Woo Audio WA6-SE Vacuum Tube Headphone Amplifier

–by Brian Hunter

Anyone who has spent time with the headphone community has undoubtedly crossed paths with Woo Audio at some point. Jack Wu has been producing quality amplifier pieces on both the loudspeaker and personal audio front for some time now. His prolific headphone amplifiers have really grown into an amazing product line, catering to the entry level as well as soaring into the high-end stratosphere with his exceptionally unique monoblock WA234 (~$15k). Yes, that’s right — monoblock amplifiers for headphones.

The good news is that Woo has a well conceived product trench dug out, leading up to the big guns, so anyone willing and able to dip their toe into the fidelity water can have at it without sacrificing and arm and a leg (or an ear). I’m not referring to an audiophile “budget” piece north of four figures either. A newcomer can dive into the Woo pool for about $520 with the single ended OTL WA3. The spotlight of this review rests on the product that lands at the pseudo-median of this line.

The WA6-SE ($1.2k) is a SET Class A transformer coupled headphone amplifier that pushes a few extra watts over the “regular” WA6 and also includes a separate power supply housed in its own casing. Unlike many of the tube-injected hybrid amps that head-fi manufactures have been introducing in greater numbers the past couple of years, the WA6-SE is of an all-tube design that incorporates a separate, upgradeable rectifier tube section.

The construction and quality of the Woo product line is absolutely first rate. Countless reviews have been written heralding his relentless attention to detail. The build of the WA6-SE is what you would expect from any grand audiophile product, even at pricepoints far exceeding its own. It is sturdy, well-designed and exceptionally heavy although its size is still surprisingly manageable. Computer desktop warriors take note. The overall look and recessed branding manages to be both classy and sexy at the same time: it’s a looker. Throw the warm glow of some shapely tubes on top of that and you can easily see one of the reasons why the old school technology has stood its ground against the imperialistic march of solid-state amplification. The well-machined casing leaves you with the feeling that it would suffice as cannon ammunition as well as it plays music. The power supply and drive tube sections are connected via a supplied “umbilical” power cord and bear a resemblance to the [CanJam design reviewed here]. When it comes to transporting the unit, a few owners I have spoken to have expressed a bias towards the ease of the one-piece units, like Jack’s WA22. While transportation might involve a small additional step, I didn’t notice any conclusive drawbacks to this separatist arrangement, both setup and use were as simple as you would expect. At the end of the day, I am fully impressed with the shell that encompasses the innards of this beauty of an amp. It is truly built like a tank and would be a welcome visual complement to any audiophile’s headphone rig.

The back of the unit includes two single ended analog inputs. The RCA connectors look and feel a step up from your usual stock part fare. The input selector switch is located in between the two inputs on the rear panel of the drive tube section, a unique variation on the usual front-facing implementation. The front of the WA6-SE features a single on/off rotating aluminum knob on the power supply and separate high and low single-ended headphone jacks on the drive tube case. I discovered that I favored the low jack when listening to the Audeze LCD-3 planar magnetic headphone.

Power with the WA6-SE is quite ample. Even when utilizing the low jack, the amplifier had no problems pushing the 300-ohm Sennheiser HD 650s to extreme levels, normal listening volumes came in around a respectable 10 o’clock. As I was running the Woo through the paces, I noticed something I’d never heard before from a headphone amplifier. With no headphones plugged in and the volume knob up near its maximum, I could actually hear music bleeding out from the amp itself. As with almost all tube headphone amplifiers I reviewed, a slight hum was detectable through headphones on the low impedance extreme, in this case the 18-ohm Sennheiser Momentums. All nit-picking aside, I found the both the 650 and Momentum to pair quite nicely with the WA6-SE. Playback through the HD650 exuded an openness and top end air that was palpable. If you are a fan of Sennheiser headphones, the WA6-SE is worth an audition. The Woo continued to impress with the closed-back Momentums. The pairing presented itself with a liveliness and satisfying fullness that pushed the $300 headphone even further from its budget roots. But the WA6-SE isn’t really about driving headphones that cost a quarter of its ticket value. The more revealing Audeze LCD-3 added some additional perspective to the listening party.

