A Look Inside Douglas Self’s "Small Signal Audio Design" 4th edition

Whether it is power amplifiers, vinyl reproduction preamplifiers, active crossover filters or, as in this case, small-signal circuits for a very wide range of applications, Douglas Self is one of those authors who consistently has produced reference works about technical audio. You may think that as a fourth edition, it would just be a refinement on the three editions that went before it but Self always adds new material and new insights to make it worthwhile to get this new book.

This article details a lifetime project from audioXpress' technical editor Jan Didden. After a successful restoration project of a pair of precious ESL-63 Quad electrostatic speakers, he opted to design and build the eDD, a well-performing high voltage amplifier to directly drive electrostatic speakers. This challenging but successful DIY project with a design goal of 1500V RMS at 20mA RMS over the full audio band, took a while to complete but was a success. This article shares every step of the construction.

A loudspeaker is a mechanically moving system and like any such system, it cannot stop moving in zero time. For example, if a tone is reproduced, and the amplifier outputs a zero voltage at the end of the tone, the speaker cone will not stop immediately but will tend to keep on moving with lower and lower amplitude and eventually come to a stop. Jan Didden explores Loudspeaker Damping Factor in simple terms.

With a visit to Dutch & Dutch, Jan Didden unveils the journey of this innovative speaker manufacturer from The Netherlands. This company, founded in 2014, has so far achieved remarkable success with a single product designed to break the vicious cycle of speakers and room acoustics. The Dutch & Dutch 8c is a no-compromise active speaker designed to work together with the acoustics of the listening room.

The principles applied by Dr. Reinhold Lutz's for precise measurement of the sound pressure frequency response in the presence of room modes, are available in its AudioChiemgau Mode-Compensator solution. Jan Didden and Rens Tellers did a basic functional test to find out how well they could make it work and they were pleasantly surprised with the results. This article was originally published in audioXpress, October 2023.

audioXpress December 2023 includes a market overview of multiroom audio, Brent Butterworth writes about new ways to measure ANC earbuds, and Stuart Yaniger measured the new Axign and GaN Systems Class-D audio amplifier board. Richard Honeycutt writes about tubes, BJTs, JFETs, MOSFETs, and ICs, and Dimitri Danyuk, discusses JFETs in audio circuits. Douglas Self explains how to optimize variable-frequency tone controls, and Jan Didden shares his eDD direct-drive amplifier project.

To reproduce an audio signal faithfully over the whole audio band, your circuit needs to have a bandwidth at least as large as the audio band. But that’s not the only requirement: your circuit needs to maintain that bandwidth from the lowest to the highest signal level. That’s where the crux lies: it is relatively easy to get a nice wide bandwidth for small signals, only to have it breakdown with high signal levels due to the dreaded slew rate limiting.

This article, originally published in The Audio Voice newsletter (#434), explores some practical experiments with Negative Feedback. "If I had a dollar for every time someone mentioned that negative feedback cannot work, because you cannot correct something after it happened, I would be a rich man," says Jan Didden. "Yes, it can be hard to get your head around feedback circuits for audio amplifiers. Yet, all it takes is to look around you," he adds.

audioXpress visited Grimm Audio in The Netherlands to learn more about the people behind this unique company, its products, and philosophy. There's nothing better to learn about product development than to visit an audio company and learn from its history and business journey. As a relatively young company, Grimm Audio has consistently put its mark on both the pro audio and hi-fi scene and Jan Didden shares what he learned about their unique in-house development philosophy. This article was originally published in audioXpress, July 2023.

What happens when you add Head-Tracking, Head Related Transfer Functions (HRTF), Room Impulse Responses (RIR), and Binaural Room Impulse Responses (BRIR)? Sharing his experience at the AES Europe 2023 Convention, held at Aalto University, Espoo, Helsinki, Finland (May 13 – 15), Jan Didden writes about listening to speakers on headphones and how good this is getting. How convincing is it? Very.