The David Berning Company 211/845 Power Amplifier

The Third Dimension

Equipment report
Tubed power amplifiers
David Berning 211/845
The David Berning Company 211/845 Power Amplifier

Just when I thought I’d heard virtually the entire spectrum of power amplifiers, along comes the 211/845 from The David Berning Company. With 60W of pure Class A push-pull tube power, no output transformer, and zero global feedback, the 211/845 certainly occupies a little-explored corner of high-end audio. But I’m glad that I gave this offbeat amplifier a listen, because it opened my ears to the starling qualities of vacuum tube power when freed from the sonic bottleneck that is the output transformer. No other amplifier is built like the 211/845—and no other amplifier sounds quite like the 211/845.

On paper, the Berning 211/845 is scintillating. For starters, it is the ultimate implementation of David Berning’s patented ZOTL circuit, which allows a tube output stage to drive loudspeakers without an audio output transformer (see sidebar). An earlier and less ambitious implementation of the ZOTL circuit (in the $8360 Berning ZH-230) was praised mightily by Dick Olsher in Issue 210. Others who have heard Berning’s amplifiers, particularly the ZOTL variety, have been similarly enthusiastic. (See also Vade Forrester’s Golden Ear Awards this issue.) Berning pulled out all the stops in creating the 211/845; in his 47-year career he has never created an amplifier this sophisticated, or lavished such expense on the execution.

The silver chassis (black is also available) is nicely finished, but the 211/845 is decidedly not a piece of audio jewelry. Visually, this amplifier exudes a no-nonsense vibe that reflects its status as an instrument for reproducing music. In keeping with the amplifier’s instrumentation feel, the power switch is on the rear panel. Balanced and unbalanced inputs are provided, selected via a toggle. Two pairs of silver WBT binding posts are provided for loudspeaker connection. The 211/845 sells for $75,000 per pair.

The amplifier’s pedestrian name derives from its ability to operate with either 845 or 211 output tubes. No user adjustment is required other than swapping the two tubes per chassis. The amplifier is shipped with pairs of both tube types, hand-matched and selected by David Berning using a curve tracer. The 211 and 845 output tubes are Western Electric replicas made by Psvane, which cost more than triple the price of Psvane’s standard versions. When turning the amplifier on, an auto-bias sequence gradually ramps up the output-tube bias, extending tube life. Once the amp is fully turned on, the user can select one of three bias currents, with the lower settings reducing output power but extending tube life. These reduced-bias modes are presumably for background listening, or if you have extremely sensitive loudspeakers. Output tube life is projected at 10,000 to 20,000 hours even when the amp is operated at the maximum bias setting.

This all-tube amplifier is shipped with the small-signal tubes in their sockets, but the user has to install the output tubes. These tubes extend above the chassis au naturel, or can be protected by a removable cage. The amplifier’s small-signal tubes are a vintage 12AT7 and a pair of 6V6 beam-power tubes (all NOS from the 1960s), along with a modern-production 6SN7. A backup set of the small-signal tubes is included, although these are current-production Tung-Sol and Sovtek units, not vintage tubes.

No expense was spared in this new design’s execution. The tube sockets are unlike any I’ve seen before, made from ceramic with spring-loaded gold contacts that wrap around the tube pins. The circuit is point-to-point wired with silver wire rather than relying on thin copper circuit-board traces. Caddock resistors and Solen Teflon capacitors abound. The mechanical isolation is extraordinary, with 36 Stillpoints standoffs used in the circuit, more Stillpoints in the power-supply sub-chassis, and Stillpoints Ultra 5 isolation devices for feet (Stillpoints Ultra 6 isolation is a $2000 option). Importantly, the height of the Ultra 5 feet can be adjusted so that the amplifier is firmly coupled to whatever it is resting on. The entire circuit and chassis assembly, including the tube sockets, have been cryogenically treated.                 

I’ve recently explored the state of the art in solid-state amplification (the Constellation Hercules II and Soulution 701, for examples) and wanted to experience the pinnacle of vacuum-tube technology. The Berning 211/845 looked like a good candidate, and the amplifier sounded spectacular at the 2015 Munich show driving Avantgarde Trio loudspeakers. I also heard the 211/845 sound wonderful driving the big Tidal Akira loudspeakers at the home of Rick Brown of Hi-Fi One, the amplifier’s worldwide representative. Calling Rick Brown the worldwide representative is technically correct, but understates the role he played in bringing the 211/845 into existence. Brown has sold David Berning’s amps for years to his select clientele, but urged Berning to create a no-holds-barred amplifier based on the ZOTL circuit. Brown funded the two-year development effort, and played a pivotal role in shaping the final product, including the extensive use of Stillpoints technology in the amplifier, the cryogenic treatment, and selection of key passive components through critical listening comparisons.

Although rated at 60W into 8 ohms, the 211/845’s output power is somewhat higher than that, dependent on which output tubes are installed. With the 845 tubes, the amplifier clips (with clipping defined as 3% THD) at 83W into 8 ohms. With the 211 tubes, onset of clipping occurs at 72W. The 211/845’s output impedance is 1.7 ohms with the 845 tube, and 3.5 ohms with the 211 installed. This is a high value when contrasted with solid-state amplifiers (whose output impedance is often less than a tenth of an ohm), but actually quite low when compared with other tube amplifiers that employ little or no feedback.

An amplifier’s output impedance is a concern because this impedance interacts with the speaker’s own impedance, which varies with frequency, leading to deviations from flat frequency response. The higher an amplifier’s output impedance, the greater this effect. Moreover, the greater the variation in the loudspeaker’s impedance (as a function of frequency), the greater the frequency-response deviations. Which frequencies are boosted and which are attenuated by this interaction are determined by each speaker’s unique impedance curve. Thus, the tonal balance will change with each speaker the amplifier drives in ways unrelated to the speaker’s intrinsic frequency response.

The take-home message from all of this is that an amplifier with a high output impedance must be carefully matched to the loudspeaker. This is doubly true if the amplifier’s output power is modest. The ideal speaker for an amplifier like the 211/845 has a flat impedance-magnitude curve (nearly the same impedance at all frequencies), a highish impedance overall, and high sensitivity. Unlike a big solid-state behemoth amplifier, which will drive any speaker regardless of the speaker’s impedance or sensitivity, the 211/845 must be matched to the right loudspeaker—not just to make the system work technically, but to fully realize the amplifier’s potential. You have to carefully create an environment that allows the 211/845 to flourish.

As it happens, my reference speaker meets these criteria. The Magico Q7 Mk.II has a fairly flat impedance, no severe impedance dips, and has a sensitivity of 94dB. This sensitivity doesn’t approach that of horn speakers (which often exceed 100dB), but it is nonetheless higher than that of most dynamic loudspeakers. (A change in sensitivity of a few dB can make a big difference in an amplifier’s perceived performance.) Keep in mind that a 60W amplifier driving a speaker of 94dB sensitivity will produce the same sound-pressure level as a 240W amplifier driving a speaker of 88dB sensitivity. (Each 3dB increase in sensitivity is equivalent to doubling the amplifier power.) Also keep in mind that 60 triode watts sound a lot more potent than 60 solid-state watts. I would not have reviewed the 211/845 unless I had a loudspeaker that was a good match for the amplifier. Similarly, if you are considering the 211/845 you must also assure that it’s driving a speaker appropriate for the amplifier.