• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Fuses do affect sound, the question is how much

Wombat

Major Contributor
Joined
Nov 5, 2017
Messages
4,545
Likes
2,913
Location
Australia
#23
No fuse expert here; I found this tube:


Rhetoric, self interest, no ABX - prove it. Fuses by nature have a current dependent resistance characteristic which can also be time duration dependent. Horses for courses re application. A well designed power supply(adequate stored energy) will obviate any steady-state fuse modulation of voltage(it should be minimal under normal operating conditions). The more important consideration is fuse performance under abnormal conditions.

My reply is: repeatedly prove it under valid testing procedures. Easy-peasy. Of course compared to subjective tinkerers, I am just a Professional EE.
 
Last edited:

Thomas savage

Power hungry desperado
Moderator
The Watchman
Patreon Donor
Joined
Feb 24, 2016
Messages
7,532
Likes
6,285
Location
uk, taunton
#26
What I learnt from spending a bunch of cash on Audiophile fuses .., don’t buy Audiophile fuse mainly because they are like all things Audiophile , unreliable.

Iv never expirenced any benefits but thought some made things worse , might of imagined that though.
 
Joined
Oct 10, 2017
Messages
160
Likes
74
#29
Fuses are typically used in three different circuits in an audio component:
1] AC power supply.
2] DC power supply.
3] Audio output of a power amplifier.
The audiophiles that hear these differences never mention which circuit the fuse is in.

Moving on, Bob Cordell is his great book "Designing Audio Power Amplifies" did measure fuse THD in an audio output stage.
It's section '13.11 Fuse, Relay and Connector Distortion' page 268.
Conclusion:
"At 20 Hz, amplifier distortion due to the fuse is calculated to be 0.0033 %."
More completely:

"
At low frequencies the audio signal can heat up and cool down the fuse element within a single cycle, causing the resistance of the fuse to vary as a function of the signal amplitude. This leads to distortion because the attenuation of the fuse resistance against the load impedance changes as a function of signal swing [5]. Fuses are often undersized with respect to the peak audio current they may be called on to pass, recognizing that a smaller fuse will provide relatively more protection and that with normal audio signals, such high currents are brief events much shorter than the time constant of the fuse element. The cold resistance of a 2-A 3AG fuse was measured to be 78 mΩ, while its resistance when passing 2-A DC was 113 mΩ. This represents a 45% increase in fuse resistance.

The distortion of a fuse can be measured by looking at the voltage across the fuse with a sinusoidal signal current passing through it. The fuse under test is put in the ground leg of an 8-Ω load resistor so that the signal voltage across the fuse can be easily analyzed. This technique largely takes the distortion of the driving source out of the picture. Figure 13.4a is a plot of fuse distortion versus frequency when a 2-A fast-blow 3AG fuse is passing a 2-A RMS sine wave signal. As expected, fuse distortion increases dramatically at low frequencies. Signal voltage across the fuse was 250 mV. Amplifier THD (due to the fuse) is calculated by normalizing the fuse distortion voltage to the amplifier output voltage. The resulting amplifier distortion is shown in Figure 13.4b. Amplifier distortion is lower than fuse distortion by a factor of 64 because of the small voltage across the fuse compared to the total signal voltage. At 20 Hz, amplifier distortion due to the fuse is calculated to be 0.0033%.
"

Other relevant papers:

Amplifier-Loudspeaker Interfacing
Author: Greiner, Richard A.
Affiliation: Department of Electrical Engineering, University of Wisconsin, Madison, WI,
JAES Volume 28 Issue 5 pp. 310-315; May 1980
Publication Date: May 1, 1980

"
Ideally the fuses used in the output current circuit would be linear resistors as well. However, since Fig. 4. Reproduction of an oscilloscope trace showing that they have to get hot (and melt) to burn out, they are actually out cycle for a fuse with a 20-Hz signal large enough to cause nonlinear elements in the output circuit. If fuses are to be burnout in about 0.8 s.


The substantial change in the slope of the V-I curve shown indicates a large resistance change with heating useful, they must blow out when the system is used at some of the fuse element. specified power level over the maximum desired. Typically, a fuse will increase in resistance to about 3 or 4 times its cold value just short of burnout. At 60% of full load it bursts just short of fuse burnout.


