Aloha Head-Fiers,

I recently picked up a used WA2 on Ebay which came with the stock tubes and upgraded 5998 power tubes. My amp has the preamp section blocked out which is a shame as I would liked to have run it as such. I ran it for a few weeks on the stock tubes and was impressed with its performance with my HD580 and Grado GS1000i. All the reviews I have seen say to use a high impedance cans but the Grados work really well with this amp. They are very detailed with strong clear bass and only the slightest hum on very quiet portions of a track if I crank the volume. After a few weeks, I popped in the 5998 tubes and then a few days later some National driver tubes. Each step was an improvement to my ears. Especially in the bass where the fuzziness went away and I could hear more nuanced bass string harmonics. I never messed with the rectifier tubes but may try it for fun.

One thing I really like is that my family and friends always want to try it out when they see it. They never paid any attention to my main stereo system which costs a pretty penny more than this amp (guess the tubes get to them). I have them listen to it with my favorites playlist and they are always amazed. Hoping to create a few more audio enthusiasts and get them chuck their earbuds.

I listen to all sorts of music off Tidal and my NAS going through a NAD M33. I have had various solid state amps and a modded X-Cans that I still use daily in my office but this is the first headphone amp I have owned that made me feel like I was in the middle of the music. I was listening to "Explorations in Space and Time" and was floored by the first track with the various percussion instruments surrounding my body very specifically located in space and so clear and nuanced. It was a "chicken skin" moment as we like to say here in Hawaii. The third track starts with a scream and it really startled me. I now put it into my rotation as it is a great recording that highlights the amp/headphone synergy.

One thing I have noticed is that some recordings I listened to before where people complain about the background noise is very evident now and I am almost distracted by it. Bill Evans at the Village Vanguard is an album that I tend to listen direct from my NAD because it mutes the table noise a bit.

I am looking forward to picking up one of the newer Sennheiser or Beyerdynamic headphones to demo with this amp and I intend to keep this amp for a long long time just like my X-cans. Hope I never run out of tubes for this beauty. If you got to this point, thanks for reading and I hope it was worth your time. This hobby is so much fun!

I owned the WA2 for a few months and I enjoyed it immensely. If you can find one on the used market I highly suggest picking it up. Mine came with with stock tubes as well as some JJ e88cc, and Slyvania 6c4. I did a little bit of rolling but ended up preferring the JJ's, they seemed to have a little more life to them and  better impact overall. I was coming from a Schiit Valhalla 2 and an Oppo ha1 so when I first plugged into the Woo it was a staggering upgrade, even with the stock tubes. It felt like I took to the HD800's to the next level and I sat in awe for several hours at their analytical presentation. It's cliche but I really did hear things I'd never heard before. That being said, on bad recordings I noticed a shrill harshness I was not expecting from a tube amp. I also had a pair of HD650's and the back and forth was fun. The Woo did a tremendous job of driving both cans, just be wary of harshness, this amp hides no secrets with the HD800's. I found the HD650's much more easy going. 
 
I really enjoyed this amp overall and would reccomend it as a starting point for anybody looking to get into more serious tube amps. So far this has been my favorite Woo product build quality is 2nd to none. 

So, a review Woo Audio WA2... I have divided it into some headings, and rated them out of 100. These are my ratings based on my personal opinion. I'm open to comments as well, feel free to voice yours!
 
 
--->PRICE (85 out of 100)
Currently listed on Woo's site for around $1200, with stock tubes and components. Woo used to also offer a component upgrade to Black Gate capacitors, and a stepped attenuator volume control, but I don't think this is an option anymore... mine came without the upgrades, so this review is for the stock WA2. As far as Black Gate caps, I haven't heard them, so can't speak to how they might change the sound. I don't think they're being produced anymore, so this is probably why the upgrade is no longer available. Also, the volume potentiometer hasn't caused me any grief at all, as far as imbalance or anything else goes, so I am happy enough having the stock amp.
 
Tubes are probably your biggest concern regarding pricing, so my recommendation would be to mindfully purchase tubes, based on your needs. Woo offers some different "upgraded" tubes from the stock ones, but they are very pricey, in my opinion. See below under "Tubes" for some prices and options...
 
