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Woo 234 Mono, a very different kind of amplifier

The Woo WA-234 Mono is two amps in one, it's an astonishingly good headphone amp, and it's just as remarkable with speakers!

Steve Guttenberg
Ex-movie theater projectionist Steve Guttenberg has also worked as a high-end audio salesman, and as a record producer. Steve currently reviews audio products for CNET and works as a freelance writer for Stereophile.
Steve Guttenberg
4 min read
The Woo Audio 234 Mono amplifiers Woo Audio

I remember the very first Woo Audio headphone amp I heard five years ago; it was the $520 WA-3, and they still make it. The little amp made a strong impression because it so radically improved the sound of Grado headphones. That amp transformed Grados, gave them more soul, more body, and sweetness. I've reviewed a number of Woo products over the years, but the new WA-234 Mono is a very different beast. First, it is as the name implies, a monophonic design, so you need two amps for stereo. The other big difference is that these tube amps can drive headphones or speakers. Like all Woos, the 234 Monos are made in New York City.

With solid-state amps the sound is unchangeable; it is what it is. A tube amp's sound is highly dependent on the tubes. The 234 Mono can be used with three different types of power tubes, 300B, 2A3, and 45, and each one has its own "flavor." So when you crave a new sound, pop out the tubes, drop in another set, and you're good to go. It takes about two minutes to swap tubes. The 234 Mono is an all-tube design -- no solid-state circuitry is used -- each 234 Mono with the tubes installed measures 8x16x16 inches and weighs 60 pounds. Connectivity options include two RCA inputs, one XLR input, one combination 6.3 mm/XLR headphone jack, and speaker-level connectors.

The 234 Monos' 300B tubes used in this review Steve Guttenberg/CNET

The extraordinary levels of fit and finish of the curvy, machined-aluminum chassis are on par with the world's very best electronics. The steampunk/retro aesthetic perfectly complemented my Abyss AB-1266 headphones, so I used them to start my listening tests.

The headphones' extreme clarity and dynamic punch are state of the art, but the 234 Monos took the AB-1266's sound to a new, higher level. It was remarkably effortless, and I found myself listening at louder levels than usual, precisely because music just sounded better and better the louder I played it. It's like driving a really fast car, you want to see what it can do. Audiophile recordings free of dynamic range compression really came alive over the 234 Monos/AB-1266. High-end headphone sound has never been higher.

With the best recordings I felt like my ears were hearing exactly what the microphones at the recording session were picking up. Stereo imaging wasn't just left/right; the sound came from all around me. Tube amplifiers' bass definition can sometimes sound a little flabby, but the 234 Monos, with either the 300B or 45 power tubes installed produced high-definition, powerful and tightly controlled bass. The tubes communicate the mass of instruments and voices in ways that solid-state devices rarely do. Most folks who buy an amp like this will probably own a few of the world's best headphones, so I tried the 234 Monos with all of my top contenders, including the Hifiman HE-6, which is known to be a beast to drive, but sounded richer and more natural teamed with the 234 Monos than any other amp I've tried.

I like the music on Elvis Costello and the Roots' new CD, "Wise Up Ghost," but the brittle sound left me cold before I heard it over the 234 Monos and my Beyerdynamic T90 headphones. There's so much more going on in the sound, so I heard more of the interplay between the Roots and Costello. Stuff like the kinetic energy on "(She Might Be A) Grenade" eluded my attention before. That's one of the things that I love about the best gear: you hear more of what's locked into recordings; musical qualities that were always there, just not noticed before. My Sennheiser HD 700 headphones were transformed by the 234 Monos; instruments and voices took on a three-dimensional quality that made the music seem more alive. Every headphone's sound quality was enhanced with the Woo.

For speaker testing I used a pair of Zu Druid Vs (review in the works). The sound was big and bold, with oodles of detail, a massive soundstage, and beautifully extended treble. Location cues on the better live recordings placed each instrument and voice in its own space, so they were more "separated" and distinct entities in the mix. Bass instruments' dynamic shadings and tone took on palpably realistic body. The Zu speakers played loud enough for me with the 234 Monos' 8 watts per channel, and most of the larger, ultra-efficient Klipsch speakers will do the same. So sure, the 234 Monos are fussy about speakers, but when the amps are well-matched to speakers the sound is on a different plane than most of the gear I've written about on this blog. Living with the 234 Monos for 12 days was a lot of fun, I was sorry to see them go.

The WA-234 Mono's retail price is $15,900 per pair. They're built by hand, so there's usually a waiting list for Woo customers.