An amplifying circuit comprises a voltage-current converter for voltage-current converting an input signal to be amplified and a current-current converter including a first transistor (NPN), a second transistor (NPN), a third transistor (PNP) and a fourth transistor (PNP). Emitters of the first and third transistors are connected to each other, collector and base of the second transistor are connected to each other, collector and base of the fourth transistor are connected to each other, emitters of the second and fourth transistors are connected to each other, bases of the first and second transistors are connected to each other and bases of the third and fourth transistors are connected to each other. Output current of the voltage-current converter is supplied to the emitters of the first and third transistors and a constant current is supplied to the second and fourth transistors. The amplifying circuit further comprises an output circuit which synthesizes and outputs collector currents of the first and third transistors after amplifying these collector currents and a circuit for negative-feeding back an output of the output circuit to the voltage-current converter. An amplifying circuit with reduced idling current and an expended range of class-A operation is provided.

The disclosed operational amplifier comprises a first pair of complementary type transistors (Q5, Q6) (of high current carrying capacity) that have their emitter-collector paths connected in series across a source of reference potential. The emitters of the transistors are connected together and to an output terminal (17). A second pair of complementary type transistors (Q3, Q4) are coupled across said reference potential, each transistor of said second pair being coupled across the similar conductivity type transistor of said first pair. A first pair of resistances (R1, R2) of predetermined value are respectively connected between the bases of the similar conductivity type transistors of said first and second pair. A second pair of resistances (R3, R4) respectively connect the emitters of the transistors of said second pair to said output terminal. Each of said second pair of resistances has a value substantially equal to said predetermined value plus the intrinsic base resistance of the transistors of the first pair. A pair of current mirror circuits (Q11, Q13, and Q12, Q14) are respectively coupled from the collectors of said second pair of transistors to the bases of the similar conductivity type transistors of said first pair to provide the additional base drive required by the first pair of transistors for large current output therefrom.

An audio surround-sound system includes a main enclosure, an audio decoder device to decode audio source signals supplied by an audio source device to provide decoded audio signals, and at least a first and second low distortion amplifier housed within the main enclosure to receive and amplify the decoded audio signals. Also included is at least a first and a second speaker element operatively coupled to the at least first and second amplifiers, respectively, to produce the audible signals, where the audible signals are received by the listener from a first and second direction. A local radio transmitter converts a portion of the decoded audio signals into radio modulated signals and transmits the radio modulated signals where a wireless receiver receives and converts the radio modulated signals into remote audio source signals. A third speaker element produces audible signals to be received by the listener from a third direction, where the third speaker element is operatively coupled to a third low distortion amplifier. The third low distortion amplifier receives and amplifies the remote audio source signals, where the third low distortion amplifier, the wireless receiver and the third speaker element are remotely located from the main enclosure. The audible signals received by the listener from the first, second, and third directions operatively surround the listener with the audible signals.

An improved working point adjusting circuit for a single power amplifier having multiple output circuits. When this simple circuit is connected to a Class B transistor power amplifier to support two or more output channels or speakers, it adjusts the working point of the transistors in the output circuit of the power amplifier to the linear portion of the current-voltage characteristics of the transistor so the amplifier works in the level of a Class A amplifier. It provides many significant advantages including (1) much higher energy efficiency on output transistors; (2) much less signal distortion on loaded speakers; (3) simple circuitry for increased reliability; (4) low component count for reduced costs; and (5) individualized adjustment for each output channels which eliminates the different effect caused by the very fine differences between the multiple loaded output devices such as loudspeakers.

A working point adjusting circuit for a power amplifier. When this simple circuit is connected into a Class B transistor power amplifier it adjusts the working point of the transistors in the output circuit of the power amplifier to the linear portion of the current-voltage characteristics of the transistor so the amplifier works in the level of a Class A amplifier. It provides many significant advantages including (1) much higher energy efficiency on output transistors; (2) much less signal distortion on loaded speakers; (3) simple circuitry for increased reliability; and (4) low component count for reduced costs.