Audio amplification used in security systems need to be robust and have failsafe capability, they also need to be compact and energy efficient. A means of providing this by combining class D amplifiers in series is provided along with means to disconnect the amplifiers in a failure mode so as to provide ongoing operation should 1 of the amplifiers malfunction or another part of the system associated one of the amplifiers malfunction. The invention comprises an audio output stage which may be further integrated into an audio system having a supervisory controller to manage the transition from normal operation to failure state operation.