However familiar a brand becomes, you should never grow complacent about it or discount its potential for surprises. As all of us think we know a lot more than we actually do, we tend to presume what a new component will sound like, based on previous experience or prejudices. I’ve personally owned, auditioned, or reviewed at least a couple of dozen models from Audio Research over the years, so I thought I knew what I would hear—but the VT50 caught me with my guard down. And I’m not complaining. What we’re talking about could be one of those future classics; it’s certainly one of the company’s best- kept secrets.
Confusion preceded epiphany because I couldn’t figure out why or how Audio Research went away from its numbering system. The VT50 costs more than the VT60, the latter remaining Audio Re search’s entry- level stereo power amp despite producing slightly more wattage. However, the VT50 shares more with costlier models in the range than it does with the sweet if prosaic 60. Billed as one of the least expensive of the latest-generation VT series of vacuum-tube power amplifiers, the VT50 is rated at 45 watts per channel from 30 Hz to 15 kHz, but its “actual power at clipping” is 50 watts per channel, hence the model nomenclature. But why does it come in above the VT60? Because it’s fully balanced and it’s more, uh, sophisticated.
Because the VT50 is based on the same circuit design as the VT 100 and VT200, it uses a true dual-mono circuit layout all the way back to its very large power transformer; this certainly distances the VT50 from the less costly, more powerful VT60. The hefty power transformer is mounted at the front, centrally, behind the faceplate and on/off switch, but the amp’s overall weight of 41 pounds is pretty evenly distributed because the separate output transformers are fit ted to the back.
Inside, mounted horizontally in what now appears to be Audio Re search’s favorite location, are two matched pairs of 6550C output tubes, one pair per channel, with four 6922 twin triodes used as input and driver tubes, two each per channel. Constant-current-source technology found in the Reference Series maintains output-stage balance and head room under dynamic music conditions. The \7T50’s distributed power supplies yield a total energy storage of 354 joules, nearly double that of the CA50 integrated amplifier.
Unlike the plug-ugly VT60, the VT50 is luxuriously appointed and unmistakably an Audio Re search amplifier. The chassis design and dimensions are a not-too-large 19x7x15 inches (not counting the handles, which stick out a further 1½ inches). But the first surprise for me was the color. I don’t know about other Audio Research fans, but I’ve always been torn between the classic, natural-metal finish with black legends and the classier black with white legends. Now there’s a new finish on the block, simply called “gray” in Audio Research parlance but closer to titanium. It’s the color worn by the review sample, and it’s simply gorgeous, making the VT50 look like it costs a whole lot more than $2,995. Be cause this color is available throughout the line, my dream of a Reference 1 preamp and a pair of Reference 600 monoblocks has been altered slightly. Purists, of course, should ignore this option and stick with the original hue, lest they suffer an identity crisis.
As for the rest, it’s typical Audio Research through and through, with only a simple rocker switch on the front for power on/off and a small green LED to indicate the former state. The rear panel contains meaty, all-metal, gold-plated, multi-way output terminals with a choice of 4-, 8-, and 16-ohm taps, which don’t like banana plugs but are perfect for spade connections. The afore mentioned balanced inputs are accessed with XLR connectors; gold-plated single- ended inputs are provided, too, but more about that anon. Also on the back panel is an IEC-type AC power socket—Audio Re search supplies a good 14-gauge, three-core cable—and a user-replaceable AC mains fuse. Setup involves simply fitting the tubes (their bias is set at the factory). Warm-up from cold to optimum operating tempera ture seems to take a mere 15 or 20 minutes.
While some would deem it heresy to use a solid-state preamp with an all-tube power amp, I did use Krell’s sublime KRC-3 to test single-ended versus balanced. The latter won out, even though my technically astute betters tell me that the difference should be apparent only with long cable runs. Rubbish:
With only 3 feet of Transparent MusicLink Super interconnects (and with playback levels matched using a digital SPL meter), balanced operation sounded clearly more re fined, more coherent, and more precise.
And refinement is what it’s all about; after all, this isn’t the amp to turn to if you’re a horsepower junkie. Not only will it not rock the rafters, its bottom registers aren’t exactly a sonic analogy for earth-moving equipment. On the other hand, neither is it a lightweight. Rather, it’s a series of blissful contradictions, just like its position in the Audio Research hierarchy.
