The input stage is where global negative feedback is applied, so it must provide an inverting and a non-inverting input, both with low noise. The triode differential pair is an obvious candidate for this stage, but the common cathode triode or pentode can also be used, in which case, global feedback is applied at its cathode. See Fig. 6.22.

Fig. 6.22: Application of global feedback at the input stage

Design of the input stage is fairly trivial, but can be slightly complicated by the usual practice of direct coupling to the phase splitter, which restricts choice of anode operating conditions.