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Woo Audio WA22


Pros: Very powerful; strong mid-range & soundstaging qualities

Cons: Lack of agility/speed & clarity

Originally published on February 22, 2010


Note: this review is an exact cross-post from post #1 of this thread on Head-Fi, which contains some user discussion on the review that may be relevant to read: http://www.head-fi.org/t/473873/mini-review-woo-audio-wa22


Below are my impressions of the Woo WA22 from while I owned it (October 2009 - February 2010). However, while I owned the amp for that long, I should add a disclaimer that I put in only 2 weeks of actual listening on the amp. This is only my opinion of the amp and even I might disagree with my own impressions later. This is not meant to be a full-length review especially given my limited listening time and I did not compare the amp to any of its competition.

My reason for buying the WA22 was to try out a tube amp after going quite a while without one (the last tube amp I previously owned was an SP Extreme in 2007). I sold the WA22 not too long ago as I was done using it, as I prefer solid-state amps for the operational convenience.

All tubes were stock except for an addition of the Sylvania 7236 power tubes.


- Source: Plinius CD-101 (power cord: Signal Cable Silver Resolution Reference)
- Interconnects: Analysis Plus Silver Oval for XLR, BPT IC-SL for RCA
- Headphones: Sony Qualia 010, Grado HP1000/HP2, Audio-Technica AD2000, AKG K701. All re-cabled to balanced with the Moon Audio Black Dragon on the Qualia 010, APureSound V3 on the HP2 and AD2000, and SAA Equinox on the K701.
- Comparison amp: HeadAmp Gilmore Lite as a point of contrast only.

Evaluation Music

Alison Krauss - Forget About It
Alison Krauss & Union Station - Lonely Runs Both Ways
Andrea Parker - Kiss My Arp
Megadeth - Countdown To Extinction [MFSL]
Julia Fischer - Bach Concertos
Porcupine Tree - In Absentia
Shelby Lynne - Just A Little Lovin'
Orbital - Snivilisation
The Crystal Method - Tweekend
The Prodigy - The Fat of the Land

Stock 6AS7 vs Sylvania 7236 power tubes

I found the WA22 to sound ok with the 6AS7 power tubes, which I tried after getting used to the 7236 tubes first. But the 7236 tubes were a clear upgrade that I would recommend for use in almost all situations. There was a greater sense of power to the sound with them, with more overall punch and bass depth and force. The 7236 simply provided a fuller mid-range and a more direct sound as opposed to laid-back. However, the 7236 tubes raised the noise floor and generated some tube hiss - not much, though noticeable with sensitive headphones. This wasn't a distraction once music was playing. The 7236 tubes also provided more volume at any one setting and a higher gain so they weren't entirely optimal for a sensitive headphone like the Audio-Technica AD2000 as one example.

Grado HP1000/HP2 (7236 tubes)

I came away from the WA22 thinking that it may very well be a very good amp for the HP2 in particular, even though I haven't heard many amps on the HP2 (the other amps being a Balanced B22, CIAudio VHP-2, Luxman P-200, and TTVJ FET-A). The WA22 had a wider, more expansive soundstage than the Gilmore Lite ("GL" from here on out) with more space between the instrument sections, especially noticeable on Julia Fischer's Bach Concertos. It also added more body to the lower mid-range and fleshed it out a bit for a richer, more natural sound. It also better delineated multiple violins and provided more spatial/ambient cues for a better representation of the "concert hall" acoustic, in contrast to the GL which has more of a compressed soundstage.

The HP1000 did not respond much to being balanced - there was maybe some marginal widening of the soundstage and more depth to the mid-bass. However, I should add that the Plinius CD-101 is NOT a dual-differential source and instead generates its balanced output via phase inversion, so results will probably be different on sources that are dual-differential.

Audio-Technica AD2000 (7236 tubes)

Despite this headphone's sensitivity, I was able to achieve satisfactory volume control, even despite the stepped attenuator. With this headphone I noticed a number of less than optimal qualities though. The WA22 didn't have the blinding speed of the GL and trailed behind it in attacks on very fast impacts that were easily heard on the spring coil effects and percussion hits in Orbital's "I Wish I Had Duck Feet" and the similarly percussive but a lot more hard-driving "Smack My B***h Up" by The Prodigy. The GL was quicker, more agile, and had a more complete sound, with harder-feeling and more sudden impacts. For its part though, the WA22 had a more intuitive positioning of the layers with a more 3D aspect and a greater "reach out and grab it" factor, while the GL felt like it was maybe a little too tightly-wound and overly controlled especially with the attack/decay. The WA22 seemed to stretch out decays longer for a more realistic sound.

