Elektor Electronics (April 2007)

Valve Amplifiers are regarded by many to be the ne plus ultra when it comes to processing audio signals. The combination of classical technology and modern components has resulted in a revival of the valve amplifier. The use of toraidal-core output transformers, developed by the author over the past 15 years, has contributed to this revival. The most remarkable features of these transformers are their extremely wide frequency ranges and their very low levels of linear and nonlinear distortion. This book explains the whys and wherefores of toroidal output transformers at various technical levels, starting with elementary concepts and culminating in complete mathematical descriptions. In all of this, the interactions of the output valves, transformer and loudspeaker form the central theme. Next come the practical aspects. The schematic diagram of a valve amplifier often appears to be very simple at first glance, but anyone who has built a modern valve amplifier knows that a lot of critical details are hidden behind this apparent simplicity. These are discussed extensively, in connection with designs for amplifiers with output powers ranging from 10 to 100 watts. Finally, the author gives some attention to a number of special valve amplifiers, and to the theory and practice of negative feedback. In summary, this book offers innovative solutions for achieving perfect audio quality. Do-it-yourself builders, as well as persons who want to gain a deeper technical understanding of the complex world of audio transformers, valve amplifiers and audio signal processing, will find this book a rich and useful source of information. Top of the range hi-fi apparatus is now termed 'high-end equipment' and the name is a good indication of the prices charged for it. For those who can not, or will not, pay these prices, there is another solution offered in this build your own (at considerable cost savings). But this book is aimed not only at this sector of the market, but also at the many enthusiasts who want to be able to experiment and make their own modifications to their 'high-end' equipment. This book contains construction projects for solid-state and valve preamplifiers and power amplifiers, active cross-over filters, an active subwoofer, a mono/stereo compressor and a headphone amplifier. To many people, the thermionic valve or electron tube is history. However, whether it is nostalgia, interest in the technical parameters, the appeal of a gleaming amplifier chassis with softly glowing valves, respect for the technical know-how of an earlier generation, or perhaps the firm conviction that the sound of a valve cannot be bettered, it is a fact that the valve is making a come-back. This book contains, apart from construction projects for preamplifiers, power amplifiers, and two amplifiers for musical instruments, information on the operation of electron tubes, while the first chapter gives a short history of the valve.