Fuses do affect sound, the question is how much

[3dbinCanada]

You're completely right: 0,1V/80V=0,00125% of the signal may be distortion, absolutely inaudible, and slight variations of the resistance don't make it less inaudible - exept of, maybe, for some audiophile bats, or other non-human animals?

Too funny.

 

[3dbinCanada]

Sorry, calculation was wrong - it's too late for maths... Nontheless I think it's inaudible.

Please enlighten us with your calculations.

 

[tomelex]

What is the magnitude of this resistance change once the fuse is warm? The fuse itself is not pulsing but the current source through it is pulsing.

Started this thread to prove that fuses do add distortion, not to prove audibility. Others came along after me with facts, but yes, the fuse element was physically moving. Others have seen that as well, what can I tell you past that? This thread has a lot of good info, if only to prove that fuses do add distortion, like most anything else does, and of course if we are pushing the envelope, we appreciate advances in the science. I have always said that it is just possible that you heard a system that was a perfect reproduction in all ways, with simple two channel stereo you might actually think it did not sound so good. The most perfect reproduction of a contrived audio trick that stereo is, might not be better!

 

[3dbinCanada]

Started this thread to prove that fuses do add distortion, not to prove audibility. Others came along after me with facts, but yes, the fuse element was physically moving. Others have seen that as well, what can I tell you past that? This thread has a lot of good info, if only to prove that fuses do add distortion, like most anything else does, and of course if we are pushing the envelope, we appreciate advances in the science. I have always said that it is just possible that you heard a system that was a perfect reproduction in all ways, with simple two channel stereo you might actually think it did not sound so good. The most perfect reproduction of a contrived audio trick that stereo is, might not be better!

Moving as expanding and contracting with heat due to current flow? If so, how does that distort the signal passing through it?

 

[Doodski]

Moving as expanding and contracting with heat due to current flow? If so, how does that distort the signal passing through it?

If the coefficient of resistance and temperature sway towards increased resistance then a small voltage divider will be created although this is minuscule in the terms of the operational circuit. There would be a tiny tiny power loss over the fuse. As a previous poster detailed the mains voltage variations over the period of a normal day will be up to 10% and maybe even 15% of available voltage dependent on where you are situated on a grid and how it is loaded over the days' period. If you are curious measure the voltage across the fuse as it elongates and contracts over the temperature variations. You might need a scope or sensitive meter and digital or analogue storage may help to observe it.

 

[NTK]

Modeled the fuse heat effect with OpenModelica. Simulation parameters were chosen to reflect "worst case".

The initial fuse resistance was 0.01 ohm (value I found for a 6.3 A fuse) at 20 °C. The temperature coefficient for resistivity of copper of 4 x 10e-3 was used. The mass of the fuse was assumed to be 0.05 gram. Thermal conductance to the surrounding was 2 x 10e-3 W/°C. Surrounding temperature is 20 °C. The driving voltage was 28.28 Vrms (40 Vpk) at 20 Hz. Speaker load was 8 ohm. Simulation time period was 0 to 300 seconds.

The first 2 plots are fuse temperature--rose from 20 °C to about 86 °C (overall and zoomed into the last 2 seconds). Fluctuation amplitude was a little over 0.02 °C (a value mostly governed by thermal inertia and heating frequency and power). The second 2 plots are voltage across the fuse (overall and zoomed into the last 2 seconds).

The voltage swing (Vpk) across the fuses was about 0.053 V. As the driving voltage was 40 Vpk, distortion was 0.053 / 40 = 0.13%. Thus, this is about as bad as it will get if a small fuse in placed in the speaker output path.

[Edit]: Oops. My interpretation of the results was totally incorrect
Much of the (sinusoidal) voltage drop across the fuse is due to its base resistance, not from the resistance oscillations due to temperature. The correct interpretation is to look at the temperature fluctuation magnitude. The distortion number should be ±0.01 °C (half amplitude) multiply by the temperature coefficient and then divide by the total resistance (voltage divider) = 0.01 * 4 x 10e-3 / 8 = 0.0005%

 

[DonH56]

Modeled the fuse heat effect with OpenModelica. Simulation parameters were chosen to reflect "worst case".

