Woo Audio WA33 Headphone Amplifier and Preamplifier - Silver

Nine Tubes, Two Chassis, One Volume Knob

The WA33 is Woo Audio's flagship, and it arrives as two boxes. One holds the amplifier, the other the power supply, joined by what Woo calls its Internal Coupling Architecture. Separating them keeps the transformer's field away from the signal.

Nine tubes do the work: four 6C45 drivers, four 2A3 power tubes and a 5U4G rectifier. The 2A3 is a directly heated triode from the 1930s, still made today, and it is the reason this amplifier looks and behaves the way it does.

Together they add up to 54 pounds across a chassis 17.5 inches wide, 12 deep and 13 tall with the tubes in place. This listing is the silver finish. Woo covers it with a three-year limited warranty.

It Is Also a Balanced Preamplifier

A front-panel switch decides whether the WA33 drives your headphones or your power amplifier. In preamplifier mode a balanced XLR output pair feeds the rest of the system, and you can select high or low output impedance to suit what is downstream.

On the headphone side there are four sockets. A 4-pin XLR runs True Ribbon mode for ribbon headphones, delivering up to 3.3A of current. A second 4-pin XLR, a 4.4mm Pentaconn and a 6.3mm jack cover everything else, at up to 10 watts per channel into 32 ohms.

Inputs are analog and balanced-first: two XLR pairs and one RCA pair. A second front-panel switch sets high or low impedance for the headphones themselves, so sensitive in-ears and demanding planars both get a sensible match.

Who Is This Amplifier Best For?

• You own hard-to-drive headphones — up to 10 watts per channel into 32 ohms is power most headphone amplifiers cannot approach, so a demanding planar stops sounding like it is being asked for a favour.
• You own ribbon headphones — True Ribbon mode delivers current rather than voltage, up to 3.3A, which is what a ribbon driver actually wants from an amplifier.
• You want one box for headphones and speakers — the balanced preamplifier output means the WA33 runs your power amplifier too, so a single volume control serves both ways of listening.
• Your headphone collection is varied — four output sockets and a high or low impedance switch mean sensitive in-ears and thirsty planars share the same amplifier without adapters.
• You might want the Elite parts later — Woo does not upgrade a Standard into an Elite Edition afterwards, so the choice is made at purchase. If the transformers, wiring and ALPS RK50 volume control matter to you, start with the WA33 Elite Edition instead.

How Does It Connect to Your System?

Connect the power supply chassis to the amplifier chassis first, then your source. Balanced sources take the two XLR input pairs, and a single-ended source takes the RCA pair. Give the tubes room to breathe above and behind.

For headphones, pick the socket that matches your cable and set the impedance switch. To run a power amplifier, switch the output to preamplifier mode and take the balanced XLR outputs to it, choosing high or low impedance to suit.

Pairs Well With

Building around the WA33? Here are some great companions:

• Headphones: This much power deserves the best — see our Headphones.
• DAC: The WA33 takes analog in, so a converter feeds it — see our Digital to Analog Converters.
• Power Amplifier: For the preamplifier output — see our Amplifiers.
• Interconnects: Balanced XLR suits it best — see our Interconnect Cables.

Frequently Asked Questions

What tubes does it use?

Nine in total: four 6C45 drivers, four 2A3 power tubes and one 5U4G rectifier. They ship fitted with the amplifier.

Can I use it as a preamplifier?

Yes. A front-panel switch changes the output from headphones to a balanced XLR preamplifier feed, with selectable high or low output impedance.

Which headphone connections are fitted?

Four: a 4-pin XLR for True Ribbon mode, a second 4-pin XLR balanced, a 4.4mm Pentaconn balanced, and a 6.3mm unbalanced jack.

How much power does it make?

Up to 10 watts per channel into 32 ohms in headphone mode, and up to 3.3A of current in True Ribbon mode.

What comes in the box?

The amplifier and its power supply chassis, the default tube set, and a quick start guide. The AC power cord and audio cables are supplied separately, so plan for those.

How big is it, and what is the warranty?

17.5 by 12 by 13 inches with the tubes fitted, and 54 pounds across both chassis, with a three-year limited warranty.

See It in Action

Woo Audio's own overview of the second-generation WA33 and True Ribbon mode:

GoldenSound reviews the WA33 as both a headphone amplifier and a preamplifier:

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Learn More

Want to learn more about tube amplifiers, headphone matching, or balanced connections? Visit our Learning Center for guides, tips, and expert advice.