The WA33 headphone amplifier is Woo Audio’s flagship amplifier for driving conventional (non-electrostatic) dynamic driver and planar magnetic headphones. It is a fully balanced, tube-based unit comprising two chassis that are permanently connected via a proprietary internal coupling architecture that requires no external cables. The power supply chassis is physically isolated from the preamplifier/amplifier electronics to minimize interference. The WA33 features a quartet of 6C45 tubes driving a quad of 2A3 tubes for the power in triode mode. 2A3 tubes are highly desired for their natural musicality and glorious sound and the WA33 amplifier lets them shine.
The WA33 offers a lot of features and flexibility. Via its front panel, one can switch between headphone output or preamplifier output, as well as between high vs. low impedance headphones. A level knob lets you optimize the WA33 for either high efficiency or low-efficiency headphones. Lastly, the input selector lets you choose between two separate XLR inputs (balanced) or the RCA unbalanced input. Just below the controls are separate XLR balanced outputs for the left and right channels, as well as a stereo XLR output, and a single-ended quarter-inch output for unbalanced headphone cables. On the rear are two XLR inputs and one RCA unbalanced input, as well as left and right preamplifier balanced outputs to feed an external power amplifier. The WA33 does not come with a power cord, but with such a high-performance amplifier, you should use a high-quality power cord.
With nine tubes, the WA33 lends itself to “tube-rolling” to subtly change its sonic character. I stuck with the stock tubes for this review and was very happy with their performance. For those who must have the ultimate, the WA33 Elite Edition at almost double the price offers premium parts, including ultra-high bandwidth custom output transformers featuring single crystal copper wires, Mundorf capacitors, and more. Unfortunately, I was unable to compare the Elite Edition with the standard version under review.
The WA33 excels at driving difficult loads that require a lot of power. Neither the Audeze LCD-4z nor the HiFiMAN Ananda headphones presented much of a challenge for the Woo. It was as if the amplifier was cruising without any serious demands on it. However, the sound of both with the WA33 was terrific with lots of fine detail, as well as exceptional clarity, transparency, dynamic headroom, and bass extension and control.
For more of a challenge, I tried the remarkable Abyss AB‑1266 Phi CC with an upgraded JPS Labs Superconductor HP XLR cable set. The Woo drove the Abyss with plenty of power and control, and its performance was absolutely stunning. What I noticed immediately was this combo’s sense of space with outstanding soundstaging, air, and focus. Fine details emerge naturally and bass is extended, powerful, and tightly controlled. Dynamic swings are explosive and the leading edges of transients are clear without any smearing or blurring, producing a high level of excitement and engagement. Voices and instruments, including massed strings, sound natural as in real life. This Abyss/Woo combination is about as good as I’ve heard, rivaling the performance of much more costly electrostatic references like the HiFiMAN Shangri-La and the Sennheiser HE1.
Some users may opt to use the WA33 as a fully balanced linestage driven by 2A3 tubes. I tried it in my reference two-