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December 2006
Superior Audio Equipment Review

David Berning Company ZH270 Amplifier
The Avant-Garde In High-End Audio
Review By Rick Becker
Click here to e-mail reviewer.

 David Berning ZH270 Vacuum Tube Stereo Amplifier

  Those of us who get out into the world have probably met people whom captivated us with their accomplishment or their persona. David Berning is such a person for me. His reputation preceded my encounter with any of his amplifiers by an uncertain number of years. But I'll never forget the first encounter with the ZH270. It was near the end of the Montreal show in 2003. The rig was an eclectic mix of brands that were all a mystery to me, except for the Merlin VSM-M loudspeakers. I was fairly familiar with the Merlin, having heard them a number of times at Montreal and New York, driven by both tubes and solid-state equipment. The music here was much better than I'd heard before from these loudspeakers and ranked among the very Best Rooms at the show. So intrigued was I that I got down on my knees to get a good look at what turned out to be the Berning ZH270. I knew very little about Berning amplifiers when I first walked into the room, and I didn't know much more by the time I left. And I was probably not alone.

I also missed the entire point of that room, which was put together by the people from Stillpoints and "featured" their high-tech vibration absorbing footers and the ERS paper that absorbs EMI and RFI. Allan, the Canadian importer was quick to jump on me for the oversight. One thing led to another, which turned out to be my rave review of these two products in November 2003 and a Best of 2003 Award for the ERS paper. To this day, ERS paper resides in my CD transport, DAC, tuner, DVD player, on top of my preamp's power supply and wrapped around strategic points of my dedicated AC lines. It is the biggest bargain in audio and one of the most overlooked.

David BerningIt also happens that Allan imports Berning amplifiers to Canada. As our friendship grew over the years, he promised that someday he would see that I got my hands on one for a listen. Through Allan, I made the acquaintance of David Berning, himself. I'll never forget the first time I met him. As Snoopy writes, it was a dark and stormy night on a Thanksgiving trip to the Eastern Shore of Virginia. Linda and I ventured off course visit David, who lives outside of Washington, DC. Up close and personal, he is even more extraordinary than his amplifiers. In conversation we shared our passion for bicycling, XC skiing and videography. Linda and I marveled at his collectibles. Among them was an unusual turntable with a built-in radio transmitter. When you play the 78 rpm record, the signal is transmitted, then picked up and played back through your table radio. I wondered if that was the origin of the idea behind the ZH270.

In the summer of 2005 David returned the visit while on a bicycle tour of the Mid-Atlantic States with a group of friends. He arrived, naturally, with his Sony tube-powered analog VHS camcorder mounted on his bicycle. Linda prepared a healthy and delicious dinner for our guest and afterward we mixed conversation with music.


On The Inside

I would be a fool to pretend I'm an electrical engineer, but basically, the ZH270 (Zero Hysteresis) amplifier uses a radio frequency as a carrier for the audio signal in a design that is loosely an all-tube, push-pull, OTL amplifier with selectable negative feedback that comes very close to matching the impedance of the loudspeaker it is driving without using a an output transformer. If what I've just said excites you, please visit the Berning website. It contains a very clear and well-written description of this patented design. It also stakes out several claims for the design:

High current delivery to the loudspeakers
High tube efficiency
Reduced speaker loading of the output tubes
Enhanced reliability


Near the end of August, Allan made good on his promise and the ZH270 arrived just before we went away for the Labor Day weekend. The brief three week visit, during which I had limited opportunity for listening, was not ample time to test these claims. For that purpose, I would need a loan of at least several years. But it did allow me to experience the amplifier's performance in a familiar system. The original purpose was merely to give me an opportunity to listen to the amplifier at home, but after I heard the effect the ZH270 had on my system I asked permission to write a review. The amplifier has been in such high demand for years that not only was it unnecessary for it to be reviewed, but no review samples have been available. This particular unit was winding its way to the Rocky Mountain Audiofest where it was to be used in the Stillpoints room, so there was no chance of buying it. It was identified as the Special Edition, which means it has an upgraded volume control on the input and upgraded wiring inside, according to Allan.

While the ZH270 is not really an integrated amplifier, it does have two pair of rca single ended inputs that allow for direct connection of a CD player and a preamplifier to handle your other sources. A toggle switch on the face of the amplifier allows you to change between the two. A second toggle switch controls the amount of negative feedback allowing you to choose between medium, normal and low. I preferred the low position, as I do with my Manly Mahi monoblocks. The sound is more fluid, less compressed, more three-dimensional and has more of that "you are there" transparency.