Tube amps in general are what I consider pricey... however, starting at $1200 for an exceptional headphone and pre-amp, I think the cost is decent. Not the cheapest option for a headphone amp, but I personally plan on keeping the WA2 and ditching my similarly priced WA7... more on that later.
 
My opinion is that if you can pick this thing up second hand for $1000 with some nice tubes, you're doing good. The tubes are the most costly part of really pushing this amp to its full potential...
 
 
--->LOOKS (90 out of 100)
Comes in black or silver, has a sizeable footprint at 13" wide x 9" deep and weight (17 lbs). Also produces a considerable amount of heat, like most tube amps. I have the black version, which looks very slick, but tends to show off any dust that collects on it. The front has a 1/4" headphone jack, as well as two sizeable dials; one to select the input source, and the other for volume. There is also a small push style on/off switch, with a slick little blue LED. Overall it looks like a quality amp...a remote control would also be awesome, although most amps don't feature one. No big deal.
 
 
--->TUBES AND IMPRESSIONS
I do my listening on Sennheiser HD-650 headphones... I enjoy their presentation for its full body, tonal depth, smoothness, and non-fatiguing highs. My opinion is that these headphones shine with OTL amps, and the WA2 can be a match made in heaven with these headphones.
 
The WA2 has two rectifier tubes, two power tubes, and two drive tubes... 6 tubes in total. 
 
--Rectifier Tubes
I left the stock NOS Yugoslavia Ei EZ80 tubes as my rectifier tubes. This is what the amp came with second hand, and I've heard that these are among the best. They're very cheap although not plentiful on eBay, but I have no ambition to try rolling in any other rectifier tubes. Woo offers a very pricey upgrade to Westinghouse NOS tubes which I haven't heard.
 
Further reading:
@lukaskite's EZ80 shoot-out: http://www.head-fi.org/t/402215/the-woo-audio-2/510#post_7243933
 
 
--Power Tubes (Current prices online and my personal impressions...)
The WA2 takes 6080/6AS7G/5998/7236 tubes, which range in price for a pair from around $20 USD to $500+ USD... here are some of the more popular tubes that are used with the WA2, and my impressions, if applicable...
 
$20 USD for a matched pair of NOS Philips 6080WC tubes - These came stock with my WA2, and sound very rich, muddled, and not very detailed. I put them in and immediately wanted to turn off the amp and swap in something different. Lots of rich, syrupy sounding mids, and not much else. Not a fan of these at all.
 
$40 USD for a matched pair of NOS RCA 6AS7G tubes - Very nice sound... warm, smooth, deep texture, nice width and decent depth for soundstage... Sound powerful, deep bass but it definitely isn't as controlled as the Tung Sol 5998 tubes... an exciting sounding tube. Sacrifices detail compared to the Tung Sol 5998's as well, but I actually am very impressed with these tubes for the price.
 
$80 USD for a matched pair of NOS Sylvania 7236 tubes - Smooth, immense soundstage... don't have the punchy bass or overall power of the Tung Sol tubes, but incredible at separating individual instruments/vocals. Nice tonal depth, and super smooth, but at the sacrifice of details. The mids also seem to be missing the magic of the above tubes, which is a bit of a deal breaker for myself. I do really appreciate the separation and smoothness these tubes produce though... kind of an eye-opener for me for how wide open everything can sound.
 
$200 USD for a matched pair of Bendix 6080WB tubes which I haven't heard, but are supposedly much better than the Philips 6080's. 
 
$250 USD for a matched pair of NOS Tung Sol 5998 tubes - Beloved by many for their deep, powerful sound, these tubes are beauties. Tight, controlled, very deep base, with an overall warm signature, fleshing out many harmonics and also very decently detailed. The high end also extends fairly well which is a welcome balance to the very deep bass these tubes push through. It has also been stated in the WA2 thread on Headfi that these are the recommended tubes from Jack Woo to use with this amp. 
 
