There’s something so alluring about tube amplifiers. My first purchase from Woo Audio was the gorgeous WA7 Fireflies. They were fantastically articulate, transparent, and quiet. Over the course of a few shows, I had a chance to listen to their WA5-LE which left an imprint on my mind. It was paired with upgraded tubes, the Abyss headphones, and JPS Superconductor cables and was memorable due to its overtly seductive sound signature. It really sang to my core. Tubes aren’t for everyone as they typically come at the cost of some resolution, depth, and defined sonic outlines but most find the euphoric golden bloom to be too much to pass up.

When Woo Audio announced their new WA33 amplifier, I was at their booth first thing in the morning at the last SoCal CanJam. The early bird catches the worm and I was able to spend plenty of uninterrupted time with this beauty. It sounded quite a bit different from the WA5-LE as it more tonally balanced and quieter. It worked. It made the Focal Utopia and Abyss Phi headphones sing and kept me firmly in the listening chair.

I knew I needed more alone time with this amp and asked Woo Audio for a review piece. Luckily my upgraded Abyss Phi came just in time for this review.

Setup

  • Source: Chord DAVE with SOtM Trifecta
  • Interconnects: Audience Au24 SX RCA
  • Power cords: High Fidelity Cables CT-1 Ultimate
  • Headphone cables: Double Helix Cables Complement4 and Danacable Lazuli Reference
  • Headphones
    • Abyss Phi
    • HiFiMan HE-1000 V2
    • Mr. Speakers Aeon Flow Open
    • Sennheiser HD-6XX (Massdrop)
    • Meze 99 Classics
    • 1More Triple Driver Over-ear

Build & Features

Price: $7,999 (base). Comes in black or silver.

Tubes:

  • 4 x 2A3 power tubes in matched quad
  • 4 x 6C45 driver tubes in matched quad
  • 1 x 5U4G rectifier tubes

Inputs/Outputs:

  • 2 x XLR inputs
  • 1 x RCA input
  • 1 x XLR preamp out

The build quality of this amplifier was immediately apparent. Installation of the tubes was a breeze. Just make sure you align the notches with the 5U4G and follow the instructions provided with the amplifier. Btw, this amplifier is pretty heavy (50 lbs). Handle with care.

The WA33 is a fully balanced, direct-heated triode, Class A, output-transformer design. Jack Wu of Woo Audio was describing their Internal Coupling Architecture (ICA) technology, which was also used in their much acclaimed WES electrostatic amplifier. Instead of using an umbilical cord with an external power supply, The signal path is shortened by connecting the amplifier and power supply internally. This eliminates any potential RFI/EMI noise from additional components. As with all things audio, the lower the noise, the better. A quality power topology will elevate a component to new heights and a proper power supply design is crucial for optimal sound quality. Nice move.

The WA33 pushes about 10 watts and could also be used to drive speakers directly. Unfortunately, I didn’t have this custom option with the review units. Would’ve been interesting to drive them with the Omega CAMs.

There’s something satisfying about hitting the orange power button and turning the knobs on this amplifier. Fantastic build quality commensurate with the price.

Dampeners

I experimented with a few dampeners, specifically the UltraSonic Rx from Herbie’s Audio Lab. These dampeners tights up the image and provide more speed at the expense of warmth and body. Imaging is also slightly improved. Placing a varying amount of dampeners affected the output almost linearly. I personally preferred not having the dampeners at all but some will prefer the speed and clarity of having them on.

Impedance and Level

With the Aeon Flow Open, I get more shine and clarity by setting the Level and Impedance to H but a smoother sound when Impedance is set to L. With the Abyss Phi, I had Impedance and Level on H which provided a very vivid and punchy sound. Having them set on L was smoother but less engaging to my ears. Having Level set to high provides more detail, a larger soundstage, more dynamics, but is a bit leaner.

These helpful knobs allow you to tune a wide range of headphones of varying impedances and sensitivities. There’s no concrete way of setting these, try all permutations and stick to what sounds best with your system. After testing with over five headphones, I find different settings could work on the same headphone for different moods. A welcomed feature indeed.

Balanced or Unbalanced?

Luckily I had two Lazuli Reference headphone cables here, one 1/4″ and one 4-pin XLR for direct comparisons. I would use only the balanced connection if possible because it’s:

  • immediately quieter and more holographic.
  • has much better layering and separation. No smearing or bleeding whatsoever.
  • more dynamically rhymic.
  • super crisp, clean, and accurate.
  • much more punchy without being in your face and aggressive.
  • sounds closer to what I hear from my 2-channel setup.

Basically, recordings sound completely different (better) in balanced mode. There’s just more music, depth, body, air, and control. The single-ended connection doesn’t even come close.

Chord DAVE vs WA33 Output Comparison

The amplifier output of the DAVE is no slouch and is usually more clean, precise, and transparent than including a separate headphone amplifier. I’ve found that it powers hungry (Abyss Phi, Hifiman HE-1000 V2, etc) headphones to sufficient levels. I’ve also found it to present room acoustics more realistically. Most external amps will introduce a thin grey veil to the sound in comparison. An A/B comparison between the WA33 and DAVE was as easy as unplugging and plugging.

Sound pressure is one thing but the beauty of an external amplifier is its handling of the actual audio signal. Musical information is fairly complex when you’re layering instruments and voices from all parts of the spectrum. How those sounds are relayed is heavily amplifier dependent. It has to push enough power with enough speed and with minimum distortion.

