The David Berning Company
Established in 1974, The David Berning Company manufactures tube audio amplifiers utilizing the patented ZOTL Impedance Conversion Technology that properly matches high impedance vacuum tubes to the low impedance realm of speakers without the use of traditional audio power output transformers or numerous paralleled output tubes common in traditional OTL designs.
The ZOTL Technology and David Berning's numerous other products have been reviewed over the decades by substantial publications including Stereophile Magazine, Audio Magazine, and The Absolute Sound. In continuous operation for over 40 years, the David Berning Company is among the oldest in audio manufacturing.
Hi-Fi+ Magazine awarded Berning's Quadrature-Z "Power Amplifier of the Year 2009".
Patent # 5,612,646 - ZOTL Technology
U.S. Patent #5,612,646 Output Transformerless Amplifier Impedance Matching Apparatus - a method that properly matches high impedance vacuum tubes to the low impedance realm of speakers without the use of traditional audio power output transformers, yet also without numerous output tubes operated in parallel, the troublesome hallmark of traditional OTL designs.
Patent # 4,163,198 - Audio Amplifier
Patent # 4,163,198 Audio Amplifier - details a hybrid tube-FET amplification stage that forms the basis of the Berning TF-10 preamplifier. An important advantage of this amplification stage is the elimination of the parasitic feedback capacitance and thus providing a stage with improved transient response. This scheme was employed by several audio equipment manufacturers.
Patent # 3,995,226 - Screen Drive Technique - The "Enhancement Amplifier"
Patent # 3,995,226 Audio Amplifier - Tube Screen Drive Technique - details "screen drive", an important part of some tube amplifier designs. The screen drive allows tubes to be operated at much higher efficiencies, much higher power output, and at greatly enhanced reliability. Whereas the patent shows transistors driving tubes, the same principles apply to presently implemented versions of tubes driving tubes. This is also known as the "enhancement" amplifier.
ZOTL Technology vs Audio Output Transformers - This paper demonstrates the electrical performance of an amplifier using the ZOTL technology versus the identical amplifier using a high-quality audio output transformer and presents these differences using oscillographs.
Electronic Devices and the Amplification Process - This paper shows how a curve tracer can be used to explore the attributes of the ZOTL technology and contrast it to the shortcomings of the audio-frequency output transformer. Also shown is how this tool can be used to optimally design an audio power amplifier.
David Berning, Design Engineer
David W. Berning was born in Cincinnati, Ohio, in 1951. He received the B.S. degree in physics from the University of Maryland, College Park, in 1973. In 1974, he joined the National Bureau of Standards (now the National Institute of Standards and Technology, NIST), in Gaithersburg, Maryland. Much of his career has focused on semiconductor device reliability, first using laser-scanning techniques to probe active devices, later on specializing in semiconductor power device reliability.
David worked for National Bureau of Standards (NBS, Gaithersburg, Md.), now National Institute of Standards and Technology (NIST), throughout the 1970s, 80s and 90s, was apparently the first person who combined vacuum tubes in amplifier stages with solid-state and microcomputer devices to maintain the operating parameters at proper, fixed points, and also regularly designed filament voltages to operate at below published specifications in order to extend tube lifetimes. Dave also built some unusual systems including a tri-amplified Magnepag Tympan III's with active equalization, a vacuum tube wristwatch, a vacuum tube D/A converter stage, and a valve front end for a Revox A77 (reel to reel) with techniques adopted from his production designs.
- USPTO patent 5,612,646
- Audio Magazine Review
- Review by Dick Olsher, Enjoy The Music
- Review of Berning ZH-270 using ZOTL Technology, FI Magazine, Dick Olsher, March 1998
- Review of Berning ZH-270 using ZOTL Technology by Martin Appel, Stereo Times, May 1999
- Review of Berning ZH-270 using ZOTL Technology by Gary Beard, Positive Feedback Magazine, Issue 5, 2002
- Hi-Fi+ Magazine, Issue #68 (October, 2009)
- USPTO Patent Search