Articles describing particular amplifier designs, or advocating specific solutions to design problems, abound in the literature, and it is evident that some quite conflicting views exist on certain topics for example, concerning the amount of negative feedback that should be used. The present approach is of a fairly broad nature, and aims to elucidate and compare various familiar and unfamiliar circuit techniques in such a way that their advantages and disadvantages may be clearly and logically appreciated.
In exploiting the very great virtues of negative feedback, the problems and difficulties that arise are largely those associated with obtaining adequate stability margins under all conditions of, operation. In a.c. coupled amplifiers, there are stability problems at both low and high frequencies, but the elimination of output transformers, together with the adoption of d.c. coupled circuitry in most modern designs, has virtually removed the low-frequency problems.
Audio Power Amplifier Design by P. Baxandall – >>> LINK <<<