John Upton

October 1997

Beginner's Guide to Tube Audio Design

Author: Bruce Rozenblit

Tube-based audio has always had a do-it-yourself (DIY) aura about it. Whether this mystique evolved from a lack of commercial availability of certain tube powered amplifiers, especially those of the single-ended variety, or whether tube-based hi-fi naturally lends itself to hobbyist involvement, suffice it to say that there has always been a dedicated underground of amateur audio alchemists pursuing that elusive goal of turning electricity into music. Up until the past few years, it appeared that this movement would remain on the outskirts of the high end. With recent renewed interest in tube audio gear, however, many of the ideas, concepts, and design theories behind the hobbyist approach have been slowly bubbling up from this "fringe" element. Today, the high end is experiencing a steady influx of products incorporating elements of the comparatively ancient technology favored by the audio underground. Reaction to this development in the industry has been mixed and hotly debated.

It is one thing to discuss, based on perceived sonic virtues, the pros and cons of many of the "tube issues" such as single ended amplification and the use of negative feedback. It is quite another, however, to understand why the use of certain design topographies and concepts inevitably result in particular sonic flavorings. Further, though there are now several manufacturers producing innovative, alternative tube audio designs, the cost of purchasing some of the premier, commercially available examples of this technology is unfortunately quite beyond the means of many audio enthusiasts. As such, the DIY approach offers an attractive alternative for those willing to invest hard work and ingenuity in lieu of tens of thousands of dollars to acquire just the right tube audio fix. Objective information on some of the more esoteric aspects of tube audio design can be hard to find, however, and for those looking to either build their own tube amplifiers or to learn more about them, this lack of basic information can be quite frustrating.

The resources available to the budding tube audio scholar/experimenter for introductory assistance in designing, building, or understanding tube-based audio products are limited. One could frequent libraries and used bookstores in search of ancient tomes on vacuum tube electronics, but modern texts on tube-based audio are rare indeed. Perhaps sensing this dearth of readily available materials, Bruce Rozenblit, President and Chief Designer of Transcendent Sound (a high end amplifier manufacturer) has just published an informative book on the subject of tube audio entitled Beginner's Guide to Tube Audio Design.

Rozenblit, a graduate electronics engineer and contributing editor to Glass Audio magazine, is clearly in his element when describing the ins and outs of tube amplification circuits and designs - both modern and antique. In Beginner's Guide to Tube Audio Design, Bruce seeks to educate the curious about what a vacuum tube does and how to use it in an audio amplifier circuit.

Beginning with a detailed analysis of the parts and functions of typical triode and pentode tubes, Bruce leads the reader on a topic by topic, chapter by chapter journey through a tube-based amplification process.

"Single Stage Basics," the second chapter of this book, describes the mechanism of the audio amplification process. In it, Bruce introduces the five basic parameters of an amplification stage- input impedance, output impedance, gain, bandwidth, and amplitude. From there, Bruce devotes chapters to simple gain stages, negative feedback, single stage feedback circuits, and multistage basics, each illustrated with numerous charts and diagrams.

After exploring the foundations of tube circuit design, Rozenblit, in a chapter entitled "Amplifier Parts," delves into an assortment of other circuits used in amplifier design. Chapters on output stages and transformers, power supplies and voltage regulators, and stability networks round out the design portion of this book.

Once the reader has become acquainted with the ways of the tube, Bruce provides practical illustrations of the ways tube-based circuitry has been applied in a number of popular amplifiers. Rozenblit walks the reader through some of the all-time classic tube amplifier designs including the Jefferson 2A3, the Williamson, The McIntosh MC-60, and the Marantz Model 5. Illustrated with schematics, Bruce points out some of the more interesting and innovative elements of each.

A closing chapter, entitled "practical considerations," offers advice on the types of equipment the tube amplifier designer should have on his workbench, safety tips for working with potentially lethal voltages, and suggestions for selecting the best parts for a particular application.

Also included in Beginner's Guide to Tube Audio Design are reprints of three of the author's Glass Audio projects. These step by step construction guides for a line level pre-amplifier, a transformerless output (OTL) amplifier, and a test bench power supply include schematics, parts lists, construction hints, and Bruce's commentary on the various choices incorporated in each design. The preamp project in particular, containing just a single gain stage, would appear to be an excellent practical application of the concepts, theories, and skills introduced in this book.

