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Subject: FAQ: rec.audio (part 2 of 4) Newsgroups: rec.audio,rec.music.info,rec.answers,news.answers From: neidorff@uicc.com Date: Tue, 26 Jul 1994 21:07:41 GMT Archive-name: AudioFAQ/part2 Last-modified: 1994/6/22 Version: 1.17 10.14 What about swapping op-amps? Many components use ICs called op amps as audio amplifiers. Earlier op amps had poor sound quality, especially if misused. Some engineers with a strong background in ICs and op amps learned that they could improve sound if they replaced slow, noisy, low slew-rate, or otherwise bad op amps with better ones. Some less informed people tried doing the same thing and made the sound worse. One pitfall with op amp swapping is that some op amps are more prone to unwanted oscillation than others. The faster the op amp, the more likely it will cause an unwanted oscillation, which will really damage the sound. For that reason, Joe may succeed in replacing 741 op amps with 5534 op amps in his gear, and you may fail. It is dependent on design, layout, etc. As technology and design expertise improves, audio op amps get better and swapping is getting less and less useful. Newer op amps are displacing yesterday's best, and sound surprisingly similar to straight wire. Still, there are different op amps for different purposes. Bipolar op amps are ideal for preamplifiers where noise is critical. The OP-27, OP-37, LT1028, and LT1115 are very well received for phono preamps, head amplifiers, and microphone preamplifiers. Bipolar op amps are also more practical for signals with low source impedance. FET devices like the OPA604 and OPA2604 have higher slew rate, higher bandwidth, and lower input current. These op amps are better for line-level inputs and high source-resistance signals. Some amplifiers, like the OP-37 and LT1115 achieve higher bandwidth by using less internal compensation. These amplifiers are not unity gain stable, and should not be used in circuits with low closed loop gain or large feedback capacitors. Some of the better op amps for audio as of today include (* means highly recommended): Single Dual AD847 AD827 AD797* NE5535 NE5534 NE5532 OP-27 AD712 LT1115* LM833 AD811 AD841 AD842 HA5112* OPA2604* LT1057 OP249* LT1028 AD744 With op amp part numbers, there is a lot of room for confusion. Here is a guide to the numbers that is often accurate: Op amp part numbers start with a manufacturer's prefix: Analog Devices uses AD Burr Brown uses OPA Linear Technology uses LT Motorola uses MC National uses LF and LM PMI uses OP Signetics uses NE and SE TI uses TL This can be confused because if TI copies a Signetics op amp, they may assume the Signetics prefix, or they may use their own. Fortunately, if the part numbers are the same, circuitry is almost exactly the same, as is the performance. (Note: almost) The next thing in the part number is two, three, four or five digits. This is invariably the key to the part. If the numbers are the same, the parts are almost surely the same. For example, an LM357N and an LM357J are electrically identical and sound the same. Next is a letter or two indicating the op amp package and possibly how it has been tested and what tests it passed. Unfortunately, manufacturers haven't standardized these letters. Fortunately, you almost never care. If it is a dual-inline (DIP) package and you are replacing a DIP, you shouldn't have to worry whether or not it is ceramic or molded. Likewise, you rarely care if it has 100uV offset or 4mV offset for audio. Finally, you don't care if it wasn't tested at elevated temperatures because you will use it in your house, inside well ventilated gear. So in general, an NE5532J is a TL5532N, and an AD827JN will sound the same as an AD827LD. If you aren't sure about some detail, call or write the IC maker and ask for a data sheet on the parts in question. They will always send data sheets for free, and these data sheets contain details on the various part numbers, internal circuitry, and electrical characteristics. 10.15 Where can I buy electronic parts to make an amplifier? There are many commercial parts distributors that sell only to Corporations. Their prices are often list, their supply is often good, and their service varies. Common ones are Arrow Electronics, Gerber Electronics, Hamilton Avnet, and Schweber Electronics. See your local phone book. There are also distributors that cater to smaller buyers These typically have only one office. Some have lousy selections but great prices. In the following list, (+) means that the dealer has a good reputation, (?) means that the dealer has insufficient reputation, and (X) means that some have reported problems with this dealer. (C) means they have a catalog. All Electronics Corporation (Surplus, Tools, Parts) (?) (C) PO Box 567 Van Nuys CA 90408 USA 800-826-5432 818-904-0524 Allied Electronics (Full Line of Parts) (+) (C) 800-433-5700 Antique Electronics Supply (Tubes, capacitors, etc) (?) 688 First St Tempe AZ 85281 USA 602-894-9503 DigiKey Corporation (Full Line of Parts) (+) (C) 701 Brooks Avenue South PO Box 677 Thief River Falls MN 56701-0677 USA 800-344-4539 Maplin (European Parts) (?) (C) +44 702 554161 (For Orders Only) +44 702-552911 (Customer Service) Marchand Electronics (?) (Crossover kits) 1334 Robin Hood Lane Webster NY 14580 USA 716-872-5578 MCM Electronics (Speakers, A/V Repair Parts, Etc) (+) (C) 650 Congress Park Dr Centerville Ohio 45459-4072 USA 513-434-0031 or 800-543-4330 MesaBoogie (Tubes, instrument speakers) (?) 707-778-8823 Michael Percy (Connectors, MIT, Wonder Caps, Buf-03) (+) PO Box 526 Inverness CA 94936 USA 415-669-7181 Voice 415-669-7558 FAX Mouser Electronics (Full Line of Parts) (+) (C) PO Box 699 Mansfield TX 76063-0699 USA 800-346-6873 817-483-4422 Newark Electronics (Full Line of Parts) (+) (C) Old Colony Sound (Audio parts and audio kits) (+) (C) PO Box 243 Peterborough NH 03458-0243 USA 603-924-9464 Parts Express (Speakers, Cables, Connectors) (+) (C) 340 East First Street Dayton OH 45402-1257 USA 513-222-0173 Radio Shack (Parts, Low-End Audio) (+) (C) Tanner Electronics (Surplus Parts) (+) 214-242-8702 Toroid Corp of Maryland (Toroidal power transformers) (+) (also sells without secondary, ready to finish) 608 Naylor Mill Rd Salisbury MD 21801-9627 USA 410-860-0300 Triode Electronics (Tubes, transformers, boxes) (?) 2010 Roscoe St Chicago IL 60618 USA 312-871-7459 Welborne Labs (Connectors, Linear Tech ICs, Wima Caps) (?) 