Fuses do affect sound, the question is how much

[DonH56]

I never understood the value of a fuses in loudspeakers. Is it to prevent over driving the speakers from someone reckless with the volume knob?

Partly, but also to protect in cases like having the volume turned up when a cable is (accidentally) pulled, another component is switched off or generates a loud pop for whatever reason (I have a cable box that will glitch occasionally), or if the amplifier itself fails. Not all amplifiers have robust speaker protection built in, and there is always the chance of the protection circuit failure (who guards the guardian?)

I have had several amplifiers in the past that would short the power supply rail to the speaker terminals when an output device shorted. Speakers tend to dislike having 100+ V of DC applied long-term.

 

[mhardy6647]

I never understood the value of a fuses in loudspeakers. Is it to prevent over driving the speakers from someone reckless with the volume knob?

That is the intent of them, yes.

 

[egellings]

It's that (excessive volume), and also to protect the speaker from an amplifier failure that places a large amount of DC voltage across the voice coil terminals. Fuses really save the day when that happens. If the fuse is included in the amplifier's feedback loop with adequate attention paid to keep the amp happy if the fuse should blow, the effects of its DC resistances can be reduced by the feedback factor, a nice little fringe benefit. Fusing is done for direct-coupled S.S. amplifiers, and is not usually needed for transformer-coupled amps like tube amplifiers, where no damaging amount of DC can get through. In that setting, the fuse would be there to protect against only excessive-volume playing. Some quasi-complementary output stages in S.S. amps with just one rail voltage would have a DC blocking cap between the output of the amp and the speaker, and in that case, the fuse would provide only excessive volume protection, since there would be no DC present unless of course the output cap were to short out.

 

[Sal1950]

I have had several amplifiers in the past that would short the power supply rail to the speaker terminals when an output device shorted. Speakers tend to dislike having 100+ V of DC applied long-term.

Can you say Phlame Linear 700B

 

[DonH56]

Can you say Phlame Linear 700B

Mine was an original 700. The B was significantly better though not great...

 

[JSmith]

JSmith

 

[egellings]

I owned the Phase Linear original 700. Thing I noticed about it was that the heatsinking was woefully inadequate for cooling that many output devices dissipating that much power. Mine went up in smoke. Thing looked seriously cool though, what with those meters and all, and you had to love that big transformer on there, too.

 

[Sal1950]

I had the 700B driving Klipsch LaScala's so even though I played things LOUD back in the day, no way I was ever stressing it to cause overheating??? It blew up on me twice and what it did to one of the 15" woofers was just plain ugly, should have been against the law. LOL
But your 100% right, inside it's walnut case it was the most handsome SS amp I ever owned.

 

[mhardy6647]

I had the 700B driving Klipsch LaScala's

I believe that that would violate the Geneva Convention.
Heck, I don't think the US Military would've even done that to Noriega in Panama.

How The U.S. Military Used Guns N' Roses To Make A Dictator Give Up

Panama's dictator, Manuel Noriega, surrendered to the invading U.S. military in 1989. He holed up at the Vatican Embassy, and gave up after being subjected to days of deafening music.

www.npr.org

 

[iwantobelieve]

Re: mains fuses, has anyone measured whether there’s a difference in dynamics with a mains fuse? E.g., a U.K. mains fuse vs an unfused (e.g., E.U.) plug? I once experimented swapping these when living in the E.U. but with a British bought power amp and subjectively it seemed to me that dynamics were better, especially in the bass. It wasn’t a controlled listening session or measured in any way, though, so I’d be interested to know whether anyone has ever measured this and if there was any objective difference in dynamic power/audible dynamic range with a fuse vs a straight wire in the power cord?

 

[MakeMineVinyl]

Re: mains fuses, has anyone measured whether there’s a difference in dynamics with a mains fuse? E.g., a U.K. mains fuse vs an unfused (e.g., E.U.) plug? I once experimented swapping these when living in the E.U. but with a British bought power amp and subjectively it seemed to me that dynamics were better, especially in the bass. It wasn’t a controlled listening session or measured in any way, though, so I’d be interested to know whether anyone has ever measured this and if there was any objective difference in dynamic power/audible dynamic range with a fuse vs a straight wire in the power cord?

I think you will find that if anybody has done measurements like this, these would not show any difference. If there was an instance of a fuse making a difference, something is seriously broken either in the amplifier or the fuse. In my experience, the resistance of the line cord and all wiring upstream can have a measurable impact on maximum power output. That's why when we test amplifiers, we use a large Variac to hold input voltage to 120VAC.

 

[SIY]

I think you will find that if anybody has done measurements like this, these would not show any difference. If there was an instance of a fuse making a difference, something is seriously broken either in the amplifier or the fuse. In my experience, the resistance of the line cord and all wiring upstream can have a measurable impact on maximum power output. That's why when we test amplifiers, we use a large Variac to hold input voltage to 120VAC.

There's a general non-understanding (not from you, of course, but from audiophiles without design experience!) of what happens on the secondary side. With normal filter caps, the actual charge time, i.e., the time the secondary "sees" the primary, is quite short for each cycle.

