David Berning
Reviews Worth Reading
Stereophile 2021– Berning EA-2100 amplifier – One of the most gorgeous-sounding and best tubed amplifiers I have heard
Enjoythemusic.com 2006 – ZH270 Amplifier– You will not be able to hide from the joy of music
Hi-Fi+ Magazine Issue #68 October, 2009– Quadrature-Z Power Amplifier of the Year 2009
The Absolute Sound 2025- Berning/Hi-Fi One Reference SET Power Amplifier– If you have the budget and the right loudspeaker, the Berning/Hi-Fi One Reference SET has no peer
An ugly little amplifier– Berning ZH270
Why buying David Berning designed equipment is a safe bet
The David Berning Co. manufactured his unique designs from 1975 into the early 2000’s
Davids new designs are available through companies like ours, that are licensed for manufacture.
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David Berning Bio (1958-current)
Early Meanderings
David Bernings interest in sound reproduction began in 1958 when his father and grandfather made a small system for him. Although it had a plastic tonearm and platter, it featured a nice wooden enclosure with a bass reflex speaker and to these young years, sounded great.
In 1963, when he was 12, a Voice of Music 740 tape recorder arrived, his father’s machine. Now it was time to begin taping. Dave used this machine so much that belt replacements and eventually a head replacement was necessary. His father wasn’t impressed.
Solution- He made his first tape recorder in 1967, based on the 740. Using a washing machine accessory motor and some parts made of wood, it left a lot to be desired. Before the end of high school, 3 more refined models followed and V4, which is still in his possession can be seen in the picture.
His teenage years in the the 1960s featured bicycling and electronics as the two main hobbies and Dave was well known in the neighbourhood as the electronic fix-it guy. A woman in the neighbourhood called with a full-sized colour TV needing service. The skinny teenager arrived on his bicycle to pick up the TV with a trailer like contraption attached to the bike.
The woman had her doubts, but allowed him to take it away. As Dave describes it, he had a choice. At the end of the driveway you could turn left and go down the steep hill or turn right and continue up the big climb. Dave chose right, lugging the beast uphill, as he didn’t trust the bike’s ability to slow down on the downhill with a 100 pound TV behind him. This early bike transporting electronics story will have relevance decades later in his electronics evolution.
As the tape recorders improved, it was now time to address the amplification and DB built his first amplifier, based on an audio output stage from a TV, a single-ended 6V6. He added input stages copied from the RCA tube manual, substituting 6SN7 tubes. This was a very successful build, which he later sold to a friend so he could build something more advanced.
With this encouragement, a push pull amp was built using 29 tubes. The end result, a lot of oscillation. The self taught student realized it was overcomplicated. He did not know at this time how to properly engineer an amplifier, so future builds contained both winners and losers. By now his father had given him a capacitor tester and an oscilloscope and the design was reduced from 29 down to 15 tubes. About this time, David was transitioning from high school to college. He graduated from the University of Maryland with a BS in physics. But during his last year he took some electrical engineering electives where he was top of the class and was able to put together a good knowledge base using a lot of experimental findings combined with formal circuit design techniques.
The Beginnings of Real High Fidelity
Now in a position to really start designing amplifiers, Dave started with hybrid designs using tubes and transistors for his own use. Unaware of the renewed interest in tube amplifiers, he met someone very knowledgeable about the audio hi-fi industry, who had many audiophile friends. This person talked David into helping him build his own tube amplifier. With new amplifier in hand, they visited many audiophiles, trying the amp in various systems. This resulted in many of these people asking David to build one for them. Thus, the David Berning brand of amplifier began in 1975. In 1976, Berning was issued a patent for his tube screen-drive using bipolar transistors. David made many Berning EA2-150B amps that sold well and then licensed the patent to Audionics of Oregon and they produced the BA-150 for several years. All of this was happening while Dave was working as an engineer at the National Bureau of Standards/ NBS/ National Institute of Standards and Technology/ NIST.
At a job interview in 1974, he brought one of his amplifiers in to show his stuff. NBS was looking for someone who could design and build new test instrumentation for special research projects. At that time no such instrumentation was available.