6836 South Universtiy Blvd. #70 Littleton CO 80122 USA 303-470-6585 Voice 303-791-7856 FAX 10.16 Where can I buy audio amplifier kits? Alas, Heath is no longer making Heathkits. Alternatives: Audio Synthesis (Many kits from Ben Duncan designs) (?) 99 Lapwind Lane Manchester M20 0UT, UK 061-434-0126 Voice 060-225-8431 FAX Crimson (UK) (?) Hafler (+) (may be out of the kit business) Hart Electronics (UK) (?) Mark V Electronics (?) 8019 E Slauson Ave Montebello CA 90640 USA 800-423-3483 213-888-8988 Old Colony Sound (+) (See 10.15) Sage Audio (Various kits UK$95 to UK$430) Construction House Bingley West Yorkshire England BD16 4JH UK Sound Values (+) (See 10.7) 185 N Yale Avenue Columbus OH 43222-1146 USA 614-279-2383 10.17 Where can I read more about building amplifiers, preamps, etc.? Audio Amateur Magazine Audio Amateur Publications PO Box 494 Peterborough NH 03458 USA 603-924-9464 Analog Devices Audio/Video Reference Manual Electronic Music Circuits, by Barry Klein Howard D Sams & Co ISBN 0-672-21833-X Electronics Australia (Magazine with audio projects) AUD47 per year 12 issues, often discounted PO Box 199 Alexandria, Austrailia +612 353 9944 or +612 353 6666 Elektor Electronics (How it works and you-build articles) (no longer published in US. Still available in Europe) PO Box 1414 Dorchester DT2 8YH, UK Enhanced Sound: 22 Electronic Projects for the Audiophile (Some basic projects and some "how it works") by Richard Kaufman Tab Books #3071/McGraw Hill ISBN 0-8306-9317-3 Glass Audio Magazine Audio Amateur Publications PO Box 494 Peterborough NH 03458 USA 603-924-9464 IC Op-Amp Cookbook, Third Edition by Walter G. Jung ISBN 0672-23453-4, Howard W. Sams, Inc. Journal of the Audio Engineering Society (Theory & Experiment) Audio Engineering Society 60 East 42nd Street New York City NY 10165-0075 USA 212-661-2355 Popular Electronics Radio-Electronics Radiotron Designer's Handbook, Fourth Edition (old, tube info) The Technique of Electronic Music, by Thomas H Wells Schirmer Books ISBN 0-02-872830-0 Vacuum Tube Amplifiers, MIT Radiation Lab series Wireless World Some of the above titles, as well as a catalog of technical books, are available from: OpAmp Technical Books, Inc. 1033 N Sycamore Avenue Los Angeles CA 90038 USA 800-468-4322 or 213-464-4322 10.18 What is Amplifier Class A? What is Class B? What is Class AB? What is Class C? What is Class D? All of these terms refer to the operating characteristics of the output stages of amplifiers. Briefly, Class A amps sound the best, cost the most, and are the least practical. They waste power and return very clean signals. Class AB amps dominate the market and rival the best Class A amps in sound quality. They use less power than Class A, and can be cheaper, smaller, cooler, and lighter. Class D amps are only used for special applications like bass-guitar amps and subwoofer amps. They are even smaller than Class AB amps and more efficient, yet are often limited to under 10kHz (less than full-range audio). Class B & Class C amps aren't used in audio. In the following discussion, we will assume transistor output stages, with one transistor per function. In some amplifiers, the output devices are tubes. Most amps use more than one transistor or tube per function in the output stage to increase the power. Class A refers to an output stage with bias current greater than the maximum output current, so that all output transistors are always conducting current. The biggest advantage of Class A is that it is most linear, ie: has the lowest distortion. The biggest disadvantage of Class A is that it is inefficient, ie: it takes a very large Class A amplifier to deliver 50 watts, and that amplifier uses lots of electricity and gets very hot. Some high-end amplifiers are Class A, but true Class A only accounts for perhaps 10% of the small high-end market and none of the middle or lower-end market. Class B amps have output stages which have zero idle bias current. Typically, a Class B audio amplifier has zero bias current in a very small part of the power cycle, to avoid nonlinearities. Class B amplifiers have a significant advantage over Class A in efficiency because they use almost no electricity with small signals. Class B amplifiers have a major disadvantage: very audible distortion with small signals. This distortion can be so bad that it is objectionable even with large signals. This distortion is called crossover distortion, because it occurs at the point when the output stage crosses between sourcing and sinking current. There are almost no Class B amplifiers on the market today. Class C amplifiers are similar to Class B in that the output stage has zero idle bias current. However, Class C amplifiers have a region of zero idle current which is more than 50% of the total supply voltage. The disadvantages of Class B amplifiers are even more evident in Class C amplifiers, so Class C is likewise not practical for audio amps. Class A amplifiers often consist of a driven transistor connected from output to positive power supply and a constant current transistor connected from output to negative power supply. The signal to the driven transistor modulates the output voltage and the output current. With no input signal, the constant bias current flows directly from the positive supply to the negative supply, resulting in no output current, yet lots of power consumed. Class B amplifiers consist of a driven transistor connected from output to positive power supply and another driven transistor connected from output to negative power supply. The signal drives one transistor on while the other is off, so in a Class B amp, no power is wasted going from the positive supply straight to the negative supply. Class AB amplifiers are almost the same as Class B amplifiers in that they have two driven transistors. However, Class AB amplifiers differ from Class B amplifiers in that they have a small idle current flowing from positive supply to negative supply even when there is no input signal. This idle current slightly increases power consumption, but does not increase it anywhere near as much as Class A. This idle current also corrects almost all of the nonlinearity associated with crossover distortion. These amplifiers are called Class AB rather than Class A because with large signals, they behave like Class B amplifiers, but with small signals, they behave like Class A amplifiers. Most amplifiers on the market are Class AB. Some good amplifiers today use variations on the above themes. For example, some "Class A" amplifiers have both transistors