Amplifier device for a condenser microphone

DETAILED DESCRIPTION It is an object of the invention to provide an amplifier with the above problems solved, or an amplifier capable of using even the FET common-source type buffer amplifier circuit with almost no effect of the ripple of the power source and which has a phase-reversing function for equalizing the phase of signal even in the FET common-source type or FET source-follower type buffer amplifier, thus the connecting operation being simplified.
In order to achieve the above object, the present invention proposes as the first arrangement an amplifier including buffer amplifier means with the output end approximately serving as a current source and current mirror means with the output end approximately serving as a current source.
In addition, the present invention proposes as the second arrangement another amplifier including current mirror means with the out-put end approximately serving as a current source and connecting and disconnecting means.
According to the first arrangement of the invention, since an audio current signal produced at the output terminal of the buffer amplifier means with the output end approximately serving as a current source is changed in the direction by the current mirror means and then caused to flow in the load resistor across which an audio voltage signal is thus developed, there is almost no effect of the ripples of the power source and the phase can be inverted.
According to the second arrangement of the invention, since the current mirror means and the connecting and disconnecting means which interfaces between the buffer amplifier means and the input and output terminals of the current mirror means are provided in the apparatus which the buffer amplifier means can be connected to or disconnected from, the buffer amplifier means of one type with the output end substantially serving as a current source or the other type with the output end substantially serving as a voltage source can be connected with ease and in this case the phases in both types can be automatically equalized particularly without being conscious of the type of the microphone, or the buffer amplifier means