Woo Audio WA6

Intro

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.

Associated Equipment

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.

Conclusion

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. ;)

Pics

I'm a relative newbie to the headphone game.

My reference system (at the time of writing) is a Burson 160D, and having a good reference is essential when you're comparing tubes.  

My reference headphone (at the time of writing) is the Sennheiser HD 650, which are known for their veil until you put great amplification with them.  I also own UERMs, which aren't appropriate for this type of listening analysis. 

First out of the box I was quite unimpressed.  The soundstage was decent, but not exactly impressive.  The bass was muddy and shallow.  More disturbing, is what happened to passages with a lot of reverb.  The decay would clamp down hard, and you'd lose a lot of transients.  I found myself running back to the Burson, wondering what I was thinking dropping $550 bucks on an experiment.  

The photos on the web site of the Princess Sophia tube had me drooling, and I ordered soon.  The upgrade piqued my interest as the WA6 began performing.  It wasn't audio nirvana, but the soundstage improved and the bass opened up a bit.  The Woo WA6 wasn't winning, but at least it was in the game.  My trips back to the Burson were suddenly less frequent.

Reading another review here on Head-Fi, I read a lot of praise for a stubby, unattractive tube called the GZ34 made by Mullard.  It appears the older you go, the better the sound becomes, so says the pricing and reviews on these short tubes.  I found one on eBay for $120.  A 1958, standard base NOS, and the WA6 was suddenly a force to be reckoned with.  

The GZ34 launched the WA6 into orbit.  I've yet to find a tube that can compete-- but if you're looking for a cheaper substitute, check out the CV593.  They're lacking a little on the bottom, but match the GZ34 in most respects, and it's a much prettier tube, to boot.

UPDATE:  I've located a 1957 metal base GZ34-- and indeed the sound did improve a bit (not earth-shattering-- but a bit better bottom end and openness.)  I've also received a tip that the Western Electric 422a 274B, if you can find one, is a step ahead of the GZ34.  I haven't tested or found one yet that was affordable.  I've also been auditioning a Telefunken GZ32 rectifier-- and have been quite pleased with its overall presentation.  It is worth noting that all of these tubes mentioned are a quantum leap in sound ahead of the Sophia Princess or stock 5AR4 tubes.

On the drive side, tube after tube after tube sent me back to the stock RCA 6DE7.  I still haven't found any worthy upgrade, though I'm currently testing a 6SN7 that's showing some promise.  Woo claims the 6GL7 is the premiere tube for power on the unit, I couldn't disagree more, and I was sorry I flushed the $110 down the drain.  While adding more drive, the GL7s added some distortion and crunch, and reminded me of an FM radio sound circa 1977.  The lesson here is the rectifier tube makes a greater impact on the tonal quality than the drivers, so put your money in a good rectifier and be happy with the stock 6DE7s.

UPDATE: When I moved from the HD650 to the HD800-- here's where the power tubes came into play.  The 6DE7 was no longer enough to drive the power hungry HD800.  The GL7 still lacked a bit in clarity for my taste-- so I tried the legendary 6SN7 tubes-- and the pairing is now quite impressive.

For intense listening, the WA6 now outperforms the Burson 160D.  That's saying a lot.  However I've spent hundreds and hundreds in tubes to get here.  The Burson excels at everything and gives you a DAC converter and pre-amp to boot.  It's a better buy. 

If you like tweaking and hunting-- the WA6 can provide that rare audio nirvana we seek.  But it's going to cost you and be prepared to roll through a lot of tubes before you find that ideal match.  

A final word on fit and finish-- this unit is just beautiful to look at and built like a tank.  

FINAL UPDATE: Eventually I was using the Burson 160D so little for actual amplification-- I sold it and moved to the Wyred4Sound DAC2.  The amp stage on the Burson was simply no match for the Woo with upgraded tubes.  I sold the WA6 in the fall of 2012 after a WA5LE (yes, I'm officially a Woo addict) came available on eBay for a huge discount.  I couldn't pass on the deal.  What the WA5LE revealed is that the WA6 doesn't have a lot of power to drive demanding headphones.  While the WA6 drove the HD800 fine with the upgraded driver, it didn't have enough power to really open up the HD800 to their full potential.  This is not to say the WA6 isn't a good amp, it's a terrific amp.  But know that by moving up in the Woo line, you do get better sound (deeper bass, better soundstage, etc).  If you're spending more on a pair of high-end cans-- you have to plan on spending more on an amp to bring the most out of your expensive purchase.

Price in review summary includes the tube upgrade.

This is a pretty limited comparison. I relied on the reviews of others before deciding to try a Mullard/Holland GZ34 in place of my stock Sovtek 5U4G in my stock Woo Audio WA6. (I should have noted the name of the Head-Fi.org: Headphones, iPod earphones, portable audio, MP3 players, high-end audio member that compared about eight rectifier and came up with the GZ34. Buddy, whoever you are, I owe you a beer.

Well, I'm amazed that an amp that I loved so much could be improved so much. The new cryro'd GZ34 set me back $250, but it's worth every penny. The Sovtek is a sexy, voluptuous looking tube, with large size and nice curves, BUT the compact little GZ34 has a much richer, complex sonic presentation. Bass has much more slam and the mids are rich with with overtones. The highs are crystalline, with no hard edge. So, I'll use the Sovtek for burning in cans and as a spare.

I used my AKG K701s and Ultimate Ears Triple.fi 10 Pros for the comparison. I tried raising the volume with the Sovtek to see if it just needed more gain, but that was not the case, it still sound plainer and less rich. I listened carefully to the highs and the GZ had smoother highes, with more harmonic content. I used Chesky's "The World's Greatest Audiophile Vocal Recordings" on SACD for the comparison. It's actually a very good SACD with lots of bass, a variety of excellent vocalists and many instruments in the arrangements, from solo bass to full orchestra. Of course, being Chesky, it's well recorded.

I bought the GZ34 off Audiogon. I'd looked a few weeks back and only saw one or two Hollands at prices over $600. That made the $250 seem a little more palatable. Apparently Mullard bought up lots of European tubes, relabelled them and cryrogenically treated some of them. I suppose the non-Mullard Hollands are even harder to find, perhaps explaining the $600+ price I first found. I can't imagine such a tube being more than twice as good as this one.