Tube Power Amp Reviews

The VTM200 is the first Audio Research power amplifier I've reviewed. It took me 13 years, and ultimately I'm glad I'd put that much mileage on my reviewing odometer before tackling what turned out to be a most difficult assignment.

At $13,990/pair, the 200W VTM200 is the baby of ARC's monoblock line, below the Reference 300 and $40,000 Reference 600 Mk.II. The VTM200 weighs 75 lbs—light enough for one person to carry, but still massive and imposing. I put the amps on Target stands, each of which has a Symposium Acoustics constrained-layer-damped board in place of the usual piece of wood. Then I put three of the large Walker Valid Points and discs under each amp. ARC suggests using a dedicated 15-amp line for each channel or a 20A line for a pair; I used the latter, with a separate line for the preamp and associated front-end equipment.

Introducing the New VTM200 monoblock
A week into the review, a fax arrived from Audio Research explaining the VTM200's circuitry: low-noise, direct-coupled JFETs followed by a single 6N1P tube amplifying stage, then a pair of triode 6L6GC cathode-follower drivers, and finally three pairs of 6550 output tubes. The power supply features 438 joules of energy storage, with screen voltage for the output stage provided by two 6AS7 regulator tubes driven by another 6N1P. If all that means anything to you. To me, it means that the ARC, like my reference Musical Fidelity Nu-Vista 300, is a hybrid. But the Nu-Vista goes the opposite route, using a Nuvistor input tube and solid-state output.

Tightly packed
As with other current products from Audio Research, you have to work for your sonic supper: I had to remove 20 screws from each VTM200 so I could insert the 12 carefully marked tubes into their sockets. The tubes come cradled in styrofoam blocks crammed into spaces between circuit boards and the output transformer. I had to be very careful when pulling the blocks out lest I catch a heatsink and yank a transistor off the board. Transistor? There are a few, including direct-coupled JFETs in the input stage.

Once the tubes were in place, the covers screwed back on, the balanced XLR connectors snapped in, the speakers connected to the very nicely machined, highly torqueable custom 5-way binding posts, and the heavy-duty AC cords plugged in, I was ready to fire up the VTM200s. A two-speed fan whirred almost silently, a relay clicked, and I was almost ready to play music.

Almost? Before listening, I let the amps warm up for a half hour, then checked the bias on the output tubes. ARC makes this easy, via a rear-mounted, seven-position selector switch and LED readout: Select the tube, read the bias, and adjust it if necessary with a small screwdriver. All tubes were in the correct range and remained there for the entire review period.

Work those variables
Standard review procedure means you substitute a new component for your reference. But I had to juggle at least two additional variables so I could listen to Audio Research's $13,990/pair VTM200 hybrid monoblocks, and that made the floor under my feet move more than once during the time I spent with them.

The VTM200's input is balanced only, and while my Ayre K-1x preamplifier offers both balanced and single-ended outputs, I'd previously been able to use it only single-ended, which the designer of the Ayre says doesn't sound nearly as good; besides, there's less gain. I run single-ended Yamamura 6000 interconnect. The only balanced cable I had was so old it was growing hair, and I'd never used it. But it was all I had, and in it went until some newer cables showed up.

So when I put the VTM200s in my system, was I hearing the amplifiers? The preamp finally performing up to its potential? Old cables? Or all three? All three, of course. Nonetheless, I went in confident that, in the end, I'd be able to sort out the variables and get to the heart of what the VTM200 was all about.

First Impressions
I began with two CD-Rs I'd made using the Rockport System III Sirius turntable, and the results were mixed. On the plus side, the ARC VTM200s produced a big, firm, three-dimensional picture. I'd never heard the Sonus Faber Amati Homage loudspeakers sound so rock-solid and well-focused, particularly the "phantom center image": the sensation of a third speaker was unusually tangible, extending from the floor to mid-room height. The presentation had weight, solidity, dimensionality, and presence. Overall, there was greater midbass weight than I was used to with my reference Musical Fidelity Nu-Vista 300 power amp, and a more intense sense of the music breaking free from the speakers. But, according to my notes, bass was "kind of rubbery" and "not in time with the rest of the music."

I found the top end to be brighter and "faster" than I expected from a tube amp, but along with the brightness came an open, airy, and extremely detailed top without etch or sharpness. But it was bright and a trace hard, and along with it came accentuation of tape hiss, surface noise on LPs, and peaky microphones and "digititis" on poorly mastered CDs. These amps were showing no mercy to the recordings or to my ears.

I thought the upper midrange somewhat thin and underdeveloped—surprising for a tube amp—though the upper bass/lower midrange sounded "gorgeous" and rich compared to my reference. But the liquidity, transparency, and musical cohesion my system exhibited with the Hovland HP-100 preamp and the Musical Fidelity Nu-Vista 300 was nowhere to be found. My notes: "antiseptic and somewhat disjointed." Still, I was impressed by the VTM200s' startling dynamic authority and weight, and by the focus and clarity with which they delivered back-of-the-hall detail from familiar recordings. There was impressive dynamic and rhythmic control and superb instrumental focus and three-dimensionality, despite the rubbery bass. But the tonal picture screamed "hi-fi," not "music." The real sonic story wasn't being told, and I was determined to hear it.

It was a week in which I found myself pulling out big, dynamic, closely miked recordings like the Count Basie Big Band's Farmers' Market Barbecue (Analogue Productions APJ 023), a wonderful-sounding LP reissue of a 1982 Pablo original. And for some reason I got into a Bernard Herrmann mood—I dusted off the Mercury Golden Import soundtrack to Vertigo (SR1 75117) and the London Phase 4 of Obsession (SPC21160), both forceful, well-focused LPs. I figured that, while waiting for some highly regarded cables to arrive, instead of forcing myself to listen to the same old references on which I always rely to make comparisons...I'd play. I ended up listening to recordings that showed off the VTM200s' strong spatial and dynamic performance. It was an exciting stretch of listening, but somewhat off-putting.

Cables, Cables, and More Cables
This review drove it home to me big time: Cables are important, and even more important is getting good cable advice from someone who knows and understands the gear you're using.

Jonathan Scull put me in touch with a number of cable manufacturers who were happy to send me samples, and boxes began arriving about a week after I put the amps in the system. First to arrive were the Analysis Plus Oval 9 speaker cables, intended for an upcoming review of an integrated amplifier. I need long speaker cables, and Analysis Plus sent a 20' pair in addition to an 8' pair.

With the long pair in the system, the overall tonal picture improved considerably, though the bass was still out of whack with the rest of the music and I still didn't feel the system was exhibiting the musical cohesiveness and transparency that I've heard from far less expensive assemblages of equipment. But with the Analysis Plus cables I felt that the surprising high-frequency extension the VTM200 exhibited was more of an asset than a liability. The extension remained, but the clinical brightness was somewhat tempered. With the ARCs, I preferred the Analysis Plus Oval 9s to my long-term reference, the Yamamura 6000s.