Loudspeaker protection network

Claim 1

A current amplifier having first and second input terminals and an output terminal, means for direct coupling said output terminal to a loudspeaker, a source of positive D.C. potential, a source of negative D.C. potential, means connecting said source of positive D.C. potential via a first fuse to said current amplifier and connecting said source of negative D.C. potential via a second fuse to said current amplifier to power said current amplifier, biasing means connected between said input terminals, a predriver transistor having base, collector and emitter electrodes, a first resistor, said first resistor being connected between one of said input terminals and one of said sources of D.C. potential via one of said fuses, said collector and emitter electrodes being connected between the other of said input terminals and the other of said sources of D.C. potential via the other of said fuses, second and third transistors connected in differential amplifier configuration and each having base, collector and emitter electrodes, means connecting said emitter electrodes of said second and third transistors to one of said sources of D.C. potential via one of said fuses to bias on said second and third transistors, means connecting said collector electrode of said second transistor and said base electrode of said predriver transistor whereby said predriver transistor is biased on from said sources of D.C. potential when said fuses are intact, means for applying an input signal to said base electrode of said second transistor, a negative D.C. feedback network connected between said output terminal and said base electrode of said third transistor and a diode connected directly to ground in series circuit with said emitter electrode of said predriver transistor, said diode being poled and connected to permit said predriver transistor to be biased on when said other fuse blows.