ABSTRACT
Why Quiescent Conditions are Critical In earlier sections of this book we looked closely at the distortion produced by amplifi er output stages, and it emerged that a well-designed Class-B amplifi er with proper precautions taken against the easily fi xed sources of nonlinearity, but using basically conventional circuitry, can produce startlingly low levels of THD. The distortion that actually is generated is mainly due to the diffi culty of reducing high-order crossover nonlinearities with a global negative-feedback factor that declines with frequency; for 8 Ω loads this is the major source of distortion, and unfortunately crossover distortion is generally regarded as the most pernicious of nonlinearities. For convenience, I have chosen to call such an amplifi er, with its small-signal stages freed from unnecessary distortions, but still producing the crossover distortion inherent in Class-B, a Blameless amplifi er (see Chapter 3). Chapter 6 suggests that the amount of crossover distortion produced by the output stage is largely fi xed for a given confi guration and devices, so the best we can do is ensure the output stage runs at optimal quiescent conditions to minimize distortion.
