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July 2009
Enjoy the Music.com Review Magazine
Woo Audio 2
Single-Ended Triode/OTL Headphone Amplifier/Preamplifier
The beauty lies in our striving and not the actual catch.
Review By Linden Park

Click here to e-mail reviewer


Basho's Minnows
At the happy prospect of being remembered as the writer of the most pretentious opening to an audio review in recent years, I will now quote a haiku by Basho:

Seaweed swarms with
Transparent [minnows] Catch them —
They shall thaw without a trace.


Woo Audio 2  A poem of any worth brims with multivalent meanings. What the "transparent minnows"  represent —  the seemingly tangible things which dissolve away in your hands once caught — can mean so many things. However, in the context of this review, let us pretend that these minnows are objets d'art. Specifically, that they embody Music itself with a capital "M." Basho's haiku, read simplistically as an analogy, corresponds rather hilariously well with the Sisyphean toil with which audiophiles approach musical reproduction, no? New megabuck cables? Check. Swap out the old AC regenerator for a NASA-grade SpacePowerModulator? Done that. All to what end? To catch that Minnow, living and breathing music itself which eludes our capture time and time again.

Here is a more selfishly practical analogy of the Basho haiku for the purposes of this review: the OTL sound. Still to this day, I can't quite decide whether I like the sound of amplifiers without output transformers. I have not heard any of David Berning's celebrated designs, but I've had the pleasure of listening to Atma-Sphere's MA-1 Mk. III OTL monoblocks for an extended period of time at the homes of two of my friends, and I've also had a brief listening session with one of Joule Electra's OTL amplifiers. Each time, I was mesmerized by the powerful clarity and transparency of the sound. Yet, for the life of me, I could never recall what the music really sounded like through those great amplifiers, even just a day after listening. Just like Basho's minnows, the memory of the sound thawed away without a trace.

Is this a good thing or a bad thing? That's for each listener to figure out. In my own limited audition with OTL amplifiers, I was on the fence. Like any other audio components, there seemed to be inevitable trade-offs. It was difficult not to be seduced by the clarity and airiness of the particular OTL amplifiers I had heard. Yet, afterward, I found myself craving a little more tonal density and the structural skeleton that the typical amplifiers with good transformers put on the music, too.


Enter Woo Audio 2
If you are jaded by the increasingly bureaucratic and commercialized aspect of the mainstream hi-fi scene, headphone-based audiophile scene will seem like a refreshing tonic. At various events and meets often sponsored by head-fi.org, manufacturers and fans exchange ideas and DIY tips with a sense of genuinely earthy sincerity and civility. People actually respect and like each other at these events, heaven forbid!

It was at one of these meets in New York that I met Jack Woo, who serves as the general ambassador of Woo Audio (for the lack of a better term), and his father Wei Woo, who is the chief engineer. I didn't have the fortune of meeting Jack's brother, Zhidong, who serves as the designer and chief-in-manufacturing. As it was with the Sopranos, it's a family business at Woo Audio, which was founded in 2004. Like many manufacturers in the still-untapped and burgeoning industry of headphone-based hi-fi, Woo Audio operates as a small-scale specialty manufacturer out of Queens, New York. Yet it would be a mistake to deem Woo Audio as a DIY operation gone slightly upscale. After a cult following among hardcore head-fi aficionados, Woo Audio is poised to branch out with more mainstream components, including the new Woo Audio DAC which has been lauded by many who have heard the prototype at the recent CanJam '09 in Los Angeles.

Woo Audio 2 InsideBack to Woo Audio 2 (henceforth referred to as WA2): as you can see from the picture, the construction of the parts and the machining of WA2's chassis are impeccable. Point-to-point wired with Teflon wires, the WA2 is equipped with Rubycon and WIMA capacitors throughout (my unit had the Blackgate capacitor upgrade). Its full aluminum die-cast chassis is anodized in its sleek finish. The aesthetic styling is pleasingly industrial if unspectacular in its Bauhaus-blockiness (which is actually a good thing in my book).

WA2 is deliberately and classically tube-y in appearance with its display of two 6AS7 dual triode output tubes in the power stage, two 6922/6DJ8 driver tubes and two EZ80s for rectification. (The only tubes I rolled instead of the stocks were the Western Electric 421As instead of the 6AS7s. And yes, tube-rollers. WA2 is VERY receptive to whatever tubes you roll.) The aluminum volume and control knobs feel heavy in operation and durably constructed. There is only one 0.25-inch stereo headphone jack (for those more inclined to balanced headphone-listening, there is a balanced amplifier which was recently released: Woo Audio 22.) On the back of the chassis, four pairs of RCA inputs and a pair of RCA output are found.