$500+ USD for a matched pair of NOS GEC 6AS7G tubes or WE 421A tubes - supposedly sound the very best. Haven't heard them.
 
Further reading: 
Nick Tam's useful 6080/6AS7 review from the Bottlehead Crack forums: http://the-key.enix.org/~krystal/review-tube-bottlehead.html
WA2 Tube Rolling Recommendations from headfi: http://www.head-fi.org/t/393811/woo-wa2-tube-rolling-recommendations
Smaller thread from headfi: http://www.head-fi.org/t/574969/good-tube-combinations-for-the-woo-audio-2
 
 
--Drive Tubes (Current prices online and my personal impressions...)
The WA2 takes 6DJ8/ECC88/6922/E88CC/7308/E188CC/Cca tubes, which range in price for a pair from around $20 USD to $500+ USD... There are so many very cheap 6DJ8 tubes that in my opinion are not even worth your time. They will work in the WA2, but they have general sonic flaws that will impair the sound... The ones that came stock with my WA2 were not offensive sounding to me... I would guess they were Russian tubes, but I personally believe in Amperex, Mullard, Telefunken, or Siemens tubes. Here are some of my comments on the Amperex and Siemens tubes...
 
Amperex 6DJ8/6922/7308 tubes - I am going to be very general and categorize these tubes into two piles - the Heerlen, Holland tubes, and all others. My reasoning is that all of the Amperex Holland tubes share the same general sonic qualities... an overall warm, clear presentation with a rich sounding midrange. The bass is generally tight and not overly pronounced, and the highs are generally polite, coming across nicely without being overly extended/sparkly or harsh. Starting from the cheapest 6DJ8's, and moving up to the 10,000 hour rated premium 7308 tubes, I hear better clarity, even better 3d-sounding midrange, and a very warm, balanced presentation. I personally prefer the 7308 tubes stamped as "Miniwatt" tubes, which go for around $100 each. I also like the "Orange Globe" tubes with solid, round dimpled getters. These can go as cheap as $20/pair.
 
How to identify the Amperex tubes:
The Holland tubes have a "Delta" date code that looks like a half triangle, and will always have creases near the top of the tube, where the vacuum tube glass was "folded" during the manufacturing process. The getter flash on the top of the tube is generally near the top and not very deep, and the getter itself is normally a round, halo style, or a D style for the older tubes. The mica on the 7308 tubes is normally round without any tiny little triangle type perforations, whereas the 6dj8/6922 tubes usually have the triangle perforations on the mica. Please note that I have never seen an Amperex 6DJ8 with a "saucer" style getter, like the Russian tubes. I have seen fakes and they sound terrible!!! Also, a "perfect" testing score for 6DJ8 tubes is transconductance of 12,500/12,500 micromhos, and a plate current of 15mA/15mA - anyone who has test results higher than those is probably not using their tester at the right voltage!!
 
Other Amperex tubes come from the USA plants, and start with a * date code. These are supposedly also pleasurable to listen to, with less emphasis on midrange... I have not heard them so I honestly cannot comment on them. Lot codes stamped above the date codes are also useful for Amperex tubes... for the regular 6dj8/ecc88 tubes, look for GA1, GA2, GA3, etc for the older tubes ('50's), and GAA, GAB, GAC... etc for the not so older tubes ('60's).  For the premiums, look for 7LA, 7LB, 7LC... 7LG etc for older tubes ('50's), and VR0, VR1, VR2, VR3... for not as old tubes ('60's). Both sound amazing... I would not recommend getting too involved in hunting down old tubes unless you want to turn into a 6DJ8 maniac like myself... you've been warned!
 
