Tube Preamp Reviews

Over the years, listening to audio systems and trying to come up with descriptions of the sounds and the contributions of various components, it has become increasingly clear to me that this critical enterprise is quite different from, and is in some ways antithetical to, listening to music for pleasure. In "critical" listening we're always trying to analyze the sound, paying attention to details, picking apart different aspects of the sound-reproduction process. Listening for pleasure is much more holistic, more dependent on the overall effect. In this type of listening, details of musical reproduction become important only when they draw undue attention to themselves, like a part of the frequency range that's overemphasized (eg, boomy bass or screechy highs), or when some things that we know should be there seem to be absent (eg, imaging and a sense of depth). Increasingly, my approach to reviewing equipment has moved more toward this holistic approach, which I believe comes closer to the way most people listen to music.

With this in mind, the best description that I can give of the sound of my system with the VK-3iX and VK-55 installed is that it just seemed right, with no specific aspect of the sound drawing undue attention to itself, and no indication that anything important was being omitted. The sound was...well, balanced, with the various parts of the frequency range all there in the right proportions, a good sense of rhythmic ebb and flow, and imaging that was convincing in its depiction of depth and the positions of voices and instruments in space. To a very large extent, the sound of the system with the BATs doing the preamplification and amplification chores was the sound of the source materials, the components doing their best to get out of the way of the music. It certainly helped that, with the BATs, my system had such a vanishingly low noise level, but there was more to it than that; a lack of noise is of little importance if the sound itself is not convincingly real. With the VK-3iX and VK-55, it was convincingly real. If it were not for the fact that I had to write a review of these components—which inevitably involves making some comparisons—I would have been quite content to ignore the equipment and enjoy the music.

Comparisons
It was obvious in listening to the VK-3iX and VK-55 that these components worked very well together, but I wanted to check out how they worked—and compared—with other components.

First on the list of comparison components was my reference preamp, the Convergent Audio Technology SL-1 Ultimate. The CAT has been around for many years in various guises, and is generally recognized as being in the front rank of preamps. The CAT is a single-ended rather than a balanced design, so to connect it to the VK-55 I ran RCA-terminated versions of the same brand and model of cable (Nordost Quattro Fils), with RCA-to-XLR adapters at the amplifier end. The CAT has a switched-resistor type of volume control with quite rough gradations, so in making the comparisons I tried to match the CAT's volume setting with the VK-55's, measuring voltage at the speaker terminals. This was still not within the ideal ±0.1dB, so I used the "bracketing" method, listening with the VK-3iX's volume control slightly above and slightly below the CAT's. With the CAT driving the VK-55, the noise level was not as low as with the VK-3iX and VK-55, but it was quite good: with everything on but no CD playing, I could tell that the system was on, but this noise was masked by music played even at a low level.

The most obvious difference between the CAT and the VK-3iX in this comparison was at the frequency extremes. The bass with the CAT was more prominent and seemingly more extended, and the highs had greater sparkle. The CAT also had the edge in dynamic flow, with a greater sense of rhythm. Soundstage depth was excellent with both preamps, but the CAT had even greater definition of images in the soundstage. The gimmicky-but-fun "General Image and Resolution Test"—track 47 on the Best of Chesky Jazz and More Audiophile Tests/Volume 2 (Chesky JD68), in which people march around the room in an uncanny simulation of multiple-speaker surround sound—was very effective with both preamps, but through the CAT the individual percussive sounds and voices were more startling.

So, is the CAT, which costs more than three times as much as the VK-3iX, simply a better-sounding preamp? Well, not exactly. In fact, comparing the CAT with the VK-3iX on a wide range of recordings made me realize that the CAT tends toward brightness, which translates to harshness with some recordings. The VK-3iX, in comparison, is smoother and more forgiving, and I preferred its sound to the CAT's on some recordings.

One of these was The New Moon (Ghostlight 4403-2), one of my latest "Records To Die For" picks. When I'd selected this recording for R2D4, I was listening to it through the VK-3iX and VK-55, and I thought it sounded very fine. However, with the CAT in the system, Christiane Noll's silvery soprano in "One Kiss" took on a somewhat steely edge—one that, having heard her live several times, I know it does not have. On other recordings, primarily of the purist audiophile sort, my preference was for the CAT's greater immediacy and transparency, but even with these recordings I felt the sound would have benefited from a tonal balance a bit closer to the VK-3iX's. My CAT is an SL-1 Ultimate, which has been superseded by the paradoxically named SL-1 Ultimate Mk.II (perhaps the Ultimate should have been renamed the Penultimate); if nothing else, my experience with the VK-3iX convinced me that it's time to get my CAT preamp upgraded.

