September 1999

Audio Research VT50 Amplifier

by Todd Warnke

Review at a Glance Sound Overall power and bass response that belie its output rating and tubed circuitry; midrange and treble are "precise," not round or sweet in a traditional tube-like manner. Features Balanced and single-ended inputs; 4-, 8- and 16-ohm outputs; can use 6550 (supplied), KT88, and KT90 output tubes. Use Todd wishes the tubes were plein aire -- visible to inquiring eyes. Value Well designed and "built like the proverbial tank"; perhaps the ideal amp for someone who wants a little of the fun of tubes without their fuss and all of their sonic traits.

Biasing

The grand old audio companies pay a constant price for their success. First, having set the standard, their products become a common target, and so those designs are often portrayed as old-fashioned and outdated. In short, whippersnappers pose the non sequitur, "If you’re in the old guard, how can you be in the vanguard?" And second, it becomes very easy for the audio-buying public to make a mental slip and credit current success to past reputation and entrenched position. I know I’ve been guilty of this last transgression, and to come clean, I even carried a slight bit of that bias into this review. But as Robin my long-suffering wife can attest, on occasion I can admit when I’m wrong.

All right, in one regard concerning the Audio Research VT50 the whippersnappers may have a point because the VT50 is neither bleeding-edge design, nor is it a trendy, trailing-edge, 300B or single-ended design. Instead, the VT50 is a ruggedly built, highly refined and superbly engineered amplifier. In fact, it demonstrates a level of engineering that may only be possible by the old guard, those companies that have years of field experience to call on, who have put a design out, lived with it and then upgraded it over the years, and who have an established, active customer base ready to provide feedback, and not just of the negative type. You gotta admit that ARC fits this profile.

Describing

The basic circuit of the VT50 is the long-lived ARC ultralinear, partial-cathode-coupled design. TheVT50/100/200 series, which debuted about four years or so ago, saw the addition of FETs to the traditional circuit, employed as a constant current source. According to ARC, this allows for greater linearity, most especially when using the single-ended inputs (the design is both balanced and dual mono from the power supply forward). Other changes in layout and design allowed for better heat dissipation, with a payoff in greater reliability and longer life. Energy storage was also increased, with the VT50 boasting 354 joules worth.

The VT series also sports parts upgrades, primarily in the extensive use of InfiniCaps and upgraded output transformers. The detachable power cord, with an unassuming look, was also specially selected, and it does indeed offer superb sound. Other parts changes were more luck than design. The supplied 6922 tubes, sourced from Russia, use a pure nickel anode. This change was due more to raw-materials shortages in Mother Russia than an engineering choice, but regardless, the result is a better-sounding tube. Finally, all tubes, not just the power tubes, are graded and matched.

When you first open the VT50’s box -- actually, two boxes as the amp comes double-boxed for its protection -- and using the supplied screwdriver, open the lid of the amp, you find the foam package holding all the tubes (a matched pair of Svetlana 6550 power tubes and a pair of Sovtek 6922 small signal tubes per side), each of which has been marked with an identifying letter and number which corresponds to a location on the circuit board. So following the supplied directions restores the amp to the exact configuration it was in when it was listened to at the factory. Like I said, the VT50 offers a degree of design, engineering and care that can only result from years of experience and listening to thousands of customers.

As for the amp itself, it’s built like the proverbial tank. The quarter-inch-thick faceplate comes in either silver or black, in the center of which are the power switch and the power indicator light. Around back the VT50 offers both balanced and single-ended inputs (the supplied shorting plugs pop into the XLR inputs should you opt to use the single-ended inputs). The binding posts, with 4-, 8- and 16-ohm posts per side, are sturdy and easily secured by hand. Overall, the physical layout gets a solid A, but I have do have one quibble. One reason I love tubes is that wonderful glow. But the VT50 hides the tubes behind the faceplate and under the perforated lid. From another perspective, the lid, far more than a traditional cage, keeps kids and pets safe, and so is a good thing. But still, with those valves hidden, I miss that strange look friends flash when they see the glow in the listening room.

Playing

Of course, the real issue is not how it looks, but how it sounds. And how it sounds is, in a phrase, 100% competent.

Whoa, that gave me flash. Ever have your wife innocently ask, "Which hair style makes my face look less fat?" The answer, regardless of how true or in what spirit it’s offered, will surely be quoted in the divorce papers. In like manner, calling the VT50 100% competent will raise some eyebrows, even if it is intended as a high compliment. So let’s try this from another direction.

The VT50, like a precision tool, takes little notice of what its driving; it just goes about the job of delivering power to the speakers. Admittedly, my speaker reference, the Merlin VSM-SE, is an easy load. Bobby Palkovich of Merlin, 100% correctly in my mind, designs for good sensitivity and smooth impedance, allowing an amp to sound its best. But even when used with other, more difficult loads (the Greybeard KB/2/1, with a minimum 6-ohm impedance and 87dB sensitivity, as well as a brief audition with a Thiel CS1.5, 86dB efficient but a 3-ohm minimum load), the VT50 was never winded. In short, inside fairly wide limits, the VT50 just goes about its job and let’s you worry about the rest of the system.

But this is not to say that the VT50 leaves no sonic impression of its own. Rather, that in doing its job, it is even-handed and very predictable. And from that view, the first thing that struck me about the sound of the VT50 was its bass. While just short of seismic, it is deep, very quick and far more powerful than the specs should allow. It is also not your father’s tube bass. Fat? Like Kate Moss. Slow? Like Michael Johnson. If anything, the bass in the VT50 is solid state and not tubed.

