RC =1 at phase shift of 45°; hence, the gain for an RC section is 1/0.707. The op amp must have a gain greater than four because the gain of four sections is 0.25. The buffered RC sections in this ...

The ideal op amp — which we can’t get — has infinite gain and infinite input impedance. While we can’t get that in real life, modern devices are good enough that we can pretend like it is ...

Looking at the circuit diagram it follows the classic op-amp with a long-tailed pair of NPN transistors driving a PNP gain stage and finally a complimentary emitter follower as an output buffer.

As a service to our readers, we're providing the LTspice files used in Dr. Dyer's article on simulation of the 12AX7 and the K2-W vacuum-tube op amp. 1. The model for the K2-W is established as a ...