To compare with the VK-55, the amplifier I had on hand was the Audiopax Model Eighty Eight SE (which I reviewed in May 2003, Vol.26 No.5), a $10,000/pair monoblock that is probably my overall favorite of all amps I've had in my system. The Audiopax is single-ended, so I used the VK-3iX's RCA outputs and, again, the "bracketing" method to match levels with the VK-55 in listening comparisons. The Audiopax has lower gain, so its volume control had to be turned up much higher to get the same output as from the VK-55, but that was no problem. The noise level was almost as low as with the VK-3iX and VK-55, and lower than when pairing the CAT SL-1 preamp with the BAT VK-55. The Audiopax inverts absolute polarity; I reversed the speaker-cable connections to compensate for this.

In evaluating audio components, a characteristic I value most highly is a component's ability to communicate the sound of the recording with the minimum of electronic artifacts. The Audiopax Eighty-Eight SE does this better than any other amp of my experience; with the Audiopax's Timbre Lock settings optimally adjusted, recordings that sound harsh and artificial (dare I say digital?) with other amps suddenly seem much more natural and musical. A CD I play quite often when I want to impress people with how good an old recording can sound is Frank Sinatra's Come Fly With Me (CD, Capitol CDP 7 48469 2). The recording was made in 1957, and the CD transfer has no special audiophile pedigree, but "On the Road to Mandalay" can have a presence in the room that is almost spooky. The Avantgarde Unos have much to do with this effect, but it also depends on the amplifier (and, of course, the rest of the system). With some amplifiers, the voice and the instruments may be all there, but I'm too aware of the fact that the recording was made 50 years ago, with microphones that were peaky in the upper midrange, and the hardness added by the transfer to digital.

With the VK-3iX and the Audiopax, my attention focused more on what Sinatra was singing and Billy May's swinging brass arrangement. Substituting the VK-55 (balanced XLR connection) resulted in some diminution of this effect, so that the recording seemed to sound more artificial than before, but the difference wasn't great. The general tonal balance of the two amplifiers was quite similar, but the VK-55 had bass that sounded a bit more firm and extended, as well as the edge in the ability to present high-level dynamics. Considering the $6000 price difference, this is excellent showing for the VK-55.

Phono stage
This may be, as Michael Fremer said in "Analog Corner" in January 2005, "a great time to be into vinyl." In that column he reviewed BAT's VK-P10SE phono stage ($8000) and concluded that it was one of the top three phono stages he'd heard, coming in No.2 after the Boulder 2008 ($29,000) and ahead of the Manley Steelhead ($7300).

Sorry, Mikey, those are all too expensive for me! I listen to LPs not so much because of their sound quality—which, I will concede, with the best equipment may still beat CDs—but for the repertoire; I have many old records that I'm fond of, and which have not been released on CD. For this, I would be satisfied with a preamp that has a phono stage that's of good quality without being absolutely cutting-edge, and at a reasonable price. That, it seems to me, is exactly what the VK-3iX's phono card provides. The phono card's selectable low and high gains provide matching for a wide range of cartridges, and the ability to plug in load resistors provides for further tweaking potential.

There was no question that the high-gain setting would be more appropriate with my AudioQuest 7000nsx low-output moving-coil cartridge, but what about a load resistor? The VK-3iX phono stage comes with a standard 47k ohm load, and when I first tried it, I heard nothing that would suggest a cartridge/load incompatibility. Still, the recommended load for this cartridge is 100 ohms (that's what I use with the CAT SL-1 preamp), so I thought I should try it. Adding a load resistor to the VK-3iX phono stage is not all that easy; you have to provide your own, and the resistor lead wire has to be just the right diameter to fit the socket. BAT's service department sent me the appropriate resistors, and they were a little loose in the sockets. However, as it turned out, I heard no benefit from using the 100 ohm resistors; if anything, I preferred the sound with the standard loading, so that's how I listened to it.

