Btw. How much amplification does the output of a little usb DAC like the Hifimediy sabre need?
Thanks a lot!
A hybrid amp is not necessarily a panacea for low-impedance headphones. Almost every hybrid amp uses the tube(s) for the signal stage (amplification stage). The buffer (which can be discrete instead of an opamp) is almost without fail, gain-neutral. However, many tubes have gains in double digits - and those are the low ones. You may find some tubes with amplification factors down in the single digits - 7, 11, etc., but it obviously depends on the tube and circuit applied.
How fast does a bicycle go?
Its your DAC (I assume) measure it.
In absence of measurements - They are all over the map, but the vast majority will work with just a buffer to drive low to medium impedance headphones.
Maybe a Millett minimax? change the output cap to larger size (680uf or larger), and use low-gain tubes. Should drive low ohm phones ok.
The minimax kits are pretty spendy but somehow completed amps are cheaper (have seen a few went for around $150 in the for-sale section lately, that was with tubes included). Not really a build, but modding is fun as well and the minimax is a proven design.