Originally Posted by madwolfa
I've been looking at Schiit Valhalla 2 specs and this is what puzzles me: how is it even possible to hear the "tube sound" with current crop of super-low noise/distortion/output impedance OTL headphone amps? Which is a great engineering feat by itself, but if the alleged "tube sound" is produced by certain harmonic distortions, how is it even audible with measured THD figures being so low?
I'm writing this in "Sound Science" as the similar question in the main forum produced a ton of over-emotional and less so informative feedback, if you know what I mean. Many people got simply upset. And it was kind of expected, but I honestly didn't want to troll... Subjectivist crowd is very sensitive.
"Tube sound" is an ill-defined concept. Often it is associated with strongly dominating second harmonic. This comes more from the topology used than from simply using tubes. As an amusing exercise, one could compare what's happening in between fig.3, fig.6 and fig.11 in this link about the Morgan-Jones tube amp. We start with an amp with strong H2. Then, balancing the White cathode follower output stage to work more like push-pull, H2 and H3 get to similar levels. Then, introducing some feedback, we reduce H2 a lot, H3 becoming the dominating harmonics. Obviously, in this example, the thd levels here are quite high.
From the explanations on Schiit's website, the Valhalla uses feedback to achieve those specs. It also uses a White cathode follower, probably correctly balanced. So, even if it had higher thd, it probably wouldn't have the "tube sound" anyway. Schiit themselves claim that it doesn't have the typical tube sound.
I designed and built some tubes headphones amp myself. Some were tubey, some weren't. It's all down to topology. But tubes are easier to use than most solid state devices in some topologies (low thd open-loop gain stage for example).