Headphones have attracted increased interest in the past decade, spurred on by a number of factors including the transition of music to computer-based storage (iPods, laptops and desktops) and the expansion of open-plan office designs. And while headphones have always been capable of very high fidelity, an expanding market has brought forth new models and new electronics to support these new models. The variety of headphone amplifiers now available in today’s market rival and may even exceed the number of high-quality headphone models. Recognizing the choices now available, I wanted to bring readers a look at one of the top-tier competitors in the headphone amplifier space, the Woo Audio WA22.
Founded by Jack Wu, Woo Audio is a New York based firm that focuses on building high performance headphone amplifiers (all of which are vacuum tube-powered designs), along with headphone related accessories. Woo headphone amps start at $495 and range on up to $4990. Following a business model that is fairly commonly seen in the headphone world, Woo is not only a manufacturer but also a reseller for three select brands of headphones: Beyerdynamic, Grado, and Stax.
Typically, Woo amps are sold factory direct on a build-to-order basis, so that customers have the option of buying standard-version Woo models or of having their new amps factory “hot-rodded” with various extra-cost tube upgrade options. The WA22 amp ($1900 in standard form, or up to $2450 with every available tube upgrade) is a fully balanced, transformer-coupled headphone amplifier that is--in terms of price--positioned at an upper-middle point within Woo’s impressive nine-model amplifier lineup. As you can well imagine, these guys eat, sleep, and breathe high-end headphone amplifier designs.
For those of you unfamiliar with the modern high-end headphone marketplace, some of the players like Woo Audio may be unfamiliar so that some context may prove helpful.
Any list of modern headphone makers would include familiar names such as AKG, Audio-Technica, Beyerdynamic, Denon, Grado, Sennheiser, Stax, and Ultrasone, along with a smaller group of relative newcomers such as Audeze and HiFiMan. When we work back up the signal chain to look at high performance headphone amplifier makers, however, a mostly new group of companies emerges. While some brand names will no doubt be familiar to traditional high-end audiophiles (e.g., Grado), there are many key players in the high-end headphone universe who are less well known to traditional audiophiles. I’m thinking, here, of manufacturers such as Apex (TTVJ), Blossom Audio, Burson Audio, Darkvoice, Headroom, Meier Audio, Ray Samuels Audio, and Woo Audio. And to be frank, even this brief list is only scratching the surface, my point being that headphone electronics are a different world entirely than conventional audio electronics.
There are other differences between headphone amplifiers and amplifiers in the traditional audio realm. These are worth reviewing because they set the stage for the potential contentious remarks to come later.
First off, it is important to understand that many of the accepted truisms regarding tube-type power amplifiers vis-à-vis loudspeakers no longer apply when we talk about using tube-type headphone amps—such as the WA22—to power typical headphones. For example, it is common knowledge among audiophiles that tube-type power amps can give “interesting” (and in some cases downright problematic) results when interfaced with certain loudspeakers, largely because various tube-amp-output-impedance-to-speaker-input-impedance matching issues can arise. These issues are compounded by the fact that speakers typically do not exhibit flat impedance curves, meaning that impedance matching problems may occur at some audio frequencies, but not at others.
But unlike loudspeakers, headphones usually do have very flat impedance curves and they offer benign and relatively high-impedance, tube-friendly loads (30-300 ohm loads are typical for headphones, rather than the 4-8 ohm loads typically seen with loudspeakers). In practice this means that for the most part impedance matching issues between tube-type headphone amps and headphones don’t come into play—at least not to the dramatic degree that they do between tube-type power amps and speakers. (If one wants an analogy to traditional full-size audio system, it is probably better to think of headphone amps as behaving more like preamplifiers than like power amps.). The bottom line, then, is that many headphone aficionados regard tube-type amps as the solution of choice for powering almost all kinds of high-quality headphones.