Siemens ECC88/E88CC/E188CC/Cca tubes - So, these tubes were generally made in Surenes, France, or Munchen, Germany. I personally have only heard the German tubes, and they have a very exciting sonic quality... deep bass, and extended, sparkling highs. Moving from the ECC88 tubes up to the E188CC tubes, the overall refinement and clarity is improved. I find the E188CC tubes to be a touch more exciting than the Amperex 7308 tubes, as the Siemens highs are spectacular, and bass becomes more and more controlled with the pricier premium tubes. BUT the Amperex tubes absolutely slaughter the midrange presentation of the Siemens tubes. Ok, maybe I'm exaggerating a touch, but the Amperex tubes do have an edge when it comes to midrange. The Siemens tubes present a superior depth of soundstage, with nice, deep, clear bass that will be maximized rolling Tung Sol 5998 power tubes, as well as breath-taking airy, sparkly highs with an extension the regular Amperex tubes just can't replicate. The danger with the Siemens tubes is that I find they're generally lacking in refinement of the midrange... they just don't seem to flesh it out as well as the Amperex tubes. This is a deal-breaker for me, and the Amperex tubes seem to be in better supply, so I personally stick with the E188CC Miniwatt tubes in my WA2. I have heard from others that the premium E188CC Siemens tubes, or even Cca tubes have beautiful mids, and I also imagine that they do a better job with imaging/micro detail in atmosphere. These tubes are outrageously expensive, and I imagine that they're worth every penny. I would recommend not hearing them, or your experience with all other 6DJ8 tubes will be ruined (Partially joking).
 
Identifying the Siemens tubes: Same as the Amperex tubes; look for the four creases along the top. Also, look for an "unequal to" sign in the date code, which identifies them as being manufactured in Munich. Good luck finding the date code, as it's extremely hard to find. Sometimes its etched on the glass sideways, and very, very hard to see. Sometimes it's etched on the actual support for the getter itself (etched on the metal), and sometimes it is also etched into the bottom of the tube, between the pins. The mica is also not entirely round, like the Amperex premium tubes... it has a couple of tiny little triangular supports, and the flash from the getter is deeper than the Amperex flashing, usually. I am generalizing here, so please do your own research before buying NOS tubes.
 
Further reading:
Joe's Tube Lore on Audio Asylum: http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html#6DJ8
Schiit Lyr tube rolling thread on Headfi: http://www.head-fi.org/t/549508/schiit-lyr-the-tube-rolling-thread
6DJ8 date codes from Brent Jessee: http://www.audiotubes.com/mullcode.htm
 
 
OVERALL SCORE  (92 out of 100)
If you want a high quality SE OTL amp, look no further. The Woo WA2 is a very powerful, smooth sounding beauty of an amp. Tube rolling options are plenty, which can seem a bit discomforting for some, but it really allows you to take the sound wherever you want to, with plenty of power from the WA2 to support your addiction. What I hear from this amp is a very smooth, pleasant presentation, with lots of tonal depth, fleshed-out harmonics, and punch. It drives HD-650's to their full potential, and also has the benefit of being used as a pre-amp to drive speakers. As I mentioned earlier, I prefer the WA2 to the WA7 simply because of its ability to bring out such a warm, romatic sound without sounding like a slouch. I find the WA7 to offer a more speedy, almost solid-state like presentation, and I miss hearing some of the harmonic warmth the WA2 excels at presenting. Both amps offer deep, exciting bass, but the WA2 is such a chameleon, being able to roll in different power, driver, or even rectifier tubes.   
 
I hope you enjoyed this review, and I welcome all comments! Happy Headfi'ing.

The WA2 is a five-star amp. The amp itself is a marvel of engineering, built on a Bauhausian aesthetic: form follows function. It's pretty to look at, but, properly upgraded, infinitely prettier to listen to. With dual driver, rectifier, and power tubes, it's possible to sculpt and finesse sound signatures: several reviewers have already noted that the amp lends itself to tube rolling--which can be both an exquisite blessing and an expensive curse. For sheer versatility, the WA2 is a wonder. Add to that the WA2's magical sound, when properly upgraded with well-regarded NOS tubes, and it's safe to say that, at its price, the amp has few, if any, peers.