Below the toggle switches is the volume control, which works on the input side of the amplifier. It is used to balance the output of the preamplifier or CD player with the input of the ZH270. Since the volume control of the Special Edition was different than the standard one, I took Allan's advice to ignore the manual and set it at the 3 o'clock position for use with my 89dB/W/m sensitivity Kharma loudspeakers. In real life, you will have to play with both the volume control and the feedback selector to find the best results for your own loudspeakers and your own personal taste.

Below the power switch on the left side of the face of the amplifier are two LEDs that burned red for 55 seconds before turning yellow to indicate that it was safe to play music. The first evening I listened, I was tired and thought my eyes were going bad, as these LEDs seemed to change color with the music. Allan assured me that this was the normal functioning of the auto-biasing system and that the amplifier constantly re-biases itself using high-speed sample-and-hold circuitry that precisely sets the push-pull crossover tube currents and balance as the load caused by the music varies. The visual effect is very subtle and was not at all bothersome.


Saying Goodbye

I promised Allan I would ship out the amplifier on Wednesday, but before I tore down the system I fired it up for two more LPs. First up was Maynard Ferguson's M. F. Horn. I listened to his renditions of "Eli's Comin" and "MacArthur Park", two songs I knew in their original pop versions. In the mid-‘70s I was worked on the live taping of Maynard Ferguson for the At The Top jazz series produced by WXXI-TV here in Rochester, NY. So I knew the sound of the live band. Running the phono stage of the CAT preamplifier to the conrad-johnson CT6 to the ZH270 to drive the Kharmas with the new ceramic tweeter, the sound zeroed in perfectly on my memory of the music, save for the ultimate dynamics afforded by standing thirty feet in front of the band at the restaurant. The rig had plenty of dynamics, for sure, but "live" is live! The second LP was one that has been getting plenty of turns lately, Jackson Browne's Running on Empty, side two. The ambience of the motel room, amphitheater, tour bus and pavilion recorded on this album were distinctly portrayed but more importantly, waves of goose bumps rolled over me as I listened this one last time. The lyrics of "Stay" (just a little bit longer) were a fitting farewell for this wonderful amplifier.

As I disconnected the cables I peered through the birds-eye sheet metal and marveled at the layout and construction quality on the circuit board — each soldered point done by David himself. In one area, thin solid core, matched crystal, 18 Ga. silver hook-up wires with a clear insulator bridged from one point to another with the precision of a spider web. To the ears it appears as an outstanding amplifier; to the eyes it is a work of superb craftsmanship. From an engineering standpoint, I suppose it is a tour de force. There was never any question that the amplifier would be sent on its journey, but nonetheless, I was filled with reviewer's remorse at having to let it go.

As the ZH270 cooled down, I hooked up my Manley Mahis and replayed Running on Empty. The loss of focus, precision, accuracy and smoothness was instantly apparent. The band immediately repositioned itself closer to the listening chair, and the bass became more prominent, if slightly less focused and accurate. The Kharmas, after all, thrive on amplifiers with strong bass. Next, I took the conrad-johnson CT6 out of the loop and returned the system to its reference configuration. The music darkened with a noticeable loss of transparency and focus, yet became fuller with greater weight.

The system did not collapse, mind you. As in hiking, the view of the distant mountains from the tree line is still beautiful. But the excitement of the view from atop of one of the 14ers in Colorado is breathtaking. So it was with the ZH270.


Standing In The Void

The conrad-johnson CT6 left shortly thereafter. So where did that leave me? Well, the reference rig is far from shabby with the tweaks I've applied to almost everything. The CT6 and the ZH270 produced the most transparent music I've ever heard through my Kharmas, though admittedly, these were among the first few components to pass through my home since the new ceramic drivers were installed. Nonetheless, it was the best I've ever heard here at home. The frequency range was focused from top to bottom, and while the bass was not as tight as the mighty Escalante Design Uinta subwoofer, it was very respectable — especially considering the moderate power output of the ZH270. And remember, the room, at 6000 cubic feet with wide openings to adjacent rooms, is not small. The soundstage was a bit further recessed behind the loudspeakers than I normally experience with the Manley Mahis. And while my personal preference is to have it closer, the focus of the ZH270 and CT6 gave me greater detail than I had before. I just felt like I was sitting a little further back from the stage. Personally, I wanted to be up closer to feel the heat and see the sweat on the performers. Your preference may vary, and is certainly respected.

