Audio Research VT80SE Power Amplifier

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Equipment report
Tubed power amplifiers
Audio Research VT80SE
Audio Research VT80SE Power Amplifier

Audio Research Corporation, the company that almost single-handedly created high-end audio electronics, not to mention preserved the vacuum tube as an amplification device, recently revised its basic line. As it has become the foundation for ARC’s more expensive gear, it is appropriately named the Foundation Series and comprises the LS28 linestage (a 2017 Golden Ear Award recipient), DAC9 DAC, PH9 phono preamp, and VT80SE power amplifier. Each of the first three pieces of Foundation Series equipment is priced at $7500; the much larger and heavier VT80SE is $8900. Starting out as the VT80, after a short production run the amp was upgraded to the VT80SE, of which the review unit was the first production sample. The only difference between the VT80 and VT80SE is that the SE’s tubes are more expensive Tung-Sol KT150s, and the price of the amp has therefore increased. (Audio Research uses the upgraded KT150s in all its amplifiers.)

All Foundation Series equipment shares similar stylistic features, making them a recognizable family, which must be helpful at hi-fi shows. Although it’s the least expensive in Audio Research’s line, the Foundation line could hardly be called budget gear. And it doesn’t try to be, offering a rich feature set that competes with almost anything on the market, and sound quality that compares favorably with anything I’ve heard, though I deliberately avoid most of the stratospherically priced gear out there—my way of preventing severe damage to my bank account. All Foundation Series components have similarly styled front panels, along with Audio Research’s signature rack handles and black-glass windows inset into brushed aluminum (black or silver) faceplates. While the other Foundation Series components make good use of the black-glass windows to display lots of operational information, the VT80SE’s faceplate is strictly for style; the only information displayed there is a pilot light telling you if the amplifier is turned on. Otherwise, the VT80SE is a large, low, open-chassis amplifier with a typical layout: transformers and output tubes in the rear, input tubes in the center, input and output jacks on the vertical rear panel. Of the many Audio Research amplifiers I’ve seen, very few have equaled the VT80SE’s attractiveness—accolades to the ARC design team. VT80SEs sold outside North America get a tube cage, which covers both tubes and transformers. (The cage is a $500 option on North American units, but necessary if anyone in your household has tiny fingers or noses that need to be protected from hot tubes.)

The original VT80 incorporated one of the biggest tech advances in Audio Research history, an automatic biasing system aimed at reducing the routine annoying maintenance required when you use a tube amplifier—prompting a rousing hooray from me! It’s the first automatic bias system ever used in an Audio Research amplifier, making replacing the output tubes just a matter of plugging new ones into the sockets. The automatic bias circuit also adds flexibility to your amplifier; in addition to KT120 and KT150 tubes, it lets you use 6550, KT88, or KT90 output tubes. If you have a stash of compatible octal-based bottles, you will probably want to see how the VT80SE sounds with different types. However, I suspect most of us won’t ever avail ourselves of that feature. I think the most useful aspect of the automatic bias circuit is to adjust the bias to let each tube perform at its best throughout its life span, even when it starts to age.

Speaking of life spans, in the VT80SE the KT150s should last 3000 hours (versus 2000 hours for the KT120 tubes in the VT80)—a long time, depending on how you run the amplifier. But unlike some solid-state amplifiers, you don’t want to leave the unit on continuously. If you use the amplifier two hours a day, five days a week the tubes should last six years. The only change to the SE version is the tube upgrade; if you decide to upgrade the tubes yourself, a new set of KT150s will set you back $1275. Other than longer tube life, no other specifications have changed.

To track how long the tubes have been in use there is a tube-life meter, located on the rear panel next to the IEC jack for the power cord. The meter’s placement makes it rather challenging to read, but it’s not something you need to check frequently, thanks to the auto bias circuit.

Tubes eventually wear out, so when it’s time to replace them, keep this information from the VT80SE press release in mind: “It is important to mention that the KT150 tubes supplied by Audio Research for all of our products are specially produced to our high standards, are tested and measured for quality control and assurance, and are burned in for 48 hours. Then using our Certified Matched process, they are hand matched in sets with tolerances 10x tighter than standard off-the-shelf tubes, thus ensuring the finest audio quality possible.”

The VT80SE has no remote control, but since all a remote would do is turn the unit on or off, there’s no real reason for it. If remote turn-on/off is important to you, you can always use the 12-volt remote turn on/off connections. Many preamps, including the VT80SE’s Foundation Series companion, the LS28, have the necessary 12-volt output jacks that will turn the VT80SE on or off when you turn the linestage on or off with the preamp’s remote control.

When an output tube fails, it usually becomes noisy or just stops working. Occasionally, however, it will arc in a shower of sparks accompanied by loud noises, and sometimes will even destroy a nearby resistor in the circuit. To prevent such a catastrophic failure, each of the VT80SE’s output tubes has its own fuse, which blows if the tube blows, protecting the rest of the amplifier. The fuses are located on the bottom of the circuit board near the tube they protect, and aren’t externally accessible. That means you must remove the bottom panel of the amplifier to replace a fuse. This happens very rarely, fortunately. If you want to try KT88 and KT90 tubes you must purchase them from another vendor, preferably in a matched quad set.

The driver tubes are two of Audio Research’s favorite 6H30 triodes (one per channel), each equipped with two damping rings around the top of the glass envelope. Life expectancy of the 6H30 tubes is 4000 hours. Unfortunately, the tube timer can only show the time on either the output tubes or the low-level tubes, not both—so you will have to track wear on the 6H30s separately. Like most Audio Research electronics, input circuitry is really a hybrid design, with triode-like JFETs as well as tubes amplifying incoming signals.

For those who think tube amplifiers must be noisy, the VT80SE has a 112dB signal-to-noise ratio—quieter than many solid-state amplifiers. It uses the same output transformers as Audio Research’s Reference 75SE amplifier, and is rated at the same 75 watts/channel output power, although the Reference 75SE accepts only KT150 output tubes and uses its front panel meters to set bias voltage—which isn’t difficult, but isn’t automatic. I suspect some users will enjoy the Reference 75 SE’s hands-on manual bias adjustment.

On the rear panel, there’s an IEC socket for connecting a power cord. Note that it’s a 20-amp connector, so your collection of 15-amp power cords won’t work unless you use an adapter. Why does Audio Research use a 20-amp connector? Dave Gordon, brand ambassador, told me: “The 20A IEC connector makes a tighter connection than the 15A IEC. We also spent a fair amount of time comparing 20A power cords, and we think the 20A cord sounds better.”

The rear panel has both balanced and unbalanced signal connectors, along with a switch to select one or the other. The amplifier’s circuitry is balanced, so the balanced input should sound better. The VT80SE sits on standard Audio Research feet, which absorb vibration and don’t make rings on your furniture. There’s also a switch that turns the amplifier off after it’s not used for two hours. (See the next section for some comments on that feature.) Finally, there are gold-plated binding posts for connecting four-ohm or eight-ohm speakers.

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