driven, yet also have both transistors always on. A specific example of this kind of amplifier is the "Stasis" (TM) amplifier topology promoted by Threshold, and used in a few different high-end amplifiers. Stasis (TM) amplifiers are indeed Class A, but are not the same as a classic Class A amplifier. Class D amplifiers use pulse modulation techniques to achieve even higher efficiency than Class B amplifiers. As Class B amplifiers used linear regulating transistors to modulate output current and voltage, they could never be more efficient than 50%. Class D amplifiers use transistors that are either on or off, and almost never in-between, so they waste the least amount of power. Obviously, then, Class D amplifiers are more efficient than Class A, Class AB, or Class B. Some Class D amplifiers have >80% efficiency at full power. Class D amplifiers can also have low distortion, although not as good as Class AB or Class A. Class D amplifiers are great for efficiency. However they are awful for other reasons. It is essential that any Class D amp be followed by a passive low-pass filter to remove switching noise. This filter adds phase shift and distortion. It also limits the high frequency performance of the amplifier, such that Class D amplifiers rarely have good treble. The best application today for Class D amplifiers is subwoofers. To make a very good full range Class D amplifier, the switching frequency must be well above 40kHz. Also, the amplifier must be followed by a very good low-pass filter that will remove all of the switching noise without causing power loss, phase-shift, or distortion. Unfortunately, high switching frequency also means significant switching power dissipation. It also means that the chances of radiated noise (which might get into a tuner or phono cartridge) is much higher. 10.19 Why do I hear noise when I turn the volume control? Is it bad? Almost all volume controls are variable resistors. This goes for rotary controls and slide controls. Variable resistors consist of a resistive material like carbon in a strip and a conductive metal spring wiper which moves across the strip as the control is adjusted. The position of the wiper determines the amount of signal coming out of the volume control. Volume controls are quiet from the factory, but will get noisier as they get older. This is in part due to wear and in part due to dirt or fragments of resistive material on the resistive strip. Volume control noise comes as a scratch when the control is turned. This scratch is rarely serious, and most often just an annoyance. However, as the problem gets worse, the sound of your system will degrade. Also, as the problem gets worse, the scratching noise will get louder. The scratching noise has a large high-frequency component, so in the extreme, this noise could potentially damage tweeters, although I have never seen a documented case of tweeter damage due to control noise. Some controls are sealed at the factory, so there is no practical way to get inside and clean out the dirt. Others have access through slots or holes in the case. These open controls are more subject to dirt, but also are cleanable. You can clean an open volume control with a VERY QUICK squirt of lubricating contact cleaner, such as Radio Shack 64-2315. Even better is a non-lubricating cleaner, such as Radio Shack 64-2322. With any cleaner, less is better. Too much will wash the lubricant out of the bearings and gunk up the resistive element. You can also clean some controls by twisting them back and forth vigorously ten times. This technique pushes the dirt out of the way, but is often just a short term fix. This technique is also likely to cause more wear if it is done too often. Try to do it with the power applied, but the speaker disconnected, so that there is some signal on the control. Sealed and worn controls should be replaced rather than cleaned. Critical listeners claim that some controls, such as those made by "Alps" and by "Penny and Giles" sound better than common controls. Regardless of the brand, however, it is essential that whatever control you buy have the same charcteristics as the one you are replacing. For most volume controls, this means that they must have AUDIO TAPER, meaning that they are designed as an audio volume control, and will change the level by a constant number of dB for each degree of rotation. Badly designed circuits will wear out volume controls very quickly. Specifically, no volume control is able to work for a long time if there is significant DC current (or bias current) in the wiper. If the output of the control goes to the input of an amplifier, the amplifier should be AC coupled through a capacitor. If there is a capacitor there, it might be leaky, causing undesirable DC current through the volume control. If you have a circuit with no blocking capacitor or a bad blocking capacitor, you can add/replace the capacitor when you replace the control. However, get some expert advise before modifying. If you add a capacitor to a device which doesn't have one, you will have to make other modifications to insure that the amplifier has a source for its bias current. 11.0 CD Players, CDs, Turntables, and LPs 11.1 What should I listen for when evaluating a turntable or CD player? For tape decks and turntables, beware first of speed variations (wow and flutter). A good check for this is Richard Strauss' "Also Sprach Zarathustra" (aka: The Theme From 2001), which has a long, low, sustained organ note that comes in well before the main theme starts, and is held through the first movement. Concentrate on that. Make sure it doesn't wobble or warble. There's also a good bit at the beginning of Pink Floyd's "The Wall", but it doesn't go on as long, so you've got less time to think about it. Tape decks are prone to losing high-frequency notes, so pick something you like which has lots of treble, and make sure it is clear. The sound of a turntable is largely bound up in the kind of cartridge mounted on it. Make sure to listen to a table with a cartridge similar to what you're buying, and not one in a different price bracket. If possible, audition the turntable with the same arm and cartridge, so that you will experience potential cartridge/arm interactions, too. Most cartridges work better with one arm than another. Treat the tonearm/cartridge pair as a system, rather than independent parts. For CD players, try some piano music. See if the high notes sound tinny. Also, try something which has some soft parts, not the