They realized quite quickly that Dave was not your average out-of-the-box thinking guy. He was hired on and worked there for 32 years.
Some of the work was focused on power transistors, finding new measurement methods that would allow the semiconductor industry to make improvements to these devices. Ironically, David designed many of these instruments as hybrids, using tubes as well to obtain a combination of speed, voltage, and power that could not be obtained with solid-state devices.
He developed a very good understanding of the limits under which transistors & tubes could reliably operate . Even more important was an understanding of what phenomena really affected these limits. The value of this understanding played a large role in improving David’s circuit design for new instruments and naturally extended to audio amplifier and power supply design. So David had two parallel careers going forward: the research position at NBS/NIST and making audio amplifiers for sale.
Doing Things Differently
In the late 1970s Berning had designed a tube preamp called the P1 with an external power supply using a line-frequency transformer. A decision was made to make a new preamp, this time with everything in the same enclosure. In order to successfully do this, the line-frequency transformer had to go and a switching power supply looked to be a good possibility.
But no respected high-end audio company, especially not one that made tube amplifiers, had done this.
With a good understanding of power transistor limits, he figured that a tube switcher could be made to work. Line-frequency hum could be eliminated, but the 30 kHz noise could be an issue. It was above audible range, but would it affect the music? So, David did some experiments of mixing the music signal with varying amounts of 30 kHz from a signal generator to see what might audibly affect the music. He could not find any affect at all, so he felt free to go ahead with the switching-powered preamp. This became the TF-10, and it was quite successful with three production runs over the course of seven years. There were certainly naysayers, but the TF-10 got good responses from respected audio reviewers. The TF-10 was also unusual in that the gain stages combined p-channel FETs with tubes, described by another patent. The tube switching power supply he continues to use to this day, especially significant in the high end preamplifiers like the DB2.
At the same time he was making the very popular EA-230 amp. This had a conventional power supply, but used the screen drive, now done with a tube driver stage instead of the patented transistor drive. He had found that the screen drive provided a much more linear transfer characteristic that is triode-like but still has the high output impedance that occurs with pentode operation and normal grid drive. So feedback is still needed to get a reasonable low amplifier output impedance. But the tube idle current can be one tenth of what might normally be used. In the EA-230 this current was only 3 mA, very close to ideal Class B. This did two things- extend tube life and better control output-transformer saturation.
Cycling Inspires Another Breakthrough
Next up for a re-design was a new and larger 100-watt power amplifier, the EA-2100 that would be followed by the EA2101.
Now we return to the bicycle theme. Still working at NIST, Dave volunteered, year after year, to provide the sound system for the Christmas party. No big deal, it was only 20 miles away and he could bike the equipment over prior to the event, in the freezing temperatures of December.
Tube-powered VHS camcorder on bicycle
After years of doing this, a bicycle inspired challenge occurred to him as he had also encountered problems with UPS that had a 75-lbs weight limit, and 100-watt 100 pound tube amps with large output and power transformers would be too heavy.
Time to consider another switcher. 500 watts was needed and the first generation of MOSFETs capable of operation from 120V/240V line voltage had just become available. These early devices were very fragile, expensive, and had reliability issues related to fabrication processes. It took developing a complex slow-start procedure to get them to work. During development of the power supply things blew up many times destroying $100s of transistors plus some other components each time. Success finally prevailed, and the EA-2101 replaced the EA-2100 as better MOSFETs were available and the 6LF6 output tubes used in the EA-2100 were becoming scarce.
Both of these amplifiers use an unusual type of switching power supply called a parallel-resonance topology. Instead of the popular pulse-width modulation this uses frequency modulation for control. There are several nice features that make the added expense worth it. Largely sinusoidal waveforms go through the power transformer instead of fast-rise pulse waveforms thus reducing noise. The other big deal for audio is that there is no limit to the amount of energy storage that can be used, and high amounts of energy storage improves bass impact. Berning amplifiers would all incorporate this topology moving forward.
