Jim Lesurf wrote:

Don't know the design, but if lucky it may be something like o/p emitter
resistors releasing magic smoke before the actual transistors died. In my
experience, resistors make more smell than transistors when failing. :-)

Sadly, the resistors usually fail because the transistors are done. Not
the other way around. And also part of my comment on fused speaker
outputs. A typical fuse that will protect the amp will blow often if
the amp is driven at/near capacity for any more than a very few
seconds. A fuse that *may* protect the speakers will generally not
protect the amp.

You who are not in the US have (to us) a strange way of
describing/naming fuses. We use Dual-Element fuses for these
applications, something that will handle a brief peak (read
"clipping"), yet blow quickly if that peak is sustained for any length
of time. Last time I mentioned D/E fuse, I got ranted at as to how they
are illegal, immoral and/or fattening other than around here. But for
all that, they are might useful beasts. By no means perfect in speaker
applications, and there are some losses due to the fuse being in the
circuit (or so the massive-cost speaker-wire advocates maintain), but
again they are very useful.

For example, I use a 1A dual-element fuse from my 375WPC/RMS SS amp
into AR3a speakers. I *can* blow that fuse at ear-splitting volume with
some source material, but I will damage neither the amp nor the
speakers in the process. A 2A fast-blow fuse will fail far more often,
and I would not risk a standard-design slow-blow fuse at any rating.

Peter Wieck
Wyncote, PA