same as turning the volume down. Distortion for CD players (as for other devices) is measured at a high output, but in fact in CD players (unlike others) it's likely to be worse in soft passages of music. Most classical recordings contain a suitable soft passage. Most rock music won't. Distortion in CD players, if you want to call it that, is a function of the granulation noise, or time-delay pre-echo that can come out of the filtering. To listen for this, use material that is rich in high-order harmonics, such as brass music. Unfortunately, you can't reliably predict how a CD player will sound by looking at specifications, features, or the technology it uses. If you want to know how a player will sound, you MUST listen to it. 11.2 Are some discs better than others? Some recordings are better than others. Some artists are better than others. Some recording engineers are better than others. Some microphones are better than others. Some music is better than others. Ignoring the above, there is some difference between discs. Some of the very earliest discs were badly made and deteriorated with time. The technical problems that caused those problems have been solved. Some "gold" discs are available which are advertised to have better life and quality than common "aluminum" discs. These sell for an extra US $15 or more per disc over the cost of the same music on a common disc. Studies have shown that there is an advantage to glass-encased, gold platters for archiving computer data that is not error tolerant and will need to be stored for many tens of years. I have yet to see a similar comparison which justified any extra effort for storing audio recordings for 50 years. Part of the reason for this is that audio recordings contain error correction codes. Another reason is that audio recorders can effectively reconstruct badly damaged audio data, even if there is data completely missing. Some discs seem to have pinholes in the aluminum, which are visible when the disc is held up to a strong light. However, these discs play fine and last very well, so the effect of these pinholes is probably nil. Some have performed studies counting errors on various discs with various players. They found that, in general, the error count was consistent from one player to another. Also, in general, most discs have a low, consistent error rate which is perfectly correctable using the redundant data stored on the disc. This study did find that one group of discs had a higher error rate than all of the rest. This group was the promotional discs, also called "music samplers" given away by music companies to introduce you to their family of artists and performers. Despite these higher error counts, these discs still played fine. If there is no abusive handling involved, I have rarely heard of a disc that degraded with time. Of the few that have existed, they tended to be from one of the bad batches mentioned earlier. There is no doubt that some discs are mastered better than others. Some are badly mixed. Some are so badly recorded that there is noticeable clipping. Some are made from damaged master recordings. CD technology is no guarantee of good music or of a good recording. 11.3 Are CDs better than LPs? Some excellent recordings are mastered digitally, and sound great on LPs. This suggests that there is nothing inherently bad about digital. Some find that LPs sound better than CDs. Advocates of LPs claim that the digital to analog (D/A) converter in home CD players isn't up to the quality of the information on the disc. They also claim that the analog electronics in a home CD player can be poor. Some believe that CDs do not sound like LPs because the CD does not have the frequency response errors, the distortion, or the stereo separation problems of LPs. In general, though, there are good and bad CD players, just as there are good and bad turntables, cartridges, and tone arms. Any ultimate comparison would require ultimate equipment, which is unaffordable. In moderately priced systems, there will be some signal damage from the turntable system and some signal damage from the CD player. LP lovers often learn the nuances of cartridge selection, record care, and even turntable and tonearm adjustment. They have found that the turntable will sound different if the arm height is adjusted, if the cartridge angles are changed, and if the tonearm wire is moved. CDs do not offer as many avenues for the home experimenter. However, Audio Amateur Magazine has published modification projects for CD players; particularly for Magnavox 560 and similar European players. Audio Magazine has also published such articles. 11.4 What turntable should I buy? Despite improvements in motor technology, most great turntables use belt drive. Rubber roller (idler) drive sounds the worst. Select a turntable with a very heavy platter for the least wow and flutter. Give the platter a rap with your knuckle. It should not "ring" like a cymbal. It should feel and sound dead. Also look for a turntable that has good isolation from base to stylus. With the amp on and the turntable selected, but with the turntable motor off, put an old record on the turntable, lower the stylus onto the record, and then tap the edge of the base. Not too hard, you don't want to send the arm flying. At worst, you should hear (through the speakers) a quick 'thump' followed by silence; if you're lucky, you'll hear nothing at all. If the sound continues beyond a quick 'thump', the mechanical isolation is not great, and you might want to look at some other make. To perform this test with some turntables, it will be necessary to unplug the turntable power cord. If the turntable has a tonearm, try to evaluate the arm, too. A good arm should be adjustable in height. A good arm should allow cartridge adjustments. A good arm should accommodate a wide range of cartridges. Despite this, some arms work better with high compliance cartridges, while others are at their best with low compliance. Ask. The original AR Turntable was very well received when it was first made, and the current AR Turntable is still very respected for its price ($450 + arm). Turntables made by Denon, Linn, Rega, Sota, and VPI are also recommended, but can cost more. 11.5 What phono cartridge should I buy for my older turntable? The $30 Grado ZTE+1 is a great value for any home user but a purist. For the purist, there are still many choices, both moving coil and moving magnet. Each sounds slightly different, and has its individual strengths. The Sumiko Blue Point has been recommended at $125 along with the $125 Denon DL-160 and the $150 Shure V15 type V-MR. 11.6 Will phono cartridges still be around ten years from now? Most likely, there will still be cartridges available, but not in the variety available ten years ago. They will become "Special Order" in some stores and unheard of in others. "Pro" or "DJ" cartridges will stay available in good supply, "Audiophile" cartridges will stay available and very expensive, "Mid-line" cartridges will become very scarce, and a few "Budget" cartridges will remain available in copious supply. At the same time, some makers will drop their cartridge lines completely. 