Hi!
Have had a discussion about fuses in the preamp….
My thinking is:
The preamp fuse is dimensioned for the inrush current during start-up - thereby probably largely oversized for the preamp after the start-up period. So what is the purpose of the fuse?
For protection? But the house electrical network has fuses…. Isn’t that enough?
Can you please explain to me why is it necessary to have an preamp fuse? Is the fuse really nescesarry ?
/Anton
Have had a discussion about fuses in the preamp….
My thinking is:
The preamp fuse is dimensioned for the inrush current during start-up - thereby probably largely oversized for the preamp after the start-up period. So what is the purpose of the fuse?
For protection? But the house electrical network has fuses…. Isn’t that enough?
Can you please explain to me why is it necessary to have an preamp fuse? Is the fuse really nescesarry ?
/Anton
Prevents fire, smoke, electrical shorts.
The large breaker in the house may be too large for protection.
Not all circuits have large inrush. Very poor practice to omit fuses.
Your insurance company could deny benefits, or you could incur liability for damage or injury.
The large breaker in the house may be too large for protection.
Not all circuits have large inrush. Very poor practice to omit fuses.
Your insurance company could deny benefits, or you could incur liability for damage or injury.
Thank you for you answer.
The outlet I use has a 10A housebreaker, the music system (preamp 2A, power amps 4A (each) and DAQ 3.15A) that has been working flawlessly for more then 15 years - can it really be a sudden shortcut?
How can the fuse prevent a shortcut? Is it not more like reducing the time period of shortcut?
But then shouldn't the Residual Current Circuit Breaker detect shortcuts? As far as I remember it protects within 30ms….
/Anton
The outlet I use has a 10A housebreaker, the music system (preamp 2A, power amps 4A (each) and DAQ 3.15A) that has been working flawlessly for more then 15 years - can it really be a sudden shortcut?
How can the fuse prevent a shortcut? Is it not more like reducing the time period of shortcut?
But then shouldn't the Residual Current Circuit Breaker detect shortcuts? As far as I remember it protects within 30ms….
/Anton
Why is the fuse a problem in the first place? And why do you suddenly start talking about RCDs when you mean fuses (because a fuse protects against overcurrent whereas an RCD protects against ground faults that could potentially expose high voltages on metal parts)?
Of course the fuse do not prevent short circuits (where did that come from?), but the usual reason for a lower-value fuse in the device is that an over-current situation in a device (so not necessarily a full short) may cause enough heating to be a fire risk without it being enough to trip the house breaker. If the fuse is small and fast enough to break before any serious damage is caused to the device that is of course a bonus, but it is typically not the main purpose.
Of course the fuse do not prevent short circuits (where did that come from?), but the usual reason for a lower-value fuse in the device is that an over-current situation in a device (so not necessarily a full short) may cause enough heating to be a fire risk without it being enough to trip the house breaker. If the fuse is small and fast enough to break before any serious damage is caused to the device that is of course a bonus, but it is typically not the main purpose.
I won't go into the multiple cases where I have seen what should have worked, didn't. And that big house/breaker is not even close to protecting other events in circuitry. I had a power conditioner go up in smoke right in front of me. Never bothered the house breaker one bit. And one example after another.
Thanks!
Nisbeth: I get that a fuse might/may by/hopefully protect other parts of the for instance the preamp. If I’m willing to risk the for instance preamp why bother with a fuse?
The fuse is chosen so that it want break during in rush current - in my case fuse needs to be 2 - 3.15A while after the start up the normal current is about 2-300mA. That is a large fuse for protection after the few sec of start up. So basically fuse is just mayby prevent a fire - but you can’t be suer…
About “prevents shorts” - please read the first reply.
Rayma: I was trying to avoid the minefield, fuses (with mysound system and listening) heavily degrades the sound… Therefore I wants to underständ why it is so important to have the fuse.
/Anton
Nisbeth: I get that a fuse might/may by/hopefully protect other parts of the for instance the preamp. If I’m willing to risk the for instance preamp why bother with a fuse?
The fuse is chosen so that it want break during in rush current - in my case fuse needs to be 2 - 3.15A while after the start up the normal current is about 2-300mA. That is a large fuse for protection after the few sec of start up. So basically fuse is just mayby prevent a fire - but you can’t be suer…
About “prevents shorts” - please read the first reply.