Also noticed with this headphone, the WA22 had a thicker, fatter bass than the GL, which is actually on the lean (but fast) side. Low "slap"-type bass sounded looser on the WA22 though, not as controlled as the GL. It did pulsate and throb low bass very well, but the GL had a more insistent, forward-moving bass while the WA22 didn't keep up as well. The GL also more easily captured details like vibrations on strings and drums, which were lost a bit on the WA22 (just a tiny bit though).

The WA22's extra dimensionality on the soundstage was easily noticed on this headphone even though it doesn't naturally have a large soundstage. To its credit the AD2000 does have an ability to tell you where the virtual walls are, so to speak.

Sony Qualia 010 (7236 tubes)

I love this headphone primarily for its treble response which is the cleanest and quickest that I've ever heard to date, and it does it without grating on the ears (or my ears, at least). One of my standard Qualia tests is Alison Krauss & Union Station's "This Sad Song." With the WA22, I noticed the treble wasn't as "hard" sounding and seemed to have less quantity. However, the WA22 helped to separate the instruments out from each other better with more accurate-sounding spatials. I still thought the GL's treble response was the better one though, as "hard" is an aspect that I think is probably more accurate for this recording, and the GL also helps the Qualia sink its claws over the metallic sheens better.

In balanced mode, the music actually took up the resident innate spatials that the Qualia allows for. There was a deeper, wider soundstage, with a greater enhanced "peering into space" effect. There was also cleaner separation between left & right with almost a perfectly mid-point center. Impulse response also seemed to increase a bit and there was less haze/blur to multiple simultaneous instruments. Overall the Qualia responded well to balanced mode, as instruments sounded off-center in single-ended mode.

AKG K701 (7236 tubes)

For this headphone, I engaged the impedance switch. On the previous headphones, I had this set at Lo, but for the K701, I turned it to Hi, and I did notice a sonic difference. At Hi, the K701 sounded clearer and less blurry. There was also more separation between instruments and a fuller mid-range & mid-bass with more body to the sound. Overall there was just a sense of the K701 being better driven, as it sounded a bit weak with the switch set to Lo.

I find the K701 to be the most average-sounding headphone that I currently own and in accordance with this, I detected no faults to the WA22 with it. In other words, the K701 sounded good, very good in fact, but it didn't reveal anything about the amp that my other headphones picked up. The WA22 simply drove the K701 well, and in fact drove it to very, very loud volume (past ear-safe levels) with absolutely no audible distortion. There was no noticeable added mid-range body, but nothing was subtracted either. It was just a strong, fluid sound that went well with the K701.

In balanced mode I found the soundstage to actually get a bit smaller but it became wider and more precise, with a better illusion of a center-point (not very apparent in single-ended mode). There was also better separation between the left and right channels and more depth to the mid-range and mid-bass, and also more dynamic range (especially on low-volume music). Impulse response improved too but still not to the point where the K701 sounded fast enough.

Final Notes

I did not listen to the WA22 with any other headphones and did not do any other amp comparisons - this review is only what it was, an informal comparison to the only other amp I had at the same time.


Pros: build quality, tube versatility

Cons: none (excpet you will spend lots on tubes)

I love this amp. Upgrades tubes are a must. It can soften the sound a bit - which can be a good or bad thing.

Woo Audio WA22

* Technical Specifications: Headphones impedance : 8-600 Ohms * Input impedance: 100 Kilo-Ohms * Frequency response: 8 Hz - 50 KHz, -3dB * Output: 810 mw with 6080, 2 watts with 7236 power tubes * Signal/Noise: 92 dB * THD: <= 0.3% * External dimension: 7”(H), 12”(W), 10.5”(D) * Weight: 25 pounds or 11.4 kg * Voltage: AC 110/220V, 50/60 Hz * Standard Features: Point-to-Point wiring * True balanced topology * All tubes. No semi-conductors in the entire circuitry * One 5AR4 [PDF] rectifier tube. Direct substitute: 5U4G * Two 6SN7 [PDF] drive tubes * Two 6AS7 / 6080 [PDF] power tubes * DACT CT2 balanced stereo stepped attenuator * One balanced XLR input * One single-ended RCA input * Two 3-pin balanced headphone output (left and right ch) * One 4-pin balanced headphone output * One single-ended headphone output * High and low impedance switch

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