A fuse is a good first line of defense, but sometimes isn't fast enough to protect.
Many years ago I had a system of a McIntosh C26 preamp, Phase Linear 400 amplifier and EPI 201 speakers, in which I had fast-blo 3A fuses in inline fuse holders in the speaker wires.
The McIntosh developed a bad or dirty loudness compensation switch, which when disenaged, triggered a huge "KA-BOOM" transient blowing both fuses AND both tweeters!
Steve
