Volume 8

Enjoy another Linear Audio issue packed with creative, innovative and thought-provoking articles:  Volume 8!

John Atkinson, Stereophile’s Editor-in-Chief kicks off on The Art and Science of the Audio Review and the complementarity of measurements and listening tests.

Signal Processing: Hans Polak writes On Digital Audio Formats and the Nyquist-Shannon Sample Theorem.

Circuit design articles: Frank Blöhbaum on Multiplied Transconductance Amplifiers –part 2: high power amplification – up to for 100W SE Class A  at vanishingly low distortion. Giovanni Stochino continues Feedback Error Correction – some further thoughts on Part 1. Stuart Yaniger completes Equal Opportunity - A Balanced Moving Magnet Phono Stage  - a prototype built and measured. Rudolf Moers  studies The Otto Schade Method - A practical design method for rectifier circuits. Marcel van de Gevel comes up with a simple rule for RIAA noise in Gramophone preamplifier noise calculations - the 3852 Hz-rule revisited. Not satisfied with Square Law amplification, Ian Hegglun goes from square law to A Cube Law audio power amplifier – Class A at ¼ of the idle dissipation, and thanks to the continued generosity of the folks at Eurocircuits.com, each Volume 8 comes with a free PCB* for his amp!

Stan Curtis explores the ago-old question:  Size does matter. Or does it?  - applied to bass speaker drivers.

We have a product- as well as a book review: Morgan Jones puts The μTracer V3.10 – a curve tracer for valves through its paces. Floyd Toole’s Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms is not really new but enough of a landmark to merit a thorough review. David Moran rose to the challenge.

Important note: the free PCB that goes with Vol 8 for Ian Hegglun's cube-law class A amp has a silkscreen error. See the correct orientation here.


Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms - Floyd Toole   Vol 8
David Moran

This book is not really new, but important enough to give it a review in Linear Audio. David Moran rose to the challenge to review a book that, in his words, is both Magisterial and Incomplete. More an essay on loudspeakers and psycho-acoustics, this lengthy review does much more than give you a rundown of the book; it highlights how Toole views these issues, how he influenced speaker development and testing at Harman, and how he is a firm believer in controlled speaker listening tests.  David’s verdict: [a book] to join Olson and Beranek and a very few others on the shelf of profoundly informative and useful acoustical masterworks.


The uTracer V3.10 – a curve tracer for valves      Vol 8
Morgan Jones

Every serious tube buff should have access to at least one tube curve tracer. Some opt for a vintage, refurbished unit, some try their hand at one of the modern, PC-driven implementations. Morgan Jones, who by his own account owns more curve tracers than oscilloscopes, puts the PC-driven uTracer V3.10 through its paces and reports with many sample graphs and usability findings. In the end, he very much likes the unit.


Size does matter. Or does it?   Vol 8
Stan Curtis

In his Vol 8 column, Stan Curtis talks about his journey through the years, trying to come up with the perfect bass reproduction. One question that has been pondered by many: do you want one large woofer driver or would a bunch of smaller drivers in parallel do as well?  Having been in both camps in many different situations, Stan can only conclude that size does matter indeed.


A Cube-law audio power amplifier – class-A at ¼ the idle dissipation      Vol 8
Ian Hegglun

Ian’s article in Volume 1 discussed the design of a square-law amplifier, that is, and amplifier that deliberately uses (output) devices with a square law transfer characteristic, to construct an amplifier that operates in class-A yet requires much less bias current and therefore has much less dissipation than an equivalent traditional class-A amplifier. Not one to rest on his laurels, Ian has extended the concept to using cube law devices. These new breed of amplifiers show class-A operation with only ¼ the dissipation, genuine ‘green class-A’! The new 100W amplifiers operate in class-A for most of the power range, but the power supply and heatsink requirements are like those for a typical 100W class-AB amplifier. Better yet, it is also possible to bias this amplifier in class AB, for even better efficiency; in this configuration, the virtual absence of switching and cross-over distortion will result in a class AB amplifier that is as clean as a class A amplifier! Options for moderate feedback are provided, and the proposed PCB also contains a distortion measurement and indication circuit as well as a clipping indicator. Each Volume 8 comes with a free PCB to build one channel of this amplifier (while stocks last); additional boards are available from Ian’s partner in this project Mason Green at www.greenchild.us

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