Which circuits to use?
We know the Cathode Follower offers low output impedances, but no voltage gain; the same holds true for the White Cathode Follower. The latter circuit uses current through the top triode's plate resistor to provide feedback for the bottom triode. This buffer works in a push pull fashion, which along with its already having a feedback loop, would make applying global feedback a bit problematic. (Still, if this circuit were made up of two 6DJ8's, a 200 volt power supply, an input capacitor and a 100 ohm plate resistor, it could easily drive the Grado headphones with zero gain and a low output impedance.) Ditto for the SRPP (Totem Pole) circuit. So it looks like the Cathode Follower wins. The output impedance of a Cathode Follower is roughly equal to the reciprocal of the tube's transconductance. The 6DJ8 has a gm of 0.01 amps/volt, which would yield an output impedance of 100 ohms. This value would be fine for the Sennheiser headphones, but far too great for the Grado. Paralleling three 6DJ8 triodes will reduce the output impedance to one third (100 ohms down to 33 ohms), a much closer value to what is needed. Adding 6 dB of feedback will halve the 33 ohms down to 16 ohms.   

The gain stage needs to provide only enough gain to drive the Cathode Follower to 3 volts out with the feedback margin included. In other words, a gain of times 6-10 is all that is needed. The Grounded Cathode amplifier can easily meet this requirement and is easy to build and understand. 

Where is the Single Ended stage?
Both stages are SE in function. Single ended means that only one active device is used to handle the whole of the signal voltage waveform. In the Grounded Cathode amplifier the single triode controls the all the current flowing through the plate load resistor; in the Cathode Follower the parallel three triodes control all the current flowing trough the load and the cathode resistor. The Cathode Follower's load resistor could be replaced by an audio output transformer, which would make the SE nature of the circuit more conventional looking. But as a good transformer is very hard to find, the OTL approach is better. (OTL means Output-Transformer-Less.) This circuit uses a coupling capacitor to block the high DC voltages from destroying your expensive headphones.

Cathode Followers sound bad, don't they?
"Not necessarily," is the short answer. Once again, a Cathode Follower need not sound bad; and, if properly designed, it can sound as good as any Grounded Cathode amplifier. A quick re-read of September's Circuit of the Month provides more detailed information on the role of transconductance and current in determining the sound quality of a Cathode Follower.

Circuit description
This month's circuit uses a Grounded Cathode amplifier directly feeding a Cathode Follower. A feedback loop is drawn around the circuit in the inverting amplifier fashion: an input resistor is placed in series with the grid and another is placed from grid to output.  This is the feedback approach taken in a lot of professional music gear, as the gain falls to unity (less noise and pop and tick sounds) when the input is opened. The output is phase inverted and capacitor coupled.

The B+ power supply is a simple single polarity type with no regulation and delivers 150 volts at 70 MA's. The heater supply is regulated and put out 12 volts for two tube heaters strung in series.

The Trick
Remember the design procedure: start at the end and move back. In this case the 32 ohm Grado was at the very end, but the real next design item is the output coupling capacitor. In order to ensure bandwidth down to 20 Hz into a 32 ohm load, a coupling capacitor of at least 250µf is needed; thus,