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By GG, Contributing Editor SEVERAL BOOKS ON ELECTRONIC THEORY have crossed my desk over the past few months. Every audio amateur, at one time or another, will need a good text book on electronics, one which will allow self-education in electronics in an accurate, concise and understandable fashion. Some of the books described below qualify, while others do not. As you will see, I have a bias: If you don't understand which way the electrons flow, you'll never really understand how tubes and transistors operate. From Our Radio Counterparts The 1989 ARRL Handbook for the Radio Amateur by the American Radio Relay iL. e Staff, Bruce S. Hale, KBIMW, editor. The American Radio Relay League, Newington, CT 06111, hard cover, $21 (available from Old Colony). Audio amateurs have much in common with their counterparts in the amateur radio field. Both seek the highest levels of performance from their custom built equipment, though not necessarily for any monetary remuneration. Amateur radio has changed greatly over the past two decades. What was once a hobby dominated by individuals who wouldn't dream of using a piece of factory-assembled gear in their shack, is now an avocation in which commercial equipment represents a major portion of the total gear in use. Not that all hams use assembled equipment these days--far from it. Still, I would hazard a guess that, today, over 50% of licensed amateur radio operators do not build their own equipment. This is particularly true in the higher frequency regions, such as 2-meter FM (which some of my ham friends call glorified CB-I guess ham radio is allowed to have purists too!). Audio amateurs are, as our editor and I would like them defined, individuals who build their own audio equipment. Now, most of us have some assembled equipment. I don't build tape decks, for example. But a true audio amateur has at least one piece of audio equipment which he or she modified, built, or perhaps even designed. If all of your equipment is factory assembled and you've never taken a soldering iron to any of it, you are an audiophile, but not an audio amateur. The Radio Amateur's Handbook, as this annually revised volume was called prior to the mid 1980s, served as a primary textbook for many of us who learned electronics theory without the benefit (or detriment-it depends on your point of view) of formal training. Over the past 25 years, The Radio Amateur's Handbook has been a constant source of valuable technical information. I learned much of my basic electronics theory from it, and I still teach basic electricity and Ohm's Law as given in my mid-70s Handbooks. Although I was never a radio amateur (I never got around to learning Morse Code), I was an active shortwave listener in high school, with serious interest in the world of radio frequency (RF). The Radio Amateur's Handbook has changed considerably over the years. It is much larger and has been updated substantially as technology has advanced. Since 1986, the Handbook has rivaled the Manhattan phone directory in size. It now thoroughly details digital theory and digital communications. The new ARRL Handbook's coverage of basic electricity, in the chapter titled ''Electrical Fundamentals," is a disappointment. Where the older Handbooks (I still have 1973 and 1974 on hand) offered adown-to-earth explanation of electric current, the newer editions are more esoteric, more mathematically oriented, and far less understandable to the beginner. I have a few rather strong opinions when it comes to the teaching of basic electricity and electronics. I have absolutely no use for the teaching of conventional current flow, i.e., positive to negative. The flow of electric current is the flow of electrons, which are negatively charged particles, and flow is from negative to positive. Fortunately, the vast majority of modern electronics textbooks have abandoned conventional current flow in favor of electron current flow. Although physics textbooks have been among the last to convert, I have seen several recent physics texts which teach electron rather than conventional current flow. Unfortunately, The 1989 ARRL Handbook has taken a step backward, explaining electricity in terms of conventional current flow, and the explanation is also less than understandable. Beyond that, the new Handbook offers good explanations of phase, the decibel, Ohm's Law, capacitance, inductance and impedance. If you are in need of brushing up on vacuum tube or transistor theory, the new edition offers excellent chapters in the basic theory. The applications, however, are primarily oriented toward RF. The bulk of The 1989 ARRL Handbook is, naturally, devoted to the theory and construction of amateur radio equipment. Although this may not seem directly related to the needs of audio amateurs, the construction aspects are not to be overlooked. The construction photos are superb examples of the caliber of work we should all be striving for. If you're looking for examples of home brew equipment that's built better than most commercial gear, the photos in the Handbook will be an inspiration. By the time you read this, the 1990 edition will probably be in print. Since the changes from year to year are normally small, most of what I've said here should still apply. The 1989 ARRL Handbook is not an essential volume for the audio amateur, and the theory of basic electricity has serious problems. But the Handbook does have much to offer and is recommended on that basis. More On Electronic