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Woo Audio WES Electrostatic Amplifier (Playback 54)

Woo Audio WES Electrostatic Amplifier (Playback 54)

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.

FEATURES/TECHNICAL HIGHLIGHTS

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.

OVERVIEW

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

SONIC CHARACTER

Woo Audio WES Electrostatic Amplifier (Playback 54)

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.

The second area in which the WES excels is tonal purity. Almost all headphones have some frequency response errors that lead mid- and upper-range instruments to sound a little distorted, especially on certain dynamic passages. The SR-009s reduce these distortions significantly when compared to many headphones. As a result, you have more opportunity to listen for a more subtle effect: the tonal continuousness and lack of grain in the signal. The Woo delivers a sense of purity—which is to say smoothness with detail—that is at a benchmark level in our experience.

Perhaps related to this tonal purity, the noise floor of the WES is impressively low, which means that another signature aspect of the Stax headphones is well handled: small signal accuracy. This matters to spatial presentation because small signals (for example, the decay of a string after it has been plucked) are the sort of low-level details that enable us to hear the acoustics of the venue where a recording was made. Likewise, the overtones of an instrument are the source of its color, but are always reduced in level from the fundamental tone. Here the Stax/Woo combination does a state-of-the-art job of revealing low-level detail in a natural way. You can hear the space in which the recording was made (though, as with almost all headphones, it isn’t presented as if on a stage in front of you).

 

The Stax headphones are also exceptional dynamically, and the Woo complements this capability nicely. The attack of strings or percussion is accurately rendered, without annoying overshoot in most cases. In addition, dynamic signals settle down quickly, which allows you to hear the decay of notes, as mentioned above. This sense of quick dynamics without accompanying edge or sizzle generally does a superb job of letting you enjoy the music.

Woo Audio WES Electrostatic Amplifier (Playback 54)

Sometimes this breakdown of sound into component parts doesn’t give you a good feel for the sound character on offer, so here is another point of view. The big thing you need to know is that the Stax/Woo combination produces a subtle but meaningful qualitative shift in the presentation of music. Sure, the qualitative shift here could be described by saying that the SR-009/Woo system is more transparent than other headphone/amplifier combos are. Or you could say the Woo-based system is lower in distortion. You might also say the Woo/Stax pair is more dynamically accurate. We’d sign up for all three. But, a point we’re trying to draw out for you is that the qualitative achievement here is one of those across-the-board shifts that affects almost everything rather than provide small, piecemeal improvement in just one or two narrow areas. Because this headphone system removes distortions and colorations that we are used to hearing, it sounds more natural (it isn’t the result of an impressive but unnatural effect confined to one area). It is this across-the-board aspect of the improvements on offer that makes Woo’s (and Stax’s) achievement so meaningful.

 

But with that said, we do need to mention one concern about the Stax/Woo system. When playing some relatively simple music, the Stax/Woo combination can sound somewhat stressed or shouty on vocals, especially female vocals. This suggests a frequency response elevation in the mid-range. Whether this is a Stax artifact or something created by the WES is not easy to say. This effect is less noticeable with other amplifiers, but that may simply mean that the WES is revealing—but making no attempt to compensate for—a small sonic error inherent to the SR-009s.

Philosophically, we note that all the electrostatic amp manufacturers in this top tier category seem to be aiming to build amps that could conceivably be used with any type or model of electrostatic headphone, rather than creating amps specifically matched to (or optimized for) the SR-009. In that sense, we think Woo’s approach has been to pursue accuracy and neutrality first, and then to the sonic “chips,” so to speak, fall where they may.

Given that the WES is quite good but not perfect, you will want to consider how the WES compares to other electrostatic headphone amps. While we haven’t completed our work on this, we would say that the Woo majors in clarity and dynamics, the Head Amp Blue Hawaii SE majors in harmonic richness and warmth, and the Cavalli Liquid Lightning falls somewhere in the middle.

Woo Audio WES Electrostatic Amplifier (Playback 54)

 

We would also suggest that prospective purchasers think about which aspects of the Stax headphones are causing them to pursue electrostatic listening in the first place. You might say “all of them” and that’s fair. But we do think there are likely to be two major camps seduced by the SR-009 and each will want different things from their amps. One camp will accept that headphones offer an alternative listening experience that is very revealing of the recordings at hand—albeit an experience that may never really sound precisely like live music (or like the presentation one might hear from fine, high-end loudspeakers). Members of this camp, we think, will value the SR-009 for its amazing clarity and ability to retrieve detail and will likewise prize the WES for its ability to maximize these attributes.

