Menno van der Veen, the most famous audio transformer designer in the world, shares his knowledge in books for DIYers. Andre Jute reviews two key books by Menno.
Transformers and Tubes in Power Amplifiers
by Menno van der Veen
Published by Plitron $26
Lab Report: Specialist Range--Toroidal Output Transformers
by Menno van der Veen
Published by Plitron $12
Reviewed by Andre Jute
Menno van der Veen's Transformers and Tubes in Power Amplifiers had been available for some years in its Dutch original before Plitron, the Canadian makers of toroidal output transformers designed by its author, commissioned an English translation. When I started out in tubes, I had Het Vanderveen Buizenbouwbook (The Vanderveen Tube (Amplifier) Building Book) on loan from a retired Philips engineer who lived nearby and, though it has long since been returned to its owner, my memory is that it was a bit thinner: the English version seems expanded.
Since I struggled all the way through it with my rusty, non-technical, literary, court- and diplomatic-Dutch, it must have been a very fine book!
The English version confirms my memory in all respects. This is a most useful handbook for the beginner in tubes, and contains many small nuggets and insights to delight the old hand.
Menno van der Veen believes, like everyone else, that the output transformer is the key to a good amplifier. But, unlike most of us, he is a transformer designer. So his first chapter is an introduction to output transformers, ratios, operating classes, and a detailed explanation of the parameters that define a transformer, exactly the sort of information that some other transformer winders try very hard not to share.
Van der Veen writes well in Dutch and engagingly in English. He has worked in education and the theatre, he is a longtime contributor to hobbyist magazines, and he is a practised public speaker. He makes transformers seem so easy, anyone could do it! Of course they can't--but van der Veen gives everyone who pays even passing attention a firm enough grasp to specify a custom transformer with some confidence.
The rest of the book is more conventionally structured, if one's convention is practical application rather than an academic and theoretical approach. The latter would start at the input and deal with voltage amplification first. But a real-life designer asks first which loudspeaker is to be used with the amplifier to be designed, and this is the van der Veen approach.
Chapter 2 is therefore revealingly called "The Output Transformer between the Tubes and the Loudspeaker";. Quite naturally the transformer designer's book uses his own transformers as examples. So we discover that there are what van der Veen considers very good reasons to settle on a 5 ohm secondary for almost all purposes. On the other hand, on the primary of a push--pull output, he likes offering the buyer the opportunity to change between common pentode, ultra-linear and triode-connected operation.
The entire book is lavishly illustrated with diagrams, tables and many, many schematics, so that one can follow most of the argument just in the pictures.
But you mustn't get the idea that van der Veen shrinks from the difficult and the complicated. He just works harder to explain it comprehensibly. Matters like damping factor, frequency bandwidth, power bandwidth and so on are all dealt with.
But, cleverly, he has separated off the really difficult stuff. "The Output Transformer in the Complex Domain"; covers matters like Phase Angle and Differential Phase that all but the congenitally obsessive now thank god can be modelled on computers--after understanding it once out of van der Veen's book!
Next he shows a complete worked example of how an output stage might be specified, concluding with specifics for two of his own transformers.
Van der Veen believes in designing with current production tubes, and not the most expensive of those either. So, for power tubes he uses EL-84 and EL-34 for most of his examples, with the KT88 getting an honourable mention. This is perfectly right. When someone is just starting out in tubes, he wants to start with goodsounding tubes that don't cost a lot, and the EL-84 and EL-34 are absolutely perfect, and KT88 needn't cost the earth.
He also believes in the 12A?7/ECC8x tube family for the voltage and phase splitter stages and, judging by the chapter on phase splitters, does not partake of the modern fad for whatever the fashionable driver topology of the week might be. He covers the classic thoroughly and gives diagrams for the lesser topologies but no great description. It is quite clear which he wants his reader to choose!
In fact, much of the chapter is given over to considerations of getting rid of hum in these stages, and so getting a quiet amp.
