I'm interested in how much fusing people add to their projects.
Im in the UK so our plugs are fused as standard.
In my amps at various times I've fused various combinations of only the incoming supply at the plug, at the iec connector and also either side of the transformer.
I don't think I've ever added fuses to the output of the PSU or the speaker lines.
What do you do and why?
Im in the UK so our plugs are fused as standard.
In my amps at various times I've fused various combinations of only the incoming supply at the plug, at the iec connector and also either side of the transformer.
I don't think I've ever added fuses to the output of the PSU or the speaker lines.
What do you do and why?
It is good practice to fuse the mains transformer primary, and the DC supplies to the amplifier both +ve and -ve.
Sometimes a loudspeaker magnetic over current resettable fuse or a standard anti surge fuse, inline with the loudspeaker, is used if there is no other protection (relay etc).
Sometimes a loudspeaker magnetic over current resettable fuse or a standard anti surge fuse, inline with the loudspeaker, is used if there is no other protection (relay etc).
I agree on the primary, that's just basic safety. I've usually fused the transformer secondaries rather than the DC supplies.
I'm always interested to see what others do and I can say I've seen much talk about this over the years.
We get schematics and build photos for the boards but minimal discussion of the protective aspect.
I'm always interested to see what others do and I can say I've seen much talk about this over the years.
We get schematics and build photos for the boards but minimal discussion of the protective aspect.
The purpose of fuses is to prevent fire, typically wiring fire. This includes transformer windings. So whenever there is a wire that can be exposed to more current than it can safely handle the circuit must have a suitable rating of fuse. Sometimes the primary fuse of a transformer will ensure the secondary circuit can't catch fire, and sometimes it won't (for instance with several secondaries of different voltages, the low voltage one may be able to source a larger current that its wire can handle).
Adding an unnecessary fuse isn't a problem, missing a necessary one is...
One problem with fusing is when a cable plugs in to the device with the fuse - you could plug in any thickness of cable, the fuse can't protect all of them. That's why the UK mains system uses a fuse in the plug, not the socket - the fuse is part of the cable it protects and is correctly rated for it (in theory).
A fuse to protect a speaker driver would ideally be part of the speaker unit. However that can add distortion as it can't be put in the feedback loop.
The thing to always be aware of is what any fuse is protecting.
Over-engineered power supplies for amplifiers make rail fuses or speaker fuses a necessity - If a 100W amp has a 1kW supply it will be capable of frying unprotected speaker leads if the amp fails. Over-large rail caps give rise to the same issue.
It ought to be common practice to label amp outputs with the minimum wire-gauge acceptable for speaker connection - I've not seen this done though.
Adding an unnecessary fuse isn't a problem, missing a necessary one is...
One problem with fusing is when a cable plugs in to the device with the fuse - you could plug in any thickness of cable, the fuse can't protect all of them. That's why the UK mains system uses a fuse in the plug, not the socket - the fuse is part of the cable it protects and is correctly rated for it (in theory).
A fuse to protect a speaker driver would ideally be part of the speaker unit. However that can add distortion as it can't be put in the feedback loop.
The thing to always be aware of is what any fuse is protecting.
Over-engineered power supplies for amplifiers make rail fuses or speaker fuses a necessity - If a 100W amp has a 1kW supply it will be capable of frying unprotected speaker leads if the amp fails. Over-large rail caps give rise to the same issue.
It ought to be common practice to label amp outputs with the minimum wire-gauge acceptable for speaker connection - I've not seen this done though.
In my opinion Fusible resistors can be a pain in the **** I have worked on many amplifiers where the fault is the resistor alone I have just done a Hitachi amplifier wher the faults were these devices In the past I have had similar problems with Sony Trio(Kenwood) etc
Trev
Trev