suggested and I await their response.

[*Scotty*]

Irregardless of claims of better sound from " tuning" fuses , depending on the fuses location in the equipment it may be critical to protecting the owner of the equipment from the danger of fire in the event of a component failure.
 The "tuning"fuses should be just as effective from a safety standpoint as a properly chosen conventional fuse or they should not be offered for sale, period. If you have test results that prove any aftermarket "tuning" type fuse has breaking characteristics that render it dangerous when used as the fuse manufacturer recommends you should publish this on your website.
 The safety questions about these type of aftermarket fuses far outweigh in importance any subjective claims of sonic improvements from their use made in magazine reviews. At the end of the day the demand for snake oil and purveyors of same with always be with us and diatribes against this aspect of our hobby won't make it go away.
 Alerting the public to a potentially dangerous device is a public service and a different kettle of fish entirely.
Scotty

[Roger A. Modjeski]

Irregardless of claims of better sound from " tuning" fuses , depending on the fuses location in the equipment it may be critical to protecting the owner of the equipment from the danger of fire in the event of a component failure.
 The "tuning"fuses should be just as effective from a safety standpoint as a properly chosen conventional fuse or they should not be offered for sale, period. If you have test results that prove any aftermarket "tuning" type fuse has breaking characteristics that render it dangerous when used as the fuse manufacturer recommends you should publish this on your website.
 The safety questions about these type of aftermarket fuses far outweigh in importance any subjective claims of sonic improvements from their use made in magazine reviews. At the end of the day the demand for snake oil and purveyors of same with always be with us and diatribes against this aspect of our hobby won't make it go away.
 Alerting the public to a potentially dangerous device is a public service and a different kettle of fish entirely.
Scotty

I have tested the fuses. I have explained in this forum the reason the fuses will provide no protection as tube fuses.  I have contacted the manufacturers of Tuning Fuses and other fuse makers as suggested in this post. The replies have been, as expected, technically disappointing. The replies from PF have been no better. The people contacted still have no idea what a high breaking (high interrupting) fuse is. All answers so far have missed the target entirely.

I chose to report my findings here as I pay for this site and we can discuss here rather than a post on my website where we would not be able to discuss. I want this information to get to the general audio public. I also ran a post on AudioGon last year with similar results. However that one was left to run its course.

[*Scotty*]

Did you also test them for suitability as AC mains fuses or speaker fuses?
Scotty

[avahifi]

I suggest you define the term "high breaking" better herein for the edification of your readers.

I assume you mean a fuse type that does not allow an overload plasma arc to continue passing current even after the fuse is actually blown such as can happen when a 32V rated fuse, for example, is used in a 120V AC application.

I also assume that a ceramic body slow blow adequately high voltage rated fuse and current rated is appropriate for your tube failure application.

I also assume the vendors of magic fuses provide no useful technical information at all.

Frank Van Alstine

[Roger A. Modjeski]

Did you also test them for suitability as AC mains fuses or speaker fuses?
Scotty

I did not. I have done all I can to inform the public that they are not suitable for tube fuses and that their claims as to microphonics and improved electrical performance are specious. I have no interest to do further tests unless they want to engage my services as a consultant.

[Ericus Rex]

There's got to be a good car analogy to make all this crystal clear.  Maybe something like 'using tuning fuses in your amp is like...

...taking the seat belts out of your car because they can be uncomfortable?

...taking all the glass out of the car to reduce drag?

...taking out the brake pads because they eventually wear out and have to be replaced?


What do you guys think is the perfect car analogy?

[Roger A. Modjeski]

I suggest you define the term "high breaking" better herein for the edification of your readers.

I assume you mean a fuse type that does not allow an overload plasma arc to continue passing current even after the fuse is actually blown such as can happen when a 32V rated fuse, for example, is used in a 120V AC application.

I also assume that a ceramic body slow blow adequately high voltage rated fuse and current rated is appropriate for your tube failure application.

I also assume the vendors of magic fuses provide no useful technical information at all.

Frank Van Alstine

I have previously defined these terms, however I will again as those posts have been Quarantined. We currently have more posts in the hospital than any other forum.

You are correct, the fuse must not allow plasma to form. It is therefore filled with sand or some other material to fill the space when the fuse element vaporizes. It is not so much about voltage rating. I think 32 volt fuses are made differently from 125 volt fuses so as to have less loss at low voltages as they typically have elements that are wide at the ends and narrow in the center thus reducing resistance which is important in a low voltage circuit. Given that I feel 32 volt fuses would be a good choice for speaker fuses where high breaking is not an issue at all.

I get more questions about the voltage ratings on fuses than any other parameter. In actuality it is the least important parameter.

The responses from vendors and manufacturers have displayed no knowledge of these requirements at all. The respondents have missed the target entirely.

[avahifi]

Years ago in the process of some power amplifier design work we were able to identify low level distortion in a 3AG 5 amp quick blow speaker fuse as used in a Hafler DH-220 amplifier.

We had designed new audio circuit boards for this amplifier and were evaluating one "feature" of the original DH-220 output wiring layout that was unusual.  Hafler had placed the speaker and output circuit protection fuses inside the overall amplifier feedback loop.

