Always use an amplifier with protection against DC voltage on the output terminals. Dead output devices can plop the full DC power supply voltage through your woofer (or tweeter) voice coil. This is typically over 70 volts DC for a 200 watt per channel amplifier, the power supply can deliver a lot of current, and it can do it fast. A fastblo fuse takes half a second to quit, yet a speaker is designed to respond to transients. That means you can be wearing your voice coil before a fuse blows.
Copyright 1996 by Barry McKinnon, first published 1978
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Mc Squared System Design Group, Inc
323 - 901 West 3rd Street
North Vancouver, BC V7P 3P9
Phone 604 - 986 - 8181
FAX (604) - 988 - 9751