And it sounded just fine! In a fit of vinyl nostalgia, I put on Depth of Image (LP, Opus 3 79-00), one of my standard test records in the days when I would fiddle with various cartridges and phono stages, tweaking VTA, etc. I quite like the first track, a Swedish pop song that may or may not be about a woman waiting for a phone call. (I know she sings "telephone ringen.") The sound was characterized by a huge soundstage, crisp percussion transients, and the voice having just the right amount of hardness on the sibilants. (I remember from my days of tweaking that the sibilants on this cut were quite sensitive to various setup parameters.) I have no reason to doubt that BAT's $8000 VK-P10SE would be better still, but the VK-3iX phono stage performs far better than anyone can expect for $500, and is likely to satisfy all but the most devoted fans of cost-no-object vinyl playback.

Paradigm shift
The Avantgarde Uno 3.0 is a wonderful speaker, and quite revealing of differences among system components, but its design—horn midrange and tweeter combined with a powered subwoofer, sensitivity about 15dB higher than the typical box speaker—puts it in the category of exotica. To check out how the VK-55 would perform with more conventional, lower-sensitivity speakers, I got hold of a pair of Paradigm Reference Studio/100 v.3s. John Atkinson followed-up on this speaker in the January 2005 issue, and I was pleased (and relieved!) that his response to them was as positive as mine had been to the v.2 (June 2000). The Paradigm's relatively small footprint meant that I was able to place them in the room next to the Avantgardes rather than having to take the Avantgardes out of the room. (Finding storage space in our fairly modestly sized house for the Avantgardes, then trying to put them back into exactly the same spots afterward, are chores I like to avoid if at all possible.)

The Reference Studio/100 v.3 was measured by JA to have an above-average 88.5dB sensitivity but to present quite a demanding impedance load. Nevertheless, the VK-55 was able to drive these speakers very effectively in my 14' by 16' by 7.5' listening room, with no indication of strain up to levels that I would describe as fairly loud—my RadioShack SPL meter (C weighting, Fast response) indicated peaks of 95dB, and this meter is known to underestimate actual peaks by several dB. The sound was wide-ranging, smooth, neutral in tonality, and engaging. I compared the performance with the speakers connected to the VK-55's low- and medium-impedance output terminals, expecting the low-impedance connection to be more optimal, but I actually found the medium-impedance connection preferable, with better dynamics.

When I reviewed the Studio/100 v.2, one of the amps I tried with it was the BAT VK-60, and I found that amp to be not as well-matched to the speaker as the high-powered, solid-state Bryston 9B-THX. I did not have that amp around this time for comparison, so I can't say whether it would have provided a better match with the v.3 as well, but the pairing of Paradigm Reference Studio/100 v.3 with the BAT VK-55 was a very good one, and, if memory serves, superior to the Studio/100 v.2 with VK-60.

Conclusions
Considered as individual components or in combination with each other, the Balanced Audio Technology VK-3iX and VK-55 are exemplars of the best that specialist home audio has to offer. Both are compatible with a wide range of associated equipment, and neither is fussy or quirky in use. Best of all, with the right sources and associated equipment, they're capable of producing sound that bears a striking resemblance to real music.

At $6490, the VK-3iX and VK-55 combo is not inexpensive, but it represents excellent value in today's audiophile market, and stands up well in comparison to some much-higher-priced references. A most welcome feature of these products is BAT's well-developed upgrade path. The VK-3iX is good enough that upgrades are not imperative, but for those who wish for more low-end oomph and greater dynamics, two capacitor upgrades are available. I've never heard of a situation where increased capacitance in the power supply was not of some benefit, however marginal, so if you have the money, these capacitor upgrades are probably worthwhile.

There is also the Special Edition upgrade, which incorporates not only the capacitor upgrades but a change from the 6922 to the 6H30 SuperTube. I would think more carefully about this one. A change in tube type tends to have a more dramatic effect on sound, and while the results may be technically superior, if you're pleased with the sound of the VK-3iX as is, you may find that the sound with the SuperTube upgrade not as much to your liking. I would certainly want to listen to an SE version of the preamp before going ahead with that upgrade.

For the VK-55, the upgrade consists of conversion from a 55Wpc stereo amp to a 110W mono amp, which would be worthwhile if your speakers are particularly power-hungry and/or if you have a large room.

Or you can get the basic combo of VK-3iX and VK-55, forget about upgrades for a while, and just listen to the music.