1. Field of the Invention
The present invention relates to a direct coupling type power amplifier for use with audio circuits and more particularly to such a direct coupling type power amplifier having a muting function.
2. Description of the Prior Art
In a typical type of audio power amplifier circuit for amplifying audio signals, an inpact or popping sound unpleasant to the ears is sometimes generated from its load speaker immediately after the power source is turned on, due to a rapid change in bias voltages in a preamplifier such as an equalizer used in a first input amplifier stage of the power amplifier circuit. The impact sound is not only unpleasant to the ears, but also exposes the speaker to the danger of being damaged.
There has been provided a power amplifier circuit free from the generation of impact or popping sounds, in which a muting function is provided by breaking a signal transfer path through the actuation of an electromagnetic relay for a certain time interval after the turn-on of the power source. However, such a power amplifier circuit is expensive since the electromagnetic relay used therein is rather costly and moreover the switching sound of the relay is felt to be unpleasant.