Class A and class B are basic operatin gmodes for audio power amplifiers. Since class A operation produces large amounts of heat, class B operation is commonly used. Thermal loss in class B operation is much less than in class A operation, but it usually produces high frequency switching distortion. A power amplifier which has low heat generating capacity but without significant high frequency switching distortion may be obtained by controlling the bias voltage to the power transistors in such a manner as to prevent either output transistor from being cut-off below the class B idling current at any time. Several proposals have been made for this type of operating mode but they have not always solved the problem of delayed response time or others which adversely affected the basic performance of the amplifier. The recently developed circuitry discussed below assures the high response speed of the power amplifier without adversely affecting its basic performance and prevents the power amplifier from generating high frequency switching distortion. Using this circuitry, high power output amplifiers may be designed which produce very low distortion over a very wide frequency range.
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