Typical measured modulawill increase to about twice its cold value. A typical fuse tion of a high-frequency signal when pulsed with tone blow-out cycle is shown in Fig. 4. The resistance change bursts that are set at 60% of burnout are shown in Fig. 5. per cycle is clearly evident. The calculations and measure- This figure shows the oscilloscope trace of a 5-kHz signal merits of this section show some possible problems with modulated by 20-Hz tone bursts. The tone bursts have been distortion caused by these changes in the fuse during normal filtered out to show only the 5-kHz modulated signal.


The program reproduction, heating and cooling cycle of the fuse is clearly visible. The Using the simple circuit of Fig. 3, it can be shown that for time constants of typical fuses are such that this heat, and a typical regular speed fuse, of the tubular type, the distortion- consequently resistance, cycling can take place for normal distortion produced could reach the values shown in Table 6. musical beats at low frequencies. To minimize interaction These figures represent intermodulation distortion for any of this type across the frequency spectrum, it would seem frequency when the output circuit is pulsed with power wise to provide separate fuses for each frequency range of a multiway system.


Fast blow fuses are worse than regular ,. fuses since they change temperature 10 times more quickly. " There is no solution to this problem except over fusing or putting inside of a feedback loop. This can be done, of course, by putting the using fuses at all, unless the fuses are included within the fuses in the power supply bus or even within the normal -- feedback loop
"

Speaker and Headphone Handbook
John Borwick
Third edition pp 293-294 (see attachment: "Fuse Disotoriton"
 

Attachments

Joined
Oct 10, 2017
Messages
160
Likes
74
#30
You're missing my point, fuses in my amp are part of the signal path, not power supply.
They are typically inside the main feedback loop or just supply current to the overall audio circuit which is inside the feedback loop. This means that in a SS amp their small distortion is further cut by one or more orders of magnitude by the inverse feedback.
 

LarsS

Addicted to Fun and Learning
Patreon Donor
Joined
Mar 23, 2016
Messages
729
Likes
403
Location
Sweden, Stockholm
#31
They are typically inside the main feedback loop or just supply current to the overall audio circuit which is inside the feedback loop. This means that in a SS amp their small distortion is further cut by one or more orders of magnitude by the inverse feedback.
Thx, nice to still be able learn something!

I've blown these fuses a number of times driving my difficult to drive speakers to party levels.
 

Cosmik

Major Contributor
Joined
Apr 24, 2016
Messages
3,075
Likes
1,939
Location
UK
#32
Some fuses may be there to protect against speaker shorts damaging the amp, and some may be to protect the speakers against a faulty amp burning out the speaker.

If someone really wanted to think about how to solve this problem without affecting the sound they would probably have to look into floating grounds, crowbars and circuit breakers. I believe that this is what Quad did with, for example, their model 306. As always, it is the most mundane bits of engineering that take the most effort.
 

NorthSky

Major Contributor
Joined
Feb 28, 2016
Messages
4,999
Likes
486
Location
Canada West Coast/Vancouver Island/Victoria area
#35
More completely:

"
At low frequencies the audio signal can heat up and cool down the fuse element within a single cycle, causing the resistance of the fuse to vary as a function of the signal amplitude. This leads to distortion because the attenuation of the fuse resistance against the load impedance changes as a function of signal swing [5]. Fuses are often undersized with respect to the peak audio current they may be called on to pass, recognizing that a smaller fuse will provide relatively more protection and that with normal audio signals, such high currents are brief events much shorter than the time constant of the fuse element. The cold resistance of a 2-A 3AG fuse was measured to be 78 mΩ, while its resistance when passing 2-A DC was 113 mΩ. This represents a 45% increase in fuse resistance.

