New York-based Woo Audio was founded in 2004 and specialises in tube powered headphone and loudspeaker amplifiers. Taking three years to develop the WA8 Eclipse reflects the company’s desire to bring the undiluted performance of their big amps to a smaller product for audiophiles who want an authentic tube headphone listening experience without being confined to a desktop setup.
The Eclipse is the world’s first transportable, battery-powered, tube headphone DAC/amp. It uses a transformer-coupled, Class A, single-ended triode (SET) using military-grade subminiature driver (1x 6021) and power (2x 6S31B) tubes and ultra-efficient custom OCC single crystal copper output transformers for high bandwidth and low loss. Build quality is impressive externally, in the hand the unit feels exceptionally sturdy and durable. Its anodised aluminium chassis – available in black, space grey or gold – is bevelled and streamlined so there are no protruding parts, making it easy to transport in the supplied hard-shell Pelican case.
Weighing just over a kilo and measuring 17cm long, the Eclipse is too large and heavy to wear and use on-person. The company instead markets it as a home-from-home travel companion that’s ideal to take to “offices and hotels around the world” and includes an external switching power supply/charger that works on all voltages. Eclipse’s lithium ion battery takes around two and a half hours to charge and provides up to four hours continuous playback, long enough for train commutes and short-haul air travel. It can also be used on mains power including whilst charging; in either situation the battery acts as a buffer to provide a cleaner feed.
The front of the unit houses a high-accuracy volume control that provides excellent channel matching throughout its operating range and is damped to make fine-tuning output levels a breeze, even with sensitive IEMs. Below the volume dial are two single-ended headphone outputs, one 6.3mm and one 3.5mm. Both outputs can be used simultaneously – handy if you want to share the listening experience with a partner or friend – though the manual states that best performance is obtained when driving only one headphone.
The cute trio of miniature vacuum tubes is showcased behind a glass window with a small switch to select either 2- or 3-tube operating mode, this not only alters the amp’s gain but also its tuning to suit different headphones. To the far left of the window is a subtle 5-bar LED battery level indicator that compliments the soothing, amber glow from the valves. The DC input, on/off switch and audio inputs are all located at the rear. While preserving Eclipse’s clean aesthetic lines, the flush-mounted power and tube mode switches are quite a challenge for large hands and short fingernails; these switches could have done with being a touch bigger.
In addition to a 3.5mm analogue line input, the WA8 is also equipped with an ESS Sabre Reference ESS9018K2M DAC capable of decoding up to 24-bit/384kHz PCM and DSD128. The DAC is fed by an XMOS xCore-Audio asynchronous USB input that has native support for PC, Mac, Android (requires micro-USB OTG adapter) and iOS (requires lightning-to-USB camera kit adapter). There’s no input switch on the Woo, the USB input mutes automatically when a source is connected to the line input, so you have to physically unplug the latter to hear the onboard DAC. This is a bit of an inconvenience if you’re predominately using Eclipse in a static system with two sources, but the amp is of course designed to be transportable and this naturally requires the connecting and disconnecting of sources whenever it’s moved from one location to another.
The Eclipse drives headphones from 8Ω to 600Ω nominal impedance and, in its most powerful high-gain (3-tube) setting, kicks out a ballsy 250mW RMS into 32Ω, enough juice apparently to drive particularly stubborn headphones like the 88dB/mW Abyss Reference. Output impedance isn’t specified, but I’m inclined to believe it’s suitably low as I didn’t perceive any change in frequency response with headphones. With a signal-to-noise ratio of 100dB, Woo claims Eclipse’s circuitry is quiet enough even for high sensitivity in-ear monitors. I’m not an IEM guy, but through the most sensitive over-ear ‘phone I had to hand, the Focal Utopia, I could hear no background hiss or hum whether in low (two tubes) or high (three tubes) gain. This amp’s noise floor is exceptionally low and that isn’t always a given when there are valves in the chain.
The stock tubes have a rated life of 5,000 hours, this equates to about three and a half years if the amp is used for an average of four hours per day. Conveniently, both the driver and power tubes are user-replaceable in a process that takes only a few minutes. The tubes are on PCBs which simply pull out and push in, the trickiest part is ensuring the PCB pins align with their corresponding sockets upon insertion. A replacement trio of tubes is available from Woo Audio at a cost of $335. The 6021 driver tube can also be replaced separately, tube rollers have the choice of four upgrades: a 6021 or 6BF7 by Thomson, GE or Sylvania ($85) or a Mullard CV3986 ($150).
