Tube Preamp Reviews

Successive pressings of Function cycle through Balance, Relative Volume, Phase, Mono/Stereo, Maximum, Fixed, Display, and Input Name, allowing you to customize each input independently for most of those functions. BAT was smart to begin with Balance; unlike Phase (more correctly labeled Polarity on the remote) and Mono/Stereo, the Rex offers no independent means of adjusting the balance, either on the front panel or on the remote. Selecting Fixed lets you set the chosen input for unity gain for use as a pass-through to an A/V system, while Display lets you select the relative volume level in numeric units from 000 to 140, in dBU (decibels relative to unity gain of 0dB), or in dBM (decibels with respect to maximum gain) for all inputs. The Name function lets you program the Rex in any of four character sets, be they numbers or the Greek, Latin, or Cyrillic alphabets —a useful feature for the chronically forgetful. Holding down Function at any time in the setup cycle returns the Rex to normal operation.

Installation, Setup, Use
The two Rex modules put out too much heat to allow them to be stacked. Each requires a separate shelf and at least 6" of space to the sides and top. Because of the tight clearances in my rack, I removed the enclosures to give them even more ventilation (not recommended if you have toddlers).

I also had to borrow three pairs of BAT's excellent RCA-to-XLR adapters, as all of my gear is single-ended (I'd previously purchased two pairs of BAT ins and a pair of outs for use in reviews of other balanced components.) Of course, running the Rex single-ended throughout much of my auditioning meant 6dB less gain, though that proved more than sufficient. Toward the end of the review period, the return of the VTL MB-450 Signature monoblock power amplifier I'd sent to JA for measuring (see January 2008) made fully balanced listening possible.

The first time you push the Rex's Standby button, it goes through a 50-second warmup cycle, during which time the display continues to blink until the Rex is ready for use. Pressing and holding Standby turns the Rex off. BAT recommended leaving the Rex powered on continuously during the review period. That's what I did, except when I was away for more than a few days. During the two-month listening period the Rex's 2-amp slow-blow fuse blew once. That usually indicates a faulty 5AR4 rectifier tube, but replacing the fuse restored operation. However, near the end of the review period one of the 5AR4s began making pretty fireworks and the fuse blew again. Replacing fuse and tube restored operation. Otherwise, the Rex performed flawlessly. (BAT supplied me with spare pairs of 5AR4s and 6H30s. If you're going with tubes, you have to be ready to deal with these small inconveniences; keep some fuses and spare tubes handy.)

Programming the Rex was quick and easy, though if you're not familiar with nested functionality (and you're a bird-brain like me), you may encounter a few confusing moments: If you accidentally push the remote's Function button and set the display a-blinkin', you might forget that you can restore the Play function by pushing Function again and holding it down. No big deal...once you've figured it out.

Programmed and gotten used to, the Rex became a user-friendly beast that was functional and that was fun to operate. What's not to like about remote-controlled Polarity and Mono switches, not to mention a numerical, repeatable volume control? They're great for reviewers, too.

Sound: Two! Two! Two preamps in one!
If you're thinking "lotsa tubes, lotsa noise," don't. The Rex was totally quiet, actually producing less noise than the solid-state darTZeel NHB-18NS (see my review in the June 2007 issue), and comparable to my reference Musical Fidelity kWP hybrid. Which means that the Rex was utterly quiet at way louder levels than you're ever likely to use. Even with the Rex at full volume and passing no signal, I could hear nothing at my listening position. Putting my ears to the tweeter produced only the faintest hiss. For an all-tube preamp, that's impressive.

More impressive, though, were the Rex's musical performances. Why the plural? Based on my experience, the internally mounted AC Shunt Voltage Regulation switch in the power module that lets you choose between pairs of 6H30 and 6C45 tubes produced huge audible differences.

Set to its 6H30 position, the Rex sounded "tube-like" in the clich éd sense of the word: rich, warm, "midrangey," somewhat soft overall, sluggish and thick in the bass —just the way some folks like it. Not me. The soundstage was narrowed and squeezed forward, producing Lava Lamp –like, slow-moving, lumpy images (I exaggerate for effect) —again, just the way some folks like it, and again, not me. I've heard this sound at audio shows and for the life of me can't understand why anyone thinks it has anything whatsoever to do with the sound of live —or recorded —music, I don't care what the genre!

