In article , Bob Latham
wrote:
In article , Jim Lesurf
wrote:

The distinction being that I relied on dc line fuses for 'protection'.
Less convenient than current limiters, but allowed the amp not to be
bothered with current limiter effects. ;-)

I applaud your intention to not use limiter circuits but may I ask, were
your designs single supply rail and AC coupled or were they dual rail?

Dual rail. Fuses in each rail, plus an ac fuse.

The reason I ask is probably obvious, if one rail fuse blows is it not
very likely the other rail will appear across the speaker as 50v of DC?

Not into a short circuit. :-)

FWIW No speaker load ever blew the fuses in my experience.

The design didn't/doesn't behave as you assume. Once one fuse had blown the
amplifier gain evaporated, and the output fell to very little. i.e. nothing
was then 'driving' the output to seek the other rail. So what you ask about
wasn't "very likely". It had been designed not to act as you fear. :-)

When testing with a screwdriver, it was a matter of 'chance' if one fuse
blew, or the other, or both. In each case once the screwdriver was removed
the o/p voltage wasn't at a rail even with no load.

Of course, if the speaker had already developed a fault and its impedance
had dropped to the order of an Ohm, then the amp might have then fried the
result, simply due to its willingness to assert the audio waveform into low
impedance loads. But I wouldn't blame the amplifier for that. ;-

Slainte,

Jim

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