The quality of WA2's construction is superb, and no technical issues — i.e. hums and otherwise - arose during the time of my audition. For the price, the level of fit and finish is unsurpassed and the amplifier feels artisanally made with care.


WA2: Headphone Amplifier
The main headphones used during the time of WA2's audition were Denon AH-D7000, Lawton Audio LA7000 (Lawton Audio's modified Denon AH-D7000; review forthcoming), AKG K-701, Sennheiser 650, and Audio Technica ESW10JPN Limited Edition headphones. Now, what's wrong with this picture? If you guessed that the Denons (both stock and Lawton-modded) and AKGs were ill-suited for WA2 theoretically, you win the final Jeopardy: tube amplifiers are known to have problems driving low-impedance headphones like the Denons (25 ohms) or Grados (32 ohms). AKGs, despite their seemingly benign 62 ohms rating, are known to be notoriously difficult for tube amplifiers to drive as well.

One thing that will immediately impress any listener upon listening to the WA2 with low-impedance headphones, is how effortlessly the WA2 drives them. With all sorts of music, from ArvoPärt to LCD Soundsystem, the two Denons and the AKG K-701s blithely made music faithfully, without strain. My Leben CS600 integrated amplifier is celebrated in the head-phile communities for its excellent transformer-coupled headphone out. As sweet as it is with high-impedance headphones, it would clip during more strenuous passages of music when used with low impedance headphones like AKGs and Denons. However, despite the tubey provenance, the WA2 mysteriously had no problems with clipping during such passages. It drove these low impedance headphones with remarkable ease and confidence with plenty of dynamic authority. In fact, my favorite headphones with the WA2 were Lawton Audio LA7000s, especially with classical music.

Now, for the listening: I tested WA2 under two conditions. The first was at home, with La Platine Verdier/Moerch DP6 with various carts (Zu 103 Grade 2, Clearaudio Virtuoso Wood, VdH Condor) providing music on the analog side, and Sony Playstation SCPH-1001 and Mac Powerbook G4/MDHTParadisea+ DAC supplying the music on the digital side. The second location was at my office. The source was Red Wine AudioiMod 5.5G/ALO Audio Portable Vcap Special Edition combo with AIFF files.

At home, the first recording I played was a CD of Igor Stravinsky's The Rite of Springswith Valery Gergiev helming the Kirov Orchestra [Philips B00005NIF6], an account which was recorded live at the Marlinsky Theater. In my subjective view, this particular account surpasses the classic versions by Dorati or Markevitch, not because the score is flawlessly executed, but because Gergiev and his Kirov gang capture the blood and the full carnal tilt of Stravinsky's score better than any other recordings extant. The bassoon solo which famously opens the piece is more sinuously suggestive and darkly beguiling than any other version, too: it's a perfect arbiter of telling how an amplifier or a component will handle tone. Through the WA2, the bassoon solo's tone was aptly mysterious and nothing less than gorgeous. However, at one of the head-fi meets, I had a chance to briefly A-B the same passage with WA5 (Woo Audio's flagship 300B amplifier), and it must be noted that even in such a limited auditioning in a less than ideal circumstance, the tonal color of the solo was more captivating with the WA5; the insidious musical line, with all its ominous undertones, came through more vibrantly on WA5 than on WA2. When compared to Leben CS-600, too, the tonal color of the WA2 seemed a bit wan, although the tonal texture was more silken with the WA2, which was very addictive. Bear in mind, though, that WA5 costs three times more than the WA2 and Leben CS-6000 five times more. In its price class, however, the tonal qualities of WA2 were unmatched in my experience with similarly priced headphone amplifiers.

Consider also the violent explosion of the grancassa in The Rite of Springs, or its terrifying trombone glissandos. My Leben handled such ultra-dynamic passages with aplomb with Sennheisers and Audio Technicas, but clipped with the Denons and AKGs even at semi-loud volumes. WA2 had no such problems handling these passages with the low impedance Denons or the AKGs, no easy feat for a tube amplifier. I asked Jack Woo how Woo Audio accomplished this, and he replied that WA2 and WA5 (and WA6, as an option) employ what is called PDPS – Pseudo-dual Power Supply. Since my eyes glaze over when the lingo gets too Trekkie, here are Jack's words, in verbatim:

PDPS splits the main power supply into 2 channel separately. Such implementation is effective to improve energy flow in the power supply. In return, it enhances channel separation, dynamic swing, and speed... The PDPS requires an extra set of filtering capacitor and resistor; build time also increases (which is why it is not standard in the more economic WA6 model)... In these (PDPS) models, we use filter choke in replace of the filter resitors. This will reduce voltage drop after rectifier and thus increase efficiency of the power supply.