11.7 Will LPs still be around ten years from now? There is a strong movement of collectors and purists who will keep their collections and buy good used discs. Count on these people to keep the used disc market hot for 25 years longer. As for new music, less is being pressed today than 20 years ago. Many popular artists are being released on LP in parts of Europe, but availability is dependent on country. One person said that many new LPs are available in Spain. LP sales have increased recently in Japan and in the UK. Polydor is now re-releasing older recordings on vinyl, and will continue to press them as long as it is profitable. Likewise, there are several re-releasing projects in Japan. Some are for Jazz collectors and others are for pure analog as well as classical music lovers. They are selling the LPs by subscription, with shipments every 2 or 3 months. Each release includes about 20 titles. Japan has released over 100 LPs this way last year. 11.8 What about CD green pens? In a nutshell, save your money. A CD player "reads" information on the disc with a laser light beam. Some believe that if you put a green stripe on the very perimeter of the disc, then the light beam will not reflect around inside the disc and will more clearly pick up the data. Scientific studies of the data coming off of the disc have failed to show any difference between a virgin disc and a green painted disc. I have not heard of double blind listening comparisons that have proved that there are people who can hear the difference, although many have performed uncontrolled tests with positive results. 11.9 What about CD stabilizer rings? In a nutshell, save your money. The data coming off of the disc is a serial string of ones and zeros. If this bit stream has jitter, then it may reach the D/A converter out of sync. If this happens, then the actual analog signal recreated will have jitter, and won't be perfectly true. The vendors of stabilizer rings say that using these rings will reduce jitter and make a more perfect signal. Vendors also claim that the rings can increase the mass of a disc, making it spin more smoothly, and reducing transient load on the power supply from the motor. Some players will not play discs that have stabilizer rings on them. The clamp can't handle the thickness. Other players play ringed discs, but do not play them well, because the disc motor was not built for the added load. With those exceptions, scientific studies of the data coming off of the disc have failed to show any improvement going from a virgin to a ringed disc. I have not heard of double blind comparisons that prove that people hear the difference, either. 11.10 What about CD spray treatments (ArmorAll et al)? In a nutshell, save your money. Current wisdom is to avoid any disc coating or spray. Some will definitely damage the disc. There are many theories on what ArmorAll can do to a disc. One is that it reduces static which will attract the delicate head of the laser detector to the disc. Another theory is that the cleaner will fill voids in the disc with silicone, thereby making it easier to read by reducing diffraction effects. Scientific studies of the data coming off of the disc have failed to show any difference between a virgin disc and a treated disc. I have not heard of double blind listening comparisons that have proved that there are people who can hear the difference. One of the strongest proponents of ArmorAll issued a "recall" on his advice. He now warns that ArmorAll can damage the disc. He also advises that you can clean ArmorAll off treated discs with Dawn dish detergent. 11.11 Are 1-bit CD players better than multi-bit players? In a nutshell, they are virtually the same. There are some excellent sounding 1-bit players and some excellent sounding multi-bit players. Some feel that the 1-bit technology has more future because it can be improved with the rapidly improving digital technology, while the multi-bit players improve with slowly improving analog technology. Multi-bit also has its advocates. All of the various D/A converters try to do the same thing, and try to achieve the exact same ideal performance. How well they succeed is more a function of their skill and the quality of the parts that they buy than the technique that they use. In other words, the architecture of a D/A converter is less important than the quality of its implementation. 11.12 Are three lasers better than one in CD players? Some players have one beam, some three. All use one laser diode to generate the beam. Three-beam is just a different method for doing track alignment. Neither is better than the other. There are good 1-beam players and good 3-beam players. Manufacturers want advertising claims and "More Beams Is Better" sounded good to some marketing people. Trust your ears. 11.13 Is the BMG 8-for-1 deal good? Yes. You have to put up with their frequent mailings. You can elect the "POSITIVE OPTION" and not have to answer each mailing to avoid an order. You should expect to pay approximately $2.00 per disc for shipping and handling in the US and more elsewhere, but even at that price and assuming that you will buy one of their discs for $16.00, you still do well. Assuming, of course, that you want at least eight of the discs that they are offering for sale. Some states requires sales tax on BMG sales, and some states tax "free" discs, but the tax still is small compared to the discount from retail. The BMG collection contains over 2500 discs. This includes classical, pop, jazz, and other. All BMG discs come from the larger labels. Some rumored that BMG discs are inferior to the discs sold in normal retail chains. This has not been substantiated. In fact, BMG distributes their discs through retail chains, as well as through the mail, so you may get a BMG disc either way. If you are interested in learning what is available from BMG, there is a fairly current list of the BMG offerings available by ftp at "cisco.nosc.mil". After logging on, give the command "get [.cd]bmg.txt". (Note: Type what's in the quotes. Don't type the quotes.) This list is NOT perfect, may have errors, may have some omissions, and may have some obsolete discs in it, but is the best total compendium easily available. The list is maintained by neidorff@uicc.com (Bob Neidorff) and the archive is maintained by mike@jammin.nosc.mil (Mike Pawka). 