Effect of the Cathode Capacitor on P-P Output Stage

ITH THE CONTINUED INTEREST in a u d i o c i r cu i t r y a n d d e s i g n , i t h a s b e c o m e w o r t h w h i l e f o r t h e a u d i o engineer to re-examine some of the procedures that formerly were taken largely for granted. Among these procedures is the use of the by-pass capacitor in a Class A push-pull output stage. The purpose of this capacitor seems evident enough, yet the engineer is constantly finding circuits without this component and just as frequently finding circuits with it. To make the matter more puzzling still, he will read one author's admonition that its use is absolutely necess a r y , a n d a n o t h e r ' s t h a t i t s u s e i s specifically to be avoided. In view of this ambiguity of opinion, it was felt that a test of the differences would be interesting. The results, which a r e n o t a l w a y s a s a n t i c i p a t e d , a r e presented in this art icle, along with some evaluation of the outcome. The nature of this investigation necessitated the examination of some of the effects of balancing techniques in the output stage as well , and the results of this phase of the undertaking are also presented here.