The STEREO CARTRIDGE
There are not many things in this world about which it can be said that they are literally "worth their weight in gold." However, streo phonograph cartridges are among these few: in fact, according to some quick calculations, at least a couple of the best of them are selling for TWICE their weight in gold.
Why are they so steap, and are they worth it? Well, let's examine the facts.
The cartridge and needle assembly that you so casually drop onto your records is an extremely intricate "electro-acoustic transducer." An electro-transducer is a gadget, of which speakers, cartridges, and microphones are the most common examples, which converts acoustic energy into electrical energy into mechanical, acoustice form.
It is interesting to note that all electro-acoustic transducers are highly individual in their performance; that is to say, no two microphones report what they hear in quite the same way, no two speakers sound quite alike in the same system, and, no two cartridges respond in kind to the same record grooves. Making a good and faithful e-a transducer is as much an art as a science at the moment; making a good phonograph cartridge may well require the highest degree of that art.
Speakers and microphones either convert air motion into electrical signal or electrical signal into air motion. A phonograph cartridge has the related but somewhat different task of converting wiggles in plastic into electrical signals approximating those originally made by the recoring engineer's mikes. While neither a speaker nor a microphone can harm the air it contacts in its attention to its duty, a cartridge can wreak havoc on its medium, the plastic of your records. Clearly, your choice of a cartridge will have a strong bearing on the satisfaction you receive from your home music system. The immediate factor of sound quality and the long range effect of record life will determine the grade you give your cartridge.
WHAT IS A CARTRIDGE
A cartridge can best be described in this way: It is a device which (ideally) travels through a record's grooves without too much heat and friction, gauges the intricacies of that groove and reports its findings in the form of electrical impulses to the amphlifier, being ever careful not to falsify its observations.
In practice, smoothly polished, spherically tipped diamond is the actual groove runner (or, if you have weak floors, groove hopper). It is connected to a control rod, or "stylus arm" which wiggles along with its maneuverings. This stylus arm is in turn either connected to a crystal against which it vibrates, causing voltages to appear across it, or it in some way moves a coil through a magnetic field, cutting lines of force, and again causing voltages to arise.
The first type of cartridge--in which the stylus arm, or shank, presses on a crystal--is called the "ceramic" type. Because they are consistently prone to distortions of the true signal and because they sually entail the necessitty of higher stylus pressures, ceramic cartridges are not popularly used today in custom audio circles, and must of our cartridges employ the electrically less efficient magnetic principle.
Anytime you move a magnet in the close proximity of a coiled wire (or vice versa) you cause a current to flow through the coil. In the stereo cartridge we can either attach a magnet to the stylus arm and hold two coils stationary in the body of the device, or we can wind two coils onto the arm in different directions and mount a stationary magnet in the body. Either way (one is called "moving magnet", the other "moving coil" for obcious reasons), when the needle does its mazurka in the groove the stylus arms follows, and the groove vibrations are "transduced" into electrical signals in the coils. Connect the coils by means of audio cable to the amplifier, and we have a stereo cartridge.
Easy, isn't it--but remember that we're doing sub-miniature work. Our coils must be wound with wire so fine it's hardly visible. Our diamond tip must be perfectly rounded and polished to .0007"--that's seven TEN-THOUSANDTHS of an inch. And, most important of all, the whole needle and needle-arm assembly must be perfectly free to trace grooves as fine as 2,000 vibrations per inch (our math upon request); must be perfectly free from resonances in the range of frequencies possible in the plastic; must be mounted in such a way that it remains perfectly centered at the resting point, with relation magnet to coils.
Reading about all these fantastic intricacies is rather fascinating, and makes the literature of a couple of cartridges available at the moment both have easily understood discussions in their promotional material of some of these incredibly complicated problems that beset the cartridge maker. GRADO'S literature (describing their particularly sweet sounding new Laboratory cartridge--$49.50) is very interesting, as is AUDIO DYNAMICS' (explaining the starting ADC-1--also $49.50--which is the first cartridge to successfully track under 1 gram and still give exceptional sound).
BUYING YOUR CARTRIDGE
Our two criteria for judging stereo cartridges were sound quality and treatment of records. A number of eartridges sound good; a shockingly larger number sound downright bad. One of the most reliable performers in the lower price range for magnetic pickups is the PICKERING 380--C. It has a smooth quality which many people prefer, and, at $29.95, it is a best buy. The afore-mentioned GRADO and ADC models are still better performers and exhibit astounding high precision in craftmanship.
Both come with individual test sheets, telling you how your particular edition tested at the factory (all of which will probably cause you to nod and smile and look blank, but which has significance just the same. The fact that such tight quality control is kept on these items is re-assuring. And in the case of the ADC models it has been interesting for me to note that every one I've seen lately has greatly exceeded its advertised specifications).
Of these two cartridges each offers particular advantages available nowhere else. The GRADO has the smoothest, sweetest sound around and tracks at moderately low pressures. The ADC-1 is possibly a shade less heavenly in sound but offers the lowest tracking pressures ever achieved--under 1 gram, which is generally agreed to be the point of vanishing record wear.
In any event, purchasing a phonograph cartridge is extremely similar to purchasing a horse--you can't judge by appearance, but you look for good characteristics and then try the thing out. With cartridges, look for a tracking pressure below 4 grams--higher will mean inordinately high record wear. Look for high compliance and low mean inordinately high record wear. Look for high compliance and low moving mass; study of specs sheets sheets will teach you what "high" and "low" are. But above all rely on your ears, as guided by those of your audio dealer, who, after all, does a lot of listening.
The cartridge is physically the smallest but technically the most important link in the chain of your home music system.