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General Notes And Information
For access to the diagrams, go to the bottom of the page.
"From the graffiti stained walls of Old Chicago, we tender these diagrams to you as a tribute to your common sense and good taste. From our computer keyboard to you." Lacking more imagination or better inspiration the management has chosen to introduce this chapter of Dusty Files by paraphrasing the back of a half-empty Rolling Rock beer bottle.
The purpose of the "Dusty Files" collection of schematic diagrams is not so much to tell you as a reader how to build an amplifier, as much as it is intended to give you the necessary information and building blocks to design and build your own creation. It is the author's contention that there is entirely too much faddism, me-too-ism, and general lemming-like behavior amongst amplifier builders, while many good, solid, fundamental, well-proven designs and potentially useful and imaginative interesting ideas are often overlooked and ignored.
A few nuggets of potential wisdom from the author:
* Either ignore entirely or read with a healthy dose of cynicism subjective-review type audiophile magazines. Not only do many of the authors of the articles in those magazines lack practical experience in electronics in general (read: they often really don't understand how the stuff works), but the examples given are generally anectodal, not scientific, and the opinions given are by definition subjective, not objective. With your own system you may get drastically different results, and informal polling of veteran customers indicates that many well-informed people do not agree with the opinions or results of the reviews. In fact in any field that I can think of, the really great minds have major disagreements and debates over what's right. (And are there really that many really great minds writing for audio magazines? I doubt it.)
*Do not discount the influence of money or vanity on people offering advice. Especially if there's money to be made by them saying it, or if being an "expert" gives them ego-gratification. Many other people just repeat what they hear without bothering to check it out thoroughly. Being a expert in one field doesn't necessarily make one an expert in another field, either.
Probably the best place to get advice is to talk to other people who have actually built amplifiers (I understand this happens quite a bit on the Internet) or people who have to fix them for a living. Take a good look at items that the repairguys have a lot of respect for, they're usually well built.
*I submit that the best method for the average person to find out what suits he or she best is through his own empirical observations, common sense deduction, and careful trial and error.
This is analogue technology, not digital, and there are too many variables present for any one solution to suit every situation. (The big variable monkey-wrenche..or spanners, thrown into the equation are loudspeakers. More on that later.) Every amplifier presented here has its good features, and every change has a trade-off. It is quite possible, and in fact may be the best solution, to graft different features off of many different amplifiers, to get what works best.
*Believe it or not, there are many ideas which either haven't been tried or if they were tried, haven't been used in many years (see Dusty Files Part 1 for numerous examples of the latter).
If you come up with any ingenious solutions, I'd like to hear about them.
*I strongly suggest you try to build something simple and straightfoward at first, and get it working properly first,then going back and experimenting with changes and "tweaks".
Note that even really great amplifiers (such as many presented here) rarely worked as the creators intended right off the drawing boards, and needed development and refinement.
*Avoid "going overboard" and/or trying to build "the perfect amp" on the first try. This phenomenon is the cause of much heartbreak and discouragement among all levels of amp builders, even experienced ones who should know better. Pegging out your credit card and neglecting one's spouse/girlfriend are symptoms of this phenomenon.
*Note that many of these amps use the same or similar transformer sets. There's no reason why you can't build one amplifier, then on the same chassis just pull the small parts and rearrange them to create something entirely different.
*Be aware of the "law of diminishing returns"..the first 10% of the money you spend gets about 90% of what you want. Thus a $1000 amplifier is usually 90% as good as a $10,000 amp.
This goes hand in hand with the "J C Whitney syndrome" (Chicagoans call it Warshawsky's) noted by the author in his youth..if one takes a 1960 Studebaker and adds every gizmo one can buy from the J C Whitney catalog, one theoretically (going by the percentage improvements claimed in the advertising) has a car with 10,000 horsepower that gets 400 miles per gallon.
*The point(s) of all this is (and not necessarily in this order) to have fun, enjoying listening to what you built and taking pride in it, and getting some useful education in the process.
I would forget about audio-purist-perfectionist-mania and just enjoy yourself. If you have a healthy attitude about it your spouse may actually approve of what you're doing.
General Construction Notes
Most of the circuits found in this volume are also to be found in whole or in part in one or more current production high-end amplifiers. That's because the basics for almost every possible amplifier circuit that may be built were designed prior to 1955, when, propotionately speaking, considerably more time, money and effort was devoted to research and development on the subject. The three basic and most popular phase splitters (which are really the "heart" of the driver circuit) are the split-load (Dynaco & Williamson used it), cathode-coupled (so-called "Mullard" or long-tail pair, nowadays called a "differential amplifier"), and the floating-paraphase (found in some Acrosound circuits). The only types not covered are transformer phase splitters and the cross-coupled phase inverter, the former mainly because of the expense of interstage transformers and the latter due to complexity. Interstage transformers also have the liability of being useful only with amplifiers that use little or no global feedback, due to the additional phase shifting.
I have tried to stick to designs which the average person can build without excessive aggravation and expense. Considerable press space (see back issues of Sound Practices) has been devoted to low-power single ended amplifiers that I will not try to duplicate here. I am also assuming that the average reader does not access to tomes such as the Radiotron Designer's Handbook (which is an interesting and educational book but hardly necessary to build an amplifier) and even if he took algebra, probably doesn't remember most of it.
The general idea is to present good fundamental amplifiers and good basic building blocks that people can put together with a minimum of calculation and redesigning. The people who designed these amps originally did most of that hard work for you and I anyway (considerable credit has to go to David Hafler who had a hand in at least eight of them) so there is little reason to try and "re-invent the wheel". There is quite a bit of truly insipired work here by folks who really knew tubes, and who were outstanding even in an era that produced many talented engineers and deserves the title "Golden Age of High Fidelity".
You should read all of the construction notes even if there is only one amplifier you want to build. Many of the notes apply to more than one amplifier, to prevent unneccessary repetition.
One last word to the wise: It's good luck to pour yourself and your buddy or spouse a beer (make it something good, I'm sort of partial to Old Speckled Hen and Carlsberg Elephant) prior to demonstrating amplifiers to third parties for the first time. At least if it don't work you've got a good brew to finish off. If indeed it doesn't work turn it off, pour another one, and wait till tomorrow.There's nothing that will induce you to goofing things up even worse than having a beer in your hand and guests looking over your shoulder at the same time.
Note, the following are printer resolution monochrome GIF files, with a low-res monitor, you'll only see the top left corner.
Just save it to disk, and print it out, or view with a graphics program that can resize it. (in Netscape, click the right mouse button)
Bonus diagram..(72 kbytes)Allen Organ Amplifier
Allen Organ Amp converted to (60 kbytes) 300B
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[Tube Data Page ][Tube
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