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Cartridge History

  Technically, the word for it is "transducer." A phonograph record is a physical fact: a thing. A turntable produces physical motion, the spinning of a disc. But the pickup lives partly in the physical world of its wigwagging stylus, and partly in the electrical world where all the rules are subtly different. It is the job of the pickup to transform the physical motions produced by the record, the turntable, the tone arm and the stylus into electrical signals containing the message from the frozen sound.

Many of the new pickups are smaller than the nail on your little finger, and most of them weigh less than five cents' worth of pennies. They are a triumph of miniaturization, a striking exception to the usual mechanical rule that the more delicate the work you have to do, the bigger the machine you need for it. For pickups deal with motions that can be measured only in hundreds of thousandths of an inch, and with electrical signals as small as a few one-thousandths of a volt-and many of them at once.

The most difficult part of the job is mechanical. The pickup must hold the stylus tightly enough to keep it in the groove even when it is jolted hard by a strong low-frequency signal. At the same time, it must let the stylus swing freely within the groove. When there's a pause in the groove's modulations, the stylus must spring back firmly to dead center, without any extraneous vibrations. At the same time, it must comply effortlessly with the correct vibrations when the music begins again.

 

Pickups: The Four Basic Types
Pickups embody various mechanical designs, and use different means of translating stylus motion into electrical energy. The four basic methods are called "magnetic", "dynamic", "piezo-electric" and "capacitance." The first two work by a "constant velocity" response, which means that the power of the signal created depends on the speed with which the needle whips around the wiggles. This is the exact reverse of the process by which the cutting head and stylus cut the record. Piezo-electric (crystal and ceramic) pickups and capacitance pickups have a constant amplitude" response. This means that the power of the signal depends on the width of the wiggle from its crest to its trough, the degree to which the stylus is displaced from its center or rest position. Neither method is necessarily superior to the other, but the fact is that a majority of the satisfactory high-fidelity pickups are constant velocity-magnetic or dynamic.

 

Magnetic Pickups
Schematic of Magnetic CartridgeThe most popular magnetic pickup made --- also one of the best
and one of the cheapest --- is the General Electric "variable reluctance" cartridge, in which the stylus is set in the end of a cantilever spring connected at its other end to a small permanent magnet. The stylus and vibrates between two iron pole pieces which extend up into the pickup chassis and form the cores of two small copper-wire coils. The pole pieces are yoked together at the top, close to the permanent magnet. This creates a complete circuit-magnet through stylus bar to pole pieces and back to magnet. As the stylus vibrates it feeds this magnetic-flux circuit alternately through the two pole pieces, inducing an electric voltage in the copper-wire coils. This voltage is led off to your preamplifier and emerges from the loudspeaker as musical sound.

Elac and GE CartridgeEarly GE cantilever stylus assemblies were too massive to transmit very high-frequency vibrations. New GE stylus assemblies, which fit the old cartridges, solve the problem. Extraneous vibrations of the stylus and the lever are damped pretty effectively by tiny elastic binding blocks. The GE comes equipped with one stylus (for 78 or microgroove) or two styli (one for each type of record) in a single cartridge. Anyone can take out the old stylus and put in a new one on the GE pickup, and the new two-stylus assembly is made in such a way that either stylus can be replaced separately. Maintenance is simple --- just clean away the dust that gathers in the gap around the stylus. GE's -new, 1958-model VR-11 is made to track at a vertical pressure of only four grams. All the other variable-reluctance pickups cost considerably more than the GE, and there is some question about whether they are worth the extra money --- except in a very expensive rig. The German-made Miratwin has extra values, however, for cheaper installations, too, because its output is five or six times as great as the GE's, since it needs less "gain" from the preamp. Among inexpensive preamps, where hum can be a problem, the Miratwin may be a safer buy-especially since the price difference between Miratwin and GE is now considerably less than the price difference between an elaborate and a simple preamplifier. The Pickering, which operates on somewhat different principles, and offers reliable viscous-damping of resonances, gives better high-frequency response than either the GE or the Miratwin, which may or may not be worth the extra cost.

A new "moving magnet" pickup --- the Shure --- is just coming onto the market now, and making a well-deserved splash. Engineered to the smallest tolerances of any pickup, the Shure is the most delicate and probably the most accurate of variable-reluctance designs; the output is very low, usually requiring a special transformer. Made to track at a vertical force of less than two grams, the Shure competes on at least equal terms with the fancier dynamic pickups, It costs as much, too.

