When to replace your stylus - article.
Found this interesting article while looking for other information on phono cartridge life. Original article written in 1972. Sorry the sketches did not paste.
Your Phono Stylus
Why and when your stylus should be replaced.
The stylus is the first link in the reproducing chain of the phonograph record and, unfortunately, often the most neglected. Giving more attention to the state of your stylus will pay off for you in better listening, but will also allow you to protect your most precious investment - your favorite records. If you are typical, you tend to spend much more on your records than on hardware or your equipment. And some records are irreplaceable.
The task of your stylus is formidable. For every hour of music played your stylus travels more than one mile. Great efforts are made to minimize the wear and tear on your extremely delicate stylus during its long journey along the moving groove wall. The stylus is highly polished, and the groove walls are burnished by the recording stylus to reduce the roughness to less than 3 millionths of an inch. With all this effort there still remains a small amount of unavoidable friction in the interaction between the hardest substance known, the diamond stylus, and the necessarily compliant and rubbery vinyl of the disc. Happily, the vinyl under friction will temporarily yield and then spring back rather than wear away.
The diamond, as hard and wear resistant as it is, will wear even though its wear rate is only a molecule or two per foot of groove travel. As the stylus wears under constant friction of tracing the record, it begins to assume a deformed shape. This new slowly evolving stylus shape adversely affects the performance of your hi fi system and, if allowed to continue beyond a certain point, will damage the groove walls of your records.
So the important and practical question becomes, "When should I replace my phonograph cartridge stylus?" To understand the answers to this question, it will help if you understand the function of the playback stylus in the reproduction chain, and how it affects the quality of the sound and music from your high fidelity system".
First, let's examine the record with a microscope. Microscopic inspection of the record will show a continuously undulating "V" groove molded into the surface. The undulations of the groove are a precise mechanical replica of the acoustic waves generated by the original musical performance, as recorded onto a master tape from which most records are made. The disc recording art has reached such a high state of development that the information on the master tape can be transferred to the disc with virtually no change or degradation.
The stylus has the critical task of tracing these superfine undulations. The stylus must change direction up to 4,000 times a second in one inch of passing groove wall in the inner grooves of the average disc, and transmit these groove undulations to the electronic system of the cartridge. The stylus, married to the cartridge, converts the mechanical motions of the disc into electrical voltages. Together the stylus and the cartridge act as a transducer - a translator of the mechanical to electrical. Your speaker system does just the reverse. The speaker translates the electrical into the mechanical motions that move the air and make sound.
Picture your playback stylus as a ball sliding along a groove modulation as shown in Figure 1.
Figure 1. Stylus motion duplicating groove undulation with perfectly shaped stylus
Use of the ball analogy (insofar as it demonstrates the tracing function) to represent the stylus holds true for spherical, elliptical, and for the new CD-4 styli such as the Quadra-Point and Shibata. To simplify the illustration only one groove wall is shown. Actually, the groove moves past the stylus, but in flat, static illustrations, it's easier to show the groove as stationary and the stylus sliding along the groove. As the record moves past the relatively stationary stylus, the stylus executes a motion that is the precise duplicate of the groove undulation, moving in two directions at once, both vertically and horizontally, up and down, with the constant varying depths of the record's groove and from side to side. When the stylus does its job well, the groove is precisely traced and the stored information on the groove is retrieved.
A worn stylus will not retrieve this stored information properly. In Figure 1 the stylus is represented by a perfect sphere. As the surface of the stylus is abraded away its shape changes as in Figure 2.
Figure 2. Stylus shape changes with wear
In this illustration we show the wear on both sides of the stylus since in actual playback the stylus is in continuous contact with both sides of the groove. As wear starts a slight flat appears on both sides of the stylus. As wear continues these flats become larger. In extreme cases of wear as shown in Figure 2D, the original ball shape has worn into a shape represent- ing a screwdriver tip. If we play the same groove undulation shown in Figure 1 with a moderately worn stylus, we can hear the effect on our fidelity play-back system. As the worn stylus traces the groove, as in Figure 3,
Figure 3. Stylus motion a distorted version of groove undulation with worn stylus
the path of the stylus no longer represents a replica of the groove undulations. The effect is the same as playing the record groove with a considerably larger stylus than was intended. When the path of the stylus differs from the shape of the groove undulations, increased distortion is the result. For good reason, engineers call this tracing distortion, for what the worn stylus now does is feed a distorted version of the groove undulation to the electrical system of the cartridge. As the stylus wear increases, the amount of distortion increases until the screwdriver shape is reached. At this stage further problems are introduced.
Some years ago when I, was director of disc research at CBS Laboratories, we were studying the effects of worn playback styli on playback distortion. One of Columbia Records quality con- trol procedures in their pressing plants was to actually play one record out of each spindle of records to make certain that the stamper in use at the time had not developed defects. Quite a few worn styli were generated by quality control testers, and we got a hold of a handful of the styli. To my surprise, I found out that flats worn on the styli were barely perceptible, even with the very sophisticated microscopes we had at our disposal.
I was very skeptical when I found out that the testers reported that, "The cartridges didn't sound good anymore," and that there was no mandatory visual inspection of the rejected styli. I could not have been more wrong.
When I visited the plant and spent some time with the quality control testers, I found out some interesting things. It's important to realize that when it's somebody's job to listen to records all day long and pick out those records that don't sound right, these listeners develop an extreme sensitivity to deterioration in sound quality. One of the testers gave me a convincing demonstration with a stylus I had brought with me. The stylus was typical of the styli discarded because of wear. Under the microscope two extremely small flats could be seen. Without her looking, I interchanged a good stylus with the slightly worn one, back and forth a number of times. Each time, by the presence or lack of distortion, the tester could instantly tell me which stylus was installed. By the end of the session I could readily tell the difference myself.
So far we have mentioned how stylus wear affects tracing function. In the more extreme cases of wear, when the stylus begins to look like a screwdriver tip, there is not only playback distortion, but damage to our precious records. In Figure 4
Figure 4. Severely worn stylus can cause groove damage.
we show a "screwdriver tip" stylus sliding along the groove wail. You can see that this new shape of the stylus will not slide harmlessly along the groove wall and permanently damage the record. Styli worn to this extent are not so rare as you might think.
When To Replace Your Stylus
So the 'when' answer to the question, "When and why shall I replace my stylus?" is - as soon as you hear an increase in distortion.
A word of caution: Not every case of distortion can be attributed to a worn stylus. Some judgment and a little intelligent experimentation may be necessary to determine where the distortion originates. Usually the first subtle indications of stylus wear can be detected in your own listening room when you hear increasing distortion, especially on sibilance in voices. If you want to know whether your stylus is approaching conditions of extreme "wear, take your stylus to one of the many hi fi retail shops that have a stylus inspection service.
To the oft asked question, "Is there a set number of playing hours be- fore a stylus should be replaced?" my answer is no. Tracking force and other playing conditions vary. The slightest variation in diamond quality and groove wall surfaces make it very difficult to predict the number of playing hours of stylus life.
My best advice - when in doubt, replace the stylus. Your stylus investment is relatively modest when you consider what you've spent on the rest of your equipment and your sometimes irreplaceable records. The stylus is not the place to scrimp. A new stylus can bring your record playback system to peak performance.
The motto: Trust your ears for the most practical test for determining if your stylus is performing properly.
Written by Arnold Schwartz 1972, former President of the Micro-Acoustics Corporation.
Published as an enclosure to the Micro-Acoustics cartridges for common information.
Micro-Acoustics Corporation on Roger Russell's Micro-Acoustics History Page. More....
Last modified: 5-Apr-2005