The US$10,000 WA-234 headphone amplifier
By Vincent Rice
October 27, 2011
Actually it's two US$5,000 (GBP3,100/EUR3,500) amps because these rather spectacular looking beasts are mono-blocks. They are two completely separate, but matched, mono amplifiers. Now it's no secret that the world of audiophile hi-fi sound systems can be a place of strange voodoo and esoterica - where the Law of Diminishing Returns becomes a way of life for deluded males of a certain age (never women it seems) but let's check our cynicism at the door for the moment. There is something interesting going on here and it may just turn out that at $10,000 for the pair, these amps are a (relative) bargain.
Woo Audio has been hand-building high quality tube amplifiers in New York since 2004. Tube amps are prized by hi-fi aficionados for their warm, enveloping sound and the sweetest circuit type of all, un-coincidentally the simplest, is called a single-ended triode (SET), and it is just this type that Woo specialize in. The downside with amps of this nature is that they are quite low powered, so Woo Audio has been producing primarily headphone amplifiers where this isn't a concern. Paradoxically, because a simple circuit means that tweaks and variations are easier to implement, using the very finest individual components possible makes these amplifiers potentially more expensive than a more complex, but mass produced, design. While many of Woo Audio's products are in the US$500 - $1500 range, with the WA234 they have pulled out all the stops and produced a SET amplifier without compromise.
The first decision was to make the amplifier a pair of mono-blocks. That is, a completely separate amplifier and power supply for each side of the stereo signal. This is done to eliminate crosstalk between the channels and maintain a rock-solid stereo image. Secondly, the circuit is completely hand-wired using the shortest cable path possible and the highest quality components, including a stepped resistor volume control rather than a potentiometer. Transformers and filter coils are wound by hand on the premises for the specific circuit requirements - hi-fi (and guitar) amp experts will tell you that the output transformer is where a great deal of the magic happens in a tube amp. The final piece of the puzzle is the massive machined chassis that reduces vibration and stray magnetic fields affecting the tubes mounted on the top surface.
All that would be fine and dandy but the WA234 has a unique additional feature. While tube amp designs can be very simple and pure, that does mean that they are optimized for a particular tube, a particular output impedance and a particular power output. Change any of those requirements and the circuit needs to change. To allow flexibility in that regard the 234 is supplied with a set of physical plug-in "keys" that actually modify the circuit configuration for different uses. One key socket allows the circuit to be optimized for 300B, 2A3, or 45 tubes (that all sound different by the way) and another socket accepts keys to change the output impedance for different headphone types, or indeed allow loudspeakers to be driven from the output. A maximum of 8 watts a side won't fill a nightclub but with efficient speakers it will fill a typical living room.
While Jack Wu's eponymous company has only been trading for seven years, it was formed to exploit the 40 years of amp design experience of his father, Wei, and the engineering experience of his brother, Zhi Dong. The company already has a great reputation in the audiophile community and press for creating very high quality amps at reasonable cost. The exemplary construction and hand-wired circuitry of this no-compromise flagship product suggest that rather than being an over-priced toy for the bored and wealthy, it might well be a genuine bargain for the serious audiophile.
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