Rayma: I was trying to avoid the minefield, fuses (with mysound system and listening) heavily degrades the sound… Therefore I wants to underständ why it is so important to have the fuse.
/Anton
If the fuse heavily degrades the sound in a preamp, the power supply design certainly leaves something to be desired.
A preamp is the easiest place for a fuse to do its job. Better not look into the power amp fuse. Or transformer regulation.
A preamp is the easiest place for a fuse to do its job. Better not look into the power amp fuse. Or transformer regulation.
The way I think of it is the fuse should blow if that much current would overheat the transformer/circuitry to the point of fire in the preamp. The house circuit breakers should be sized so that if a current of that amount or more would overheat the wires in the walls, the breaker should trip.
Though it may not be predictable what a fuse might protect, I was mostly referring to the preamp circuit itself.
In my years of service at a communications company, I learned that the larger fuses were used at the main circuit locations that we called BDFB (I forget what that stood for, but it was one of many large DC service locations for power distribution). The smaller fuses in each panel of equipment, starting from a main fuse for the entire piece of equipment, and then on to the smaller sections. I must add that I realize that this doesn't necessarily transfer to home audio, but rather for our purposes, DC current came down the line at say 70 amps, and then distributed to a rack of equipment that was separately fused for each shelf. Sorry to be confusing, but let's just say that it mattered very much in that environment, and I carried that thinking everywhere else when it comes to electricity.
In my years of service at a communications company, I learned that the larger fuses were used at the main circuit locations that we called BDFB (I forget what that stood for, but it was one of many large DC service locations for power distribution). The smaller fuses in each panel of equipment, starting from a main fuse for the entire piece of equipment, and then on to the smaller sections. I must add that I realize that this doesn't necessarily transfer to home audio, but rather for our purposes, DC current came down the line at say 70 amps, and then distributed to a rack of equipment that was separately fused for each shelf. Sorry to be confusing, but let's just say that it mattered very much in that environment, and I carried that thinking everywhere else when it comes to electricity.
I'm surprised no one has mentioned slow-blow fuses, particularly in view of the discussion of higher in-rush currents. A slow-blow fuse is designed to pass a much higher current than its rating, but only for a short time. But that short time is long enough for the in-rush currents to settle down. Slow-Blow fuses are commonly used in power supplies like we see in audio equipment. A good place to start is to use a slow-blow fuse with a rating of 2 times your steady-state current. This will prevent nuisance blowing at start-up, and still offer adequate protection in case of a serious over-current condition. Don't do away with fuses, no matter how bad you think they sound. This is a matter of your safety.
I had a DIY preamp that developed a short in the transformer primary winding. Kept blowing the fuse in the unit. Much easier to diagnose than if the house breaker would have tripped repeatedly - at least it saved a lot of steps from my little workshop to the breaker box as I figured out the problem. I had a similar occurrence with a power amp. Maybe you could try some of those $600.00 fuses that some use when they hear a degradation in sound due to fuses. Luckily, I am free of that audio hell.
The power transformer windings will have a vastly higher resistance than any fuse can have.
Said resistance will cause far inferior regulation (sometimes 30% to 40% for small transformers) in comparison to a fuse.
Said resistance will cause far inferior regulation (sometimes 30% to 40% for small transformers) in comparison to a fuse.
Yes, a bad filter capacitor or rectifier will cause over current and heat up the transformer, a fuse will prevent a fire and if you're lucky it will save the transformer from shorting.
If you really can hear the fuse degrades the sound in your system, there's a product "Swiss digital fuse box", or you can diy it using current sensing relay.
Thank you for your input!
Oh yes the sound is clearly degraded by the fuse. Thanks, I will check out the Swiss digital fuse box.
(I’m using the slow-blow fuses (T).)
Where I am it is now well beyond midnight so for me it’s time for some eye shut, time to hit the sack etc….
/Anton
Oh yes the sound is clearly degraded by the fuse. Thanks, I will check out the Swiss digital fuse box.
(I’m using the slow-blow fuses (T).)
Where I am it is now well beyond midnight so for me it’s time for some eye shut, time to hit the sack etc….
/Anton
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Crappy fuse holders having contact problems are not unheard of, check the fuseholder if you thinck you can "hear" your fuse
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There are fuses with leads you solder to the board. They don't blow unless service is needed anyway.
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