I would be remiss if I didn't address the SET vs. Push-Pull issue. Normally, I experience substantive difference between the two with SET amplifiers being more holographic, as well as softer at the extremes, while PP amps tend to be more linearly focused from top to bottom and less three-dimensional. At least, that's the stereotype from some years ago. My more recent experiences with the KR VA340 amplifier with both the 300BXLS and 842VHD tubes, the KR Kronzilla DX monoblocks with their T1610 monster tube, as well as my humble, but mighty, Manley Mahis with their EL84 tubes, suggests that this is not always the case. The Mahis, with their ability to switch back and forth between triode and ultralinear mode, as well as adjust the negative feedback, were an education in itself. The ZH270 was extremely linear from top to bottom, not only in tonal balance, but also in focus, with the slight caveat to the lower mid-bass that I mentioned. Moreover, it had outstanding focus from the front of the soundscape to the rear. Back-up singers and distant soft percussion were easily heard and naturally positioned. This outstanding focus, combined with the outstanding transparency in the ZH270 masked the less holographic dimensionality of the musicians. There is a small trade-off here, to be sure, but it is one that I think most listeners would jump at.


Stereo Or Monoblocks?

Another perception crept into my consciousness that I am reluctant to mention, because I had no way of testing it. Was it real or merely suggested by the visual reality that the ZH270 is a stereo amplifier? The Mahis, being monoblocks, seem to have a more real sense of space with a more defined, cleaner air between the musicians in small to moderate size groups. The positioning and the size of the soundstage were not different, but the quality of the space among the musicians was slightly cleaner or emptier. This is not to say the Berning was not more focused or transparent than the Mahis — it was, but still, there was this difference. Perhaps this is why monoblocks are so coveted. And if you'd like it that way, you can always buy a second a second ZH270.

Allan tells me you can easily convert a ZH270 to monoblock by strapping the inputs and outputs. This involves connecting the two positive output posts together by soldering a short piece of wire between them, and doing the same with the two positive input posts. Making this connection with a piece of high quality wire on the inside of the unit is preferable to using a RCA Y-adaptor on the inputs. (Take it to an expert technician if you don't feel you are qualified to do this). In case you're wondering about the need to strap the grounds, Allan tells me the circuit is common ground so there is no need to connect the grounds — further evidence of the complicated nature of this unique amplifier. Thus wired, it becomes a 100-watt monoblock into an 8-Ohm load and 140 watts into 4 Ohms. Unlike most strapped amplifiers, Allan tells me the distortion drops almost in half, seemingly breaking all the rules.

"What distortion?" I might ask. Notice that the distortion figures given in the specs below are all unweighted. I had listened for a while both with and without a sheet of ERS paper shielding the top of the amplifier, but could hear no convincing difference. I also used the ZH270 to compare the noise of the conrad-johnson CT6 with the CAT preamplifier. Of course, without setting comparable output levels of the preamplifiers, this was pretty meaningless. Nonetheless, with the volume of each preamplifier cranked to the max, there was only a faint hiss from the tweeter and midrange of the loudspeaker with my ear maybe two inches away from each driver. I was very careful to turn the volume down after making this observation. Don't let your kids watch you try this at home.

Above, I mentioned several of the claims made for this unusual design: high tube efficiency, reduced speaker loading of the output tubes, and enhanced reliability. These three go hand in hand, each one helping to implement the other two. And the three together also argue in favor of this unusual design. While it would not be prudent to touch the tubes, the ZH270 seems to give off less heat than I would expect of a 70 wpc tube amplifier. With the cage in place, as it should always remain, there is no danger of this. The birdseye sheet metal cage and the large 4.25 by 2.27 inch window on the 0.25-inch thick faceplate allow a modest glow in the neighborhood of the amp when listening in the dark. The tube plates do not glow like some other amplifiers that drive the tubes harder. The airiness of the cage also helps keep the operating temperature lower, which will enhance reliability in the long run. I'm told David has never had one go down on him over all these years.

Running the tubes at high efficiency under reduced speaker loading also improves the longevity of the output tubes. The 6JN6 tube, used in push-pull configuration, is a television tube that is no longer in production, but the supply is plentiful and the prices are reasonable, like $5.00 to $15 each, depending on the brand. Since they are so readily available, David does not bother to offer them. But should you need one, you can easily replace just the deficient tube rather than buy a complete matched set. The smart auto-biasing circuit will take care of any differences. If you can afford the amplifier, you can afford a few sets of back-up tubes…not that you're likely to need very many with the estimated tube lifespan being in the neighborhood of 15 to 20 years. Compare that with your own life expectancy. But be sure to buy a sufficient supply to sustain the amplifier's inheritance value. Clearly label them and bequeath them along with the amplifier in your will.

