Audio de-emphasis circuit

摘要

The de-emphasis function of an FM audio system is provided by the impedances of the sound reproduction components, including an audio output transformer and the speaker. The high frequency rolloff of these impedance devices can provide complete FM de-emphasis by using an audio output transformer with a selected leakage inductance and a speaker with a selected voice coil impedance. If the inductances of the components are insufficient to provide the full amount of compensating rolloff, the remaining portion of the de-emphasis can be provided by a partial de-emphasis circuit coupled between the FM detector and the transformer or speaker. In addition, the provision of the de-emphasis function at the output of the audio power amplifier provides filtering of the objectionable high frequency harmonics resulting from power amplifier clipping. A transformer which exhibits sufficient leakage inductance for the entire de-emphasis function will generally provide a substantially increased inductance in shunt with the audio signal path. The low frequency (bass) response of the audio system is thereby improved.