"Pooh Bear" wrote in message
...
Fleetie wrote:

"Graham Holloway" wrote
Jim, for the purposes of seeing how a fuse might affect linearity,
some sort of frequency response of resistance change vs frequency
would be needed. If a fuse has a very low thermal inertia, it might
change its resistance significantly during a cycle, particularly at
low frequencies. This would cause distortion if it was in series with
a speaker. At higher frequencies which it could not track, it would
simply cause amplitude compression - I've used a light bulb for this
in the past.

d

Pearce Consulting
http://www.pearce.uk.com


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.

What happens to the voltage at the speaker output then? And could it
toast the speaker?

Sounds well dangerous to me.

Far more reliable is to fit 'crowbar protection' on the output to guard
against
excessive DC. Whatever else - the speaker won't see prolonged DC. Supply
rail
fuses will blow.


Graham


If either fuse blew, the output would float to zero.

We used it because it was cheap. In fact, the 100W amplifier modules cost
under one UKP (circa 1982) in parts, including the heatsink.

Graham Holloway.