In practice, the PDPS technology did wonders in bringing alive the Denon and AKG headphones with music which features extreme dynamic swings. Whether it was an LP of Horenstein/London Symphony's account of Mahler Symphony No. 3 [Nonesuch], or the shrilly recorded but gleefully careening alterna-pop of Animal Collective's Merriweather Post Pavilion [Domino, LP], the WA2/Lawton Audio L7000 combo almost captured the full spectrum of the dynamic scale well. The bass response was surprisingly taut and structurally coherent, although the mid-bass did have a somewhat bloomy presentation and lacked the taut definition of solid state amplifiers. The midrange presentation was honest, truthful and entirely smooth yet convincing. Still better was the treble, which was entirely silken, grainless, and lovely in its purity. A fine tonal presentation. However, with more texturally complex material like Ben Webster's throaty vibrato-laden exchanges with Art Tatum on the 45s of The Tatum Group Masterpieces [Analogue Productions, AJAZ 2310-737], I missed the richer, more golden tone color of the Leben CS-600 with its more resplendent decay.

Rhythmically, the WA2 was splendid. It subverts the notion that tube amplifiers do not have the pace of solid state amplifiers. When the music called for it, WA2 grooved and rollicked with an unerringly right sense of propulsion. However, when it came to tracking music with subtle temporal shifts in music (i.e. the opening of the first movement of Sibelius's Symphony No. 2, Radiohead's "Pyramid Song," the Recitativo from the third movement from Beethven's Opus 110 Sonata and, uhh, basically everything sung by Joaõ Gilberto that I got to hear for the review), the Leben CS-600 subtly outclassed the WA2 by delivering such shifts with more naturalism and believable ease.

But I'm really splitting hairs here.


WA2: Office System
Woo Audio 2I work in a typical office skyscraper near Wall Street. As such, the quality of electricity is highly suspect. So one Sunday, when I had to put in some overtime, I lugged the WA2 with me to the office along with Top Gun power cord by the now-sadly-defunct Custom Power Cord Company. Plugged the WA2 in. No problemo: I ascended immediately to tube heaven. The source was Red Wine Audio's iMod, 5.5G/80GB, and it was connected to the WA2 via ALO Audio's external Portable VCap, which employs oil caps. As far as I'm concerned, the iMod/Portable VCap is THE ideal source for an office setting. No suspect electricity to doubt, no external DAC to further clutter your already cluttered desk space. From the VCap, Audio Tekne ARSP-500 interconnects delivered the signals to the WA2. Most of the listening was done either with Audio Technica ESW10JPN Limited Edition or Lawton Audio LA7000 headphones. All files were ripped in AIFF.

And let me tell you, ladies and gents: the WA2/iMod-Vcap combo had me listening to more music than any other equipment set-up I've had, including my beloved turntable set-up at home. The convenience was definitely a factor, but the greater factor was that the music just sounded like the genuine article: as buoyant and lilting and joyous, as thought-provoking and sad… well, as musical and real as any piece of music required the combo to be. No, the combo did not have the resolution of a dCS/mega-wattage amplifier system or the presence of the Zanden system, both of which I have heard, but it was more FUN. There is something intimate and conspiratorial about having an office system. The WA2/iMod-Vcap system fit neatly onto the wedge of my L-shaped desk. Daily, I plugged the Lawton LA7000 into the WA2 and cued the iMod to The Kinks or Steven Isserlis' Bach Solo Cello Suites [Hyperion UK, B000OQDV1U] or my personal Sonic Youth playlist at 9:30 AM. And rather shamefully, I admit: a Def Leppard playlist got the call one day. Except for the lunch hour, the music played on while the bureaucratic wheels turned around me. The sonic qualities that I noted with the WA2 in my home system were the same in the office, obviously, but with a significant caveat: I just did not give a crap about how some amplifier sounded a hair fuller, with finer texture, when the music itself sounded so bone-chillingly good.

Many times in my small office, I was often caught off-guard, left breathless and moved by an unexpected gust of feeling, by the music I was listening to. It felt as though I was listening to music that was meant only for my ears, and at no time was I aware of the machine, despite the filaments of the WA2's tubes warmly glowing in close proximity. Just the music only. What better compliment can anyone pay to a hi-fi component?


