Any comments on different fuse types and how they affect the sound of a supply? Glass vs ceramic and or sand filled. Is this strictly an issue of microphonics? Is there such a thing as a low impedance fuse? What are the mechanics behind fuses impacting the sound of a supply. Are there recommended types of fuses for audio or ultra low noise measurement equipment? Not referring to cryo treated fuses here but fuse style types. Thanks best regards Moray James.
I'm not very much into changing one component and hearing drastic difference, but I believe it's mainly because non linear impedance of a fuse, the main reason for not putting one directly at the output of an amp. Better than trying different fuses is to make an amp less prone to supply non linear impedance distortions. Simple RC for VAS will be helpful. Best to use IC regulated supply for everything but last output follower stage. The unregulated part of supply has than virtually no impact on quality and for the rest IC has its in built current limiter. Sorry for not answering your question directly but I had to say this. Maybe ask some 'gainclone' guys, they'll tell you the pricier the component the better. Fuses too I suspect.
Dear Sirs,
I would like to get anyone opinion on this problem.
I have a power amp that has 4A/250V glass fuses in series with the + and - power rails between the filter caps of the PS and the amplification circuit (for me an unelegant protection method).
I wonder which kind and value of impedance these fuses present to the current flowing in the supply rails.
Could they be a bottleneck ?
Thank you so much.
Kind regards,
beppe
I would like to get anyone opinion on this problem.
I have a power amp that has 4A/250V glass fuses in series with the + and - power rails between the filter caps of the PS and the amplification circuit (for me an unelegant protection method).
I wonder which kind and value of impedance these fuses present to the current flowing in the supply rails.
Could they be a bottleneck ?
Thank you so much.
Kind regards,
beppe
beppe61 said:
There is not such a thing as "current bottlenecks" in electronics. I strongly recommend you to study some papers on electronics basics (use google) in order to understand concepts like current flow, electric potential, resistance and impedance.
A fuse has an impedance, mainly resistive (it works like a resistor most of the time). The power lost on the wire is I^2*R and it will manifest itself as a temperature increase, and ultimately as glowing. The resistance of the fuse gets higher and higher as its temperature increases in response to higher currents flowing though it, until a point is reached where thermal runaway happens and the filament starts glowing. Looking carefully, the filament may be observed dilating and bending before that happens.
The fuse only works as a current limiter when it enters thermal runaway, as both temperature and resistance will increase dramatically in response to any current increase reached this point. However, it will fuse almost inmediately. That's why fuses work as resistors during normal operation.
In other words: If you can't see the filaments of your fuses bending or glowing with the music, then they are acting as harmless and linear resistors, whose value would be probably several dozens of miliohms (nothing to worry about). Otherwise, try fuses of a slightly higher current rating.
Hi Beppe,
Try measuring the voltage drop across the amplifier fuses.
I have found 8mV to 30mV across them in quiescent condition. With care you can also measure the mains fuse on the AC mV scale.
A good clean often removes much of this volts drop. This seems to indicate that the corrosion and dirt that builds up on the recepticle and fuse cause much of the resistance.
For mine, converting the volts drop of a cleaned F2A fuse and receptacle to resistance came out at 9mohm. Bigger fuse ratings will have lower resistance. Undisturbed fuses that have been used for a long time will almost always be much worse.
That's why vendors pedal the contact cleaning fluids and fine abrasives (brasso in UK) can also be used to really polish the surfaces.
Try measuring the voltage drop across the amplifier fuses.
I have found 8mV to 30mV across them in quiescent condition. With care you can also measure the mains fuse on the AC mV scale.
A good clean often removes much of this volts drop. This seems to indicate that the corrosion and dirt that builds up on the recepticle and fuse cause much of the resistance.
For mine, converting the volts drop of a cleaned F2A fuse and receptacle to resistance came out at 9mohm. Bigger fuse ratings will have lower resistance. Undisturbed fuses that have been used for a long time will almost always be much worse.