11.14 What should I do if there is a problem dealing with BMG? The number to reach BMG is 317-542-0414. Their people have been very cooperative with me and others. It is always good policy to confirm any phone call with a letter, restating the problem and the resolution you were promised over the phone. It is good practice to write down the name of the person you speak with. If BMG sends you something that you didn't order, DON'T OPEN THE PACKAGE. Write REFUSED on the package and put it back in the mailbox. They will accept the return and credit your account for any charges. 11.15 How do I get out of the BMG racket? If you have taken any discs from BMG, you must either return what you have ordered or fulfill the terms of your original agreement. This often means buying one disc at full price and paying for the shipping on all discs you ordered and received. Once you have done this, you can quit the club at any time. Take your next order form and mark it with a bold marker in large letters "CANCEL MEMBERSHIP" and mail it to: BMG COMPACT DISC CLUB, PO BOX 91413, INDIANAPOLIS, IN 46291 USA. It may take a month to fully take effect, but they will honor your request. While waiting for the cancel order to take effect, be sure to return all future order forms marked the same way. Otherwise, you may wind up with unwanted discs. 11.16 How do I get the most out of BMG? Only buy one disc at full price, fulfilling your obligation. Request the "POSITIVE OPTION" so that you save on postage. Only buy from special fliers. Every month, except November and December, they send out a "Two for half price then one free" flier. They have almost all of the stuff in the regular fliers. They even offer "Buy one get two free" sometimes. Wait for those special deals. You can even order discs from an October catalog using the order form that came in the February catalog. You can get even more out of BMG by signing up, getting 8 discs for the price of one, quitting, signing up again, etc. People have done this successfully. BMG reserves the right to deny membership to anyone, so you run a very slight risk of being denied membership the 20th time. However, I have never heard of anyone ever being denied membership for any reason. 11.17 What are the differences between multibit and Bitstream/MASH Analogue to Digital converters (16-bit vs 1-bit CD players)? Audio data is stored on CD as 16-bit words. It is the job of the digital to analogue converter (DAC) to convert these numbers to a varying voltage. Many DAC chips do this by storing electric charge in capacitors (like water in buckets) and selectively emptying these buckets to the analogue ouput, thereby adding their contents. Others sum the outputs of current or voltage sources, but the operating principles are otherwise similar. A multi-bit converter has sixteen buckets corresponding to the sixteen bits of the input word, and sized 1, 2, 4, 8 ... 32768 charge units. Each word (ie sample) decoded from the disc is passed directly to the DAC, and those buckets corresponding to 1's in the input word are emptied to the output. To perform well the bucket sizes have to be accurate to within +/- half a charge unit; for the larger buckets this represents a tolerance tighter than 0.01%, which is difficult. Furthermore the image spectrum from 24kHz to 64kHz must be filtered out, requiring a complicated, expensive filter. Alternatively, by using some digital signal processing, the stream of 16-bit words at 44.1kHz can be transformed to a stream of shorter words at a higher rate. The two data streams represent the same signal in the audio band, but the new data stream has a lot of extra noise in it resulting from the word length reduction. This extra noise is made to appear mostly above 20kHz through the use of noise-shaping, and the oversampling ensures that the first image spectrum occurs at a much higher frequency than in the multi-bit case. This new data stream is now converted to an analogue voltage by a DAC of short word length; subsequently, most of the noise above 20kHz can be filtered out by a simple analogue filter without affecting the audio signal. Typical configurations use 1-bit words at 11.3MHz (256 times over-sampled), and 4-bit words at 2.8MHz (64 times oversampled). The former requires one bucket of arbitrary size (very simple); it is the basis of the Philips Bitstream range of converters. The latter requires four buckets of sizes 1, 2, 4 and 8 charge units, but the tolerance on these is relaxed to about 5%. MASH and other PWM systems are similar to Bitstream, but they vary the pulse width at the ouput of the digital signal processor. This can be likened to using a single bucket but with the provision to part fill it. For example, MASH allows the bucket to be filled to eleven different depths (this is where they get 3.5 bits from, as 2^(3.5) is approximately eleven). Lastly it is important to note that these are all simply different ways of performing the same function. It is easy to make a lousy CD player based around any of these technologies; it is rather more difficult to make an excellent one, regardless of the DAC technology employed. Each of the conversion methods has its advantages and disadvantages, and as ever it is the job of the engineer to balance a multitude of parameters to design a product that represents value for money to the consumer. 11.18 What is the best under-$200 CD player? Once, Magnavox (and the identical Philips) CD players were known for poor reliability. They are much better today. Some believe that for sound, an under-$200 Magnavox is as good as any in its price range. Be sure to listen for yourself before you buy. 11.20 What is the best under-$500 CD player? Some recommend the Rotel 855 and 955. 