Overview
Less is more. Or at least, so we are told when it come to audio signal processing: the more parts, the worse the sound. In general this is true. This argument has often  been voiced in favor of tube circuitry because a tube circuit usually requires many fewer components than a comparable solid-state device. In fact, it is amazing just how few elements are needed to make a good sounding tube phono or line stage. But if this logic holds, then even the tube circuit must yield before the passive circuit, for example a passive switch box with attenuator. What could sound better than just wire and resistors?

Yet when the shoot out between passive and active commences, this logic does not always predict the victor. Yes, the passive is almost always cleaner and more detailed; but it is also often strangely eviscerated, thin sounding, seemingly bass shy as well. Well, the answer is obvious: the active tube circuit is adding euphonic distortions to the mix. Maybe. Or maybe something else altogether. Whatever the reason, the tube circuit is often preferred. And only a masochist or someone so gripped by the logic or theory of "less must be more" would forego the preferable sound of the active.

Design Goals

So what we have here are some very simple Cathode Followers that can be used in those cases where a large voltage swing is not needed--for example, after the I-to-V converter in a CD player, or in an ultra simple line stage, or anywhere only a few volts of signal are present. The trade-off is between complexity and voltage swing. By adding more resistors and capacitors, the Cathode Follower can be designed to handle huge voltage swings. But where this requirement is not present, less is probably more. 

Easy Triode Circuit Description
Just how little is required to make a working ground level Cathode Follower? Two resistors and a triode is the answer. One resistor to bias the grid at 0 volts, and one cathode resistor, is all it takes. The addition of a grid stopper resistor is prudent, as Cathode Followers can oscillate under certain circumstances (lead inductance and stray capacitance working into the supremely high input impedance of the grid can make a Cathode Follower oscillate at a few MHz) and this resistor is cheap