I don't know if its common practise but Rotel used to do this and in my experience it worked well in terms of protecting the speakers. I've had a few of these amps fail and if one rail fuse blows and the other rail shorts to the speakers the other rail fuse blows as well.
It causes one rail voltage to be at the output and if there is no DC protection circuit and if the filter caps are large value it will possibly cost a woofer. One rarely see the other fuse blow as well so the caps discharge in the loudspeaker with full rail voltage and as the current goes down relatively fast the voice coil overheats/melts instead of the fuse. Of course it will never occur that both fuses of both rails blow simultaneously. IMHO it is only to protect against fire etc. but so does a primary fuse. When a primary fuse blows both rails will go down. I used to repair British cottage brand amplifiers that had no loudspeaker protection but they usually did have the fuses. Defective amplifier practically always meant a defective loudspeaker.
Some try to prevent all possible horror that may possibly happen but doing so may have some drawbacks... just don't leave stuff powered on unattended so when leaving the home, sleeping, holidays etc just switch off stuff with real mains switches or by switching off the audio power distributor. It won't prevent stuff breaking down but it will prevent stuff breaking down when no one is around to notice it.
I am into low power amplifiers myself as one really does not need much power in the majority of cases but I did not realize until recently that some are so light they can not even damage loudspeakers unlike 2 x 400W amplifiers.
Some try to prevent all possible horror that may possibly happen but doing so may have some drawbacks... just don't leave stuff powered on unattended so when leaving the home, sleeping, holidays etc just switch off stuff with real mains switches or by switching off the audio power distributor. It won't prevent stuff breaking down but it will prevent stuff breaking down when no one is around to notice it.
I am into low power amplifiers myself as one really does not need much power in the majority of cases but I did not realize until recently that some are so light they can not even damage loudspeakers unlike 2 x 400W amplifiers.
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Well I've seen it work and obviously the fuses are after the caps so the situation is identical for each rail fuse independant of the cause. It is also true that the speaker will fry if its power capability is not matched by the fuse rating and type but that is obvious.
I am not advocating rail fuses in general just stating that they can offer some speaker protection in a simple and low-cost manner. Or putting it another way, its a better way to protect your speakers than just the mains fuse.
I am not advocating rail fuses in general just stating that they can offer some speaker protection in a simple and low-cost manner. Or putting it another way, its a better way to protect your speakers than just the mains fuse.
Best is a DC detection/loudspeaker protection circuit. No fuse will protect a loudspeaker reliably enough. Rail fuses are an extra risk to the loudspeaker IMHO a they now offer a full rail voltage when one blows.
Fuses in general are there to prevent fire and secondary damage to cabling. They are not there to protect a load.
Fuses in general are there to prevent fire and secondary damage to cabling. They are not there to protect a load.
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I couldn’t have written it better either. With many amplifier topologies, however, it’s just STUPID to fuse the power supply to the front end/differential amps. You can provide a method of current limiting there that is independent of the necessary fusing for the FOLLOWERS. I know it’s dumb not to have loudspeaker protection, but if you blow a rail fuse on a Phase Linear (due to loudspeaker current alone, no amplifier failure), it WILL CONTINUE TO OPERATE clipping off exactly half of the waveform, only producing the amount of DC inherent to the half wave rectified signal. There is no loss of DC feedback. More advanced amplifiers, perhaps with DC servos, will fare even better.
Every self-respecting amplifier should have both protection systems: the fuses on the rails and the DC protection circuit for the speakers.
Fuses only serve to prevent the amplifier from bursting into flames. They do not prevent damage to the amplifier or the speaker in the event of a fault.
The DC protection circuit serves to prevent damage to the speaker in the event of an amplifier failure.
Both systems are complementary and should be essential in an amplifier.
Fuses only serve to prevent the amplifier from bursting into flames. They do not prevent damage to the amplifier or the speaker in the event of a fault.
The DC protection circuit serves to prevent damage to the speaker in the event of an amplifier failure.
Both systems are complementary and should be essential in an amplifier.
Could fusing the rails not also cause a problem too. If one rail fuse failed and the other side went open loop to rail voltage, would that not cause smoke?
It seems having DC speaker protection and a properly sized primary fuse would be safe.
Edit: I'm not arguing against them, I just want to understand the pros are worth the cons. More components equals more failure points.
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If only one rail fuse blows and the other doesn't, nothing ever catches fire. That's exactly what happened to me once.
