well, in all my years repairing amps and looking at schematics, i haven't seen any undervoltage protection in any amp that i know of, and the i understand the reason for that, there is no need for it whatsoever. i have explained in my previous post.
Ofcourse, I should have mentioned that undervoltage protection is fairly common in many Class D amps. I read their nature of operation requires one.
now motors are a different animal altogether, operating motors on undervoltage causes the rotor to move very slowly thus mimicking a short circuit. so here is where you get the idea! this have no correlation with amps....
Another ofcourse. But if you read my statements in the proper context of that post, it was more an example to support my premise that undervoltage "can have detrimental effects on some appliances." And for the same reason, cited the existence of undervoltage protection circuits. But for most lnear amps, I agree, undervoltage will just result in underpower. But i think a severely voltage-starved amp, when you increase the volume, will just output current-starved square waves that are harmful to the speakers. IOW, it will attempt to extract the current needed to amplify the signal as you go up in volume. There being none, you get clipped signals. Now if such adverse output condition will triger the protection circuit, it should, but I have no experience in that.