That's why vendors pedal the contact cleaning fluids and fine abrasives (brasso in UK) can also be used to really polish the surfaces.
I just received an E-mail from an associate concerning fuses. Apparently, they changed the sound in one of my designs. I also spoke with a German guy who made exotic audio fuses, at CES, and he made sense to me. They are pretty expensive though, and I would think that other things should come first.
Hi Beppe,
if your amp was designed to include fuses then it would be rash of you to change the values.
You are inviting disaster if you bypass them.
The amp should be designed to reject some power supply ripple.
A small resistance in the supply leads gives a small increase in this PSU ripple. A well designed amp should not produce bad sound with clean fuses. But, I will reluctantly accept that dirty and/or corroded fuses may affect the sound, particularly if the volts loss across them is substantial and not linear.
if your amp was designed to include fuses then it would be rash of you to change the values.
You are inviting disaster if you bypass them.
The amp should be designed to reject some power supply ripple.
A small resistance in the supply leads gives a small increase in this PSU ripple. A well designed amp should not produce bad sound with clean fuses. But, I will reluctantly accept that dirty and/or corroded fuses may affect the sound, particularly if the volts loss across them is substantial and not linear.
First of all, fuses most often protect you from a fire, rather than the equipment from overload failure! There must be one at some point in the appliance fort his function.
Most cheap fuse HOLDERS will have higher and more nonlinear resistance than the fuse. Instead of paying $ for gold plating them, the simple remedy is to solder them in or use pigtail wire fuses.
Fuses themselves can produce thermal distortion, the resistance of some fuses is quite nonlinear (PTC usually). In the overwhelming majority of cases, fuses in power lines are include within the corrective action of global feedback. Not so for most cases of output fuses, and there they can be a problem, especially if the wrong type or rating is used. That bieng said, that sort of fuse application is rare.
Most cheap fuse HOLDERS will have higher and more nonlinear resistance than the fuse. Instead of paying $ for gold plating them, the simple remedy is to solder them in or use pigtail wire fuses.
Fuses themselves can produce thermal distortion, the resistance of some fuses is quite nonlinear (PTC usually). In the overwhelming majority of cases, fuses in power lines are include within the corrective action of global feedback. Not so for most cases of output fuses, and there they can be a problem, especially if the wrong type or rating is used. That bieng said, that sort of fuse application is rare.
Remember that the things that we usually don't see or understand are the ones that affect sound mostly. Fuses are easy to blame because most people can see them and understand them, but what about voice coils?
Don't you know that most loudspeaker voice coils are also made with a long and thin wire of copper (similar to the wire of a 4A or 6.3A fuse)? This wire is also subject to the same heating, dilation, and PTC resistance increase effects seen on a fuse. Furthermore, it's usually subject to the same or higher current levels than a rail fuse.
It's not so hard to measure resistance increases of one to two ohms in the voice coils of 8 ohm loudspeakers after playing loud for several minutes. Of course, this does affect sound because these little voice coils are (in) the signal path, and this is plain open-loop stuff without any feedback system to correct it.
However, nobody complains because most people has never seen a voice coil nor measured these effects, but everybody knows what a fuse is... (some even seem to know how to sell them
)
Don't you know that most loudspeaker voice coils are also made with a long and thin wire of copper (similar to the wire of a 4A or 6.3A fuse)? This wire is also subject to the same heating, dilation, and PTC resistance increase effects seen on a fuse. Furthermore, it's usually subject to the same or higher current levels than a rail fuse.
It's not so hard to measure resistance increases of one to two ohms in the voice coils of 8 ohm loudspeakers after playing loud for several minutes. Of course, this does affect sound because these little voice coils are (in) the signal path, and this is plain open-loop stuff without any feedback system to correct it.
However, nobody complains because most people has never seen a voice coil nor measured these effects, but everybody knows what a fuse is... (some even seem to know how to sell them
)Hi Illimzn,
I do not necessarily agree.
Mains fuses are there to protect you from fire. Particularly from cable damage.