Switching from one tube mode to another whilst Eclipse is powered on is very strongly cautioned against, it apparently causes audible distortion and can damage the amplifier’s circuits. We are also advised to turn the volume to zero before plugging and unplugging headphones. The reason for this is not clear but I assume it’s to protect the output circuitry from the momentary short that occurs as the TRS jack is inserted and removed from the socket. (Some designs are more sensitive than others to output shorting so it’s a good idea to get into this precautionary habit regardless.)
Plugging my Macbook Pro into the Eclipse’s USB input, I begin my audition in 2-tube mode with the trusted Sennheiser HD600, a high impedance open-back headphone that strikes the perfect balance between neutrality and musicality and is great for quickly finding the lay of the land with partnering gear. The HD600 shows Eclipse to be a warm, silky-smooth amp with an especially lush midrange. Human voice and acoustic instruments are intimately portrayed with rich, woody fundamentals and sweeping, elongated overtones. The highest octave is more laid back and less incisive than I’m used to, but the way notes linger in the air like Cuban cigar smoke in a Havana jazz club is very alluring.
Switching to 3-tube mode reveals an even more sumptuous side to Eclipse with increased heft and bloom in the lower registers. With two tubes, bass response is essentially linear down to 30Hz and gently begins to roll off below. When all three tubes are in play, as well as offering +6dB more gain overall, low bass sees an additional boost. Not only counteracting the aforementioned sub-bass roll-off, this mild elevation really helps bolster dynamic-driver, open-back headphones whose low frequency response invariably starts falling below 100Hz. It adds strength and body to all the headphones I tried, making them sound bigger and more rounded. If accuracy is the objective then sealed ‘phones that need no help extending all the way down into the lowest octaves are best served by one less tube. However, I must confess to revelling in the positively thunderous, sledgehammer-like delivery from Dan Clark Audio’s Aeon 2 low-impedance closed-backs with all three tubes engaged.
Sensing this amp would make the ideal partner for headphones that are sometimes a bit too dry and analytical with solid-state amplification, I eagerly reached for the Sennheiser HD800S and Audio-Technica ATH-ADX5000. Both of these ruthlessly transparent open-back flagships synergise wonderfully with Eclipse’s bloomy midrange and mellow treble and reveal a sweeter and more intimate persona. This is especially the case in 3-tube mode, where Eclipse’s weightier lower octaves also help to beef up these cans’ somewhat polite bottom-end and redress their comparatively bright tunings. On the other hand, ear-speakers with a thicker tone, such as the Sennheiser HD650, are too rich for my palate with this amplifier.
The built-in ESS Sabre ESS9018K2M DAC compliments Eclipse’s amplifier stage very well, resolving enough detail to adequately contour the smooth and broad brushstroke approach of the tubes. You don’t get the micro-dynamics, precise timing and snappy transient response that you do from the likes of a Chord Hugo 2, of course, but that’s part of the Woo’s charm; it has an uncanny ability to slow down time, letting you savour music in a more relaxed and contemplative state of mind. The Chord is so different in its design objectives and end delivery it really is an apples to oranges comparison.
While the onboard Sabre chip is more than good enough to appreciate what Eclipse has to offer, an even higher level of performance can be squeezed from the Woo by connecting an external DAC to its line input, though you must of course weigh this up against the additional cost and potential reduction in portability. My Schiit Yggdrasil 2 multibit DAC offered up more nuance and resolve, but a standalone converter that costs almost £2,500, is 10x the weight and almost 20x the size only makes sense if it’s already part of your static hi-fi system. If torn between spending money on an external DAC or an analogue source such as a turntable and phono stage for Eclipse, I’d prioritise the latter.
As for comparisons with other tube headphone amps, the WA8 displays a much stronger personality than those I’ve auditioned. The plucky Schiit Valhalla OTL, powerhouse Schiit Mjolnir 2 hybrid and sublimely refined Audio-Technica AT-HA5050H hybrid, for example, all lean more to the solid-state end of the spectrum and inject comparatively modest streaks of colour. The Schiits can of course acquire more personality by rolling different tubes, but straight out of the box the Woo definitely makes the strongest and most authentic impression. For undiluted tube flavour, Eclipse is the tastiest dish on the menu.
Woo Audio’s innovative WA8 Eclipse headphone DAC/amplifier makes the impossible possible and brings unbridled tube performance to those who refuse to be confined to an immovable desktop system. It packs genuine Class A, SET topology into a transportable, battery-powered and surprisingly versatile device with enough power to drive both high- and low-impedance headphones, a noise-floor that’s quiet enough for sensitive IEMs, and the ability to tune the sound to taste at the flick of a switch. For listeners that favour legato over staccato and atmosphere over accuracy, the beautifully lush, intimate and smooth-sounding Eclipse is guaranteed to woo.