Woo Audio has a very full line of headphone amplifiers that have come to be respected by many knowledgeable headphone aficionados. In 2011, Woo unveiled an amplifier specifically for electrostatic headphones, and particularly aimed at the new Stax SR-009 headphone (Stax’s flagship model), which we have reviewed here. As we said in that review, the SR-009 is easily a contender for “best headphone in the world”, so it makes sense that high-end amplifier manufacturers (Woo Audio, Head Amp, Cavalli Audio, Ray Samuels Audio) are offering products with top-tier headphones such as the SR-009 in mind. Of course, the WES will work perfectly well with other Stax models like the SR-007 Mk II. We recently had three of these new electrostatic amps in the Playback headphone lab and we’re kicking off our coverage with the Woo WES, the first of the amps to arrive at our door.
The WES is a large, two-chassis, fully balanced tube amplifier. The bottom chassis houses the power supply, and uses two 5AR4 rectifier tubes plugged in horizontally and protected by a Plexiglas plate. Woo has provided two on/off switches as a way to reduce the inrush spike when you power the WES on (assuming that you use these one at a time). The lefthand power switch turns on the tube heaters, while the righthand switch turns on the rest of the main power supply (once the tubes have been pre-heated).
The top chassis of the WES houses the signal amplification circuits. There are four 6SL7 driver tubes and four EL34 power tubes employed in, as we said, a balanced design. Two balanced inputs are provided, along with one single-ended input. For the latter, two 12AU7 tubes are on the back of the box as the basis of a phase splitter circuit. Again, a Plexiglas screen is used to deter users from attempting to touch the tubes.
The volume control is a DACT 24-way stepped attenuator. Auricap capacitors and Teflon tube sockets are used, along with extensive point-to-point wiring. The metal work is heavy, though we wouldn’t say that a lot of cost was sunk into jewel-like cosmetics, the overall styling and appearance falling more in an “industrial chic” vein, rather than striving for lifestyle-grade smoothness.
Our test amplifier had two Woo-authorized tube upgrades installed, with Sophia 6SL7 driver tubes and Shuguang 50 Years Treasure 6CA7 power tubes. If you like tubes, the resulting amp looks pretty darn cool, especially at night. But, you’re not here for an industrial art history discussion, so let’s get on to listening.
Consider this electrostatic headphone amp if:
• Signal purity and mid-range clarity are the signal reasons you use electrostatic headphones in the first place, and you want to ensure these characteristics are preserved, without any major downsides. The WES is a seriously revealing headphone amplifier.
Look elsewhere if:
• You love electrostats, but want to balance their analytical clarity with a touch of warmth or glow.
Ratings (relative to other cost-no-object electrostatic amps):
• Tonal Balance: 9
• Clarity: 9.5
• Dynamics: 9.5
• Input/Output Flexibility: 8.0
• Value: 8.0
The very good news about the Woo WES is that it mostly gets out of the way and doesn’t impose much character on the sound of the Stax headphones. We judge this by looking at how accurately the Stax portrays well-known musical sounds.
The first area where the Woo performs with admirable accuracy is in the deep bass and mid bass regions. The SR-009s can offer impressive bass, delivering dynamic and detailed bass without bloat or blur. We know this because you can hear the SR-009 deliver accurate drum and string bass sounds (accurate when compared with the sound of live music) through the Woo WES. With the Woo, you just get the sense that the headphones are being well controlled and yet are amply supplied with power and drive.