 

[BoredErica]

Do most amps/speakers have fuses to protect them, or only good ones?

 

[Holmz]

There's a general non-understanding (not from you, of course, but from audiophiles without design experience!) of what happens on the secondary side. With normal filter caps, the actual charge time, i.e., the time the secondary "sees" the primary, is quite short for each cycle.

Can elaborate a bit on this?
I know I can compute the phase angle using the SINC, COS or TAN the rail voltage.

But what does that matter?
I know with some of the amplifiers in the past (tubes in particular) the music would play for ~10 seconds or longer after shut off…. Basically the capacitors held energy longer than the heaters in the tubes would boil off electrons.

 

[MakeMineVinyl]

Do most amps/speakers have fuses to protect them, or only good ones?

I can't speak for 'most', but generally there is a breaker on the incoming AC and rail fuses on each channel module. Some amplifiers do have fuses on the incoming AC instead of a breaker. In any event, this is a blind alley as far as looking for differences in sound quality, or even objective measurements.

 

[SIY]

Can elaborate a bit on this?

Basically, you're pulling charge off the caps until the voltage across them drops more than the turn-on point for the rectifiers, then the caps pull charge from the transformer for a refill for the next cycle. This is one reason that the fashion for adding capacitance to the rails is a dangerous one- the peak current through the rectifier increases, the charge time decreases, and you get both rectifier stress and higher radiated noise. Win-win!

 

[iwantobelieve]

I think you will find that if anybody has done measurements like this, these would not show any difference. If there was an instance of a fuse making a difference, something is seriously broken either in the amplifier or the fuse. In my experience, the resistance of the line cord and all wiring upstream can have a measurable impact on maximum power output. That's why when we test amplifiers, we use a large Variac to hold input voltage to 120VAC.

I would assume a fuse upstream, e.g., in the mains plug, would increase resistance and therefore power output? So doesn’t that mean there would be a potential decrease in dynamic peaks with a fuse/greater resistance in the mains plug? Or did I misunderstand? I’m not suggesting this would make a difference at general low volumes or on program material which is fairly constant volume - the subjective impression I got (again, without objective checks) was on either sudden dynamic peaks, e.g., drums, and even more on sustained dynamic peaks (e.g., orchestral climaxes). It would be interesting to see some measurements under dynamic conditions to see if such a fuse had the potential to limit anything, or if so at what stage and the amount of limiting?

 

[MakeMineVinyl]

I would assume a fuse upstream, e.g., in the mains plug, would increase resistance and therefore power output? So doesn’t that mean there would be a potential decrease in dynamic peaks with a fuse/greater resistance in the mains plug? Or did I misunderstand? I’m not suggesting this would make a difference at general low volumes or on program material which is fairly constant volume - the subjective impression I got (again, without objective checks) was on either sudden dynamic peaks, e.g., drums, and even more on sustained dynamic peaks (e.g., orchestral climaxes). It would be interesting to see some measurements under dynamic conditions to see if such a fuse had the potential to limit anything, or if so at what stage and the amount of limiting?

The resistance of a fuse is going to be insignificant compared to the resistance of the AC line cord and upstream wiring in your walls. When we do testing on high power amplifiers, the limitation (dynamic power and RMS) is droop from the resistance on the incoming AC line, not any fuses - and we regularly test at full power sometimes >1000 watts. And don't forget that there are other resistances before the power gets to the amplifier's rails, such as the resistance of the wire in the power transformer.

 

[iwantobelieve]

The resistance of a fuse is going to be insignificant compared to the resistance of the AC line cord and upstream wiring in your walls. When we do testing on high power amplifiers, the limitation (dynamic power and RMS) is droop from the resistance on the incoming AC line, not any fuses - and we regularly test at full power sometimes >1000 watts. And don't forget that there are other resistances before the power gets to the amplifier's rails, such as the resistance of the wire in the power transformer.

Thanks, that’s reassuring. Can you explain to me why the resistance in my AC cord is higher than the fuse in the plug, though? I don’t understand that part - if so, wouldn’t the wire in the cord just burn through before the fuse did? I know my mains cables are heavy gauge, but my question applies to any cord as the fuse in the U.K. is rated according to the gauge of the wire…

Perhaps I’m misunderstanding how a fuse works, my assumption has been that the fuse is deliberately capable of handling less current than the cord it’s protecting, which is why it blows before the wire melts, and so forth. Would actually be grateful if someone could clarify this.

 

[SIY]

Thanks, that’s reassuring. Can you explain to me why the resistance in my AC cord is higher than the fuse in the plug, though? I don’t understand that part - if so, wouldn’t the wire in the cord just burn through before the fuse did? I know my mains cables are heavy gauge, but my question applies to any cord as the fuse in the U.K. is rated according to the gauge of the wire…

Perhaps I’m misunderstanding how a fuse works, my assumption has been that the fuse is deliberately capable of handling less current than the cord it’s protecting, which is why it blows before the wire melts, and so forth. Would actually be grateful if someone could clarify this.

The fuse is far shorter (remember, resistance is proportional to length) and made of a different material.