Another Linear Audio packed with creative, innovative and thought-provoking articles: Volume 8!
Guest Editorial: 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 completesEqual 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 inGramophone 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!
Column: Stan Curtis explores the ago-old question: Size does matter. Or does it? - applied to bass speaker drivers.
Product review: Morgan Jones puts The μTracer V3.10 – a curve tracer for valves through its paces.
Book review: 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 for Ian Hegglun's cube law class A amp has a silk screen error - see correction here.
Jan Didden, Publisher/Managing Editor
Feedback & Error Correction Master Class!
Some time ago I did a presentation for Menno vanderVeen's Tube Society, on feedback and error correction. The folks at Elektor International Media taped the whole shebang (I talked for more than three hours!) and the result is a very nice DVD. It has the presentation, or, as they call it, the Masterclass, plus a sizeable number of articles and background papers, as well as the sheets I used.
In this Masterclass I address several aspects of feedback in audio amplifiers. The focus of this Masterclass, although not entirely math-free, is on providing insight and understanding of the issues involved. Amongst others, I talk about:
- Basics of negative feedback and its influence on amplifier parameters;
- ‘Gotchas’ like Slew Rate Limiting;
- The impact of feedback on internal overload;
- Stability of feedback amplifiers;
- Feedback ‘speed’ and the difference between delay and phase shift;
- Positive feedback and its effects;
- Simultaneous application of positive and negative feedback in a 50-ies tube amplifier;
- Error Correction according to professor Malcolm Hawksford;
- Error Correction as used in the paX amplifier as published by Elektor in April and May 2008;
- Feedback or Error Correction - a case study: QUAD Current Dumping.
This Masterclass provides a clear overview of the benefits that can be obtained by feedback and its sibling, error correction; but also of its limitations and disadvantages. Note: This Masterclass is also available in the German language.