 

Dynamic Pickups
Pickering and Fairchild CartridgesIn magnetic pickups the voltage which corresponds to the motion of the stylus is induced in a stationary coil by a "moving iron" element. In dynamic pickups the coil itself moves. Generally speaking, this design produces an even smaller voltage than the variable-reluctance magnetic design. Thus dynamic pickups give extremely low output and require either a top-quality preamplifier or a separate booster transformer. The most popular of them is the Fairchild, in which the wire coil is wound directly onto the duralumin bar that holds the stylus. It is an extremely accurate pickup, and the least fragile of the low-output dynamics. Fairchild makes only single-play cartridges, which means that you must buy two (each of which costs as much as a double-play GE) if you have both microgroove and 78-rpm records. The cartridge must be returned to the factory for stylus replacements minor drawback.

About the only disadvantage of the Fairchild (except for its price) is that the magnetic field extends some distance beyond the cartridge itself. If your record player has an iron turntable, the magnetic pull will increase the effective tracking weight of the stylus, speeding up both record wear and stylus wear. Most people who want to spend $75 for their pickups will also want to spend the necessary money for a machined-aluminum custom turntable. For those who use this pickup with a record changer, however, Fairchild makes a pad which sits on the turntable and keeps the cartridge safely away from the pull of the steel turntable.

Schematic of a Dymanic PickupMany experts f eel that the new Electro-Sonic Laboratories cartridge, especially in its imported Danish version (the American model is built to a Danish pattern), is or ought to be inherently the cleanest dynamic pickup, perhaps because of the appealing logic of its design. It is, however, extremely expensive (up to $100 for a single-play cartridge and balanced arm; no dual-stylus model is made) and terribly temperamental about working conditions. Like all pickups using magnets, it gathers dust, and cleaning it requires elementary knowledge of mechanics. In short, the ESL (as it is affectionately known in the catalogues) is for hobbyists and specialists rather than the average listener. Even here, it is seriously challenged by the Shure and the splendid British Leak ($70 with arm), which knowledgeable people say measures "flatter" than any other pickup. But it has almost no vertical compliance --- which means it won't play warped records. The new Grado, just coming on the market at the end of 1957, gains vertical compliance by an ingenious plastic stylus bar and viscous-damped conical assembly. This is the one, you may recall, that has the radium dot to ionize record surfaces.

 

Piezoelectric Pickups
Crystal and ceramic pickups operate on an entirely different principle, chemical rather than electrical. It has been known for some time that a crystal made of Rochelle salts will bend without breaking, and will give off an electric signal when made to bend. In piezoelectric pickups the head of the stylus (or, more commonly, a lever attached to the head of the stylus) is inserted into the crystal or ceramic (a synthetic crystal). Its side-to-side swing bends the crystal, and the result is a fairly sizable electric signal. The piezoelectric pickup has certain advantages over the magnetic. It gives off a much larger voltage, which means that it can be used without a preamplifier. Moreover, any extraneous noises that enter the system through the pickup will be far less important, because the intrinsic musical sounds are coming through with 60 to 70 times the strength they would receive from a magnetic cartridge.

Electro-Sonic and Leak TonearmThe induction coil that makes the electrical signal in the magnetic pickup may in its wanderings come within the field of the turntable motor and transmit a dose of 60-cycle hum, while the piezo-electric pickup is impervious to stray magnetism. Finally, the magnetic is unsatisfactory in moist climates, because condensation forms between the poles of the magnet, eventually corroding the guts of the pickup; the ceramic (not the crystal) is impervious.

Nevertheless, a satisfactory magnetic pickup is easier to design than a satisfactory crystal or ceramic. The stylus in a magnetic pickup need push only a light coil of wire or an equally light metal tube, while the stylus in the piezoelectric pickup must bend a crystal. A baseball which hits a heavy wire screen at 60 miles an hour may dent the screen; a locomotive which hits the screen at that speed will go right through it. In every pickup, the stylus moves at the same speed. If it is to do more work, it must have greater mass.

The greater the effective mass of the stylus, the less responsive it will be to the back-and-forth push given by the moving wiggle on the phonograph record. It will have greater inertia, greater tendency to keep traveling in whatever direction it has been pushed. The strong low-frequency pushes, therefore, will tend to drive the stylus right out of the groove. Keeping the stylus in the groove will demand more stiffness inside the pickup, more resistance to the free motion of the stylus. Most piezoelectric pickups are therefore inaccurate at the lower f frequencies. And the piezo-electric pickup is a constant-amplitude device. The electric signal is caused by the bending of a crystal: the greater the degree of bending, the greater the signal. Records are cut, however, by a constant-velocity cutter, which makes the strength of the recorded signal proportionate to the speed with which the stylus whips around the wiggles. Low-frequency signals become wiggles of considerable amplitude, and high-frequency signals wiggles of infinitesimal amplitude.