WA2: Preamplifier
I did try WA2 as a preamplifier, although not to the extent to merit a conclusive analysis. Yet WA2's performance as a preamplifier merits a comment. First, I bypassed the pre-amp stage in my Leben CS-600 to use it as stereo power amplifier, and ran the WA2 as the preamplifier. The virtues inherent in WA2 as a headphone amplifier were also evident when used as a preamplifier: the music sounded SET-liquid, silken, and ultimately guileless in expression. Again, tonally speaking, I missed some of the drama and the more varied tonal palette that the Leben's built-in preamplifier stage had which added more sinews and flesh to the music's skeleton. Yet there was no way to fault the WA2's performance as a preamplifier, especially at the price. It never stood in the way of the delivery of the music, and its top-end performance, with its effortless and airy quality, was frankly better and more seductive than some $3-4K preamplifiers that I have heard. I will reserve my ultimate judgment of WA2 as a preamplifier for when and if I audition it more thoroughly for such a purpose.

Still, it is an easy recommendation to make to a novice audiophile to invest in the WA2 as a top-rate headphone amplifier, so that he/she can eventually use it as a preamplifier when ready to make the jump to the home hi-fi involving separates. Such a versatile bridge product is rare in the hi-fi world, and WA2 is a genuine bargain. As a matter of fact, it will be tantalizing to see how WA2 will serve as a preamplifier to one of Atma-Sphere's OTL power amplifiers. My guess is that it will more than suffice for a while until you save up enough to move up in the pre-amplification.


Catching The Minnows
But enough conjecture. This is what I know for sure: as a headphone amplifier, WA2 is one of the most musically involving amplifiers I have heard, and for the price, awfully close to the state-of-the-art. If one considers the price/performance quotient, it may be unparalleled among the products in the marketplace now and represents a phenomenal value. I tend to prefer tube headphone amplifiers to the solid-state counterparts, not because of their "lush" colorations, but because the music tends to retain its fluidity of line better with most tube amplifiers than solid state ones, at least those that I've had auditioned. Often, the revered qualities of "fast transients" and "dynamic slam" are not positive qualities to me when it comes to headphone listening, simply because such attributes almost invariably lead to fatigue in monitoring situation in my case. Still, consider the fact that if one preferred low-impedance headphones like Grados and Denons, there weren't many tube amplifiers that offered themselves up for the task. But now, we have a tube amplifier that can be ideally mated with a plethora of dynamic low-impedance headphones, at a very attractive price. Does WA2 offer the ultimate standard in headphone listening? No. As I mentioned, in some respects, amplifiers like Leben CS-600 and Woo Audio's own WA5 300B SET amplifier better it in terms of tonal and rhythmic performance. Still, especially in these economic times, how many hi-fi equipments can bring you so close to the ultimate thing for such a little sum? I can't think of too many.

WA2 does not catch the elusive minnows, but as Basho's haiku may be telling us, the point or the goal of the exercise may not be in their capture: the minnows are forever out of our grasp. The drama of trying to catch the swarming minnows in the seaweeds, which is the very same futility of our constant and sometimes foolish endeavors, doesn't seem too removed, in the end, from the drama and the rationale behind why we audiophiles love music and why we go to torturous lengths to catch it. We always struggle toward that elusive goal - capturing the "absolute sound" or whatever equivalent term you have for such an ideal. Call me a cynic, but I am pretty sure we will never capture that goal. Anything reproduced is a simulacrum, no matter how well it is reproduced. To expect otherwise would be like straining your eyes to physically see two parallel lines meeting at some theoretically true, non-Euclidean end. The beauty lies in our striving and not the actual catch. And Woo Audio 2 definitely serves that beautiful process well.

Highly recommended.



Sub-bass (10Hz - 60Hz)

Mid-bass (80Hz - 200Hz)

Midrange (200Hz - 3,000Hz)

High Frequencies (3,000Hz On Up)



Inner Resolution

Soundscape Width Front

Soundscape Width Rear  
Soundscape Depth Behind Speakers

Soundscape Extension Into Room


Fit And Finish

Self Noise

Value For The Money


Type: Single-Ended Triode, OTL headphone amplifier/preamplifier
Tube Compliment: Two each 6AS7 power tubes, 6922 drive tubes and EZ80 for rectification 
Frequency Response: 8 Hz to 100 kHz (-3dB)
Signal/Noise: 95 dB
Headphones Impedance: 30 to 600 Ohms
Input Impedance: 100 kOhms
Preamplifier Gain: 10 dB
THD: <= 0.08%
Dimension: 5.5 x 13 x x 9 (HxWxD in inches)
Weight: 17 lbs
Price: $990 in stock form
      Premium parts upgrade package with Blackgate caps - $400
      Other upgrade packages available at varying costs.


Company Information
Woo Audio
E-mail: feedback@wooaudio.com
Website: www.wooaudio.com













































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