Theory Basic Electronics Course by Norman H. Crowhurst; 2nd Edition, 1987; Tab Books, Inc., Blue Ridge Summit, PA 17294-0214, softcover, 423 pp., $14.95. Crowhurst's latest book on electronic theory is an extremely thorough text, but he gets off on the wrong foot by illustrating conventional current flow on the very first page. He shows some batteries to illustrate how current produces a magnetic field and the arrows indicating the direction of current flow are drawn from positive to negative. Yet, in his chapter on tubes, he correctly states that 'Electrons emitted by the heated negative electrode, called the filament or cathode, are attracted by a positive voltage applied to the other electrode, called the plate or anode; thus current flows in this direction." This contradiction is compounded by his illustrations of rectifier circuits in the chapter titled ''Diodes and Simple Semiconductors.'"' Here, we are back to conventional current flow, with the arrows flowing from positive to negative, or from anode to cathode. What he is actually illustrating here is hole movement within the diode, but this does not tell us the direction of electron movement in the circuit. In fact, this chapter lacks any illustration of a semiconductor junction with an accompanying explanation of the direction of electron current flow within the device. I dislike giving such short coverage to such a lengthy book, but all of this is like ly to be extremely confusing to the be ginner. Being self-taught in electronics myself, [remember being rather confused during my high school days by similarly contradictory explanations of which way the current flows. When I asked (and still ask) physicists why they still teach conventional current flow, they usually tell me to ''just accept it as a convention." Sorry folks, but that's simply not good enough for those of us requiring a working knowledge of how all these devices operate. I wish I could recommend this book, but I can't. Understanding Electronics, by R. H. Warring, Edited by G. Randy Slone; 3rd Edition, 1989; Tab Books, Blue Ridge Summit, PA 17294-0214, softcover, 205 pp., $11.95 (available from Old Colony). I have been using Understanding Electronics in my Audio Fundamentals class for several years, going back to the first edition. The present edition has been substantially enlarged and updated. War ring is a British author and one drawback of previous editions was the use of European, rather than American, schematic symbols (sometimes they differ, as is the case with resistors). I suspect that Editor Slone's contribution has been in converting the British symbols and terminology to their US counterparts, a very helpful move. Since I use this book, it will come as no surprise that Warring explains electricity in terms of electron flow rather than conventional current flow. He even offers a correct explanation as to why conventional current flow was used for so many years. Beyond this, Warring offers some of the best explanations of the workings of basic electronics that I've seen. Ohm's Law, resistance, capacitance and inductance are presented in concise and understandable fashion. Warring's explanations of solid-state theory are particularly fine. After studying the chapter on semiconductors, you'll understand exactly what happens in a junction, which way the electrons flow, which way the holes move, and which is most important. For the newcomer, War ring's explanations of FETs are among the best. Unfortunately the author introduces solid-state rectifiers in his chapter on transformers, which precedes the section on diodes. All of the material is here, it's just the order which is bad. Warring's chapter on tubes is too brief (4 1/2 pages). If you're looking for a source for vacuum-tube theory, this isn't it. We really shouldn't fault him for this. Understanding Electronics wasn't aimed specifically toward audiophiles, and in virtually all other fields of electronics the tube is a dead issue. Several integrated circuit types are explained, but his coverage of op amps is inadequate. His chapter on amplifiers provides a good introduction to the basics of solid-state amplifier design. He also offers the basics of circuit board design, explaining how to take a simple project from schematic to board layout. Warring's book is far from the only electronics text you'll ever need, but it ex plains all the basics in a clear, correct fashion. Some of his explanations, such as solid-state theory, are exemplary. With the background he provides, you'll be able to move on to more advanced and more specialized books with a solid level of understanding. Understanding Electronics is highly recommended. Getting Started in Electronics, by Forrest M. Mims III; Radio Shack Cat. No. 276 5003; softcover, $2.49, available at all Radio Shack stores. Ed Dell suggested I look at this book, since he believes it's ideal for the absolute beginner in electronics. After reading it, I agree. Getting Started in Electronics is written in outline form, literally hand printed on lined paper and reproduced as such. Numerous cartoon-like illustrations amplify concepts explained in the text. This non-intimidating approach is ideal for the newcomer. Mims is also a convert to electron current flow and uses this approach through out. Like Warring, he explains the reason for all of the confusion and sets the record straight. Throughout the book, Mims offers simple (sometimes crude, but effective) experiments to illustrate the theoretical points. All common semiconductor