Volume 6

Linear Audio, your tech audio resource, continues to offer you stimulating, interesting and thought-provoking articles as well as projects you can build. Volume 6 is our 7th issue. There are several articles on phono preamps, from the very flexible creation by Erno Borbely with Sigurd Rushkowski to a revamped Peter Walker-inspired minimal design from Hannes Allmaier, supported by a revisit of RIAA noise spec interpretation by Hans Polak. Two articles by David Zan and Bob Cordell address advanced power amplifier compensation. An article on a practical circuit to control class AB bias by Daniel Joffe to prevent output device switch-off, and a very unusual set of designs involving Octode tubes by Frank Blöhbaum. For those of you interested in Static Induction Transistors, Michael Rothacher presents an interactive app to develop SIT Spice models. Robert Munnig Schmidt fine tunes his sensorless motional feedback subwoofer, while David Moran lifts the veil on how to design a blind-preferred speaker. Vol 6 is concluded with an extensive Book Review by Jean-Pierre Vanderreydt of Douglas Self’s 6th ed. of Audio Power Amplifier Design. Vol 6 includes a pair of free JFETs courtesy Linear Systems Inc: one LSK170B and one LSJ74B!
Also, don’t forget to visit the Letters and Articles area on this website for complementary papers and comments to articles. Happy reading, but don’t forget to listen to your music!


Towards advanced audio power amplifiers Vol 6
David Zan

In his Guest Editorial, David Zan argues that almost all power amplifier designs have gyrated to a few standard design topologies. However, he believes that significant improvements are possible with what he calls advanced designs, which focus on advanced compensation methods beyond the ubiquitous Miller-dominant pole compensation. In this article he gives a brief overview of the topologies he is considering, and he will be back in a future article with detailed designs and solutions.


TPC and TMC Feedback Compensation for Power Amplifiers Vol 6
Bob Cordell

Bob Cordell explored power amp compensation techniques that allow the designer to employ more feedback loop gain at higher frequencies, improving amplifier linearity at higher frequencies. Two-Pole Compensation and Transitional Miller Compensation are the two techniques Bob is treating in this article. He describes the theoretical background, comparative simulation results and detailed design guidelines. He concludes that such techniques can give up to 20dB more loop gain at 20kHz with an accompanying reduction in distortion at the top octave, without compromising amplifier stability.


Fine-tuning and measurements of a sensorless motional feedback subwoofer Vol 6
Robert Munnig Schmidt

In his earlier article, Robert Munnig Schmidt described a subwoofer system with an electronic solution to adapt and control the subwoofer mechanical-dynamic behaviour. One reader commented observed a anomaly in the system transfer function, a small 90Hz response peak. One thing lead to another and resulted in this article focusing on the nature of the driver inductance and its variance from a pure inductance. The article also addresses fine-tuning the system and the distortion reduction that can be achieved.


RIAA revisited, or how to better judge documented figures Vol 6
Hans Polak

Hans Polak noticed that the noise specifications of RIAA preamps are often given in units and operation conditions that make it hard to easily judge the comparative merits of different designs. He set out to develop a model that can be applied to ‘translate’ such specifications to a common base for easy comparison; to find out what weighting should be applied to the result to obtain a noise figure that reflects human perception, and to find a S/N ratio that should be considered as the minimum acceptable for good reproduction.

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