There is no headphone circuit in the Raven. There are different taps on the output transformer, like a tiny power amp, and the headphone output is simply a different turns ratio. You could use planar headphones with a 30 ohm impedance ... nothing would harmed ... but distortion would be higher than we would recommend, so we advise against it. But it would certainly work, music would play, nothing would overheat or crash, and no transistors or fuses would short out. The power supply would not care at all.
All that happens is the tubes see a low impedance load, that’s all. Distortion goes up, not catastrophically, but a fair amount. So our advice to stick with 200 ohms or higher isn’t meant to scare anyone. This is not like connecting 1-ohm speakers to your favorite receiver and blowing the protection circuit, or taking out the output stage.
There’s no protection circuit, there are no transistors at all in the signal path, and the 6SN7 is designed to operate with a watt or two on the plate. Unlike transistors, tubes like high temperatures, and don’t need heat sinks. All that happens with low impedance headphones is an increase in distortion, nothing else.
It’s hard to convey just how simple the Raven is. The entire signal path is: input jacks -> input selector -> custom input transformer -> Khozmo balanced volume control -> 6SN7 in balanced mode -> custom output transformer with various output taps -> output jacks. There are no circuit boards in the audio path, all signal wiring is hand-soldered point-to-point.
That’s also why the Raven has a medium price by high-end standards. There’s a lot of labor in every single part, most of all, the transformers, vacuum tubes, and final assembly. By contrast, a circuit board filled with op-amps inserted by pick-and-place robots would be about 1/10th to 1/20th the build cost of a Raven. That's why Shenzen-made products are so inexpensive ... op-amps are cheap, and robots can fill a circuit board in moments.
