Well...it's unconventional, to say the least. These voltage regulator tubes are not typically used in series in the supply, they are used in parallel, which is how they regulate voltage. Also paralleling five capacitors feeding one power stage...this isn't how it's normally done. Anyway, I digress.
Getting back to the noise issue, I plugged this supply into LTSpice. Assuming I have it right, and the simulation is accurate, the ripple at the output stage is too high for a headphone amp, in my opinion. If putting in a choke really did make a big improvement, that would suggest there is too much ripple. One thing you could do is switch both of those 100uF electrolytics to 220uF, which would drop the ripple tenfold for the output stage.
Again, just going off of what you're giving me here, but that may be the issue.
I agree, I think increasing capacitances will definitely help. Thank you for simulating it! I probably should have planned and simulated before building, kind of an expensive lesson but that’s what I get for rushing
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