11.21 What's wrong with the CD longbox? Some CDs are sold shrink wrapped in a square plastic storage box known as the "jewel" box. This is the ideal packaging for CDs. It has almost no unusable components and adequately protects and displays the disc. The shrink also implies that the disc is new and unopened, but shrink can never assure a new disc. Some CDs are still sold in a cardboard box that is more than 2X the size of the jewel box. This "long box" is ecologically wasteful and useless. It rarely contains additional information about the disc or the artists. Its primary purpose is to discourage theft in retail stores, but it is even poor at that. These boxes are BAD. Some stores use a reusable plastic long box. When you buy a disc in one of these boxes, you take the disc and jewel box with you and leave the plastic long box with the cashier for reuse. Not perfect, but a good compromise. 11.22 How can I promote better CD packaging? Vote with your money. Don't buy CDs packaged in the long box. If you go to a store and they have CDs in the long box, tell the owner that you never buy CDs in the long box. Then find stores which don't use the disposable long box. People have been doing this over the past few years and have made a difference in many stores. (The fact that the long box costs more than simple shrink wrap has also helped the cause.) 11.23 How can I clean a dirty CD? Use a drop of dish detergent and lots of clean water. Do not rub. Never rub or wipe in a circle. Rinse the disc in running clear water, shake off most remaining drops, and lightly pat dry with a soft, clean cloth. 11.24 Can you repair a damaged CD? If the disc is lightly scratched on the bottom, then you can polish out the scratch and probably repair the disc perfectly. If there are lots of scratches or deep scratches, or there is damage on the top, you may be facing a lost cause. The music information is immediately under the label. If you scratched the reflective layer, the disc is normally unrecoverable. Before trying any repair, try washing the disc with clear water and a bit of liquid dish detergent. Do not scrub or rub hard. Rinse the disc with clear water and shake off as much water as you can. Finally, wipe the last few drops off with a soft, clean cloth, in a radial direction. SMALL scratches can be removed with a scrufty T-shirt and toothpaste, such as Tom's Toothpaste. You may wish to try a thin coating of Johnson's Klear floor wax on the bottom of the CD. Often it will cover the scratches enough to allow playing. The refractive index is pretty close to polycarbonate, so filled scratches will be nearly invisible. Noteworthy Music (800-648-7972) sells CD repair kits (#CDR 200, $11.99, one shipping unit). They seem to work as advertised, although getting the disc to the point where you can't see any sign of the scratch does take real care and persistence. You can buy professional plastic polishing compounds at many hobby shops. The ones used for polishing acrylics, plexiglas, etc. work. Ordinary lapidary jeweler's polishes also work. You'll need a rough polish to remove the scratches, then tin oxide to polish to a mirror finish. Telescope lens kits also work. Novus plastic polish and cleaner has been recommended. T-Cut, a car paintwork polish, works well for big scratches. Reviewers at Audio Magazine recommend the "Memorex CD Repair And Maintenance Kit" as the best tool for badly damaged CDs. 11.25 Can I add digital output to a non-digital-out CD player? Some Magnavox CD players using the Philips chip set can be modified. Look for a SAA7220 IC. If it has one, then it can be modified. If you have experience modifying electronic equipment, follow this procedure: Take pin 14 of the SAA7220 IC and remove whatever terminating resistor is on it. Connect it through a 560 ohm resistor to the input of a wide band pulse transformer. Tie the other end of the primary of the transformer to ground. Pulse Engineering PE65612, Schott Corp 6712540, and Scientific Conversions SC916-01 all will work. Bypass the primary through a 620 ohm resistor. Connect the output of the transformer to an RCA jack. Do not ground either side of the RCA jack. This output is now S/PDIF compatible. (Thanks for the tip to Positive Feedback) 11.26 What can I get in the way of a CD test disc? Many use the Hi-Fi News & Record Review test discs. So far, these have received only positive comments. Chesky produces 2 test discs. The first, "Chesky Jazz Sampler Volume I" contains some excellent imaging test signals (called LEDR), some well-recorded acoustic jazz, and other test signals. The second, "Chesky Jazz Sampler Volume II" has similar music & different tests. Stereophile produces two test discs. The first seems of limited value. The second just came out. Denon also produces two test discs. The first, "Digital Audio Check" is more useful for home use. The second, "Audio Technical" is more for repair shops and test-disc addicts. If you are looking for test CDs, one source of supply that stocks lots of different test CDs is: DB Systems Main Street Box 460 Rindge Center NH 03461 USA 603-899-5121 11.27 How do the letters ADD on my CD relate to sound quality? The simple answer to this question is that there is no relation between the three letter code and sound quality. Those three letters refer to the recording and mastering tools used in making the CD. The first letter refers to the recording process. For example, a disc labeled ADD was ANALOG recorded, where a disc labeled DDD was DIGITALLY recorded. Analog recording means that some form of conventional analog tape recorder was used, whether it be a two-track home-quality recorder or a very expensive wide-tape, high-speed, multi-track recorder. Digital recording could be as simple as a two-track DAT recorder, or can be a much fancier multi-track digital recorder. The second letter refers to the recorder used in the mixing and editing process. Mixing and editing is the process of combining a multi-track master recording, setting levels, editing out defects, adjusting equalization, and creating a two-track final tape. There are good machines available for this which are analog and good machines which are digital. The third letter refers to the final master, which for a CD is always digital. I have seen discs that are labelled as AAD, ADD, DAD, and DDD. Future releases may not have this three letter code on them because they don't tell you anything that is significant. Also, some codes have been used incorrectly on some discs, which makes the information that much more meaningless. 