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Glass Audio Klippel triode SRPP Rudolf Moers DIY audio audio electronics DIY
project tube amplifiers Christopher Paul Dimitri Danyuk Roon Labs GIK Acoustics
Menno van der Veen tube sound Purifi Audio Andrew C. Russell Hifisonix Tim
Mellow TubeSociety May 2024 English Acoustics zero output impedance Pure
Acourate Sound Okto Research AudioVero Rose Handwerk Joachim Gerhard Tom
Christiansen Neurochrome
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 * by audioXpress Staff
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AUDIOXPRESS MAY 2024 GLASS AUDIO SPECIAL ISSUE NOW AVAILABLE

April 12 2024, 12:00
In the 2024 Glass Audio Special issue there’s Menno van der Veen’s TubeSociety
TS-2022-OTL hybrid amplifier, and a Low-Feedback Triode Amplifier With Zero
Output Impedance (ZOI) as DIY projects, designed by Tim Mellow and Peter Farrow.
More great audio electronic articles by Rudolf Moers, Christopher Paul, and
Dimitri Danyuk. Read about sustainable acoustical absorption, the Pure Acourate
Sound Project, and The Neurochrome Story. And Andrew C. Russell concludes his
High-Performance 60-Watt Class A Amplifier project.
Every May, we publish the Glass Audio/Tube Focus edition of audioXpress. For the
2024 issue, audioXpress is proud to present two high-quality practical projects,
together with two in-depth explorations of tube electronics, all written by
leading experts in this field.

The first DIY article details the theory and construction of the TubeSociety
TS-2022-OTL amplifier, another unique project conceived by Menno van der Veen’s
TubeSociety. Every year, TubeSociety designs and builds a new type of tube
amplifier, and for this project they decided to explore an
output-transformer-less (OTL) hybrid design: a non-feedback hybrid amplifier
with a Tube driver and push-pull MOSFET output stage. As Menno van der Veen
described the result, “Without any global negative feedback, this amp shows the
beautiful tube-amp spacious sound character and mild overdrive where we were
aiming at, plus a lot of power.”

The second article in the DIY perspective, written by Tim Mellow and Peter
Farrow, is a Low-Feedback Triode Amplifier with Zero Output Impedance (ZOI).
This is a very high-quality project that resulted from the collaboration between
the two authors, now working together on a new venture called English Acoustics.
Mellow previously designed an OTL amplifier with inherent load protection and
symmetry throughout, which was published in audioXpress in February 2010. He is
designing circuits and audio transformers for English Acoustics, which Farrow
started in 2016. Farrow has designed many tube amplifiers in multiple
topologies, always praised for their sound and build quality.


Divided in two parts, this issue introduces the Zero Output Impedance amplifier
concept, and discusses the design for a single-ended input version. In Part 2
(June 2024), the concept is extended to a balanced input version, with
performance measurements. There will be two Appendices that provide detailed
design calculations for both configurations.

Evolving from a practical to a theoretical approach, the next article is written
by Rudolf Moers, discussing Tube Output Power, or more precisely, determining
output transformer impedance for maximum output power. Motivated by one of the
pervasive myths in single-ended audio tube amplifier design, that the maximum
output efficiency that can be obtained is 25%, Moers compares several methods to
determine the output transformer impedance for a triode tube amplifier output
stage to obtain maximum output power. The methods give different results that
can be questioned, nevertheless showing that efficiencies greater than 25% are
possible.

A second article in the broader audio electronics domain, brought by Christopher
Paul, explores the possibility of extending the features of the venerable SRPP
circuit, and specifically some concepts involving matched and unmatched triodes.
In Optimizing Single-Stage Dual-Triode Totem Pole Drivers, Paul states that what
makes these dual-triode circuits interesting is the ability to combine some of
the low impedance output characteristics of a cathode follower with the voltage
amplification capability of a common-cathode stage, all while sharing the load
driving responsibilities equally between the two triodes. But that’s just the
start of the exploration.


This issue also features a new contribution by Dimitri Danyuk, which many of our
readers recognized from previous very high-level contributions. In a previous
article for audioXpress, Danyuk discussed open-loop complementary current
followers, which have generated great interest and numerous requests for
additional information. For this add-on article, the Open-Loop Complementary
Follower as an Amplifying Stage, Danyuk delves deeper into transconductance
stage implementation, and other considerations.

Although there’s more in the audio electronics domain in this issue, we step
away from tubes to enter the always fascinating world of acoustics. In his Sound
Control column, Richard Honeycutt writes about acoustical absorption and how new
21st century materials enable balanced sound absorption while meeting an
increasingly important requirement: sustainability. Meeting those two goals
effectively deserves some explorations with real examples, which is what this
article details.

And from acoustics, we go straight to another fascinating project that combines
all disciplines that make great sound. Rens Tellers and Jan Didden traveled to
Germany to learn about the Pure Acourate Sound Project, which aims to create the
lowest distortion sound in a listening room. The initiators of the Pure Acourate
Sound project are Ulrich Brüggemann, Markus Grelka, and Ralf Höllmann. The
partners involved in this unique system are Purifi Audio, Okto Research, GIK
Acoustics, Klippel, Roon, AudioVero, Rose Handwerk, and Joachim Gerhard. Ahead
of the presentation at the May 2024 Munich High-End show, audioXpress offers a
preview of the project.

Next, Tom Christiansen offers his very own account of his professional journey
that led to the creation of his company, successfully serving audio enthusiasts
all over the world with a complete range of power amplifiers kits and circuits,
ranging from 40W to 240W (8Ω) - all well-engineered, thoroughly tested, and
well-documented. In The Neurochrome Story, Christiansen shares what it is like
to build a small, highly dedicated audio company, providing inspiration, or
perhaps a forewarning, for those wishing to venture into the audio business.

And finally, there’s even more practical builds, with the second part of A
High-Performance 60-Watt Class A Amplifier, by Andrew C. Russell. This project,
named the ax-Amplifier, uses Augmented Feedback Error Correction (AFEC) to
achieve ultra-low distortion and improve key audio performance parameters
without adding too much complexity and cost. The first part of this article
described the amplifier design in detail, with this second and final part
detailing the power supply system and conclusion with measurements. We know many
of our readers would like to build a high-quality amplifier, and this project,
designed by the founder of Hifisonix.com, delivers on every front.
 


All the content contained in every issue of audioXpress is the reason, month
after month, 12 times per year, this publication continues to reinforce its role
as an essential resource for the audio industry. Your support and that of our
advertisers is what allows us to keep this publication in print and all digital
platforms and pay our independent authors and contributors for their work.

Subscribe if you haven't done so yet in order not to miss future issues or renew
your subscription. Subscribing to the digital online version allows immediate
access and is available here: audioXpress Subscription Services

If you wish to buy a single printed issue or the complete audioXpress archive on
USB, from 2000 to 2024 (yes, including the latest issue), just visit our online
shop at www.cc-webshop.com

Don't miss out, get your copy of audioXpress right now at www.gotomyxpress.com


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