The initial fuse resistance was 0.01 ohm (value I found for a 6.3 A fuse) at 20 °C. The temperature coefficient for resistivity of copper of 4 x 10e-3 was used. The mass of the fuse was assumed to be 0.05 gram. Thermal conductance to the surrounding was 2 x 10e-3 W/°C. Surrounding temperature is 20 °C. The driving voltage was 28.28 Vrms (40 Vpk) at 20 Hz. Speaker load was 8 ohm. Simulation time period was 0 to 300 seconds.

The first 2 plots are fuse temperature--rose from 20 °C to about 86 °C (overall and zoomed into the last 2 seconds). Fluctuation amplitude was a little over 0.02 °C (a value mostly governed by thermal inertia and heating frequency and power). The second 2 plots are voltage across the fuse (overall and zoomed into the last 2 seconds).

The voltage swing (Vpk) across the fuses was about 0.053 V. As the driving voltage was 40 Vpk, distortion was 0.053 / 40 = 0.13%. Thus, this is about as bad as it will get if a small fuse in placed in the speaker output path.

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Nice work! I am not sure the 53 mV is distortion, however. The only distortion would be from any varying resistance that is modulated with the signal. In steady-state, a constant 53 mV drop is not distortion, just a reduction in amplitude. It may increase distortion in the system in a secondary way by increasing the amplifier's output impedance if used as a speaker fuse.

 

[NTK]

Nice work! I am not sure the 53 mV is distortion, however. The only distortion would be from any varying resistance that is modulated with the signal. In steady-state, a constant 53 mV drop is not distortion, just a reduction in amplitude. It may increase distortion in the system in a secondary way by increasing the amplifier's output impedance if used as a speaker fuse.

Yes. I was incorrect. I edited my original post. I hope my new interpretation is correct now.

 

[3dbinCanada]

Yes. I was incorrect. I edited my original post. I hope my new interpretation is correct now.

Is voltage attenuation considered distortion or just attenuation? IHO, if it doesnt introduce a phase shift, disruption of signal such as cross over distortion in a class AB amp as an eg, or produce harmonics, I would consider it attenuation, not distortion. A negligable attenuation at that.

 

[A800]

Fuses should only cause a slight voltage drop depending on the current due to resistance.

 

[DonH56]

The voltage drop varies with temperature which in turn depends upon the current through the fuse. That leads to modulation of the voltage drop with signal and that causes distortion. With a reasonable fuse it is not an issue in the real world but is one reason to not place a fuse in series with the speaker. That said, even if you do, it will be virtually inaudible until it is on the verge of failure. After failure, it is quite audible. Or should that be inaudible? I'm so confused...

 

[Doodski]

I would consider it attenuation, not distortion. A negligable attenuation at that.

We have been dealing with this in the context of a linear power supply. If it where a pulse width modulation switched mode power supply then the 10%-15% voltage variations from the power mains, the voltage drop across the resister and the fuse thermal resistance coefficient would not matter until of course the fuse opens. That's just one of the advantages of PWM SMPS designs.

 

[3dbinCanada]

The voltage drop varies with temperature which in turn depends upon the current through the fuse. That leads to modulation of the voltage drop with signal and that causes distortion. With a reasonable fuse it is not an issue in the real world but is one reason to not place a fuse in series with the speaker. That said, even if you do, it will be virtually inaudible until it is on the verge of failure. After failure, it is quite audible. Or should that be inaudible? I'm so confused...

From previous posts, the temperature of a fuse remains fairly constant once warmed up. Voltage drop does not cause modulation and does not cause distortion. That is an incorrect assertion. I whole heartedly agree that putting a fuse in line with a speaker is poor design.

 

[3dbinCanada]

We have been dealing with this in the context of a linear power supply. If it where a pulse width modulation switched mode power supply then the 10%-15% voltage variations from the power mains, the voltage drop across the resister and the fuse thermal resistance coefficient would not matter until of course the fuse opens. That's just one of the advantages of PWM SMPS designs.

Is there a point to this point in you quoting me? You just went off on a tangent and totally stepped around the attenuation verses distortion aspect.

 

[Doodski]

Is there a point to this point in you quoting me? You just went off on a tangent and totally stepped around the attenuation verses distortion aspect.