Even without DC protection, if the speaker is connected and only one rail is live, the fuse would blow before the speaker coil catches fire. The coil would be shorted out, and before it caught fire it would blow the other fuse.
But in any case, that's why both protection systems are essential.
But in any case, that's why both protection systems are essential.
I've seen many speaker coils short out, but I've never seen one burst into flames.
In my opinion, there's a difference between burning a component and burning in flames and fire. When there are no fuses, flames and fire are guaranteed in the event of an electrical failure.
As I said before, the fuse does not prevent a component from being damaged, but it does prevent it from burning in fire and flames, there is a big difference.
In my opinion, there's a difference between burning a component and burning in flames and fire. When there are no fuses, flames and fire are guaranteed in the event of an electrical failure.
As I said before, the fuse does not prevent a component from being damaged, but it does prevent it from burning in fire and flames, there is a big difference.
A voicecoil overheating is not one that burst into flames, it just melts itself open. That's all.
You never saw what the singer in a “girl with guitar” band did to a pair of Pioneers once, with a 300 wpc QSC. There was smoke and flames. They don’t actually “handle 500 watts”….
Just read this in Elliot Sound Products:
"Complete failure is nearly always a shorted output transistor, so the amp's output jumps from around 9V RMS (10W into 8Ω) to 42V DC. That's a power of 294W, and it's continuous (the speaker only has resistance at DC, assumed to be 6Ω). This forces the voicecoil out of the magnet gap and because it's not moving there is no effective cooling. The voicecoil will reach a dangerous temperature in a few seconds, and if the DC isn't disconnected quickly, the speaker will fail. This can include catching on fire!"
If one has seen a few of such failures one learns. Especially that an amplifier without loudspeaker protection is playing Russian roulette. Also that 2 x 400W in a normal home without loudspeaker protection is Russian roulette with 2 machine guns both with full rounds. They can melt a voice coil with ease.
Create amplifiers that have normal output power and always include a µPC1237 circuit (or similar) and you'll never experience power on/off phenomena and loudspeaker failure regardless if you will use a simple or complex fusing scheme. It is that simple.
When building both loudspeakers and amplifiers was a common hobby many audio magazines (can you imagine a kiosk having many DIY/audio magazines?) advocated that protection circuits were bad for sound so many skipped this. This was a bad marriage with the silly habit to build very high power amplifiers. In that period I have seen several of such failures with 1 thing in common: it was expensive to solve. Velleman K4700 was born out of necessity.
https://cdn.velleman.eu/downloads/0...*1k2sitn*_gcl_au*MTA0MTEzNzIzNy4xNzQ5NzA4NDE0
Create amplifiers that have normal output power and always include a µPC1237 circuit (or similar) and you'll never experience power on/off phenomena and loudspeaker failure regardless if you will use a simple or complex fusing scheme. It is that simple.
When building both loudspeakers and amplifiers was a common hobby many audio magazines (can you imagine a kiosk having many DIY/audio magazines?) advocated that protection circuits were bad for sound so many skipped this. This was a bad marriage with the silly habit to build very high power amplifiers. In that period I have seen several of such failures with 1 thing in common: it was expensive to solve. Velleman K4700 was born out of necessity.
https://cdn.velleman.eu/downloads/0...*1k2sitn*_gcl_au*MTA0MTEzNzIzNy4xNzQ5NzA4NDE0
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My father had a Marantz 2245 that my brother and I sent to the repair shop at least a couple times. I'm surprised it never blew the speakers since it had zero protection.
I'm currently building a P3A amp which has on board rail fuses, with a µPC1237 for protection as well.
That Velleman is nice in that it has a built in transformer. Too bad they don't make a 120v version.
I'll probably do the ESP project 33 on my next build. The Chinese stuff isn't so cheap anymore.
I'm currently building a P3A amp which has on board rail fuses, with a µPC1237 for protection as well.
That Velleman is nice in that it has a built in transformer. Too bad they don't make a 120v version.
I'll probably do the ESP project 33 on my next build. The Chinese stuff isn't so cheap anymore.
Velleman K4700 is as old as the road to Rome but it sure cuts the cake.
You can of course use the same transformer but then the 115V version. Or use a micro toroid instead.
K4700 is at last out of production but it still is available at online shops.
You can of course use the same transformer but then the 115V version. Or use a micro toroid instead.
K4700 is at last out of production but it still is available at online shops.