However, flipping the switch to the 6C45 position completely changed everything about the sound. It was like tightening a set of Koni shock absorbers (old school): now the sound was fast, properly stiff, taut, and responsive. The soundstage widened and receded to a proper "get outta my lap" distance, while maintaining its outstanding depth. Images suffering from elephantiasis shrank to their proper size and crystallized cleanly. The tonal balance became airy and expansive on top, rich and supple in the midrange, and tight and deep down below, combining the best of tubes and solid-state in one mesmerizingly excellent presentation.

System-dependent or whatever, the 6H30/6C45 switch was like Jekyll and Hyde in its ability to change everything about the Rex's sound. Still, in neither position did the Rex ever sound electronic or mechanical, and it always produced that cushiony musical flow and drive that tube advocates claim —rightly, I think —can be achieved only with tube rectification.

Set to the 6C45 position, the Rex produced an essentially neutral tonal picture: neither dark nor bright, with ideal top and bottom extension, and creamy-rich mids that brought out the fleshy essence of human voices, polished the brasses, rounded the woodwinds, slipped the drums some skin, and had the strings sporting wood. Yet at the same time, the Rex was able to pass with ease the essential spit and distortion of solid-bodied electric guitars and the squarewavy sound of purposely distorted digital overdrive, all laid out with unforced enthusiasm on a big, wide-open soundstage. In other words, in the 6C45 position, the Rex produced fast transients along with tubey warmth and grace.

The Rex's performance at the frequency extremes was exemplary: extended, airy, and detailed on top; full, fast, and extended on bottom. Though some solid-state preamps I've heard are faster and tighter on the bottom, they couldn't compete with the Rex's expression of bottom-end weight and texture. Dynamically, the Rex was fully fleshed out at the whisper end of the scale, and packed a wallop at the other end. I could have happily and enthusiastically listened for weeks on end to this kind of sound. In fact, I did. But with the Rex set to its 6H30 position, I couldn't listen happily at all.

Your tastes and system may produce very different results. However, if the goal is to route and control a signal's volume without otherwise altering the signal itself, the 6H30 position failed the test. It was like adding too much ground clove to an otherwise excellent apple pie: the Rex's sonic character was overwhelmingly large, and not subtle enough to recede into the background even after my ears had adjusted.

Why should making such a seemingly minor change of tube cause such a huge sonic shift? I'll leave that to designer Victor Khomenko to explain. But one thing I know: the switch, which is inside the power module, should be easer to get to.

By definition, a preamp shouldn't "sound"; at the very least it should subtract as little as possible from the sound; and if it's going to add anything, it should be subtle and nondestructive.

While both the darTZeel NHB-18NS and the BAT Rex handily passed that test tonally, texturally they couldn't be more different. The fast-moving darTZeel produces more of a fine-grained, crystalline transparency and purity that lets me see further into the musical presentation —like viewing a high-definition video broadcast at full 1920x1080 resolution. The somewhat slower-moving BAT's presentation was more soulful, more viscerally textured and tactile, and more cinematic, though equally well resolved. With the Rex set to 6H30, this sound was in-my-lap excessive through my system; the 6C45 setting produced an ideal balance of detail, harmonic expression, and especially —something harder to describe but more easily experienced —musical flow.

The Rex wasn't in a hurry. It took the time to allow full musical expression to develop, moving to the next event well before impatience or boredom could set in. After a few days with the Rex, unless I was in full reviewer mode, I stopped noticing its sound, but I couldn't help but feel its soul.

Conclusion
If you're going to ask $18,500 for a preamplifier, you'd better deliver high technology and build quality, attractive cosmetics, ergonomic satisfaction, and —most difficult for a component that, by definition, should not express a sonic personality —sound that is simultaneously neutral and special.

The Balanced Audio Technology Rex manages both the high build quality and high tech, pleasing if somewhat dark appearance (better faceplate lighting would help), and excellent, full-featured ergonomics. Listened to at its 6C45 setting, was the Rex utterly neutral, adding nothing to the signal? No —no audio component can do that. However, what the all-tube Rex did to the signal was subtle, slightly additive without being overbearing, and, in the end, wholesome —similar to what a brilliant mastering job can do for an already excellent recording.

The Rex —or any excellent audio component —couldn't polish turds, but it did manage to put a brilliant shine on those recordings I consider to be the diamonds of my collection, while leaving intact the sharp edge of each gleaming facet. If you're lucky enough to spend some time with the BAT Rex, I think you'll agree that it's among the most beguiling-sounding control preamplifiers yet devised. Is it worth $18,500? Let your bank account be your guide; your ears will say Yes.