Thus the piezo-electric pickup distorts the recorded signal by giving a loud voltage to the low-frequency notes and a soft voltage to the high-frequency notes. Moreover, there may come a time, at very high frequencies, when the amplitude of the wiggle is not sufficient to make the crystal bend, and the piezo-electric pickup will not respond at all.

None of this is quite as bad as it looks. As explained previously, high-frequency signals are boosted when records are made, to mask surface noise; low-frequency signals are attenuated, so that grooves can be kept narrow and lots of grooves cut into a single disc. The piezo-electric pickup, in boosting the bass signals and diminishing the treble signals, acts to equalize the distortion built into the phonograph record. While it will not boost or diminish on a curve that exactly matches the "recording characteristic" of the record, it will do a fair-enough job. And by eliminating the equalizer as well as the preamplifier, it enables a big cost corner to be snipped off. No piezo-electric pickup yet produced commercially will respond throughout the audible range, but a few of the new designs fit the stylus so closely into the ceramic that an electric signal will be produced by wiggles as narrow as 14,000 cycles. From 14,000 cps to 17,000 cps, which is the utter limit of normal hearing, represents a range of less than two whole tones in the musical scale, so a pickup which responds to 14,000 cps is quite adequate even for very high fidelity. Two piezo-electric pickups are made for installation in a full high-fidelity rig: the Electro-Voice Ultra-Linear and the Sonotone. Both companies make special preamps to handle their pickups.

Weathers StylusAmong all the other piezoelectric pickups, the experts have good words only for some Astatic crystals, the Sonotone, the British-made Collaro and the Dutch-designed Ronette ceramics. These would be adequate for low-cost hi-fi machines, except that even the minimum hi-fi amplifiers now include preamplifiers and are built for use with magnetic pickups. Most of the straight amplifiers presently on the
market do not even have an on-off switch, let alone such refinements as a volume control. They are meant to be used only with a separate preamplifier control unit. So the crystal or ceramic cartridge fades away as a possible buy for anyone building a set from individual components. Where it is still important is in the packaged machine, usually portable or table-top, which uses the stronger voltages from the piezo-electric pickup to sidestep the expense of a preamplifier, and thus gives value for money in the $125 to $175 price range. People who are looking to improve a well-loved package unit with a crystal pickup, though, might try substituting a Ronette for the old crystal. They'll hear the difference.

 

Capacitance Or FM Cartridges
The less work the stylus must do, the more accurate the pickup can be. In magnetic, dynamic and piezo-electric pickups the electric signal is generated by the motion of the stylus itself, which requires a certain minimal bulk. Even with the most careful engineering a vertical pressure of four to eight grams is necessary to make such pickups work properly, and the moving mass of the stylus must remain a measurable quantity. If you could design a pickup, though, in which the signal voltage was already there, and the motion of the stylus would merely modify it, then...

Then you would approach the perfect pickup. Literally hundreds of
patent applications have been filed on such designs, and a few such
pickups have actually been manufactured. The most successful of
them is the Weathers, which is called a "capacitance" pickup because engineers enjoy using such words, or an "FM" pickup because it works similarly to FM broadcasting. Briefly, the works of the Weathers pickup consist of a fixed metal plate onto which is fed a very rapidly oscillating charge, and a free-floating plate which in rest position stands parallel to its neighbor, a tiny air gap away. The floating plate is attached to the stylus. As the stylus traces the wiggles in the groove of a spinning record, it causes the floating plate to flutter toward and away from the charged plate. As the air gap expands and contracts, the oscillating current is modulated by the frequency of the vibration of the stylus.

Images of StylusThe Weathers pickup cannot be bought alone. You also need the Weathers box with the oscillator which feeds the unmodulated and detects the modulated current, the way a radio tuner detects an FM broadcast. The combination costs $40 with a sapphire or $55 with a diamond stylus. Since the Weathers will not operate properly in any tone arm but its own, you had better add $15 for the arm and buy the package. The advantages of the Weathers are numerous. Since it tracks at a pressure of only one gram, it wears both records and styli much more slowly than any other pickup -- except, perhaps, the Shure. A stylus will last about 20 times its normal life in a Weathers pickup. The moving mass of the stylus has been reduced to the point where it is scarcely measurable, which means that the frequency response is practically unlimited: the Weathers has tested out to 30,000 cycles. Because the vertical pressure is so low, the record can safely be played while resting on a center cushion no wider than the label. The grooves never touch the turntable, and thus they pick up much less surface dust than those of the average record.

