“The same thrill, the same awe and mystery, come again and again when we look at any problem deep enough. With more knowledge comes deeper, more wonderful mystery, luring one on to penetrate deeper still”
Richard P Feynman, The pleasure of finding things out, Helix Books/Perseus Books, 1999. Read it.
New Linear Audio Volume 7 published!
Linear Audio, your tech audio resource, continues to offer you stimulating, interesting and thought-provoking articles as well as projects you can build. Volume 7 is our 8th issue.
We start of with a guest editorial by Joachim Gerhard who documents, from a personal view, his year-long adventure through listening space to end up with the G-pole speaker.
We welcome several new authors: Barrie Gilbert contributes the 1st part of several, starting with explaining how to use simulation for design in an intelligent way. Malcolm Hawksford draws on many years of teaching to give us an overview of equalization in audio. Giovanni Stochino reviews the results of many years of research covering different error correction topologies and discussing their pro's and con's.
Several circuit design articles discuss advanced power amplifiers (David Zan), a simple yet effective low noise measurement amplifier (Burkhard Vogel), and a hybrid phono preamp (Stuart Yaniger).
George Ntanavaras went on a quest for the ideal speaker enclosure shape for surround use and came up with the Prisma loudspeaker.
Vol 7 has two reviews: Marcel van de Gevel read Morgan Jones's 2nd edition of Building Valve Amplifiers, and Stuart Yaniger and yours truly reviewed the Smyth Research Realiser A8, a 'listening room / speaker virtualiser'.
And, traditionally, Stan Curtis in his column throws down a gauntlet with a possible way to explain (and cure) audible differences between different implementations of the same circuit. If you have an idea on how to verify his solution in a controlled way, let me know!
Enjoy another issue packed with creative, innovative and thought-provoking articles!
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.