Due to some recent problems with fuses blowing, I've been contemplating the zen of fuses!
I'd be interested in your comments.
It seems to me that, in a component which has a mains fuse followed by some DC-rail fuses, we probably need to use two different types of fuses. However, there's a difference between power amps (with potentially high DC rail currents) and source components (with generally low DC rail currents).
For instance, in an AKSA you have an AC mains fuse (typically in a case-mounted fuse-holder) and then 2 DC rail fuses located on the AKSA PCB. The DC rail fuses have to cope with significantly varying currents yet the reason for having these fuses is to blow quickly in the case of a fault developing ... to stop (or at least minimise) any consequent damage to circuit components.
In my active crossovers, on the other hand (whose power supply is Hugh's "1st generation" regulated power supply), there is an AC mains fuse, then another fuse on each DC rail. In these (and similar "source" components), unlike with power amps there is not much variation in DC rail current during "normal" (steady-state) operation - yet when the PS filter caps charge up (at switch-on), a much larger current flows.
Up till recently, I had always used fast-blo ("F") fuses everywhere - and these would blow occasionally ... most commonly on power-up. However, after thinking about this issue, I have decided to change the mains fuses in my AKSAs to slow-blo ("T"). My reasoning for this is as follows:
* when the amp is switched on, a large "in-rush" current passes through the mains fuse, due to the toroid being energised. This is many times larger than the currents which normally pass through the mains fuse, during "normal" AKSA operation.
* hence the mains fuse should be slow-blo, so that it can withstand this short current burst.
* the DC rail fuses, however, should be fast-blo for circuit protection.
With a source device powered by Hugh's regulated PS, the situation is different. The mains fuse should likewise be slow-blo, to withstand the in-rush current to the power transformer, but the DC rail fuses should also be slow-blo, to withstand the filter cap charge-up currents.
Any comments anyone?
Regards,
Andy