Despite the presence of these detailed construction projects, Bruce's book is not so much about how to build someone else's amplifier as it is about designing your own. Using the informational foundations contained in Beginner's Guide to Tube Audio Design, Bruce encourages the reader not only to build some of the circuits described, but also to experiment with ideas of his own. Bruce clearly believes that the "hands on" approach, coupled with the reader's own imagination and creativity, will yield far more satisfying results than merely reading words on the page. Given the fairly technical nature of much of the information presented, this "hands on" approach would certainly appear be most helpful in fully understanding this material. In that sense, what the beginning reader gets out of this book is very likely dependent on the effort he is willing to put into it.

While Bruce Rozenblit titled his book Beginner's Guide to Tube Audio Design, it should not be confused with an introductory book on audio electronics in general. As indicated above, this book contains some fairly technical information and Bruce pulls no punches as he launches into the heart of the subject matter from the opening pages. Though the material is presented in a simple, direct manner, the tube audio beginner is by no means being "spoon-fed." In other words, I believe that it is fair to say that some degree of familiarity with basic electronics is assumed in the reader. This is not the type of book that can be read and understood over a casual bowl of breakfast cereal and a glass of orange juice, and those lacking an elementary, pre-existing understanding of electronic circuitry may find themselves a bit overwhelmed. With time and effort, however, the design concepts introduced in this book (at least to me) gradually become clearer.

If nothing else, Beginner's Guide to Tube Audio Design illustrates the choices facing any tube amplifier designer and the host of inevitable trade-offs and compromises inherent in every tube amplifier design. The act of balancing these compromises into a sonically satisfying audio product emerges as an art form in itself.

Introductory texts on any subject invariable walk the tightrope between overwhelming the reader with technical information or boring the reader with too much explanation and too little useful content. While Rozenblit may tiptoe on the on the edge of technological overload for the electronics beginner, his straightforward, no-nonsense style is easy to read, even if the material is not so easily digested. With that proviso, Beginner's Guide to Tube Audio Design, which packs a tremendous amount of basic tube audio information into a comparatively slim volume, is recommended to anyone thinking about jumping aboard the DIY bandwagon or otherwise interested in learning more about tube amplification.

...John Upton

Beginner's Guide to Tube Audio Design by Bruce Rozenblit
Price: $24.95 USD

Published by:
Audio Amateur Press

Distributed by and available from:
Old Colony Sound Lab
P.O. Box 243
Peterborough, NH 03458-0243

Phone: 603-924-6371
Fax: 603-924-9467

Bruce Rozenblit Responds:

Writing this book was very difficult precisely because of the "tight rope walking" that the reviewer refers to. I had to balance providing enough information to be useful but yet not overwhelm the reader. I have been working with electronics since I was 10 years old and it is so easy to take things for granted. I tried my darndest to provide a simple explanation for every term and concept used and felt I was successful at that task.

The book most definately assumes a rudimentary knowledge of basic electricity. It was not my intention to write a book about "Mr. Electron" hopping around a piece of wire. There are dozens of excellent books available that teach the absolute basics. You can pick one up at Radio Shack for 5 bucks. One could easily assume that if someone was motivated enough to build his or her own audio gear, they would be motivated enough to take the first step on their own. Many instructional books try to be all things to all people and the target audience is only interested in 100 pages of the 400 that they payed for. I did not want my book to have that problem. It is highly focused on tube audio design.

The book is really a condensed course in analog circuit design featuring vacuum tubes in audio applications. You could spend four years in college studying that. Virtually all currently available texts on tube design were written for engineers and hence not reachable by the layman. I tried to distill and condense that information into its bare and most useful essentials so it could be grasped by the so called non-professional. Many concepts used in electronics are very abstract and difficult to rationalize. I absolutely expect the reader to be overwhelmed from time to time when introduced to them. In time, with some effort, they will become clear. This process can take months, if not years.

You don't read my book like a novel. You read a few pages at a time, let it sink in, preferably try to build something, and then re-read in a month. It is a "teaching book," a design reference, not a cookbook of recipies. Tube circuitry is much easier to work with than transistors. There is absolutly no reason why the motivated individual cannot build their own tube amp. Likewise, there is no reason why the motivated audiophile cannot understand the basics of tube circuitry.

...Bruce Rozenblit