audioXpress Magazine      May 2024

  audioXpress remains the authority on audio and reproduced sound by connecting manufacturers and distributors with developers, buyers and consultants around the globe! It's readers are the audio product designers, consultants, integrators, DIY enthusiasts, opinion leaders and your best customers. All of them agree that the coverage of trending topics, unique in the audio industry, make audioXpress a must read.

Every month, audioXpress combines the best educational articles on topic such audio electronics, speaker and headphone design, amplifiers (from tube to Class D), acoustics, practical test and measurement, audio engineering praxis, and standards. audioXpress provides inside stories on new audio developments, on R&D Stories, the most complete objective reviews of innovative products and software, and selects some of the best DIY audio projects from worldwide experts.

From the Editor's Desk
No Truth. Just Joy.
Music and audio is one of the noblest endeavors.
Editorial By J. Martins
My experience of over three decades in the audio sector reinforced a conviction that no matter how hard we try, there is no way to achieve truth in audio, just joy. And that the latter is completely independent of the former. This is a fundamental principle on my standing about audio technologies. I care about good audio experiences and I believe that our efforts should be focused on eliminating bad sound, not so much about achieving exceptionally great fidelity — that illusive quest. Do I have a low bar when it comes to audio experiences? I just know when I find joy listening to music. That's why I admire product designers that manage to create great sounding products that are also affordable. The joy they bring to so many is incomparably more impactful than any $100,000 high-end piece of gear could ever induce.
---> No Truth. Just Joy.

5 Supporting Companies

Features
46 Pure Acourate Sound Project
Greater Than the Sum of Its Parts
By Rens Tellers And Jan Didden
What happens when many talented people focus
on a common objective aiming to create the lowest
distortion sound in a listening room? The Pure
Acourate Sound project is the result! audioXpress
was invited for a preview and reports, ahead of the
planned presentation at the 2024 Munich High-End
show.

52 The Neurochrome Story
By Tom Christiansen
Audio enthusiasts often dream of setting up their
own audio company, few actually do, and even
fewer succeed in creating a viable business. Tom
Christiansen accomplished both of these things. His
story offers a glimpse into the daily life of a small
audio company, providing inspiration, or perhaps a
forewarning, for those wishing to venture into the
audio business.

56 The Open-Loop Complementary Follower
And An Amplifying Stage
By Dimitri Danyuk
In a previous article, Dimitri Danyuk discussed
unusual applications of the open-loop complementary
follower for current transfer. Following numerous
requests for additional information, this add-on article
delves into transconductance stage implementation.

60 A High-Performance 60-Watt Class A Amplifier
Part 2 — The Power Supply and Measurements
By Andrew C. Russell
This project, named the ax-Amplifier, uses Augmented
Feedback Error Correction (AFEC) to achieve ultralow
distortion and improve key audio performance
parameters without adding too much complexity
and cost. The first part of this article detailed the
amplifier design, while this second and final part
discusses the power supply system and conclusion
with measurements.

Columns
Sound Control
40 Sustainable Acoustical Absorption
By Richard Honeycutt
Acoustical absorption is often needed in new or renovated
buildings to tame reverberation times. New 21st century
materials enable balanced sound absorption while meeting
an increasingly important requirement: sustainability.

Glass Audio
8 The TubeSociety 2022 OTL Hybrid Tube Amplifier
By Menno van der Veen
TubeSociety designed a non-feedback hybrid amplifier
with a tube driver and a push-pull MOSFET output section.
The result? Fifty watts of real tube power!

16 A Low-Feedback Triode Amplifier With Zero Output Impedance
Part 1 — Introduction and Single-Ended Input Amplifier Design
By Tim Mellow and Peter Farrow
This article introduces the Zero Output Impedance (ZOI)
amplifier concept and discusses the design for a
single-ended input version.

22 Tube Output Power
Determining Output Transformer Impedance For Maximum Output Power
By Rudolf Moers
One of the pervasive myths in single-ended audio tube
amplifier design is that the maximum output efficiency
that can be obtained is 25%. In this article several methods
are compared to determine the output transformer impedance
for a triode tube amplifier output stage to obtain maximum
output power. The methods give different results, but it will be
clear that efficiencies greater than 25% are possible.
The validity of the different methods will also be addressed.

30 Optimizing Single-Stage Dual-Triode Totem Pole Drivers
By Christopher Paul
Following some recent discussions and exchanges involving
the possibility of extending the features of the venerable
shunt regulated push-pull (SRPP) circuit, this article explores
some concepts involving matched and unmatched triodes.

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