Vrail fuses are there to prevent the output stage transistors and heatsink combination from overheating when the "limiting" is operating to prevent near instantaneous output stage failure.
The limiting referred could be current limiting or VI limiting or inherent/natural limiting due to internal resistances stacking up.
The effect of excessive heating of the output stage is raising the Tc and Tj of the output stage leading to excursions outside the SOAR and ultimately output stage failure.
The Vrail fuses are a very effective timed delay on the supply line switch off that prevents overload failure. Here we reach our disagreement; output stage failure will not necessarily lead to fire. If Vrail fuses are not fitted then much more likely that the transistors will either go short circuit or open circuit and if short circuit then eventually something else will go open circuit. Maybe the mains fuses due to transformer overload. This last one I am in agreement. Transformer overload, because it can generate enormous heat could cause fire.
I do not necessarily agree.
Mains fuses are there to protect you from fire. Particularly from cable damage.
Vrail fuses are there to prevent the output stage transistors and heatsink combination from overheating when the "limiting" is operating to prevent near instantaneous output stage failure.
The limiting referred could be current limiting or VI limiting or inherent/natural limiting due to internal resistances stacking up.
The effect of excessive heating of the output stage is raising the Tc and Tj of the output stage leading to excursions outside the SOAR and ultimately output stage failure.
The Vrail fuses are a very effective timed delay on the supply line switch off that prevents overload failure. Here we reach our disagreement; output stage failure will not necessarily lead to fire. If Vrail fuses are not fitted then much more likely that the transistors will either go short circuit or open circuit and if short circuit then eventually something else will go open circuit. Maybe the mains fuses due to transformer overload. This last one I am in agreement. Transformer overload, because it can generate enormous heat could cause fire.
I have a weird problem a while back. My speaker fuse goes via a fuse holder in the rear panel. The fuse holder was condidered cheap but I had a bad contact because it's rather low contact pressure in the ends of the fuse. The sound in the speakers sound like a broken speaker but only in certain levels. After I had removed the fused and put them back everything was OK then.ilimzn said:
what a can of worms.
IMHO there can be no argument about fuses impacting negatively on sound.usually they are there for cheap protection of output stages and usually where there is no fault condition they are never needed.Otala in his Electro amp monitored output stages and opened a relay under fault conditions. this is avery elegant way of avoiding fuses if they are for output stage protection.
if you must have fuses always keep the receptacle very clean this push in contact is very susceptible to noise. if at all possible hard wire the fuse wire across the fuseholder. not terribly safe, but an end to contact problems. after all this is diy.....yes.
and i know some will wince at my suggestions, but try replacing fuse in mains supply by hardwiring. every time i do this i hear a small but audible gain.
fascinating topic.
IMHO there can be no argument about fuses impacting negatively on sound.usually they are there for cheap protection of output stages and usually where there is no fault condition they are never needed.Otala in his Electro amp monitored output stages and opened a relay under fault conditions. this is avery elegant way of avoiding fuses if they are for output stage protection.
if you must have fuses always keep the receptacle very clean this push in contact is very susceptible to noise. if at all possible hard wire the fuse wire across the fuseholder. not terribly safe, but an end to contact problems. after all this is diy.....yes.
and i know some will wince at my suggestions, but try replacing fuse in mains supply by hardwiring. every time i do this i hear a small but audible gain.
fascinating topic.
I agree that the weak link is often the fuseholder. I always use decent quality axial screw-up ones, and if in any doubt would replace the standard clips with these. Apart from the better contacts, they are at least partially sealed and thus avoid some of the oxidation due to air pollutants.
Inspection reveals that the clips often become weak and malleable. I speculate that sometimes minor surface corrosion increases the resistance, leading to heating which causes the clips to lose their temper.
An alternative would, of course be to solder the fuse in.
Inspection reveals that the clips often become weak and malleable. I speculate that sometimes minor surface corrosion increases the resistance, leading to heating which causes the clips to lose their temper.
An alternative would, of course be to solder the fuse in.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.