Tube Preamp Reviews

However, The Tube Mk.II's unique circuitry makes hearing the effects of different input tubes incredibly easy. Change the stock pair of tubes associated with a given input to some pricey new-old stock (NOS)—for example, the gold-pinned Telefunkens I tried (supplied by Einstein importer Brian Ackerman)—and, by switching a particular component between two inputs, you can easily hear the differences, although another idiosyncrasy of The Tube's circuitry makes instantaneous A/B comparisons impossible. All five inputs are always "live" and in-circuit. Rather than routing the input to a common gain stage, the input-selector switch activates the chosen input tubes' heater supplies. The other four pairs of input tubes remain dark. While this unique arrangement better preserves the purity of the signal—and because low-level signals don't pass through a switch, it probably prolongs tube life—it also means that when you change inputs, there's a minute-long "crossfade" as the previously chosen input dies out and the newly chosen one comes to life. If you don't think you can live with such a delay, make sure you never hear The Tube Mk.II—you might become seriously conflicted!

Sound Basics
How should a preamplifier sound? Ideally, like nothing. It should offer a linear transfer of the signal with gain. It shouldn't add noise or distortion. It should neither gin up nor diminish harmonics. It should pass along the soundstage produced by the source component. It should reveal a recording's genuine details, not produce false details of its own, and it should reproduce the source's natural dynamic range, moving nimbly between the extremes of that range. It shouldn't smear, coarsen, or soften transients, or fatten the bass. It shouldn't add or remove richness and warmth. The sonic signatures of different-sounding sources should survive the journey from input to output without being indelibly stamped with the preamp's own character. If your source has fixed and variable outputs, a fixed output sent through the preamp shouldn't sound all that different from a variable output sent directly to your power amp; one shouldn't sound veiled, dynamically diminished, distant, and flat while the other sounds transparent, explosive, immediate, and holographic.

That's the ideal, but every preamplifier I've heard gives the sound some kind of flavor or enhancement or subtraction or veil—something that changes the overall personality of the source's signal. This is sometimes for the better, in terms of listening pleasure, if not in the interest of greater accuracy. But it's difficult to be sure what any source actually sounds like: Its variable output must go through a built-in volume control of some sort, and who knows what that does to the sound? When I used to compare the Manley Labs Steelhead preamp's built-in volume potentiometer to an outboard preamp I was reviewing, I almost always preferred the outboard preamp, even though I could identify its contribution. Why? I'm not sure. Maybe it was the sound of the Manley's potentiometer.

In other words, I'm not a "purist" because there's no such thing as purity. That said, the damage done to the signal should be infinitesimal, and any tint on the glasses should be blush, not burgundy. In my opinion.

Last year, when I was reviewing the dCS Scarlatti SACD stack, its volume-controlled output sounded only marginally more dynamic and transparent than its fixed output did through the darTZeel NHB-18NS preamp—and I doubt I could tell one from the other without looking, which is as it should be with a $29,000 preamplifier! On the other hand, a friend who owns a highly regarded tube preamp was dismayed by the results of a similar comparison I conducted with his gear. I shouldn't have to tell you which routing sounded better—it was with the dCS driving the power amps directly.

The sound . . . or lack thereof
The Einstein Tube Mk.II came as close to adding and subtracting nothing from the signal as any tube preamp I've heard. If silence is golden, The Tube was 24K pure gold. It was dead quiet even when cranked to the max, proving that tube preamplification need not add noise. Overall, regardless of technology, it was among the most transparent preamplifiers I've heard—but particularly so for an all-tube design.

In that transparency and in many other ways, The Tube reminded me of the open-sounding, gratifyingly linear Musical Fidelity AMS Primo that I reviewed in May 2010, which also made use of multiple tubes. However, the Einstein produced a more refined picture overall, particularly in its tidier soundstaging and compactness of image sizes. Its remote-controlled motorized volume potentiometer was more user-friendly than the Primo's, in terms of both the gradualness of the taper and its ability to follow commands.

Describing The Tube Mk.II's sonic personality was made somewhat more difficult because the NOS Telefunken tubes I was using in the line-level "Phono" input produced a sound very different from that of the other inputs fitted with the stock tubes. It's impossible to describe the preamp's "sound" independent of the input tubes chosen.

The profound sonic differences produced by the NOS tubes weren't really about tonal balance; both inputs were essentially neutral in that regard, and free of bottom-end bloat, excessive midband richness, and rolled-off or softened high frequencies. Both sounded remarkably linear and well extended at the frequency extremes. The differences had more to do with the NOS tubes' almost supernaturally blacker backgrounds, freedom from grain, and more vivid harmonics, all of which might have been masked had the rest of The Tube's presentation been noisy and/or severely colored.