It's always a special moment every year, when audioXpress looks back at its roots in Glass Audio and combines some of the best tube-based audio articles. This year, our cover highlights another unique project from tube expert Menno van der Veen, in direct collaboration with his TubeSociety students Erwin Reins and Hans Gubbens who built and validated prototypes based on the project described in this issue.That project is the Vanderveen Trans PP80 Valve Amplifier, a new push-pull valve amplifier, featuring the Trans technique researched by Menno van der Veen, and the focus on much of his work. In fact, this valve amplifier is described as "the next step" in the author's research on transconductance. The Trans PP80 amplifier delivers 80W of refined resolution, valve-sound envelopment, with the lowest distortion plus good speaker damping. And for DIY builders, this is a simple-to-construct design.
The next article, which will expand into the June 2023 issue of audioXpress, is a detailed report of a very unique project by Thomas Perazella. In this case, his project is a rebuild of an amplifier that our readers will enjoy. Rebuilding an amplifier for reasons of better reliability, better aesthetics or bringing it up to the latest standards can be very rewarding. And if it is a classical, technological grandstand, with a different angle on audio amplifier design with 300B tubes, even more so. Tom embarked on such an adventure with nothing less than a famous David Berning ZOTL amplifier. In Part 1 of this article, Tom presents the amplifier and discusses its unique circuitry. In Part 2, he will proceed to dismantle and rebuild the amp for a new owner on a new chassis.
The third article in our Glass Audio special comes from Peter Dieleman, which many of our readers likely know from his books on the theory and practice of tube amplifiers. His article on this issue focuses on Myths in Tube Circuit Designs which repeatedly show up, reflecting some common misunderstandings. To debunk some of them, he discusses load (mis) match in output stages, which is by definition perceived as a bad thing, when that might not be necessarily the case. Another myth example regards the efficiency of a triode output stage versus a pentode. The article is complemented with more detailed mathematical derivations, available as Supplementary Material on the audioXpress website.
Also for this tube-focused issue, Richard Honeycutt decided to travel Down Memory Lane in his Hollow-State Electronics column. In this case, how the history of tubes was also written - and continues to thrive today - in amplifiers for electric guitars. Richard remembers his first contact with "starter" guitar amps as a teenager, including an unbranded 1950s model that was naturally good on... hum, followed by a Silvertone Model 1484 Twin Twelve in the 1960s, and a 1972 Rickenbacker B-115. And he includes the schematics.
The next article is not about tubes, but is certainly one of the most eagerly awaited reviews of a modern module amplifier. The new NCx500 amplifier board is the first of a new NCOREx family of modules that evolves from the extremely popular NCORE Class-D amplifier technology, one of the most successful options among high-end audio and studio monitor brands. Stuart Yaniger was able to spend a few weeks with this next flagship from Dutch manufacturer Hypex Electronics. How will this improved NCOREx technology measure up? And will it deliver the "x" times improvements over the proven NCORE? Stuart shares all the juicy details.
For those who need to refresh their knowledge or learn about audio test and measurements, our technical editor Jan Didden reviews a great - and big! - book on the topic. Audio Tests & Measurements by Igor S. Popovitch is one of the many self-published works by this proficient writer based in Australia, also the author of several popular books on vacuum tube amplifiers.
Next up, this issue includes the second part of Burkhard Vogel's article on Vintage Op-Amp Noise Simulation, which is actually an expansion of his extensive work on the topic, and of his book Slopes and Levels Spice Models to Simulate Vintage Op-Amp Noise, which audioXpress reviewed recently. An expert on calculations of the input noise of vintage operational amplifiers, this article follows his study on the deviations from realistic noise figures in datasheets, based on measurements and calculations for real op-amps. Part 2 expands his findings through the use of Mathcad calculations, culminating in an accurate Spice model for the noise sources, and conclusion about noise source correlations.
Our DIY readers will also enjoy Part 2 (and conclusion) of Bruce E. Gillingham's article that was initiated in the April issue of audioXpress, describing the MB1 high-power (300W into 4Ω), bipolar, Class-AB, monoblock audio power amplifier featuring an original precision bias controller. This month, Bruce completes the details of the system circuitry, mechanical design and its performance measurements. A very high-quality project from an expert in analog preamplifiers and power amplifiers.
And finally, Chuck Hansen continues to explore the fascinating history of transformer cores, construction methods and materials, and the various technical parameters of transformers. The initial group of articles focused on the history of transformer cores, construction methods and materials, and various testing methods. Part 7 looks at the various transformer core types, their advantages and disadvantages, and the coil winding machines used to make them into transformers.
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