Patent ID: 7564304

Claim:
An audio power amplifier apparatus, capable to receive as input an external audio signal and to provide an amplified signal Vo for a load connected to at least one apparatus output terminal (IO 4 ), the apparatus comprising an input section, capable to receive as input said external audio signal and to output an audio signal Vi, a main power amplifying section having an input connected to the output of the input section, wherein the amplifying section provides an output signal Vma having non-inverting gain with respect to the input audio signal Vi, and in that it further comprises a cascade of one or more sections, having two inputs, which are one non-inverting and the other inverting, the former being connected to the output of the input section, and the latter being connected to the output of the power amplifying section, and an output terminal coinciding with a corresponding terminal out of two terminals of a first secondary of a transformer T 1 , that is connected to said at least one apparatus output terminal, the load being connected to the output of the power amplifying section and in series to the first secondary of the transformer T 1 , so that the amplified signal Vo is equal to the difference between a signal Vmo obtained from the signal Vma at the output of the power amplifying section and a signal Vb present across the two terminals (Vb 1 , Vb 2 ) of the first secondary of the transformer T 1 (Vb=Vb 1 −Vb 2 ), the cascade being capable to extract an error component Ve, with respect to the amplified signal Vi, from the signal Vma at the output of the amplifying section, and to stably provide substantially a copy of such error component, without interactions with the amplifying section, across the two terminals (Vb 1 , Vb 2 ) of the first secondary of the transformer T 1 , the cascade having such a frequency response that the signal Vb present across the two terminals (Vb 1 , Vb 2 ) of the first secondary of the transformer T 1 has substantially the same behaviour of amplitude and phase as the error component Ve in a first predetermined frequency band.