Mu Followers and Mu Stages have been available to the audio community for some time. Various resources associated with these circuits are available on the web and elsewhere. They offer descriptions (some accurate, some not) of how the circuits operate. You can also find some basic design guidelines. But there is one thing that is scarce to non-existent: a set of equations and schematics which can help you to intuitively understand and design the circuit, and to reverse engineer a completed design by turning its component values into a set of useful performance parameters. Such parameters include gain, power supply rejection ratio (PSRR), output impedance (Zout), the load TL presented to the plate of the bottom triode, and the load XL on the cathode of the top tube. (TL and XL are important because generally, the higher the load impedance on a triode is, the lower its distortion.)
The main purpose of this article is to present the means to analyze, understand and design these circuits. Says Chris: “I think that it’ll contain some surprises for most of us. I know it did for me”.