[Chris Hornbeck]

On 12 Dec 2006 19:21:20 -0800, "Bret Ludwig"
wrote:

Use the relay to short the output to ground, rather than open it. The
power amp should have circuitry that protects it from running into a
dead short. If THAT fails, better to blow up the output transistors
than a potentially $10K+ speaker system

Crowbars, including solid-state ones using SCR's, have
been used since the 1970's, for example, the McIntosh
MA6100.

They do have their limitations, as you've noted, and
their advantages. To take advantage of crowbars, the
designer must integrate them with a slow-start regimen
to prevent turn-on transients (under *all* conditions)
and with a soft turn-off (under *all* conditions).

Do-able, obviously, but not trivial. For critical use,
the contact resistance of a relay idling for years(?)
is too problematical, so it's never done.

All good fortune,

Chris Hornbeck
"Too soon oldt; too late schmardt."