Pros: Soundstage & imaging
Cons: Slow impulse response, limited treble extension, low bass quantity
This mini-review was originally posted on another forum in November 2008. Cross-posting it here for the Head-Fi archives. Other than this intro, the mini-review below is posted in its entirety as originally written - nothing was modified or updated.
This was an accelerated mini-review - all listening was done over only 4 days. The amp was received as a loaner from another local Head-Fi member for that time.
Power cord: Black Sand Silver Reference MKV
Digital source: Plinius CD-101
RCA interconnects: Analysis Plus Silver Oval
Comparison amplifier: HeadAmp Gilmore Lite (used only as a reference point of contrast)
Headphones: AKG K701 (re-cabled w/ SAA Equinox), Audio-Technica W5000 and AD2000 (both re-cabled w/ APureSound V3)
Evaluation CD Tracks
A Fine Frenzy - One Cell In The Sea - "The Minnow & The Trout"
Alison Krauss & Union Station - New Favorite - "Let Me Touch You For Awhile", "The Lucky One"
Alison Krauss & Union Station - So Long So Wrong - "Little Liza Jones"
Porcupine Tree - In Absentia - "Blackest Eyes", "Trains", "Lips of Ashes"
Priscilla Ahn - A Good Day - "Dream"
Rachel Portman - Chocolat [OST] - "Main Titles"
The Crystal Method - Tweekend - "Murder" (aka "You Know It's Hard")
The Prodigy - The Fat of the Land - "Smack My Bitch Up"
Vienna Teng - Dreaming Through The Noise - "Nothing Without You"
Features, Operation, etc.
The WA6 was heavier than expected - looks compact but with clearly substantive weight, primarily from the dual power transformers. Relatively nice-looking amp too, with a clean finish that can come in either silver or black.
Not much in the way of features, but the amp does have an impedance selector switch that flips between 8-99 Ohms and 100-600 Ohms. I flipped the switch to 100-600 Ohms and plugged in my Audio-Technica AD2000 to check for noise - and found the tubes to be completely silent. Literally the only noise that could be discerned was a very low-level hum from the power transformers. The lack of tube noise was amazing, the WA6 is the first amp I've found to have absolutely no audible noise from the tubes.
I neglected to check if the impedance selector switch actually changed the gain multiplier or just increased the output power.
Sound - with K701
On Priscilla Ahn's "Dream," the WA6 placed Priscilla Ahn's voice closer than the Gilmore Lite did, for a more intimate presentation. The added prominence felt like a detraction though, and reduced the sense of overall depth to the soundstage. There didn't seem to be much air around the instruments. Treble was also not as sharp as the GL's, and not in a good way - there was a severely noticeable lack of razor-lined edges to the guitar strings. Dynamics also seemed to be a bit restrained compared to the GL, but the amp was still quite dynamic on its own.
On A Fine Frenzy's "The Minnow & The Trout," and Vienna Teng's "Nothing Without You," the WA6 gave a softer tone to the piano keys than the GL, but it was still strong enough to convey proper dynamic range. It also gave a stronger lower-mid/mid-bass anchor that made the piano sound heavy and deep. Overall there was more fullness and body, and it was very fluid as well - long piano notes with strong decays, fleshed out very well.
AKUS' "Let Me Touch You For Awhile" revealed some serious detractions though. The WA6 was a tad sluggish on the bass action and not really rhythmic enough. There wasn't enough "spring" to the guitar or mandolin notes either. Dynamic range also seemed to suffer here - the track overall felt too loud, with not enough contrast between softer and louder parts.
And on "The Lucky One" also by AKUS, while the WA6 removed a sense of Alison's voice carrying on air, it did make her voice sound more luscious and sultry. It was also positioned more closely/intimately and much more fluid. As far as detractions here, the WA6 missed conveying the metallic overtones and pops on the steel guitar, and the ambient air and space also felt significantly reduced - enough that the sense of space felt more like an enclosed studio room as opposed to an open hall. The various instruments comprising the band were discretely positioned though and were easy to locate by ear.
Porcupine Tree's "Blackest Eyes" went ok on the WA6 but not particularly great - the amp wasn't totally aggressive and dynamic on the opening overdriven guitars. It lacked a sense of brashness and intensity. It was still very dynamic though, and exuded its own confidence and power. It also separated the multiple guitars well to line up a convincing soundstage. Its presentation was also very direct - almost borderline in-your-face, but still a sense of some air around the band to not sound too suffocating.
Sound - with W5000
Revisiting Priscilla Ahn's "Dream," the WA6 paired well with the W5000 - although a closer, more intimate presentation, the W5000's intrinsic soundstage created a good outward curve to the image - that may still be too intimate for some people. The track was highly fluid with the W5K but not overly so, with a bold mid-range and strong firm bass. The lack of treble on the guitar was even more noticeable with the W5000 than the K701 though.
On Porcupine Tree's "Trains" and "Lips of Ashes," the most noticeable detraction was in treble extension, as it was audibly rolled off, but in spite of that, both tracks still sounded relatively good. The amp also gave more substance and body to the male vocals than the GL which was nice.
Rachel Portman's "Main Titles" from Chocolat [OST] went very well with the W5000 - the amp organized the soundstage much better than the GL. The individual orchestra sections were placed more realistically with percussion & strings on the left, brass and woodwinds in the center and center-right. It wasn't exactly as wide a soundstage as the GL, but there seemed to be more discrete horizontal positions within the image. There was also a better sense of depth in relation between the violins and the flute, as the flute felt distinctly further away.
Sound - with AD2000
On The Prodigy's "Smack My Bitch Up," the WA6/AD2000 pairing had its quirks. The GL had the clearer bass, as the WA6 felt a tad indistinct, even almost had what could be called generic-sounding bass. It was also less agile and didn't power through the bass as deftly. But it did pump up the >50Hz area for a nice added punch and boom that felt more satisfyingly deep. It didn't take much away from the AD2K's inherent speed - slightly less, but not too much that it made anything sound too slow.
The Crystal Method's "Murder" went worse for the WA6. Bass on this track sinks to a lower level than The Prodigy track, and the WA6 struggled to deliver it, it just didn't sound low or deep as the GL does, which maintains clear control over the low bass current. TCM's "Over The Line" is another bass reference, and it was here where it was obvious that the WA6 amped up 50-70Hz more than the GL, and 30-50Hz less than the GL, as it simply conveyed more impact than it did rumble (and conversely, the GL conveyed more rumble than impact). There was audible bass roll-off on the WA6, approximately around 40Hz. The amp just didn't creep or ooze low bass.
For a non-electronic test, both Vienna Teng and and Priscilla Ahn tracks were spun on the AD2000. The WA6 had the more realistic imaging than the GL. There was maybe less horizontal span than the GL but it was very integrated, very rounded, and very existential. The amp gave a proper impression of weight and realism to both voices and instruments.
The Woo Audio 6 is a solid tube amp all-around. I found it to have some key flaws but none really take away from what's essentially a very decent amp that can work well with different headphones. It may not really be optimal for the headphones I tried it with, but it works well enough and may very well be acceptable for listeners not as discerning as I was. ;)