But all this is balanced, in most households, by the Weathers' one overwhelming disability: it is disgustingly fragile. A cross look can give it a case of intermodulation distortion. It must be fixed in place and left alone, and it is not recommended for any household in which more than one person has access to the phonograph. For bachelors, or people with unnaturally good control over the spouse and children, the Weathers is excellent. For others, it is just too delicate.

 

Styli
The Weathers pickup can be purchased with any of five styli: a 78 diamond or sapphire, a microgroove diamond or sapphire, or a "truncated" sapphire which will play all kinds of records. Because of its exceedingly low tracking weight, the Weathers can use an all-purpose needle without ruining records. No other pickup today can make this claim. Some of the cheap crystal pickups come with a single all-purpose stylus, but they invariably chew up both vinylite and shellac records in a very few playings.

Images of NeedlesA new and correctly shaped stylus will ride in the grooves of a record with its weight on two points at the sides of the groove. As the stylus wears, it will develop "flats" at these two points. Now a 10,000-cycle wiggle, halfway through a long-playing record, has a length of about .001 inch. If the flat on the stylus has a length of .001 inch, the stylus will simply ignore the 10,000-cycle wiggle. A worn stylus will therefore cut the frequency response of the phonograph, regardless of the newness of all the other elements. Worse, it will cut the record. A sharp edge forms at the point where the hemisphere tip of the stylus begins to flatten, and the edge gouges away the wiggles in the record groove. At four grams of vertical pressure the stylus presses on its two resting points with a weight of nearly 20 tons per square inch, and a sharp edge with such weight behind it will soon ruin a record.

 

Osium
An osmium stylus, which is standard equipment on crystals and ceramics of the second grade, will develop slight flats after playing only two or three LP's and may begin to damage vinylite records after as few as 10 playings (the wider groove of the old 78 does less damage to the stylus and, generally speaking, a 78 stylus will be safe enough for three times as many hours as a microgroove stylus). Few people are willing to change needles that often, and even if they were, the expense would be enormous. No need for it: the the sapphire is much cheaper.

 

Sapphire
An average sapphire stylus will give about 35 or 40 long plays before it begins to scratch records. With luck, it may go to 75 plays in safe condition. Since an LP plays almost an hour, this is not an insignificant amount of music, and in the average home would mean that the stylus would need to be replaced every two months or so. For most pickups the replacement cost is about $2. Pickups that must be sent to the factory for stylus replacement should not, however, be bought with sapphire styli. The replacement charge on them is usually higher.

 

Diamond
For LP's the recommendation is always the diamond. The purchase cost of the stylus will run somewhere between $8 and $16, but the diamond will last from eight to 30 times as long as a sapphire, which means that it costs much less over the long run. It also gives you fewer worries about what is happening to your records. A worn stylus will ruin records long before it begins to sound bad, and the man with a sapphire usually loses part of the fun of his phonograph because he is listening for that first sign of wear. A diamond should be good for at least 300 hours, and it may give 1,000 hours of listening before it goes sour. There is a considerable difference between 300 and 1,000, and the man who lives far from the madding crowd may find it difficult to decide when his stylus wants replacement. In most larger cities, however, a record store or hi-fi shop will have a 150-power microscope set up for the purpose of examining styli -- and you can see for yourself whether or not the tip is dangerously worn.

 

Buying A Stylus
It is dangerous to try cutting corners on the cost of a new stylus. When you buy a stylus you do not buy just a tip, but a complete assembly which is a vital part of your pickup. A "retip" soldered onto the old assembly is likely to change the very delicate balance within the pickup and produce distortion in the final sound. For the more common pickups-notably the GE-stylus manufacturers such as Walco and Tetrad produce perfectly good stylus assemblies which will work as well as the manufacturer's own. For other pickups, however, it is advisable to buy the stylus made by the company that makes the cartridge. You have put a lot of money into a phonograph, and the sound of that phonograph depends initially on the accuracy of its pickup. It doesn't pay to save two bucks on a stylus and distort the performance of the machine as a whole.

(Excerpts from the book Hi-Fi All-New 1958 Edition)

 

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