This is where the Woo Audio WA33 shines. Although admittedly not as transparent, it provides more height and depth in the soundstage, more slam, and most importantly a more fuller and full-bodied sound. The DAVE output could be a bit “technical” or dry for some (and probably measures better) but transparency isn’t everything. Transparency is great but when the music pulls you in and invites you into its world…I find that more compelling.

With the power hungry Abyss Phi (some were using speaker amps to power the Abyss, for good reason), I preferred the WA33 with 100% of my listening. There’s an application of palpable textures and visceral impact to all genres of music and I’ve found it sounds great with poor/harsh recordings. Guitars have more crunch, drums have more smack, and violins are tactile. The WA33 provides a more dimensional and weighted sound which complements the DAVE’s DAC beautifully. Separation and smoothness are also better presented. Surprisingly enough, I felt some of the micro-details were brought forth in natural fashion while female vocals and cymbals had improved timbre. From direct DAVE, the detail was there but it quite a bit leaner and thinner. I also felt the image was larger and more forward with the WA33. There’s also more sonic extension and headroom with the WA33.

The WA33 provides all the textural bumps that make listening more cohesive and enjoyable.

The Sound

Wonder Woman Theme – Tina Guo

Dynamics are on full display here. The atmospherics from drums, guitar crunches, and violin strokes is nothing short of immersive. Although a very busy track, layering of the different players are made apparent with their own sense of individualism and space. There’s also more dimensionality and air in all directions. It sounded pretty dam flat from direct DAVE. I really enjoyed the weight and umph the WA33 provided for this track.

You’re a Weaver of Dreams – Cannonball Adderly and Coltran

The saxophone just floats gracefully as it plays. Cymbal brushes are tactile and well textured and remain engaging throughout. Background is amazingly quiet and there’s no blending of instruments. Bass plucks play undisturbed in the left rear. Once again, the layering capabilities of this amplifier are astounding. One interesting thing to note is the presence of a physical body or object. The WA33 provides this contouring and weight that makes it sound like what I would hear from a live performance. The piano solo sound so organic and naturally airy.

A Groovy Kind of Love – Jheena Lodwick

Drum hits deep with relentless intent. It has the proper amount of speed, detail, and decay. There’s this addictive golden hue to her voice and a dynamic articulation to the drums and strings. The music just breathes and draws you in. The presence region is sweet and seductive in the most natural way. I thoroughly enjoy the expansive and lush sound of this amplifier.

Empire State of Mind Pt.2 Broken Down – Alicia Keys (VH1 Storytellers)

Quite honestly, I didn’t know there was much detail in the drum hits on this track. The reverberations decay and travel realistically into the venue. Incredibly taut and weighty. Quite addictive. Finger snaps and claps have appreciable density and presence. Piano sounds like a frickin’ piano. Having seen her perform live in an intimate venue, the WA33 has brought me back to those memories of being in the first few rows. There’s a cohesion to the performance. The backup singers and instruments never interfere with Alicia’s voice. The whistle at the end of the track sounded startlingly real.

Welcome to the Machine – Pink Floyd

Makes me feel like I’m strapped into a chair in a psychedelic room at some art installment in Burning Man. As the strings and synths dance between the two channels, can’t help but to be mesmerized. The soundstage is mind-blowing in its depth of presentation. No complaints, perfect.

You Go to My Head – Judy Garland (Judy at Carnegie Hall)

Probably my favorite album for the WA33. Judy’s voice is graceful, intelligible, and unmistakable. She has free reign of the acoustic space with her mannerisms. Bass hits are clean and tight. Brass is voluminous yet controlled. The WA33 becomes a teleportation device and brings you back to 1961.

Dream Weaver – Charles Lloyd

Brace yourself for this one. Explosive dynamics and articulation abound. If you have a chance to listen to the WA33, try out this track. All instruments play with amazing cohesion and individuality. Tone and timbre are on point and there’s an insightfulness in the golden bloom of this amplifier. The overlays of brass and piano are presented so convincingly.

What a Wonderful World – Eva Cassidy (Live at Blues Alley)

There aren’t any well-defined edges (as expected) but the tubes make it sound like you’re actually in the venue. There is a more emotional presence and aural nuance in the music. Cymbals and guitar have this intimate sweetness and tactility. It got me thinking about how tragic it was to lose such an amazing voice.

Final Thoughts

The Woo Audio WA33 is exactly what a tube amplifier should sound like. It’s the right amount of everything. It’s not overly warm or sweet and doesn’t mask the finer details of the music. It improved the fidelity of not just the power-hungry headphones but those with lower sensitivities as well. The WA33 fills the music with textural colors, a naturalistic body, and improved dynamics across all genres. It doesn’t sound “tubey” in the traditional sense but perfects the balance required to provide just enough midrange bloom to be emotive and engaging. While this bloom sounds a bit artificial with some amps, there’s an accuracy and tastefulness in the coloration of the WA33. It presents a cozy and dreamy sound without losing accuracy and intent. This is especially the case with live music.

If you have a Chord DAVE and Abyss Phi or HiFiMan HE-1000 V2, the WA33 is a heavenly pairing. There’s more physicality, depth, tonal density, and insight into the recordings. Inner-details and macro-dynamics are brought forth in organic and natural fashion. This provides a coherence to the sound that doesn’t sacrifice acoustic independence and clarity for warmth. All parts of the music have their own acoustic space yet play in rhymic harmony.

Many will try to roll their own tubes but I felt the stock configuration was outstanding and good enough for my ears. This is the best tube headphone amplifier I’ve ever heard and will be the end-game headphone amplifier for many. The sound of the Woo Audio WA33’s is simply unforgettable.