The distortion of a fuse can be measured by looking at the voltage across the fuse with a sinusoidal signal current passing through it. The fuse under test is put in the ground leg of an 8-Ω load resistor so that the signal voltage across the fuse can be easily analyzed. This technique largely takes the distortion of the driving source out of the picture. Figure 13.4a is a plot of fuse distortion versus frequency when a 2-A fast-blow 3AG fuse is passing a 2-A RMS sine wave signal. As expected, fuse distortion increases dramatically at low frequencies. Signal voltage across the fuse was 250 mV. Amplifier THD (due to the fuse) is calculated by normalizing the fuse distortion voltage to the amplifier output voltage. The resulting amplifier distortion is shown in Figure 13.4b. Amplifier distortion is lower than fuse distortion by a factor of 64 because of the small voltage across the fuse compared to the total signal voltage. At 20 Hz, amplifier distortion due to the fuse is calculated to be 0.0033%.
"

Other relevant papers:

Amplifier-Loudspeaker Interfacing
Author: Greiner, Richard A.
Affiliation: Department of Electrical Engineering, University of Wisconsin, Madison, WI,
JAES Volume 28 Issue 5 pp. 310-315; May 1980
Publication Date: May 1, 1980

"
Ideally the fuses used in the output current circuit would be linear resistors as well. However, since Fig. 4. Reproduction of an oscilloscope trace showing that they have to get hot (and melt) to burn out, they are actually out cycle for a fuse with a 20-Hz signal large enough to cause nonlinear elements in the output circuit. If fuses are to be burnout in about 0.8 s.


The substantial change in the slope of the V-I curve shown indicates a large resistance change with heating useful, they must blow out when the system is used at some of the fuse element. specified power level over the maximum desired. Typically, a fuse will increase in resistance to about 3 or 4 times its cold value just short of burnout. At 60% of full load it bursts just short of fuse burnout.


Typical measured modulawill increase to about twice its cold value. A typical fuse tion of a high-frequency signal when pulsed with tone blow-out cycle is shown in Fig. 4. The resistance change bursts that are set at 60% of burnout are shown in Fig. 5. per cycle is clearly evident. The calculations and measure- This figure shows the oscilloscope trace of a 5-kHz signal merits of this section show some possible problems with modulated by 20-Hz tone bursts. The tone bursts have been distortion caused by these changes in the fuse during normal filtered out to show only the 5-kHz modulated signal.


The program reproduction, heating and cooling cycle of the fuse is clearly visible. The Using the simple circuit of Fig. 3, it can be shown that for time constants of typical fuses are such that this heat, and a typical regular speed fuse, of the tubular type, the distortion- consequently resistance, cycling can take place for normal distortion produced could reach the values shown in Table 6. musical beats at low frequencies. To minimize interaction These figures represent intermodulation distortion for any of this type across the frequency spectrum, it would seem frequency when the output circuit is pulsed with power wise to provide separate fuses for each frequency range of a multiway system.


Fast blow fuses are worse than regular ,. fuses since they change temperature 10 times more quickly. " There is no solution to this problem except over fusing or putting inside of a feedback loop. This can be done, of course, by putting the using fuses at all, unless the fuses are included within the fuses in the power supply bus or even within the normal -- feedback loop
"

Speaker and Headphone Handbook
John Borwick
Third edition pp 293-294 (see attachment: "Fuse Disotoriton"
Thank you sir Arnold for giving us your dedicated time on this.
I did more research on this subject, in addition to what you provided, with measurements and testing, listening from trustable scientific professional audio expert physicists, and they were all from the same planet as you, Earth.
They said things of that magnitude in verisimilitude.
 

LarsS

Addicted to Fun and Learning
Patreon Donor
Joined
Mar 23, 2016
Messages
729
Likes
403
Location
Sweden, Stockholm
#36
Some fuses may be there to protect against speaker shorts damaging the amp, and some may be to protect the speakers against a faulty amp burning out the speaker.

If someone really wanted to think about how to solve this problem without affecting the sound they would probably have to look into floating grounds, crowbars and circuit breakers. I believe that this is what Quad did with, for example, their model 306. As always, it is the most mundane bits of engineering that take the most effort.
So, in a nutshell the designer of my amp took the easy way out protecting the amp ...
 

NorthSky

Major Contributor
Joined
Feb 28, 2016
Messages
4,999
Likes
486
Location
Canada West Coast/Vancouver Island/Victoria area
#38
Enjoying the recent legalization and regulation in Canada?
Regarding pot or housing market or interest rate or oil pipeline; pot most likely which I never used because I was/am too busy breathing clean air for my brain.

☢☠☣ https://www.canada.ca/en/services/policing/justice/legalization-regulation-marijuana.html

Smoking pot while drinking impairs your driving faculties.
I know, some of my friends they told me so, from their graves and ashes spread to the four winds of the globe into the stratosphere and ocean's undercurrents.