We could evaluate that design idea by driving the amplifier to near full power with 20Hz sine waves.  We placed our scope test probes not at the audio outputs, but at the output of the voltage amplifier section driving the current amplifier section.  This way we could observe the correction signal the feedback was applying to the output signal.  Sure enough the correction signal showed a tiny 20 Hz sine wave correction, which was of course caused by the change in thermal resistance of the fuse as is alternately heated and cooled depending upon the power from the input signal across it.

Inasmuch as our general design goal is to make the feedback loop do as little work as possible, we then redid the output wiring to take the fuse out of the loop, thus eliminating the correction signal it demanded. This ended up with a bit cleaner and more refined deep bass response in the amplifier.  The tiny bit of thermal distortion in the fuse was less harmful then trying to make the feedback loop correct for it unnecessarily.

Perhaps a ceramic output fuse would have lower thermal distortion, but since they are not available in the quick blow fast breaking type necessary to protect the speakers and amplifier output circuits, we do not use them for this design purpose.

Frank Van Alstine

[Roger A. Modjeski]

Years ago in the process of some power amplifier design work we were able to identify low level distortion in a 3AG 5 amp quick blow speaker fuse as used in a Hafler DH-220 amplifier.

We had designed new audio circuit boards for this amplifier and were evaluating one "feature" of the original DH-220 output wiring layout that was unusual.  Hafler had placed the speaker and output circuit protection fuses inside the overall amplifier feedback loop.

We could evaluate that design idea by driving the amplifier to near full power with 20Hz sine waves.  We placed our scope test probes not at the audio outputs, but at the output of the voltage amplifier section driving the current amplifier section.  This way we could observe the correction signal the feedback was applying to the output signal.  Sure enough the correction signal showed a tiny 20 Hz sine wave correction, which was of course caused by the change in thermal resistance of the fuse as is alternately heated and cooled depending upon the power from the input signal across it.

Inasmuch as our general design goal is to make the feedback loop do as little work as possible, we then redid the output wiring to take the fuse out of the loop, thus eliminating the correction signal it demanded. This ended up with a bit cleaner and more refined deep bass response in the amplifier.  The tiny bit of thermal distortion in the fuse was less harmful then trying to make the feedback loop correct for it unnecessarily.

Perhaps a ceramic output fuse would have lower thermal distortion, but since they are not available in the quick blow fast breaking type necessary to protect the speakers and amplifier output circuits, we do not use them for this design purpose.

Frank Van Alstine

As a speaker fuse I am not surprised you found something going on if that fuse was in series with the speaker. How much do you think simply changing the fuse for a premium fuse would have changed the result of your test before you made the circuit change.

There are very few instances when a fuse is right in the signal path. If people hear a difference there I am fine with it and it is explainable. The bulk of these fuses are used in power line and tube fuse applicators where I cannot imagine them making any difference. I would like to hear your thoughts on those applications.

[RDavidson]

As a speaker fuse I am not surprised you found something going on if that fuse was in series with the speaker. How much do you think simply changing the fuse for a premium fuse would have changed the result of your test before you made the circuit change.

There are very few instances when a fuse is right in the signal path. If people hear a difference there I am fine with it and it is explainable. The bulk of these fuses are used in power line and tube fuse applicators where I cannot imagine them making any difference. I would like to hear your thoughts on those applications.

Roger, I think Frank is referring to the speaker output fuses on the back of the Hafler Dh220. I've seen other amps with fuses at the output, usually older designs. I'm assuming they're there, as more sophisticated protection circuitry had not yet been developed or more sophisticated protection was too expensive to implement or was simply just a design choice.

[Roger A. Modjeski]

Roger, I think Frank is referring to the speaker output fuses on the back of the Hafler Dh220. I've seen other amps with fuses at the output, usually older designs. I'm assuming they're there, as more sophisticated protection circuitry had not yet been developed or more sophisticated protection was too expensive to implement or was simply just a design choice.

Most likely a design choice for short circuit protection because electronic protection (current limiting) is often a problem with difficult loads.  As long as the output devices are protected from shorts I prefer a fuse to current limiting. If it has any effect it is far less than current limiting. It takes twice as many fuses to put them in the power rails outside the signal path, but that is a good place to put them.

The one place a fuse might be audible is in the speaker output. This is widely known and perhaps the reason that premium fuses got a foothold in other applications. It is typical of people with limited knowledge to paint something with a broad brush or generalize. In this case since a fuse in a speaker might be audible then fuses in all applications might be audible. With proper knowledge of the situation one can be more specific.

[*Scotty*]

Hence my comments regarding the fuse behaving as a non-linear resistor. Rodgers comments about a 32volt rated fuse when speaker protection is desired should be taken to heart, they might sound quite a bit better than a fuse rated at 120v. If the fuse is between the output transistors and the loudspeaker load, it is likely to be in the feedback loop, I have noticed an improvement in sound when I bypassed a 5A 120v rated fuse with a 4uf PP foil and film cap. I am still protected against clipped waveforms and DC over-current conditions but I have compromised the protection from HF oscillation if it happens to occur.
Scotty

[avahifi]

I thought I made it clear that the fuse behaved better when not in the feedback loop.  The fuse is a low value resistor and very very low level thermal distortion, a very low frequency effect, is likely insignificant compared to all the other abounding non-linearities, such as thermal distortion in speaker voice coils themselves.

I consider the "sound of fuses" to be a none issue. Just because we could actually identify this effect does not make it a game changer. We certainly can't hear any difference testing two identical amps, one with all fuses replaced by bus-bars, using our ABX box.

Frank Van Alstine