Yeah I figured these attenuations as you refer to them are what the advantages of a SMPS Class D amplifier is about and so I thought maybe that would be of interest to you. These attenuations are literally parts of the impedance of the linear power supply, output from the secondary and then not attenuating but simple decreasing the available power due to current limiting. They are simply voltage drops, a power loss and we don't refer to them as attenuations or a attenuating process.

 

[mansr]

The voltage drop varies with temperature which in turn depends upon the current through the fuse. That leads to modulation of the voltage drop with signal and that causes distortion. With a reasonable fuse it is not an issue in the real world but is one reason to not place a fuse in series with the speaker. That said, even if you do, it will be virtually inaudible until it is on the verge of failure. After failure, it is quite audible. Or should that be inaudible? I'm so confused...

The fuse temperature depends on the average current over a period of 100 ms or more. It does not track the signal waveform. If it did, slow-blow fuses for AC couldn't exist.

 

[3dbinCanada]

Yeah I figured these attenuations as you refer to them are what the advantages of a SMPS Class D amplifier is about and so I thought maybe that would be of interest to you. These attenuations are literally parts of the impedance of the linear power supply, output from the secondary and then not attenuating but simple decreasing the available power due to current limiting. They are simply voltage drops, a power loss and we don't refer to them as attenuations or a attenuating process.

This whole thread was talking about fuses and whether or not they introduce distortion and off you go on yet another meaningless tangent. Lets stick to the topic and stop introducing power supplies and voltage drop and duty cycles.

 

[3dbinCanada]

The fuse temperature depends on the average current over a period of 100 ms or more. It does not track the signal waveform. If it did, slow-blow fuses for AC couldn't exist.

Exactly my point so there is no voltage modulation and introduced distortion. Just an extremely minute voltage drop across the fuse that is inaudible. Like I posted previously, attenuation is NOT distortion and many people on this thread are incorrectly asserting that attenuation equals distortion. Attenuation and distortion are mutually exclusive definitions.

 

[Pjetrof]

NO AUDIBLE DIFFRENCE! Maybe an other interesting topic.
Speakers, sources, amplifiers music in general... Fuses!!!!!!

 

[DonH56]

The fuse temperature depends on the average current over a period of 100 ms or more. It does not track the signal waveform. If it did, slow-blow fuses for AC couldn't exist.

I wasn't thinking of it tracking the instantaneous signal level. I agree it's a thermal issue with long time constant, sorry I did not make that clear. It does track the average power and that varies with listening level and so forth.

From previous posts, the temperature of a fuse remains fairly constant once warmed up. Voltage drop does not cause modulation and does not cause distortion. That is an incorrect assertion. I whole heartedly agree that putting a fuse in line with a speaker is poor design.

No, voltage drop that varies with signal causes distortion; it creates a nonlinear result. The modulation will be different at different power levels; the temperature is only constant for a given steady-state power (current) level so changing power (SPL) changes temperature and thus voltage drop.

The distortion a speaker fuse adds usually shows up in power sweeps on the bench. And generally only when the fuse is near its breaking point when the resistance rises rapidly. As far as audibility is concerned, it is in the mud, and like many other things audio, the marketing that played up lack of fuses in the output signal path neglected both its impact and the orders-of-magnitude greater distortion generated by the speakers themselves. But, back in the 1980's or so when vanishingly low amplifier distortion numbers were all the rage, fuses were eased out of the signal path because they added measurable distortion. Extremely high damping factors (or low output impedance, same thing) were also in vogue and again a speaker fuse increased output impedance so was undesirable (some amps put feedback after the fuse and/or moved the fuse elsewhere in the circuit; eventually different protection schemes were implemented).

I don't think any of this matters for audio, at least as far as the end user is concerned. I have had to deal with metal tempco and such designing precision ADCs and DACs, where temperature change caused the metal resistance to vary, and upset my fine-tuned trimming algorithm since metal and resistors varied differently (so a precision-trimmed resistor did not track others over temperature due to the metal connecting them). Made for a layout nightmare. That was on an IC, however, and at the end was fixed on the chip so the customer never saw it. There was much gnashing of teeth and hair-pulling before I solved it, however. And again there it was a long-time thing. The really nasty thermal settlers are the ones inside the transistors themselves...