11.28 How can I clean LPs? There are expensive machines for this purpose which work very well. One popular model goes by the name Nitty Gritty. These machines spray cleaner onto the record, work it into the grooves, and then vacuum the cleaner and dirt out. If you are serious about records and have lots of them, it may be a good investment for you. If you have a more reasonable collection, you might be happy with a good hand washing every now and then. To give your records a good hand washing, start by preparing this wash: 1 gallon distilled water 90 ml 70% isopropyl alcohol 1 gram Alconox (a laboratory detergent) Also, get a natural bristle brush and trim it to the correct stiffness/bristle length so that the bristles can get into the grooves but aren't stiff enough to scratch the record. Lay the LP flat and pour a thin coat of the above fluid on it. Brush the wash into the grooves with the bristle brush. Brush in the direction of the grooves, going through all grooves. Flush the wash and dirt off with cool, running tap water. Rinse the record with distilled water and pat it dry with a soft, clean cotton cloth. 11.29 How do you set the stylus pressure correctly? Stylus tracking force is typically adjusted at the back of the tonearm with a knob that is calibrated in grams at the stylus tip. With the control set to zero, the stylus should sort-of float above the record surface. The control is then increased to the number recommended by the cartridge manufacturer. Do not, under any circumstances, use a lower than recommended force, as the cartridge may lose the ability to maintain contact with the groove wall on passages of large amplitude. This WILL result in RECORD DAMAGE. If you want the best possible tracking and sound quality, you will want to fine-tune the tracking force. Use a test record and listen very carefully, or get the help of a good dealer with a battery of instruments. 11.30 How do you set the anti-skating on a tonearm? If you have a recommendation or suggestion from the tonearm manufacturer, follow their advice first. They will give you the best starting point. Some tonearms come with calibrated anti-skate. The manufacturer of these tonearms has tried to calibrate the anti-skate control so that if you match the setting of the anti-skate to the setting of the stylus pressure, you will have nearly perfect anti-skate. Read the manufacturer's recommendations to see if this applies to your tonearm. You can see gross errors in anti-skate by looking at the stylus. If you shine a light on the front of the tonearm while playing a record, you will be able to see whether the stylus is centered in the stylus holder. If the stylus is biased to one side or another while playing a record, then the anti-skate is way off. More subtle adjustments can be made by listening for mistracking. If you can, obtain a record with equal left right modulation at high frequency with ascending modulation magnitude (volume), such as the Shure ERA-III, IV, or V test record. They have five bands of "greensleeves" played on flute, and you fiddle until the audible breakup is equal in both channels, and adjust tracking weight until it occurs in the highest band. This is, like other cartridge and tonearm adjustments, easier for the experienced hand than the beginner. Some high-end dealers have electronic instruments which allow them to accurately adjust anti-skate and other cartridge and tonearm parameters. If you can get this service, consider yourself fortunate. 11.31 How else do you adjust a tonearm/cartridge/stylus? There are a few other critical adjustments. Again, a good high-end dealer may be your best resource. Your ear may also be your best test instrument. You need a level turntable. Use a quality carpenter's level. Some people like the Shure stylus force gage for setting stylus pressure accurately. Other tools which are well recommended are the Geo-disk, a good protractor, and above all, the Cart-Align, which uses a very precise etched plastic mirror for cantilever alignment. You'll also want to set the tracking angle. It CAN be done by eyeball, but is best done with test instrumentation and a record. There is also the cartridge angle, tonearm height, etc. Read the instructions which came with your tonearm for the best specific advice for that tonearm. Tonearm cable is more critical than any cable anywhere else in the signal chain. Cable capacitance directly sets the high frequency characteristics of the cartridge. In addition, the correct grounding of the shield is essential to minimize hum. It may be necessary to change preamp input capacitors so that the cable/preamp combination loads the cartridge with the right overall capacitance. Replacing tonearm cable will have a similar effect, but may be harder to change tonearm cable than to change preamp input capacitors. Consult the cartridge, tonearm, and preamp manuals for specific advice. Also refer to 16.6 for more information on tonearm cable. An excellent article on setting up a turntable is: Stereophile, July 1990, Pages 62-85. 11.32 Do CDs deteriorate with time? What is their life span? A CD consists of a polycarbonate top layer, an aluminum (or gold) metal reflective layer, a polycarbonate bottom layer, and some miscellaneous printing ink. Of these materials, polycarbonate seems to be extremely stable with time provided that it is well cared for. Do not use any liquids on a CD that contain silicones or solvents. Do not leave CDs in sunlight or other bright light. Do not stick labels on CDs. Do not write on CDs. Do not expose CDs to temperatures higher than normal room temperatures. Don't leave a CD under water. Even the top side of a CD is critical and subject to damage. Some pressings from the early 1980s used ink which damaged the polycarbonate top layer and eventually got into the aluminum. These inks are not in use today. Some earlier discs were made with imperfect sealing around the perimeter of the disc. This was evident because the aluminum in the disc extended all of the way to the disc edge. These discs were known to fail due to moisture getting to the aluminum and causing it to oxidize. Modern CD factories have solved this problem as well. With those cautions, modern CDs will last for more than 30 years without deterioration. Most of the CDs which were made in 1983 are still around today and still sound good. 11.33 How much music can you possibly cram into a CD? The longest I have found are a Musical Heritage recording of Bach: Goldberg Variations at 79:02 and an MCA reissue of Steely Dan: Greatest Hits at 79:17. Modern CDs are pressed using tighter track spacing than the first CDs, because modern equipment is capable of holding tighter tolerance than the original machines.