While many look to Class D amplifiers as the ecological saviors of the encroaching energy crisis, there will likely continue to be an elite coterie of aficionados of tube amplifiers, just as there are with old Chris Craft and Garwood wooden motor boats. With the ZH270 being far more efficient than traditional power hungry OTL amplifiers, and more efficient than most other tube amps of this power rating, this looks like a good investment. Granted, it requires more power than a 2A3 SET amplifier, but it opens the door to a wide variety of loudspeakers. The ZH270 also compares favorably with many solid-state amplifiers, particularly those operating in or close to Class A mode.

And of course, you can always choose to join the Green Party, the Sierra Club and simultaneously enhance your musical experience by listening in the dark. That's how it all began for me back when rock ‘n roll was being born — listening on a tube radio in my bedroom late at night with the lights off.

Speaking of conservation, this design goes back to the original energy crisis (in my lifetime) in the 1970's when David invented and patented the screen drive system to achieve higher efficiency. (Check out his website for intricate details). This striving for efficiency extends to the soul of the man who uses a bicycle for his mode of transportation, usually arriving at work before his co-workers when the streets of Washington, DC, are clogged with snow. Rumor has it that when he presented his amplifier at CES in Chicago years ago, he delivered the amplifier himself — on his bicycle! All the way from Maryland! So much for questioning the build quality!


Beauty Is In The Ear Of The Listener...

Aesthetics are another question. The ZH270 reminds me more of laboratory instruments that probably surrounded David in his profession as a government engineer. It also reminds me of the ham radio equipment that absorbed my father the way high-end audio absorbs me. Perhaps that is the source of my respect for his creation. It certainly does not look like typical high-end audio equipment. Nor does it sound like it. Acoustically, it leaps over almost the entire field, landing in the upper echelon of the finest sounding amplifiers. Swathe it in the proper attire, add a remote control and I wouldn't blink an eye at a $10K price tag. But that isn't David Berning; at least not up to this point in his life.

I've written before that he is a man whose body fat approaches the distortion figures of his amplifiers. He is lean and purposeful, just as his creations. The simplicity of his lifestyle and the visual appearance of this amplifier conceal the complexity of both. His formal training as a physicist has given him the creative paintbrush for novel approaches to amplifier design. At a large turnstile, he sits humbly, crafting each and every amplifier to his own perfectionist standard, one part at a time, in small batches. If he were an artist, each one would be different, and he would be a major figure in modern art. But this is audio, and excellence lies not only in design, but also in identical replication. The finished works have a serial number instead of a signature, but they should have both.

By the time you read this David Berning will have retired from his formal career and will no doubt turn his attention to further development of the prototypes he showcased at recent Festivals du Son-Image in Montreal. Astute readers may recall my mention of his million microfarad monoblocks. Undoubtedly, these will be far more expensive than the ZH270. The ZH270 is a Here and Now amplifier that will take your system to the edge of the art, depending on what you surround it with. It has been that way since 1996, with only the adoption of wire and cap options in 2002, which, in this rapidly evolving medium, qualifies it as a classic. The state of the art in audio, after all, is a lot like the avant-garde in the art world. As the saying goes, there is no such thing as the avant-garde; there are only those of us who arrive a little late. It would be very easy to spend a lot more, and receive a lot less. Lucky were the ones who got on board with the ZH270 early on. They were just a little bit late. And the rest of us? You may well relegate it to the bottom of your equipment rack or put it out of sight altogether, but you will not be able to hide from the joy of music.



Type: Push-Pull stereo amplifier

Power Output: 70 watt per channel

Frequency Response: 1.5Hz to 60kHz (at 1W, 8 ohms; +0, -1dB)

Input impedance: 50kOhms

Output Impedance: 1.8 ohms, 

Signal To Noise: 94dB, all feedback settings. 20kHz

Distortion: 1 percent

Dimensions: 12.5 x 15 x 4.5 (WxDxH in inches)

Net Weight: 10 lbs.

Warranty: Limited Two Year

Price: $4995


Company Information

The David Berning Company
12430 McCrossin Lane
Potomac, Maryland 20854

Voice: (301) 926-3371
E-mail: info@zotl.com
Website: www.davidberning.com 













































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