Woo WES Balanced Electrostatic Headphone Amplifier

Built for One Kind of Headphone, and Built All the Way

Electrostatic headphones need a special amplifier. They run on hundreds of volts, not watts, and no ordinary headphone amp can drive them. The Woo Audio WES is that special amplifier. It is a fully balanced, all-tube, Class-A design made for 5-pin, 580-volt Pro Bias electrostatics from Stax, HiFiMan, Dan Clark Audio and others.

It comes as two boxes. The lower chassis is the power supply. The upper chassis holds the audio circuit. Keeping them apart keeps the power supply's hum and heat away from the signal. Each box weighs about 20 pounds, so this is a piece of furniture, not a desk toy.

Twelve tubes do the work. Four EL34 power tubes and four 6SL7 drivers handle the balanced signal. Two 12AU7 tubes act as a phase splitter for the single-ended RCA input. Two 5AR4 rectifiers sit in the power supply box. The circuit is self-biasing, so tubes can be swapped without test gear.

What the Second Generation Changed

Woo updated the WES in April 2017. The second generation uses a matched set of four output chokes wound with single-crystal copper wire. Woo says the change improves clarity, space and dynamic range. V-Cap ODAM output capacitors are part of the build as well.

Everything else that made the first WES a reference stays. The main audio path is wired point to point by hand. A four-channel balanced volume control sets level. Two 5-pin outputs let two pairs of electrostatics play at once. Two balanced XLR inputs and one RCA input feed it.

Two power switches on the front are a nice touch. Turn on one and the tube heaters warm up in standby. Turn on both and the amp runs at full power. That spares the tubes the shock of a cold start. The amp is built in New York and runs on 100 to 220 volts without a converter.

What Reviewers Are Saying

Tom Martin reviewed the WES for Playback, the digital magazine of The Absolute Sound, on March 14, 2012. He called it "a seriously revealing headphone amplifier" and found that "the noise floor of the WES is impressively low."

Tyll Hertsens of InnerFidelity paired it with the Stax SR-009 in December 2012. He recommended the WES for "all those who love the lush sound of tubes," and found the pairing a strong match for chamber music and jazz.

Martin also noted that the WES does not add warmth. Listeners who want a glow from their tubes, he suggested, may prefer another amp.

Who Is This Amplifier Best For?

• You own Stax or other Pro Bias electrostatics — the WES is one of the few amplifiers built from the ground up to drive them properly
• You want a fully balanced chain — two XLR inputs and a balanced circuit from input to output keep a balanced DAC balanced all the way
• You want to roll tubes — the self-biasing design and PTFE sockets make swapping EL34s and 6SL7s simple
• You listen with a partner — two 5-pin outputs drive two pairs of electrostatics at the same time
• You own dynamic or planar headphones — the WES drives electrostatics only, so a conventional amp from our headphone amplifiers is the right choice

How Does It Connect to Your System?

Connect a balanced DAC or preamp to one of the two XLR inputs, or any line-level source to the RCA input. Plug your electrostatic headphones into either 5-pin output on the front. Connect the power supply to the amplifier with the supplied umbilical cable.

Switch on the heaters first and give the tubes a few minutes. Then switch on the main supply. Leave room above and around both chassis, because twelve tubes make real heat.

Pairs Well With

Building your system? Here are some great companions for the Woo WES:

• DAC: A balanced source makes the most of the XLR inputs — see our Digital-to-Analog Converters
• Interconnects: Balanced XLR or RCA, depending on your source — see our Interconnect Cables
• Audio Rack: Two 20-pound chassis need a solid, ventilated home — see our Audio Racks
• Power Cable: The AC cord is not included, so choose a good one — see our Power Cables

Frequently Asked Questions

Which headphones does it drive?

Electrostatic headphones with a 5-pin, 580-volt Pro Bias connector. That covers current Stax models and Pro Bias designs from HiFiMan, Dan Clark Audio and others. It will not drive dynamic or planar headphones.

What tubes does it use?

Four EL34 power tubes, four 6SL7 drivers, two 12AU7 phase splitters and two 5AR4 rectifiers. All sit in PTFE sockets, and the circuit self-biases with compatible tubes.

Why two boxes?

The power supply lives in its own chassis so its transformer and rectifiers stay away from the audio circuit. That lowers noise and spreads the heat.

Can I use a single-ended source?

Yes. The RCA input runs through a pair of 12AU7 tubes that split the signal for the balanced circuit.

What changed in Generation 2?

Matched output chokes wound with single-crystal copper wire, introduced in April 2017. Woo says they improve clarity, soundstage and dynamic range.

What's the warranty?

Woo Audio covers the WES with a three-year limited warranty for the original purchaser. The stock tubes are covered for 30 days.

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Learn More

Want to learn more about electrostatic headphones, tube amplifiers, or building a reference headphone system? Visit our Learning Center for guides, tips, and expert advice.