Audio amplifier and audio power amplifier
A first circuit unit of an audio amplifier includes a first emitter follower connected to an pre stage input terminal, a second emitter follower connected to an pre stage input terminal, a main transistor connected to an output path of the first emitter follower and an output path of the second emitter follower, a first resistor and a second resistor, which are series-connected between the output path of the first emitter follower and a DC voltage source, and a zener diode connected to a series-connection point between the first resistor and the second resistor. A second circuit unit has a circuit configuration that is complementary to the first circuit unit. A path leading to a collector of each transistor configuring the first and second emitter followers in one of the circuit units is connected to the series-connection point in the other circuit unit.
1. An audio amplifier comprising a first circuit unit and a second circuit unit that are complementary to each other, wherein
each of the first and second circuit units includes:
a first emitter follower connected to a first input terminal of the audio amplifier;
a second emitter follower connected to a second input terminal of the audio amplifier;
a main transistor of which a base is connected to an output path of the first emitter follower, of which an emitter is connected to an output path of the second emitter follower, and of which a collector outputs a signal;
a first resistor and a second resistor series-connected between the output path of the first emitter follower and a DC voltage source; and
a constant voltage generator connected to a series-connection point between the first and second resistors,
a path leading to a collector of each transistor configuring the first and second emitter followers in the first circuit unit is connected to the series-connection point in the second circuit unit,
a path leading to a collector of each transistor configuring the first and second emitter followers in the second circuit unit is connected to the series-connection point in the first circuit unit, and
the output path of the first emitter follower in the first circuit unit and the output path of the first emitter follower in the second circuit unit are provided with a bias setting circuit for the first and second circuit units.
2. The audio amplifier according to claim 1 , wherein
each of the first and second circuit units includes:
an auxiliary transistor of which an emitter is connected to a path leading to an emitter of the transistor included in the first emitter follower and of which a collector is connected to a path leading to the base of the main transistor; and
a third resistor connected between the collector and a base of the auxiliary transistor,
the audio amplifier further comprises a fourth resistor between the base of the auxiliary transistor included in the first circuit unit and the base of the auxiliary transistor included in the second circuit unit, and
the fourth resistor, and the auxiliary transistors and the third resistors in the first and second circuit units configure the bias setting circuit.
3. The audio amplifier according to claim 1 , wherein
each of the first and second circuit units includes:
an auxiliary transistor of which an emitter is connected to a path leading to an emitter of the transistor included in the first emitter follower and of which a base and a collector are connected to a path leading to the base of the main transistor; and
a bias resistor on the path leading to the emitter of the transistor included in the first emitter follower, and
the auxiliary transistors and the bias resistors configure the bias setting circuit.
4. An audio power amplifier comprising:
the audio amplifier according to claim 1 ; and
an amplifier circuit connected to each path extended from the collectors of the main transistors of the first and second circuit units, to which power from the DC voltage source is supplied.