It's good to experiment and not lose our fuses.
 
Last edited:

DonH56

Technical Expert
Technical Expert
Patreon Donor
Joined
Mar 15, 2016
Messages
3,400
Likes
4,489
Location
Monument, CO
#39
Some fuses may be there to protect against speaker shorts damaging the amp, and some may be to protect the speakers against a faulty amp burning out the speaker.

If someone really wanted to think about how to solve this problem without affecting the sound they would probably have to look into floating grounds, crowbars and circuit breakers. I believe that this is what Quad did with, for example, their model 306. As always, it is the most mundane bits of engineering that take the most effort.
Yup.

Quad loudspeakers would essentially short the amp terminals to protect the loudspeaker. Now that's a difficult load... Most modern amplifiers use various sensing techniques that monitor voltage, current, and temperature to determine if the amp is in its safe operating area (SOA). No output (speaker) fuses. Not sure the last time I saw an output fuse in an amp.

Speaker fuses tend to be used to protect tweeters from overzealous listeners. Example: old farts like me cranking up 20 kHz (or even 10 kHz) to where they can hear it when their hearing sensitivity is 20-40 dB down. Yup, in years gone by replaced tweeters after exactly that, dad trying to prove to kids he could still hear 20 kHz. Don't do that.

The influence of the fuse on the sound very much depends upon whether or not it is in the signal path, and if so if it is in the feedback path. Decades ago I included a fuse in the output as I was nervous about my failsafe circuits failing (I had a PL 700 that liked to short the rails to the speakers). I dithered but ultimately put it inside the feedback loop with a high-value resistor across it so when the amp was unloaded the feedback was still present though lessened. It was enough to prevent strange output waveforms and instability when the amp was unloaded.

Swapping speaker fuses for wire was popular in the 1970's and 1980's and gave me a lot of extra work. I did run some tests and in most cases nobody could tell if the speaker fuse was in-circuit or not.
 
Last edited:

restorer-john

Major Contributor
Joined
Mar 1, 2018
Messages
3,054
Likes
5,471
Location
Gold Coast, Queensland, Australia
#40
Some fuses may be there to protect against speaker shorts damaging the amp, and some may be to protect the speakers against a faulty amp burning out the speaker.

If someone really wanted to think about how to solve this problem without affecting the sound they would probably have to look into floating grounds, crowbars and circuit breakers. I believe that this is what Quad did with, for example, their model 306. As always, it is the most mundane bits of engineering that take the most effort.
Most competently designed amplifiers do not use fuses in the speaker line or in the feedback loop for protection. Placing anything in the main feedback loop that requires monitoring the voltage drop across a very low resistance is a recipe for disaster. At the point of failure the entire amplifier goes open loop and the results are generally not pretty.

Several manufacturers over the years tried a similar approach to compensate for the effects of speaker cable on damping factor, Kenwood being a notable one with their "Sigma Drive' in the early 1980s. Having repaired many dozens of 'Sigma Drive' equipped Kenwoods, I can assure everyone the idea was interesting but it translated to a large number of failures in the field.

+/- rail fuses for each channel are standard practice and serve to allow currents up to extreme fault currents to flow with little effect. In addition to rail fuses, most competently designed amplifiers have DC monitoring, over-current, temperature and switch-on delay circuitry, which uses high current relays to disconnect the speakers from the output stage.

Crowbar circuits are brutal, destructive and primitive IMO. In any case, all they serve to do (with the Quad 306) is trip a circuit breaker on the primary, blow a line fuse, and often several other parts (transistors, and in earlier models, SCRs) I don't like crowbar 'protection'- it is like throwing an actual crowbar over power lines- spectacular but not very clever.

Circuit breakers in speaker lines or feedback loops are also unreliable IME. Harman Kardon for example, used them for decades in the 70s and 80s to allow for 'high current' designs with no relays. However, as time went on, the breakers became oxidized internally (silver oxide) and ended up having significant resistance and caused distortion or intermittent operation.

The Japanese had it all sorted in the late 70s. They developed complete protection circuits on a single SIL IC and they are still reliably saving gear and speakers from all types of failures and abuse.

examples: uPC1237HA, TA7317 etc
 
Top Bottom