Van der Veen's transformers are most famously made by Plitron, who must have creamed themselves to discover that the longest chapter in the book consists of detailed description, with full circuits with all component values included, for no fewer than five bulletproof push-pull amplifier designs--all using Plitron transformers! (Plitron even sells a $60US board for one of these designs, though it must have been added after the book was published because it isn't mentioned in the Plitron advertisement in the back of the book.) These are designs for amplifiers from 10 to 100 watts that anyone can build after reading this book. Van der Veen offers full information about setting up and adjusting the built amp, and there is a complete later chapter called "Construction Hints"; to ensure practical success.
The next two chapters seem a little oddly out of sequence, since we already built the amp and are sitting back, relaxing, listening to it, not wanting to stretch the grey cells with a chapter introducing feedback intuitively, followed by another dealing more analytically and practically with feedback. Still, van der Veen makes a good case for the correct amount of feedback, and helps the budding designer decide what is the right amount, but once more, thank god one can build a computer model with the information he provides rather than working it out on a calculator! Van der Veen, incidentally, himself is a big fan of putting the hard stuff on the computer to leave himself and us time and leisure to move the nulls and poles in the Laplace domain we each have in our heads.
The final chapter consists of layout and construction hints, with a thorough consideration of ground (already touched on in earlier chapters) and safety.
There is an also eclectic bibliography which demonstrates better than words that building amplifiers is both a science and an art, in the service of a great art, music. Finally there is a glossary of symbols used in speaking or writing about amplifiers, though it is heavily slanted towards transformer design usage: nothing as simple as plain old RL for load on the tube!
This is followed by many pages of detailed calculated and measured characteristics of van der Veen transformers in the range available from Plitron, and by a Plitron order form, and then by some biographical information about the author.
For 26USD this book seems a bargain. It is well-written, intelligently developed, comprehensibly structured, and has the bonus of those classic designs laid out in detail. It is a fun way to get serious with tube amps.
Of course, however much we might enjoy a grand engineer when he is being entertaining, behind the scenes the good ones always do their own heavy lifting. Menno van der Veen is no exception.
In Lab Report: Specialist Range--Toroidal Output Transformers he introduces the thinking behind a new range of advanced toroidal output transformers, also made by Plitron. Essentially these are a response to the need for larger damping factors required by the advent of digital audio. Van der Veen is far too experienced to try and do it with more and more global feedback, so these six new output transformers are in effect hardware solutions to providing greater damping via local feedback.
This 28-page booklet explains the thinking behind the three strategies used. It is not too tricky to follow, actually, because van der Veen relates what he's doing to known designs, for instance explaining the new SSCR types with their separate screen windings as a way to use ultra-linear with 6550WA or 6L6GC or other tubes which require lower DC voltages at the screen grids than at the plate. Similarly, he relates the cathode feedback techniques of the new CFB types to McIntosh, Bogen, Walker (Quad) and AR designs, and the Unity Coupled design to McIntosh. He also demonstrates a fascinating new circuit he calls "the super pentode".
If you want to be up with the latest thinking in push-pull amps, you need to get and master this $12US booklet from Plitron.
Plitron, #8 601 Magnetic Dr., Toronto, Ont., Canada, M3J 3J2 Tel: 1-800-754 8766 416-667-9914 Fax: 416-667-8928 E-mail: email@example.com, firstname.lastname@example.org
Ir. Menno van der Veen, Ir. buro Vanderveen, Vordensebeek 34, 8033 DE Swolle, The Netherland. Tel 31-384-547-704 Fax 31-384-533-178
© 1998 Andre Jute
André Jute was educated at universities in South Africa, Australia and the United States in psychology, economics and business management. He has worked in advertising, management consulting, and as a political and military advisor, and is now Chairman of the graphic and industrial design house Communication Jute. He is a distinguished novelist and writes a column on classical music read every week by 9.2m music lovers. Before taking up tube amp design, he designed and built complete automobiles.
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