"Fleetie" wrote in message
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"Graham Holloway" wrote

When I worked for ILP Electronics many years ago, they suggested the
use of a fuse in series with the loudspeaker as protection against a
DC fault. I found that distortion was significant due to the
modulation of the fuse resistance by low frequencies. I have no
records of the tests I did. However, I did suggest an alternative,
and that was to put a fuse in each (+ and -) supply rails. It was
possible to use fuses of a lower rating than that in the output line
because of the lower (half cycles) duty.

One of the fuses will blow before the other.

Agreed.

What happens to the voltage at the speaker output then?

Depends, but its possible and often done so that the output of the amp does
not swing to the other rail. This may take some care, as I've definately
seen amps with the output firmly stuck on one of the power supplies.

And could it toast the speaker?

Yes, hence the desireability of some additional other kind of protection -
often a relay or a thyristor.