devices are covered in Mims' book, including triacs, thyristors and photo de vices. Digital and linear ICs are explained. Mims does not cover tube theory. The final chapter contains 100 simple electronics circuits. Don't expect to find your next state-of-the-art preamp; all the audio circuits use 741 op amps! But for the beginner, these projects will provide a basic understanding upon which to build. I'm no snob when it comes to learning electronics and I take pride in bringing concepts down to an elementary level so that they are understandable to the new comer. There are no mysteries in electronics, only bad teaching. I've always believed it's best to “learn it right the first time'' to avoid having to undo earlier mis takes. My advice is to ignore any book that teaches conventional current flow. These theories stem from the misunderstandings of Ben Franklin's era, and it seems senseless to perpetuate past errors just for the sake of consistency. We now know that the Earth is not flat, and even the Pope has admitted that Galileo was right, after all. If you've never seen a resistor before, start with Mims, continue with Warring, and then move on to more specialized books covering specific applications. Tube Substitution Handbook No. 21, by the Howard W. Sams Engineering Staff; 21st Edition, 6th printing, 1989; Howard W. Sams & Co., 4300 West 62nd St., Indianapolis, IN 46268, softcover, $5.95 (available from Old Colony). Tube lovers will find the latest Sams Tube Substitution Handbook as indispensable as the previous editions. There isn't much to say about it except that it is still the most comprehensive and accurate tube substitution guide available. The book is divided into seven sections, each devoted to a particular vacuum tube category. The sections include American receiving tubes, picture tubes, industrial substitutes, communications and special purpose tubes, foreign substitutes for American types and American substitutes for foreign types. The last section illustrates all of the common basing diagrams. Only one word of caution is in order. When building or servicing your favorite state-of-the-art vacuum-tube power amplifier or preamp, a substitute device will often change the sound of the amplifier, not always for the better. Normally, you should make tube substitutes as a last resort, when you can't locate the original device. When you purchase the Tube Substitution Handbook, you actually receive two copies: a 5.5 x 8.5” copy for your bookshelf and a miniature 3.5 x 5.5” version for your toolbox or tube caddy. Those who work with vacuum tubes should have at least one substitution guide on hand. This is the one to buy. PC Board Aids TEC-200 Image Film, The Meadowlake Corp., PO Box 497, Northport, NY 11768. 5 sheets: $3.95, 10 sheets: $5.95, plus $1.25 postage. Larger quantity prices available. TEC-200 film is a specially coated plastic film designed to simplify the manufacture of printed circuit boards. The film is used in conjunction with any high quality dry-toner photocopier. First, the circuit board pattern, perhaps one published in TAA, is photocopied onto the film. Next, using an electric iron set to the ''cotton-linen'' position, the pattern is transferred from the film onto the surface of the copper-clad board. The heat from the iron melts the toner and forms a varnish-like coating on the board which is resistant to acid. After the board has cooled, the TEC-200 film is carefully peeled away, leaving the coating adhering to the board. Finally, the copper-clad board is etched in the customary fashion. TEC-200 film should be extremely use ful to audio amateurs who construct their own circuit boards. It will simplify the reproduction of board patterns published in TAA and will be of value to those who design their own as well. If you use a CAD program for designing circuit boards, your dot matrix or, preferably, laser printout can be photocopied onto the TEC-200 film. The manufacturer guarantees the product for 30 days. If you are not satisfied with the product's performance, you can return the unused portion and receive a full refund of your purchase price. With terms such as these, it's certainly worth a try. READERS' QUESTIONS POOGEing a TEAC CD Player I've just purchased a TEAC CD player and opened it up since want to start POOGEing it right away. Unfortunately, I found that the output op amps come in a non standard Single Inline Package (SIP), part number Mitsubishi M5218L. I've tried some Far East data books, with no luck. In your infinite wisdom, perhaps you might help me with the pinout of such a device. Otherwise I'm stuck with it. Fernando Garcia Viesca, 87300 Matamoros, Tamps, MEXICO REPLY I checked with a friend who is head technician at our local audio-video service center and he found a schematic containing this device. He even had some of them in stock since he is a Yamaha service center and Yamaha has used this device in some of their pro audio products. According to the Yamaha schematic for the P7X8 Percussion Tone Generator, the M5218L has the same pin numbering as a standard dual op amp in an 8-pin DIP package (4558, TL-072, NE5535, etc.). Facing the label side of your SIP device, with the left pin as #1, the pinout is as follows: 1: Amp A output 2: Amp A - in 3:AmpA + in 4: Negative power supply 5: AmpB + in 6:AmpB - in 7: Amp B output 8: Positive power supply I'm quite sure that the Yamaha schematic is accurate (assuming their wisdom is infinite!), but I would check pins 4 and 8 with a voltmeter just to verify that they