ejektor, more negative feedback with positive

Almost any audio power amplifier can be considered as a combination of a . relatively low-distortion voltage- amplifier (A1) with an output stage producing relatively high distortion (A2 with distortion d2 ). In our case (see the figure), positive feedback is applied via path K1 around A1. At the same time there is overall negative feedback via path K2. The equation for the output voltage Vu is given with the figure; there is no point here in dragging you through the derivation!