Concurrent with the EA-2101 David made the TF-12 preamp. An all-tube design with an unusual 80-dB stepped attenuator volume control with digital control.
New Horizons in 1995 – An Output-Transformer-less Amplifier
Around 1995 David was getting tired of the audio business and figured he would quit after all remaining TF-12s and EA2101 amplifiers were sold. But curiosity got the best of him and he started experimenting with trying to use the same parallel-resonance principles used in his power supply to make a power amplifier. The attractive characteristic that he was trying to make use of was the fact that in this topology, the full operating current is recirculated continuously, but power not used by the load is returned to the power supply capacitors rather than being dissipated as waste heat. Perhaps this could have the virtues of Class A without the heat. David actually got it to work but there were distortion issues that he didn’t think he could solve. In the process of experimenting, he tried using a tube as a load for an unregulated square-wave inverter and noted that the tube load would transfer to looking like a load on the power being supplied to the inverter. This had nothing to do with a non-dissipative emulated Class A, but interesting. He wondered if this discovery might work sort of like an output transformer. After a few more experiments, David decided to see if he could build an output-transformer-less amplifier (OTL). He would target a stereo 50-watt unit with resonant switching power supply that would be very light and small.
As an avid cyclist, David had many times carried heavy amplifiers by bicycle and if this designed worked that would be a great improvement.
The NIST office Christmas party was coming up and he always provided the music. He figured that the amplifier could not be very good as it was absurd to think that he could make a pair of switching inverters compete with a good audio-output transformer. But the people at NIST were quite technical and might be fascinated with such a light-weight and small amplifier using tubes.
After completing the amplifier and doing some bench tests, David hooked it up to his speakers and was astonished with what he heard. He had a Shostakovich string quartet LP that he could get only two of the four instruments to sound convincing through his transformer-coupled amps. He could change some parameters and pick up another instrument but he would lose another one in the process. It was very frustrating. But with this crazy new amplifier all four instruments sounded right. At this point David decided not to quit audio, but file a patent instead. The patent issued in 1997 and the ZOTL was born. The late Harvey Rosenberg came up with the ZOTL name, combining OTL with Zero hysteresis as it eliminated the hysteresis present in audio output transformers. The new technology greatly extended the potential frequency response of tube amps and could now pass dc thus allowing good autobias to be included. The first production amplifier was the highly successful ZH270 which is a compact integrated dual 70-watt amplifier that came out in 1996. It has a reliability track record that far exceeds that of any prior Berning transformer-coupled amplifier in spite of its complexity. All Berning amplifiers made since this time have been of the ZOTL type. At the time of this writing, the David Berning Co continues to maintain a website but has not been manufacturing any new equipment for quite a few years.
DB is of the opinion that ZOTL designs most beneficial in power amplifiers and not necessary for our preamplifier designs.
The external, tube switching power supply used in the DB2 tape head preamplifier is very sophisticated and effective but does not use this technology.
Credentials
David Berning (M’03–SM’03) received the B.S. degree in physics from the University of Maryland, College Park, in 1973. He joined the National Bureau of Standards (now the National Institute of Standards and Technology), Gaithersburg, MD, in 1974. Much of his career has focused on semiconductor device reliability, first using laser-scanning techniques to probe active devices, and later using electrical methods to explore safe operating area for power devices. He is currently involved in developing techniques for characterizing high-voltage, high-speed SiC power diodes and MOSFETs. He owns three U.S. patents in the area of audio amplifier design.
Publication Topics
Insulated Gate Bipolar Transistor,Adiabatic Heating,Antiparallel Diode,Blocking Voltage,Bus Voltage,Current Stress,Current Switching,Drain Current,Drain Voltage,Dynamics Simulation Approach,External Capacitor,Extraction Parameters,Figure Of Merit,High Voltage Direct Current,I-V Curves,Junction Barrier Schottky Diodes,Junction Capacitance,Junction Temperature,Node Density,Opposite Characteristics,PIN Diodes,Power MOSFETs,Reverse Current,Reverse Recovery,Reversible Charge
