Tube Power Amp Reviews

Although one of the most innovative firms in the audio electronics field, the David Berning Company seems determined to keep as low a profile as possible. The company advertises little, does not actively seek out new dealers, and seems content to let potential customers seek it out, as though to say "Okay, here's my product, take it or leave it." Thus, even though both Stereophile and The Absolute Sound, in a rare outbreak of agreement, a couple of years ago declared Berning's TF-10 to be one of the best preamplifiers available, most serious audiophiles are still unaware of the Berning Company's existence. Perhaps the EA-2100 will change that.

My first reaction to Berning's latest product was incredulity. Only somewhat larger than your average tubed preamp, the EA-2100 almost gave me a strained back when I first went to pick it up. You see, I knew it was rated at 100 watts per channel and, having just schlepped the identically rated 90lb Quicksilver out of the listening area, I expected to encounter as much weight with the Berning. Instead, I almost lost my balance backwards. This amplifier is light. So light, in fact, that one was inclined to be dubious about its power-supply capabilities. After all, a proper amplifier, and particularly a tubed amplifier, has to be heavy because of its power supply requirements.

Well, that's untrue, at least when the amplifier uses Berning's unique power supply. The power supply departs from standard practice as soon as the AC leaves the on-off switch. In virtually all other power amps the AC goes through a power transformer, then through a rectifier and possibly a voltage regulator, and thence to the power supply capacitors (this is a simplified version). Not in the Berning! The EA-2100 first rectifies the AC. The DC output of the rectifier is fed to a fancy oscillator circuit which produces a squarewave output whose frequency can be varied from 50 to 70kHz. This variable-frequency squarewave goes into what's called "an inductive tank circuit." The key characteristic of this tank circuit is that it transfers power most efficiently at a particular frequency (50kHz) and less effectively at higher and lower frequencies.

David Berning runs the oscillator circuit at 70kHz at no- or low-load conditions; that gives him the ability to "goose" the power supply under high-load conditions (voltage-sensing devices on the capacitors tell the oscillator what to do) by dropping the oscillator frequency to 50kHz and making the tank circuit run more efficiently.

Following the tank circuit are the transformer and the power supply capacitors, just as in a standard amplifier—except that in the EA-2100 the transformer can be very small, in this case only 2lb. Why so small? Because the transformer is running at very high frequency—the large size of most transformers is there because they're handling essentially a bass frequency (60Hz).

The small size of the transformer is actually an advantage. Because the number of turns are low, the output impedance is low and the transformer can more easily replenish the capacitors. And because it's operating at such a high rate of speed, there's much less time for the capacitors to sag between "fill-ups." I'm sure that the remarkable low end of this amp is directly attributable to this innovative power supply design.

Unlike Berning's hybrid TF-10 preamp, which uses cascoded tubes and FETs to offset each other's distortion characteristics, the EA-2100 uses tubes only. The outputs are General Electric 6LF6s—a type I have never before encountered—which look like the kind that were used in pre–solid-state television receivers for horizontal output. The other tubes consist of a 6SN7 driver and two 12AT7s, per channel. The outputs are run in class-B (footnote 1), and the amplifier runs very cool, particularly considering its output capability.

Sound Quality
The Berning TF-10 is one of the most neutral-sounding preamps available. Its sonic earmarks hew almost dead-center between the slight laid-back quality of transistors and the alive, up-front quality of tubes. The EA-2100 is not quite so neutral, but does succeed at being one of the less "tubey" tubed power amps I have heard.

The most immediately noticeable things about its sound are its aliveness and immediacy. Although it has little of the spurious brightness of a typical tube amplifier (it does have some), the mid and upper ranges have a truly startling clarity and focus, and front-to-back perspectives are superbly reproduced. The really surprising characteristic is at the low end, where most tubed amps tend to be heavy and woolly (overly warm). The EA-2100 has a tightness and impact that sounds more like a high powered solid-state amplifier. In fact, the only respect in which the best high current solid-state amps exceed the Berning is through the bottom-most region (30–50Hz—and very few systems go lower), where the Berning delivers somewhat less rock-solid punchiness. This low-end performance is even more amazing in view of the amplifier's weight, but is a tribute to the lightweight power supply—it really does its job!

Soundstage presentation is excellent—wide and spacious—as is stereo imaging, which is specific and stable. Extreme highs are slightly soft, as is frequently the case with tubes, but a little less silky-sweet than what you hear from the C-J Premier One, and noticeably less sweet than what you hear from the Paoli S.O.B. For this reason, I found the Berning to be less comfortable sounding with the electrostatics I had on hand, and particularly not an appropriate match for the Quad ESL-63. The Acoustat 2+2s sounded a bit hard and unrelenting, the first time I've heard that from the 2 + 2s driven by a tube amp.

On the Watkins WE-1 and the Spica TC-50 dynamic speakers, the enhanced depth and aliveness gave an even greater feeling of live music than I'm used to with my reference solid-state amp, the Electron Kinetics Eagle 7a. The slight apparent dulling of high end merely added musical sweetness without impairing detail. On the Thiel CS3 the improvement was even greater: that speaker's superb bass was not significantly compromised, the speaker's slightly cool and laid-back quality was compensated for a bit, and the high end was simply beautiful.

Summing Up
As can be seen from the above remarks, an amplifier like this is different enough from the standard run that a rethinking of one's assumptions about tubes and solid-state is in order. My conclusion is that, on the right speakers, it's one of the most gorgeous-sounding and best tubed amplifiers I have heard, at a not-unreasonable price. Highly recommended.

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Footnote 1: Class-B is typically frowned upon in audio amplifiers because of the notorious "crossover distortion" which occurs when the signal is transferred from the positive-amplification device, which then turns off, to the negative-amplification device, which must immediately turn on. The bad reputation comes primarily from transistor amplifiers; transistors have a very non-linear response characteristic as they turn on and off, and sound terrible in class-B. David Berning tells me that tubes are "soft enough and fast enough" so that whatever waveform distortion occurs because of the class-B operation is minimal. The benefit of class-B to the owner of the amplifier is large: because the tubes are biased at such a low voltage, they run very cool and Berning promises tube life of 10–20 years (!), compared to the year or two typical for high-powered amplifiers.—Larry Archibald