are, indeed, the power supply connections. If they are, you're probably in good shape. It should be possible, using a small perfboard or header, to adapt an 8-pin DIP device to the SIP connections on the TEAC circuit board. Try the Analog Devices AD712 or Signetics NE5535 as a replacement, but verify that TEAC has not exceeded their absolute maximum power supply ratings ( + 18V). I don't have any other data on the M5218L, so I don't know whether they might have run it on higher supply voltages. Amplifier Anguish Consumer Reports' July 1988 issue reviewed about 30 receivers. Except for the two Fisher models, all show that more power can be delivered to a 4 ohm load than to an 8 ohm load, but of these, 17 note ''manufacturer recommends against use of 40 speakers." Can you explain this anomaly? Or (better), can anyone explain the dangers of decreasing load values on solid-state amplifiers? For years I've wanted to experiment with active crossovers, but have been restrained by the considerable expense of quality amplifiers. Almost affordable may be Marchand Electronics' PM2, and even more affordable, Art Newcomb's use of National's LM-12 (SB 4/88, p. 22). It would be nice to read a review of these amplifiers in TAA. If the LM-12 based amplifiers are ''quality'' amplifiers, it would be even nicer if Old Colony offered them as kits (along with its active filter boards). David J. Meraner Scotia, NY 12302 REPLY Amplifier power is determined by the relationship of Ohm's Law among cur rent, voltage and load resistance. Three formulas yield the same results; which one you use will depend on your avail able information. The formulas are: P=E/R;P=FPR and P = IE Solid-state amplifiers generally produce a constant voltage output regardless of changes in load impedance; thus the voltage output, measured across the loud speaker terminals, will be the same with 4, 8 or 16 ohm loudspeakers connected. Let's say an amplifier has a voltage output of 30V RMS and the load is 8 ohm. Using the first formula given, you will find the power output is 112.5W RMS (because you used RMS voltage in the formula). If you change the load resistance to 4, the power now becomes 225W. If you use a transposition of the third formula (I = P/E) you can discover how much current the output stage of the amplifier must deliver to the load to achieve those power levels. The current delivered to an 8-ohm load is 3.75A. With the load reduced to 49, the current is now 7.5A and delivering this current is no mean feat for an audio amplifier. You can see from this why a solid-state amplifier should deliver more power into a 4 ohm load than into one that is 8 ohm. An ideal amplifier (in this case one with a hefty output stage, plenty of heat sinking and a conservative power supply) will deliver exactly twice the power in to 4-ohm it does into 8-ohm. Unfortunately, most amplifier designs are not up to the task. When an amplifier must provide large amounts of current, two things happen; the output transistors run much hotter and the power supply is taxed by the additional current it must supply to the output stages. Many amplifiers simply can't provide enough current into 4-ohm to deliver twice the 8 ohm power rating. When an amplifier's current capability is exceeded, its output voltage decreases, delivering reduced power to the load. The Fisher models you cite are obviously minimal designs that collapse when presented with a lower impedance load. I wouldn't buy such an amplifier, and I certainly would avoid any the manufacturer admits won't drive a 4-ohm load. The danger of decreasing load impedance is that the output transistors may overheat, causing them to self-destruct if the amplifier doesn't include any protection circuitry in its design. Ideally, a well-designed amplifier should be able to drive loads down to 20 safely. The Hafler DH-200 will supply 10A of current into a short circuit (0 ohm) without turning into a Fourth of July display. In the real world, an 8 ohm loudspeaker is not always 8 ohm. The impedance varies with frequency and will often dip to half the average value at certain frequencies, which can present serious problems for marginal amplifiers. All this must be taken into account if you plan to add extension speakers. Two 8-ohm speakers in parallel will present a 4-ohm load to the amplifier. If the '' 8-ohm"'' loud speakers have impedance dips down to 4-ohm to 62, you will be presenting a load of 2 ohm to 3 ohm to the amplifier at certain frequencies. Regarding your source of information, I wouldn't recommend anyone get audio advice from Consumer Reports. Don't misunderstand me; this is a magazine of the utmost integrity. With products such as washing machines, lawn mowers and canned tuna, which are not my areas of expertise, they seem to do well. I usually find them barking up the wrong tree when it come to audio equipment. The last time I read a CR review of stereo receivers (a while back), they tested only the FM tuner sections, stating there were no significant differences between the phono preamplifiers. You don't need to read a nonprofit magazine to find out all phono preamps sound the same. You can read that in Stereo Review. CR's loudspeaker reviews are similarly misguided. Loudspeakers are rated with an ''accuracy score,'' based solely on static frequency response. You will find no tests for distortion, transient response, phase or a host of other factors equally important in determining a loudspeaker's accuracy. Finally, they really don't listen to equipment. It's bad enough