Speaker protection and mute

Speaker protection and mute

Many high-fidelity amplifiers and professional power amplifiers (as well as speaker systems) offer some form of protection, either protecting the speakers from amplifier failure and/or vice versa. Some of this protection is implemented at a very basic level—for example, using a "polymer switch." A polymer switch is a non-linear resistor that has low resistance at normal temperatures and much higher resistance at a specified temperature. Unlike "ordinary" thermistors, which have more or less linear characteristics, polymer switches exhibit a rapid switching behavior after reaching their limits.

The circuit also includes a mute function that keeps the speaker disconnected until the amplifier stabilizes and disconnects it as soon as power is removed to prevent shutdown noises that some amplifiers produce. These noises range from a low-level pop 5 to 10 seconds after power is off to whistles, squeaks, and other strange noises that I've heard from amplifiers over the years.