Mids are 100% precise as well. Pop in a disc like the Reference Recordings Bruckner Eighth [RR-81CD], and each and every instrument occupies its own textural and sonic space. The subtle differences between players in a string section are distinguishable and yet not pushed to the point that the ensemble feel falls apart. The mix between string and body on guitar work, for another example, was explicit, but obviously emanating from a single instrument.

Treble performance was equally skilled. The M•A recording Sous Les Voûtes, Le Serpent… [M•A Recordings M048A] features incredible percussion, and unless an amp can get it just right, the sound will either be overemphasized and hence too aggressive, or rolled and too laid-back. The VT50 walks that thin line with perfect balance: full of light, but not bright; able to cut through the sonic fabric, but not too sharp for the ear.

Dynamic contrasts, on both the micro and macro level, were precisely ordered. As for power, ARC specs the VT50 at 45Wpc. With the standard disclaimers in place (my room, my speakers and gear, listening to music I like) those are some big-ass watts. Not once, even with the full bass thump of Me’Shell Ndegeocello’s Peace Beyond Passion [Maverick 9 46033-2] putting out mid-90 SPL forces, did I hear a clip, cry or crack. This is power like that in a 3-series BMW. It’s compact, smooth, quick, and dynamic, capable in every way except for those who are impressed by big numbers on a piece of paper.

The picture the VT50 re-creates is, as befits a tube amp, wide, deep and easy to listen to. While unable to match the stage size of the Conrad-Johnson MF2500 I reviewed recently (and I think I shall never hear an amp with a stage like that again, so remarkable was the size of C-J’s stage), it was nonetheless a well laid out view of the recording. It also provided a view with excellent clarity. Details toward the rear of the stage, whether percussion on a classical recording, background singers on a rock disc or those odd sounds that Bill Laswell puts here and there on his recordings, were distinct and individual.

As for that traditional tube sound, I was talking with a fellow audiogeek several months ago and when I mentioned that I had the VT50 in for review he commented how his tube buds point to the 6550 power tube as proof that you can make a solid-state tube. To a large degree, his friends are right. Rather than romance, the 6550 delivers clarity. And in the place of euphony, it serves up top-to-bottom control. The VT50 certainly maximizes those inherent 6550 qualities, with the result being the 100% competent and 100% reliable amp I referred to earlier.

Comparing

The Blue Circle BC6 has been my long-term reference in its general price range. At $3700, it is quite a natural competitor for the VT50, even if it is of considerably different design. With 25 single-ended, class-A, solid-state watts per channel, it sounds more powerful than its specs suggest, and is smoother than the typical silicon-based amp. Where it really excels is in communicating the emotional content of recordings. It does this not by highlighting some sonic aspects while obscuring others, but rather by accurately reproducing those subtle details of music-making that let you feel the musician on the other side of the recording chain. Still, compared to other amps, its deep bass extension is good but slightly less powerful than the best. This may be a factor of its modest power rating. Overall, and in contrast to the output stage, the BC6 sounds more like a superb and fairly neutral tube amp.

On the other hand, and also in contrast to the thermionic devices at its heart, the VT50 has a near solid-state sound. Placed in reasonable surroundings, its degree of bass control and extension will shock you. The rest of the tonal palette is a very slight bit cool, adding to the solid-state analogy. But its tubed soul wins out in the end. The VT50 stages like a tube-based amp, and the grainless window it offers only happens when the sand in an amp is used to make a glass envelope and not output devices. The BC6 does get more of the emotion in a recording, but even though it is only slightly warm, when compared to the VT50, it departs from absolute neutrality a skoosh more, albeit on the other side of the fulcrum point. The two amps offer contrasting views, and which is your choice is indeed a highly personal matter, as well as one of system matching.

For those who opt for the VT50, the good news is that you can customize the sound a bit. Besides 6550s, you can drop in KT88s or KT90s. By the way, I don’t consider it cheating to roll power tubes in a review simply because the set the amp comes with will wear out, and when it does you get to roll ‘em yourself at home. With this in mind, I ran several sets of tubes through the VT50. The ARC circuit is so revealing that tube games have a great payoff, and yet the circuit is also so stable that the amp sounds good with a wide variety of tubes, not just one make or model.

To my ears the Sovtek KT88 offered the best balance of 6550-like extension, control and clarity, with just a bit of the traditional tube harmonic richness and body. Others have found that the EI KT90 works superbly in the VT50 as well. I liked it too, but I preferred both the Sovtek and stock Svetlanas by a small margin. This flexibility gives the ARC VT50 a significant leg up on any and all solid-state competitors, while the superb engineering and damn-near-invisible circuit design gives it a leg up on nearly all its tube-based competition.

Concluding

Frankly, I’m surprised at the quality built into the VT50. This really is engineering and build quality that impresses. An example. I had two VT50s over the review period. The first broke in well and everything was progressing nicely until, in the middle of a quiet listening session, one of the bias-control resistors literally blew apart. The bang was quite loud and accompanied by a flash and smoke, and yet everything shut down cleanly. There was no damage to any ancillary equipment; in fact, except for the fuse and the tube, there was no other damage to amp. The issue was obviously a faulty resistor and not ARC’s doing, but the superb engineering confined the problem and saved my gear.

Is this reason enough to buy an amp? No, but it sure instills confidence. And in the final count, even though I found the VT50 to sit just a hairsbreadth to the lean side of the tonal continuum, I am mightily impressed by the overall sound quality of the VT50, which is a reason to buy the little ARC. Neutral in octave-to-octave balance, possessed of clarity and superb staging, dynamic, offering fantastic bass and sounding far more powerful than 45 watts should, the VT50 is clearly an amp to build a system around.

...Todd Warnke
todd@soundstage.com

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