Quite clearly, the VT5O is aimed at customers with moderate or highly sensitive speakers. While I would never accuse Audio Research of marketing cynicism (despite those years when the company drove its users crazy with innumerable upgrades that endowed their models with suffixes more typical of computer software), it strikes me that the VT5O is perfect for exploiting the sort of speakers designed to coddle owners of single-ended triode amplifiers. The single-ended triode craze has resulted in a flood of speakers boasting very high sensitivities, some horns delivering as much as 96 or 98 dB sound pressure level (SPL) for a single watt input, and they have but one virtue: the ability to work with stupid little amplifiers producing naught but 3, 5, or 7 watts. While the VT50 isn’t in that anorexic category, neither is it suffering a surfeit of juice.
Far from feeling that it is restricted by the number of speakers that could fully exploit it, I prefer to think of the power limitations as simply narrowing the field of possibilities to high-sensitivity dynamics or most electrostatics. And this is a good thing, be cause it makes life simpler for the easily be wildered, confidence-lacking consumer. (To quote the great Gilbert Briggs, “The customer confused buys nothing.”) Ditto the harried reviewer. I soon learned that my time would best be served using Quad electrostatics, both the original and the ESL63, the Rogers LS3/5A (to best test the 16-ohm tap), the Wilson WATT/Puppy V.1, and New Audio Frontiers’ high-sensitivity transmission-line speaker, the Reference One S; conversely, I haven’t owned any real amplifier-eaters since I said farewell to the Apogee Divas.
I would have used the LS3/5As anyway, but what they did was emphasize the need to pay attention to the choice of impedances. While it’s well known that an amplifier’s electrical behavior—especially its power transfer—will be affected by impedance mismatches, some might discount the degree of sonic degradation resulting from as simple a mistake as connecting an 8-ohm speaker to a 4-ohm tap (or vice versa). The differences are audible. I tried speakers requiring each impedance as well as mixing them up (for example, a 15-ohm speaker on the 4-ohm tap) and soon learned that (1) the matching of nominal impedance to the correct tap is the safest and easiest way out, but (2) that Audio Research is right to state in its instruction manual the following: “In the case of speaker systems with significant variations in impedance throughout the frequency spectrum, such as most electro static types, the best impedance match should be determined by listening.” If in doubt, consult your dealer.
In the end, I settled on the Krell KAV 300cd CD player fed into the Krell KRC-3 preamp for balanced listening, with the Krell KAV-300cd driving the Jadis DPL2 preamp in single-ended mode. Most of the time, I used the old Quads and the New Audio Frontiers speakers. Whatever the system, the following emerged with repeatability and consistency.
As I said before, the VT50 is no brute. Neither, though, did I force it into clipping, because I was able to keep the volume control between 10 o’clock and 1 o’clock and still hear 85 dB SPL at 2 meters. What struck me first was the transparency, which in turn lets you hear subtle, low-level de tails. More delicious still was the openness and sense of air and space. If you really love the effect of your speakers disappearing (as much a part of the speaker’s design and positioning as anything else), the VT50 will help to achieve this. It consistently delivered a wide and deep soundstage that—and here’s the neat thing—remained constant regardless of the playback levels.
This was the VT50s slickest trick, its ability to sound commanding and in full control whether playing at background or blasting out at its max. Given the remote control facility of the Krell KRC-3, I was able to stay in the listening seat with eyes closed, gradually increasing the volume, in stead of hopping out of the chair each time. It was this facility that enabled me to detect another aspect of the VT50’s consistency.
Not only did the soundstage retain its dimensions regardless of level, so did the bass quantity and quality.
Quantity and quality are the key words here, because the VT50 trades a little of the former to provide the latter. As one known for not craving overwhelming bass, I barely noticed the sacrifice. Okay, so the “Theme from Shaft” lost some of its impact around the 2-minute mark, and I quickly abandoned attempts at rattling the windows with “Little Green Bag,” but so what? What remained was tight, con trolled, free of lumps and overhang—just the way I like it.
But it’s the mid-band that makes me want to hang onto the VT50. It possesses clarity, just the right amount of warmth without screaming “here be tubes,” and (almost) enough richness to counter any sense of loss down below. Whoever did the final tuning or “voicing” on this must love vocalists of the Sinatra/Dino/Nat “King” Cole variety, because this sucker could wear a purple Capitol badge and I wouldn’t have raised an eyebrow.
So, those of you who lust not for maxi mum SPLs and who can live without Godzilla-footfall bass, here at last is a tube amplifier that fills the gap between the big mutha push-pull designs on one hand and the severely power-limited single-ended triodes on the other. It’s a wholly satisfying way of driving high-sensitivity loudspeakers without resorting to the mismatches of either too much or too little power. And it just loves electrostatics. The VT50 is, by my reckoning, a way of having your cake and eating it, too— with no calories to fret about whatsoever.
Adapted from 1998 Audio magazine article. Classic Audio and Audio Engineering magazine issues are available for free download at the Internet Archive (archive.org, aka The Wayback Machine)