The stock tubes the amp ships with are a disservice. That's not entirely the company's fault: short of raising the base price of the amp by several hundred dollars, the WA2 needs to ship with inexpensive tubes--and cheap tubes means comparatively mediocre sound. But the tubes should, at the very least, work. Many WA2 owners have complained that the stock tubes were defective. I myself received defective tubes, which took about $200, 15 hours, and some slow, casual indifference from Woo Audio to diagnose (I had to rule out a ground loop to prove the tubes were at fault). Woo Audio, almost comically unapologetic for the expense and inconvenience, did the absolute minimum to address the matter--i.e., by sending cheap reimbursement tubes after I had already bought and installed replacement tubes to correct the problem. A company with better customer service would have sent better tube replacements (even if not top-tier NOS tubes) as a token apology. Sadly, the forums demonstrate that customers after me--after Woo Audio claimed to have addressed the matter--experienced the same problem. Exactly why a $1200 amp--arguably, the company's flagship, even if not its most expensive, product--is being shipped to customers without first having its stock tubes tested in the amp is an uncomfortable mystery. Certainly, though, I've never had to work so hard to spend so much money. If it were any other product, I would have returned it--but perfection is worth some pains.

If you buy the amp, you should be prepared immediately to buy tube upgrades. The WA2 with stock tubes is merely enjoyable. With upgraded tubes, the WA2 is absolutely enchanting, and puts other amps at similar prices to shame: upgrade the power and driver tubes first, as they affect the sound the most. Upgrade the rectifiers last, as their effect on the sound is comparatively small (though ultimately important). I'd advise against buying those upgraded tubes through Woo Audio, however, since the company consistently charges a significant premium on NOS tubes compared to market prices.

You should also be prepared to supply your own power cord since the WA2, much to the surprise and chagrin of some customers, ships without one. Personally, I think the amp's sound benefits greatly from an audiophile-grade power cord, but a $3 power cable will get you started, and may be all you ever need.

My interactions with Woo Audio have been consistently off, often odd, and occasionally rude. However, I don't think these rudenesses were intentional so much as the result of distraction and misunderstanding. I got the sense, perhaps mistakenly, that Woo Audio's staff was simply overworked--the result of a company's infrastructure lagging behind its own success. I never once, in my interactions with Woo Audio, felt like a valued or respected customer so much as a hurried duty. In fairness, many customers find their interactions with the company perfectly affable and helpful.

The WA2 is, for the price, about as close to perfection as one can find in this world. The amp, with proper NOS tube upgrades, offers a vast soundstage and, without aggrandizement, breathtakingly gorgeous timbre and divine imaging, subtle and layered. There's something magical about the amp, something pure in its presentation: it makes sense of complicated musical passages that, on lesser--even if more expensive--amplifiers, are just confused convolutions. To call this amp awe-inspiring is simply to state fact: I have whiled away untold hours listening in awe. I'm genuinely distraught that I can't give the amp the five-star rating it so justly deserves. But the company's faults--its quality assurance and customer service--tarnish the amp's perfection.

--Update. I've updated this to a 5 star. Whatever the initial difficulties with customer service, this amp has given me years of joy.

I have owned the WA2 for about a year now. I typically listen to Alternative Rock, occasional Rap and some Blues. I am using a Arcam rDac with it and I also have a Rega RP-3 and a Project Phono Box.   
 

In Summary

Amazing amp best $1000 I have ever spent on my headphone set up! Works well with all sources and has loads of room for upgradeability! 
 
 

This wonderful amp deserves more reviews. I'll make a better write up later, but for now I just post a link to my WA2 vs WA22 comparison http://www.head-fi.org/t/615810/the-beauty-and-the-beast-wa2-vs-wa22

This is not a full review, just a rating and a few comments.  I bought my WA2 used, and was really surprised how good it is.  The WA2 is among the better headphone amps available.  It actually surprises me that it's not even more popular than it is.
 
The WA2 has some pretty impressive power delivery, and it works wonders with high-impedance cans like the Beyerdynamic T1, and is also remarkably good with the Audeze LCD-2 and HifiMan HE-5LE.  Only very low impedance dynamic drivers, where the damping factor could be an issue, and not in the WA2's sweet spot.  But with the T1, the WA2 is absolutely stunning. 
 
The WA2 is an outstanding headphone amp, and the fact that it has multiple inputs adds to the string value.