Although designed specifically for our new Class-A Stereo Amplifier, this unit can actually be used with any audio amplifier with supply rails up to about 70V DC simply by selecting two resistor values to suit.

Basically, the unit provides the following features:

(1) it protects the loudspeakers against catastrophic failure in the amplifier – eg, if an output transistor goes short circuit;

(2) it provides muting at switch-on and switch-off, to prevent thumps from the loudspeakers; and

(3) it provides an input for an over-temperature switch to disconnect the
loudspeakers if the output stage heat-
sink rises above a certain temperature.