The new DAC2 D by Benchmark offers a solid DAC and headphone amplifier combination. Running the single-ended output into the WA6-SE begged for a direct comparison against the almost “0 Ohm” headphone amp built into the DAC2 D. The resulting Benchmark output is precise, almost to a fault. And in turn the Woo felt a little less dry in the vocal region by comparison. Listening to Diana Krall’s Glad Rag Doll, the WA6-SE presented wider than average soundstage. While the overall perceived articulation of the midrange was perhaps slightly less, the Woo rang true with a more pleasing sense of tonality. Like a good steak, the midband was both juicy and thick. It leaves you with a sense of vocal fullness, but not without perhaps a hint of color as well. The 24/96 track Lucia by Marta Gomez felt as if the vocals were a bit less biting as airflow passed though Marta’s windpipe as she sang. This subtle smooth texture was further complemented by a believable sense of air and space surrounding her performance. The overall reproduction of the 6SE is flat and neutral as any good amplifier should be. The low end didn’t reproduce any unruly anomalies, and tightness and texture are both on par with other amps at this price range. The second half of the Nine Inch Nails track “Ringfinger” from the early album Pretty Hate Machine features a slight change in direction around the 4:07 mark that is riddled with dynamic and rhythmic bass synth sounds. During the outro, the Woo didn’t falter or hesitate with its unaltered recreation of the intricate passage. The synths darted in and out with fullness and surprising dimensionality for a virtual instrument that exists only in the dark, dusty corners of Trent’s mind. For all this low frequency vibrancy, the Benchmarks solid-state amplification did highlight perhaps the unavoidable wrinkle of the tube. So subtle it almost flew under my radar, but while listening to Metallica’s Master of Puppets I did notice a bit more bass slam and impact from Lars’ syncopated bass drum beats than from the Benchmark direct. The Woo is by no means weak in the knees when it comes to bass, but rather subject to the slightly common trait I have noticed from products on the tubular side of headphone amplification. This subtlety is not something that you would probably ever notice without a direct comparison to draw from. Orchestral and vocal-centric music will benefit greatly from the WA6-SE’s strengths.

The Sophia Princess Rectifier tube is a popular upgrade to the WA6-SE. It’s double mesh screen houses a glowing “V” that is a real ocular treat to the amplifiers presentation. The tube is available as an add-on and can be purchased directly on the Woo site along with the amp. Compared to the stock 274B tube, the Princess sounded a bit more open with a wider soundstage. This slightly more enveloping sound carried a dash of vibrancy with it that made it easier to pick out individual instruments out of the mix. While this tube doesn’t come cheap ($160 on the Woo site), its addition was pleasing and is a great starting point for a tube rollers collection.

Overall the Woo WA6SE packs plenty of punch tied to a tonal richness that can stand toe to toe with any headphone amplifier in its price range. It is the classic amp of its time, built with a keen eye for detail and a welcome sense of longevity that makes you think it’s one of those pieces that you could hand down to your kids. The build is in a class all its own, one that far exceeds its price bracket. The fine craftsmanship of its construct is just a window into the capabilities of its inner sonic beauty. If tubes are your thing, then Jack Wu is your man. While many of Jack’s products would be a great addition to any audiophiles collection the WA6-SE will strike a sweet spot in the price to performance balance for many. It’s power output is as impressive as it’s aesthetics.

About the Author

Brian Hunter is a recovering musician turned audio reviewer. He currently manages and writes reviews for his own head-fi site Audio-Head.com and freelances with several other publications. He loves tech and the tools of music, especially the ones involved in reproduction. After he finished his undergrad degree in business, he went to the local community college and got one in photography, which was way more fun. He likes it when people have unbridled enthusiasm for something and he seems to have the utmost respect for individuals who try to create, and even more for those who are good at it.