Woo Audio – WA234 MONO (Mk2) As a result of posting some poor-quality “iPhone-at-night type” shots of my WA234 MONO in the “Amplifier Porn” thread, I was asked to provide some insight to the unit. This’ll likely be somewhat episodic/SoC, and may, or may not, turn into an outright review of the unit, but we’ll see on that front … for now this and/or these post(s) will constitute those insights and thoughts etc. So, what exactly is the WA234 MONO? In short, it’s a pair of mono-block (one amp-per-channel) single-ended-triode driven, transformer-coupled amplifiers, operating in pure class-A, and capable of driving both headphones and speakers (up to 8w at 8 ohms), while utilizing 2A3, 300B or 45 type power tubes. To add to that, it’s a capability delivered with elegantly configurable output types/impedances, and delivered in a sumptuous, luxurious, chassis the form, and build, of which compete with the topmost echelons of the audio world. While the aesthetics may not be every one’s particular cup of tea, they are distinctive, rich, ridiculously well finished, luxurious and very … solid. How solid? I had to re-inforce my listening station to install my WA234 MONO. It’s predecessor, the Woo Audio WA5-LE was no lightweight at 70lb. But ... EACH of the two mono-block units that comprise a WA234 set weigh 60lbs. The “big Woos” are a commitment in multiple dimensions. … For me, single-ended triodes are the “holy grail” of tube amplification. I’ll go further there. They’re the holy grail of low-power (<10 watts) amplification for me, period. And, nominally, when it comes to single-ended-triodes … I’m a “300B slut”. While I can fully appreciate the raw resolution and transparency of the 2A3, and the unique (and beguiling) tone of the 45, the 300B gives me most of my desires in both of those camps while delivering an absolutely liquid midrange and an overall sense of space and holography that I’ve not yet found elsewhere. How much of a 300B slut? I keep a set of 300B for photographic “pretties” (Sophia Electric Princess, punched-plate ... see picture below), a pair of Takatsuki’s for general listening, a pair of now-exhausted original WE 300Bs for display, and a set of good/strong original WE 300Bs for serious listening. And I have various others (KR, EML, Sovtek, VA, Svetlana, PSVANE ) for variety and/or other purposes (e.g. amplifier burn-in, comparison, completeness etc.). And I was on the list for new-production WE-300Bs about four seconds after I heard about them. I digress … -- Context: All comments here are based on my “Mark 2” version of the Woo WA234 MONO. This has several internal updates and component upgrades versus the original, but the biggest change is the switch from using 6SN7 series signal/driver tubes to 13EM7. You could reasonably consider me to be a 6SN7 fan. My prior WA5-LE used them. To this point it has been my favorite driver/signal tube, with the possible exception of the 6922 family – specifically as implemented in the Decware Zen Taboo Mk 3 and 4. And, in that incarnation, it has been the fastest, most resolving, drive tube I’ve heard … until the 13EM7 in the WA234 MONO Mk2. But I’m digressing again … -- Time from order to delivery was about 12 weeks. The WA234 MONO package arrives in three boxes. One each for the two amplifier units, and a third containing the stock-tube complement and the output and tube “switching keys” (more about which shortly). Just the packaging for these units, weighs more than some other actual components. I’m fairly sure if any of these units were dropped, the only casualty would be whatever they landed on. Fit and Finish: Fit and finish is nothing short of spectacular. High-end audio gets lambasted, and often rightly so, for excessively costly casework. First looks at the WA234 would tend to promote the same reaction. However, they’re simpler than they look. Essentially, they’re a stack of separate, but identical, plates. This greatly simplifies tooling and reduces cost, since once you can make one of these plates, you can just keep repeating it to finish up the amp. Now, I’m not saying this is “cheap”. They’re lavishly finished and look and feel fantastic. But it is definitely a more cost-effective approach than, say, trying to mill the entire thing out of a single block of aluminum. WA234 MONO Mk2 Details: This amplifier is unique (as far as I’m aware) among headphone amplifiers in a number of ways: First, it’s implemented as a pair of mono-blocks*. In other words, there’s a completely separate PSU, amplifier, attenuator and chassis for each channel (perfect channel separation – any crosstalk isn’t coming from the amplifier). Second, it allows the use of three different types of Single Ended Triodes, selectable via a plug that configures the amplifier for the tube you want to run. Third, you can choose how the output is taken from the tubes (Plate or Cathode output) and, at the same time, elect for either high or low Z outputs. Plate-output yields higher power, Cathode-output gives a better sound. Power output is dependent on whether you’re using Plate Output or Cathode Output, Low or Hi Z and, of course, the impedance of your headphones. To quote the extremes, 300Bs in Plate/Lo-Z into 8 ohms will yield 8 watts, and 45s in Cathode/Lo-Z into 600 ohms will give you 40mW. Configuration and Setup: This is very straight-forward, once you have things unpacked and power cables and interconnects run. First, you choose what sort of power tubes you are going to use. As previously stated you can use 2A3, 300B or 45 series tubes. The unit is provided with “Tube Switching Keys”, which are short metal plugs, configured with tube-like pins, that determine which tube configuration you’re’ going to run. For my first outing with this amplifier I selected the 300B “Tube Switching Key” and plugged it into the “Tube” configuration socket. This is exactly like installing a tube in any “normal” tube amplifier. Next, you choose what output you want. There are several options, including “Speaker” and options for headphones for “Plate” or “Cathode” output at high or low Z (output impedance). I elected to take my first listen with the Focal Utopia and, accordingly, inserted the Cathode Output, Lo-Z “Output Switching Key” into the “Func” configuration socket. Note, you need to power-off the amplifier when switching/installing these keys. And THEN: Pressing the “on” button on each amplifier results in a roughly 20-second start-up/warm-up period. A softly glowing orange ring around each power-button will flash steadily, as some buzz/hum is briefly emitted from the headphones … which rapidly fades away … and then the rings stop flashing, there’s the click of the relays in each amplifier, and the headphones go silent. Absolutely silent. Headphones-not-plugged-in-silent. Black-button-lighting-up-black-on-a-black-background-levels-of-blackness. Utter … … VOID. The first time I fired these babies up, I thought they’d shut down when the relays clicked, it was that quiet. And that’s compared not just to the WA5-LE Mk2, which I already considered to be extremely quiet, but also to the Pro iCAN. I’m used to there being some low-level noise, at full volume, with tube and/or tube-hybrid amplifiers. Residual “noise” was extremely minor with the WA5-LE Mk2, and quieter still with the Pro iCAN. It’s entirely absent with the WA234 MONO. Color me surprised. And quite delighted. This isn’t just the quietest tube amplifier I’ve had my hands on. It’s the quietest headphone amplifier I’ve heard, period. At least with full-size cans (even sensitive, low-impedance units). --- MORE TO FOLLOW ... --- *One quirk of this is that you have to adjust the volume for left and right channels independently. There are independent attenuators for each channel. Fortunately they are stepped (46 positions). Initially you'll be counting the steps as you adjust volume, but with a bit of time spent with the unit it becomes easy enough to eye-ball the positions of the volume indicators. Either way, it's not really a chore and you adapt to it within the first couple or three hours.