Second, it is important to bear in mind that headphones behave much differently than speakers do, from the listener’s point of view. In particular, the performance of speaker-based audio systems is governed—or at least heavily influenced—by the speaker-room interface. But for obvious reasons, the “speaker-room interface” isn’t part of the deal in headphones. My experience in reviewing many headphones is that the absence of room interface issues makes frequency response errors and distortions in headphone-based systems much easier to identify and to focus on. This is fine up to a point, but it also exposes one of the potential limitations of headphone-based systems; namely, the fact that you can’t compensate for problems by tweaking room-related variables as you can with speaker-based audio systems (for example, there really are no headphone equivalents for changing speaker placement within the listening room, or for applying room surface treatments or resonance control devices). But two things you can control are the electronics and signal cables you will use in powering your headphones. Since those are essentially the only variables at your fingertips, it becomes easy to understand the heightened role the amplifier plays in any headphone-based system.
Which leads to a final distinctive point about headphone audiophilia. Experienced headphone listeners are often more at peace than traditional audiophiles are with the idea of using components with offsetting and complementary strengths to achieve optimal sound (perhaps the sonic equivalent of the notion that “two wrongs can make a right”). I find that many traditional audiophiles want to believe that each piece of equipment in their systems is very close to perfect. As a result, their mental model for improving music reproduction then involves reducing small, residual system imperfections one-by-one, but with a somewhat Wizard-of-Oz-like denial that error compensation and synergy is part of the package.
Headphone aficionados, on the other hand, are somewhat more willing to mix-and-match complementary components with an eye toward achieving a well-balanced result. Thus, one might hear a headphone enthusiast say something like this: “the Sennheiser HD 800 has an upper mid-range dip which is nicely enlivened by the Meier Corda HA-2.” I think this philosophical difference is helped along by two factors. First, because the room is removed from the equation, listeners’ experiences with a given headphone are likely to be similar (though not necessarily exactly alike), and second, it is harder to argue that problems aren’t problems. Adding to this, there are far fewer manufacturers of top-tier headphones than of top-tier loudspeakers, so that more people can hear more of the field. This leads to some convergence in the discussion. Finally, headphone lovers may not be influenced by the biases, strictures and unspoken “rules” of purist-grade high-end audio, and may therefore be more open to unorthodox methodologies as they pursue top-tier sound.
All of the above serves as a necessary preamble to my remarks about the Woo Audio WA22, because, quite frankly, I am going to talk about how this delightful amplifier “enhances” the sound of most headphones (which is precisely the kind of talk that isn’t allowed in polite but hide-bound high-end audio circles).
As I mentioned above, the WA22 is an all-tube headphone amplifier that offers a fully balanced design (it accepts balanced inputs and can drive balanced headphones) with Class-A push pull topology. The output transformers are hand wound using a special winding approach, and two output impedances are offered via a selector switch on the front panel. Woo offers multiple tube options, with hot-rod versions using selected 6SN7 driver tubes and 7236 power tubes. The base model is $1900 and the maximum supreme tube version is $2450. Beauty is in the eye of the beholder, but I simply loved the design, especially at night.
A description of the sound of the Woo sounds like an audiophile rave checklist. It is transparent, particularly in that you don’t notice any treble veiling or grit as you do with some lesser headphone amps. Bass is solid, well defined and can be very deep with the right headphones. Tonal balance is very, very good, with no sense of treble roll-off or brightness.
This is one of those difficult-to-review products because it is hard to find deficiencies. Perhaps there is an even better headphone amp, and I’ll be back to explain problems with the Woo. Perhaps as D/A converters get better, distortions in the WA22 will be revealed. But right now, these problems are below the error noise floor in most cases. Maybe even more important, the errors in headphones are much, much greater than any you’ll find in the WA22.