The other camp will also value the clarity and detail retrieval of the SR-009, but likely will be thinking that Stax has already over-achieved in both areas and will therefore look to balance out the detail retrieval of the SR-009 with an amp that—to some degree—supplies a subtle, almost analog-like kind of warmth. The WES, heard on its own, will seem very good to members of this second camp, but when compared to alternatives it may not be the preferred choice (largely because the Woo will faithfully reveal, but never even subliminally sweeten or warm up, the sound of the recording).

 Woo Audio WES Electrostatic Amplifier (Playback 54)

 

 

MUSICAL EXAMPLES

On Kate Rusby’s album 10 [Compass], the song “I Wish” offers treble that is clear without stridency (this is rare) and as the track plays through the WES the amp shows good dynamics without overshoot, while preserving (without overstatement) all of the delicacy the song has to offer. Similarly, the string bass is “there,” but is not overly or unnaturally prominent as reproduced by the Woo; instead, the WES gives the bass more of a foundational presence, just as the instrument might sound if heard live. Finally, the WES presents a good sense of the recorded space, and instrumental separation is excellent.

Later on this same album, the song “Maid of Llanwellyn” sounds a little midrange forward, with the slight sense of upper mid (2 – 3 kHz) rise and occasional resonance or clipping sound on Kate’s voice. This effect is not one we hear on most headphone/amp systems (or on live music if the PA is well done). This is an illustration of the subtly “stressed or shouty” quality we mentioned above, which—as we said—could be attributable to the SR-009, the Woo, or perhaps both. It doesn’t significantly undercut the many other things the Woo/Stax combo does right, but it is audible because it’s a small aberration that fall in a frequency band where the ear is quite sensitive.

On The Eagles’ Hell Freezes Over [K2 HD Music], “Love Will Keep Us Alive” has a delicacy and smoothness that sounds quite real and true to the sound of live music. Later on the same album, “Hotel California” has great guitar dynamics and separation, while deep bass seems excellent and very well defined. The bass in particular is impressive because the detail is sufficient that the drums clearly have the sound you get when you mic a drum, as was the case here, and then present the drum sounds through an amp with a touch of equalization added. The weight and depth of the bass are also very well rendered.

 

Turning to Shelby Lynne’s Just A Little Lovin’ [Lost Highway] the song “Just A Little Lovin'” has good bass level and detail that is better than almost all other headphones on this track, at least those in our memory. Vocals sound a bit shaded and with a slight resonance, while cymbals are clear and clean and rim shots sound right. Turning to the track “Willie and Laura Mae Jones” we find superb instrumental separation on a moderately complex mix. This quality of clarity without stridency, and a good sense of pace, really makes this track a standout—as is the Woo amplifier, itself.

 Woo Audio WES Electrostatic Amplifier (Playback 54)

VALUE

Let’s face it: the Stax SR-009 is the most expensive headphone on the market. The amps for the SR-009 are all in the same rather elevated price range, though some cost less than the Woo WES. If your questions about value examine the price of the whole system, this is a very costly setup. But, based on the “show me better for less” test, the Stax/Woo combination does quite well, and we think it can hold its head high.

 

On the other hand, if your view of value hews more to the question “is there something 80% as good for 50% of the price?” then you may not feel the Stax/Woo combination is attractive. Both views are understandable, though it is hard to deny that this system is something special.

BOTTOM LINE

Woo Audio has produced an amplifier that maximizes the distinctive attributes of a benchmark headphone, the Stax SR-009, and, as a result, we have to consider the Woo WES a benchmark design in its own right.

SPECS & PRICING

Woo WES electrostatic headphone amplifier
Inputs: two fully balanced stereo analog inputs (via XLR jacks); one single-ended stereo analog input (via RCA jacks).
Outputs: two five-pin Stax compatible output jacks (optionally, the amp can be configured with one Stax-compatible jack and one Sennheiser-compatible jack)
Output Voltage Swing: 1300 V p-p

 


Bias voltage(s):

•Stax bias: 580 V
•(Optional) Sennheiser bias: 500 V

Total Harmonic Distortion: below 0.3%
Line Voltage: 110/220-240; 50/60 Hz selectable
Dimensions (H x W x D):

•Amp module: 7.5” x 16.5” x 12”
•Power Supply module: 4.5” x 16.5” x 12”

Weight: 40 lb. (both modules combined)
Warranty: 1 year, parts and labor
Price:

•Base price, $4990
•Price as tested, $5790

Manufacturer
WOO AUDIO
Fax (718) 764-6393
wooaudio@gmail.com
www.wooaudio.com

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