How to add Global NFB to a circuit with LED bias and cathode follower?

[Nailbunny7]

Your issue will be drive capability. 32 ohms is a pretty tough load for tubes driving directly unless you use a pretty large output tube for the cathode follower. You might consider using an output transformer and skipping the feedback idea.

Remember, low source impedance does NOT mean low distortion into low loads!

I'm aware of potential power and distortion issues (and I appreciate your patience). I planned on using a few power tubes in parallel, plus NFB.
However, I've already done the transformer coupled approach and feedback free OTL for headphones, so I wanted something new to try something new this time by making an OTL for low impedance 'phones.

 

[SY]

OK, then you'd do better with something like a White CF topology. If headphones were made rationally, you'd have separate returns for each channel and could go circlotron. Unfortunately, they usually aren't...

I'd take a close look at the Morgan Jones headphone amp as a good starting point.

 

[Chris Hornbeck]

You might also want to look into the "anode follower" feedback volume control, as described by Boegli in the early 1960s. It's just a fixed resistor in series with the first grid and a variable resistor to there from the output.

All good fortune,
Chris

 

[Koonw]

Here is sim I just finished, based on the post on this thread. Have a look see if that is what you're looking for. Power output for 32 ohms is limited to about 2Vp or 50mW for tube with 5W dissp. If you want to see some more plots such as FFT or using particular tubes, let me know.