to omit thorough listening tests from reviews, but much worse to combine this with in complete bench results. There are no ''cheap'' ways to get a quality amplifier, although a number of products offering good performance at moderate prices exist. Several Old Colony offerings fall into this category, including the Borbely amps and the Pass kit. I'm still using the Pass on the tweeters of my tri-amped system and I still find it an excellent amplifier. If you're looking for a bargain basement tweeter amplifier, try the Hafler DH-120. This 60W/channel amplifier is a respect able performer in its price class, although it offers less of a challenge to builders than the Old Colony offerings. The Marchand and Newcomb amplifiers may also be fine, but I have no personal experience with them. Perhaps other readers will share their views with us. Contrary Capacitors I want to modify my Hafler DH-330 tuner per R. N. Marsh's article (''DH-330 FM Tuner Upgrade," TAA 3/88, p.21), but I cannot find Wesco capacitors. The alternative is a metalized polypropylene type; would they do as well? In an unrelated matter, I can hear electrolytic capacitors. I have heard what happens when they are removed from the signal path of amps and preamps: POOGEing. When I listen to compact discs, the electrolytic harshness in the high frequencies assaults my ear. I cannot listen for more than a few minutes. I return to James Boyk recordings and my older records. Some sound mixing consoles, recording amps and analog tape recorders use electrolytic capacitors everywhere. James Boyk records sound better because tube equipment does not need e-t-l in the signal path, only in the power supply. My old tube era records sound fine, and my preamp and amp do not use e-t-l. No radio station has advertised ''no e-t-l in our signal path." Since our FM tuners use e-t-1 along with the radio stations, a good sound that audiophiles prefer is not possible. That leaves CD. For those DDD recordings, the analog microphone signal is immediately sent to analog-to-digital conversion. If that converter has no e-t-l, we are home free since digits placed on compact disc are not affected by any capacitor. In our home signal path we are on the verge of total elimination of e-t-l, and onto the best sound ever recorded. The transistor sound should be just as good as James Boyk records. I would like to know more about DDD recording practices regarding the interface between the microphone and analog-to-digital converter. Gil Lytton, Los Angeles, CA 90066 REPLY I don't know where to buy Wesco capacitors either, but I have an alternative; Old Colony still has a supply of the 5uF poly-carbonate caps used in the POOGE-4 CD player modification. Two of these in parallel would solve your problem and they should fit physically. Old Colony also carries a 10uF metalized polypropylene capacitor of excellent quality, but I don't know if it will fit in the space available. I agree that electrolytic coupling capacitors adversely affect the sound, but I would caution you against assuming all sonic ills result from bad capacitors. If you look inside some tube tape recorders used to make those great analog recordings back in the fifties you will find many coupling capacitors you would consider inferior by today's standards. I took a look at my ancient Ampex 350-2 tape recorder manual and found paper capacitors (called ''condensers'' in this manual) were used for all coupling applications. This would be unthinkable today, yet the overall design of this recorder enabled me to make hundreds of excellent recordings. Better capacitors would certainly improve these already excellent recorders, but quality capacitors will not fix a bad design. If you POOGE an amplifier such as the Dynaco Stereo 120, it still will sound harsh and transitory. There's no single record company policy I can quote that will answer your question regarding DDD practices. Every record company has its own equipment preferences. You may find it educational to tour the exhibits at an Audio Engineering Society convention. Some of the most highly respected mixing consoles are still using electrolytic coupling capacitors and ceramic power supply bypasses. Neotek, which makes the "audiophile quality'' mixer used in many Telarc digitals, was still using electrolytic capacitors for coupling at its most recent New York AES exhibit. Most digital tape recorders also have electrolytic coupling capacitors in the analog circuitry. Some record companies don't use off-the-shelf equipment, prefer ring to design their own. Decca/London is such a company, but you won't be able to pry any circuit details from them. They're rightly very secretive about their designs. The move toward transformerless microphone outputs and console inputs has improved mixing consoles and microphones. Most microphones have output transformers to convert the signal from the capsule into a low impedance balanced output. On the other end, the tape recorder or mixer also has a transformer at its input. With this setup, the audio signal passes through two transformers (and often two more en route from the mixer to the recorder). Many mixer manufacturers (such as Neotek) have dispensed with transformers, as have a few microphone manufacturers (such as Schoepps). Although transformers can have a detrimental effect on the sound, nearly all the great analog recordings of yesteryear were made with microphones, mixers and tape recorders that used transformers. Also see: |
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