After a very successful three succesive weekends at Burning Amp, Rocky Mountain Audio Fest and AES 135th Convention, I'm now getting ready for the European Triode Festival in Berlin end of November. Another very interesting gathering of (tube) audio diy-ers with lots of listening, discussing and plain fun!
New Linear Audio Volume just out - Volume 6!
Comes with a free LSK170B and LSJ74B, courtesy Linear Systems, Inc!
I was again very fortunate to have excellent articles from very knowledgeable authors for this 7th bookzine.
David Zan is preparing to write about Advanced audio power amplifiers in a future issue – in his Guest Editorial he explains his reasoning and what he means by ‘Advanced’. Our friend Bob Cordell explains his own perspective on Advanced Amplifier concepts in TPC and TMC Feedback Compensation for Power Amplifiers. Robert Munnig Schmidt is back with Fine-tuning and measurements of a sensorless motional feedback subwoofer. In RIAA Revisited, or how to better judge documented figures, Hans Polak reconciles phono preamp specifications that often excel in data that cannot be compared between units. In his Introduction to noise Ronald Quan provides a nice, clear overview of noise issues in circuit design.
Then it is on to circuit design with Frank Blöhbaum showing that you can use an unseemly collection of exotic vacuum devices to make great Multiplied Transconductance Amplifiers. Diehard Erno Borbely teamed up again with Sigurd Ruschkowski to design Proteus – a current input moving coil preamp. In contrast, Hannes Allmaier went back to Peter Walker’s 3-transistor design and morphed it into The High-Octane phono preamp. Daniel Joffe tried his hand – successfully – at Practical Electronic Control of Class AB Output Stage Quiescent Current.
Michael Rothacher, no newcomer to SITs, developed an interactive app for A Concise Model for Static Induction Transistor IV Characteristics which you can use with any Spice-compatible simulator. And if you ever wondered How to design a winning, blind-preferred loudspeaker – David Moran tells all.
Our columnist Stan Curtis notes that The map is not the world and reviews what can go wrong with your wonderful prototype on its way to a real-world product. Finally, Jean Pierre Vanderreydt reviews Douglas Self’s latest tome, Audio Power Amplifier Design, 6th edition, and likes what he reads.
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.