Phil Allison wrote:

"msg"

Phil Allison wrote:


** Be very wary of adding +/- DC rail fuses to any power amp designed
without them.

Very likely if one or other DC fuse blows or is removed, the amp's output
will swing fully to the rail with its fuse still intact.

snip

One could add overcurrent shutdown circuitry on each rail designed to shut
down the entire supply,



** How idiotic !



or for antique simplicity use 'indicator fuses' which
have a spring-loaded plunger which makes contact with an endstop terminal
when they blow -- the endstop is often connected to a crowbar which blows
main fuses upstream.



** Or simply use no DC rail fuses and let the AC supply fuse blow when
overloaded - as originally intended by the designer.

Evidently the designer did not account for the sort of catastrophic
failure described by the OP. The large capacitive reservoir in the supply
is very much like that in the line printers that employed the sorts of
protection I described, including the "idiotic" independent supply rail
overcurrent protection scheme with very fast response times (faster than
any fusible link).

Those power amps that DO use +/-DC rail fuses, almost invariably have them
fitted in line with the output devices but NOT in line with low power,
voltage amplification circuitry.

Indeed that was implicit in my response; the rails in question are the
power amp rails, _not_ low-power rails.


It must be possible to remove either DC ( or both) rail fuse with the amp
under load and drive and have no circuit damage occur. Any competent amp
designer can arrange things so this is the case - but not likely the OP.


Yes, but the OP did not design the amp and short of re-engineering it he
would need workable solutions.

Regards,

Michael