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Part 1 - A General Introduction

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 Why Vinyl?
The process of audio recording on discs of one kind or another is a technology which began a hundred and fifteen years ago, and though as a medium for the mass marketing of music it has been largely replaced by the audio CD, it is still going strong in the areas of house, hip hop and scratch music, and those who appreciate the sound of well-reproduced music in the home are still reluctant to part with their vinyl collections.

My own collection of 3000 or so vinyl recordings from the early fifties to the late eighties has been put together almost entirely from second-hand sources, and reflects my interest in Western keyboard and chamber music -- as well as the must-have standards of the classical repertoire. The playback equipment is a Thorens TD124/II turntable with SME 3009 arm, and a selection of cartridges in interchangeable headshells, but principally a Shure V15 Type 3 magnetic cartridge tracking at 1.25 grams. The styli are elliptical on the better cartridges, but a couple of spherical styli are used for tracking older mono or crackly and decrepit records. The preamp stage of a consumer-level amplifier (an Akai) is used to provide tone control and to boost the audio signal to RCA level for the speakers. The speakers are the incomparable Lenard Sarabande four-way active systems. Each unit has four dedicated amplifiers -- each amplifier optimized for the natural bandwidth of its particular speaker in the four speaker combination.

All methods of reproduction have artefacts peculiar to the method employed. Whilst vinyl disc recordings had their share, the clicks, pops and crackles that accompanied the playing of most people's records were due less to the technology than the record owner's level of care for their records. CDs are far less prone to these drawbacks, but not immune, and it has to be said that the erstwhile owners of crackly records are now the owners of mistracking, stuttering and unreliable CDs. It would seem that there is no escape from the need to care for your music, whatever the format.

This article is addressed to the people who are still in love with their vinyl collections. Long may they find replacement styli and belts for their turntables, for amongst the neglected discs from the early days of stereo recording now turning up in charity shops and car-boot sales are what many discriminating listeners believe to be the finest examples of recorded sound in the entire history of the medium.


 Part 2 - Examining the Grooves
 The Record Surface
Low power stereo microscope over plastic foam support When faced with the task of identifying the cause of an obstinate click on a vinyl record which cannot be removed by brushing with a carbon fibre brush or by prodding with stiffer nylon bristles, the following procedure is recommended.

Before removing the record from the turntable, visually locate the source of the click by noting the position of the record label in relation to the stylus, and how far the stylus is in from the edge of the record. Use a hand magnifier of x6 to x10 to examine the area. This will quite often be enough to give a clear idea of the cause of the problem. If closer examination is needed, the setup shown in the picture on the right is useful. A low power stereo microscope with its own illumination, suspended on an adjustable arm over a suitably large piece of foam plastic should enable the record to be positioned and manipulated without risk of damage. Beware of using too high an intensity of illumination if the lamp concentrates the light from a tungsten filament lamp onto the record, as local heating may cause a warp in the record surface. Use low power to locate the obstacle, and higher powers as required. Swing the lamp around on its pivot to illuminate the area from different directions as the grooves catch the light and cause reflections which may be confusing if the left and right eyes see markedly different images.

 Groove Details
The following image is of a mono recording, photographed using an epi-illumination setup in which the incident light is directed onto the record surface by a system of annular reflectors concentric with the x21 power objective, producing an incident light darkfield. Total magnification is x300.
Mono record: incident darkfield
A mono vinyl record in epi-illumination darkfield. X300.
The image below is of a fairly heavily modulated (loud) section of a stereo record, and has been photographed in incident brightfield -- an arrangement whereby the illumination is directed down through the objective, which acts as its own condenser as well as producing the image. Magnification is x400.

The light coloured areas of the picture is the flat record surface -- the land between the grooves. The grooves themselves are more complex than in the mono record due to the fact that one wall of the groove produces the right stereo channel, and the other wall produces the left.

Stereo record: Incident brightfield
A stereo vinyl record in epi-illumination brightfield. x400.
The picture also shows a lip or burr of vinyl which extends slightly above the record surface along the upper edge of both sides of the groove. It explains the strange phenomenon known only to owners of a light-tracking cartridge and a well balanced, bias compensated tone arm, whereby the stylus tracks the record by running on the land between the grooves, requiring a nudge to drop it into the groove.

The burrs are an artefact of the lacquer-cutting stage of record production, and are called "horns" in the trade. They are faithfully reproduced through all subsequent stages of manufacture. The technique of cutting the lacquer master with a heated stylus largely eliminated this phenomenon, and the example shown here is probably due to non-optimum heating of the engraving stylus. They do not directly affect the sound produced by the record, but they are fragile, and if the record surface is lightly scraped or rubbed, they can overhang the groove, causing noisy playback.


  The Microscopy of Vinyl Recordings
 Part 3 - Surface Contamination, Old Styli
 Biological Agents of Vinyl Degradation
The particles which obstruct the grooves of, and detract from the listening experience provided by, vinyl records can be, as you would expect, of animal, vegetable or mineral origin.

The two pictures below show one animal and one vegetable agent -- the latter following close upon the heels of the former for reasons which will become apparent.
The animal (below) is a young silverfish with its extended cercae overlapping the closing bars of the final movement of Bruckner's third symphony. I mention this as it is not possible to tell from the photograph. There are few places in a Bruckner symphony where the sound of a diamond stylus colliding with a dead silverfish would be less welcome. The cadaver was removed by brushing with a carbon fibre brush.

Young silverfish on LP
Dead silverfish on a vinyl record surface. x35
The vegetable agent in the picture below is an anonymous fungus. The mycelial threads are seen radiating from small lumps stuck on the record surface which are dried silverfish droppings. Four as yet fungally unexploited items of the same kind are seen in the right-hand portion of the picture. It has been estimated that one silverfish turd would keep the average fungus happily fed for God knows how long -- depending on the temperature and humidity conditions in the location of your record collection.

Fortunately, all of this softens easily when water is applied, so unless the fungus is one of those that manages to etch itself into the vinyl, a careful wash or a local scrub with a wet cotton bud will remove it.

Fungus on LP
Fungus growing on a vinyl record surface. x35.
Organic contamination of record surfaces includes things like impressed dandruff flakes, dried specks of saliva resulting from conversations conducted during the record changing process, crumbs from the last cheese sandwich you made, etc.
Any of these specks will provide ample nourishment for any fungal spore fortunate enough to land on it. Storage of records in a warm, damp place (or even a cold, damp place) will then guarantee fungal longevity and record unplayability.
 Older Styli
This picture shows a cheap diamond stylus with a spherical tip. The diamond is the dark portion at the top of the conical structure. It is fused to a metal mount which is glued into a hole in a hollow aluminium arm called the cantilever.
Spherical diamond stylus
A spherical diamond stylus from a cheap cartridge.
The picture below is of a replacement stylus assembly of which the top picture is a part. The cantilever is fitted with two styli having a 180 degree rotation lever which brings one stylus or the other into the playing position. The lower stylus is a coarse spherical (probably sapphire) tip for playing 78 rpm records.
Dual stylus assembly
A turnover stylus assembly for a dual LP/78 rpm player.
The final picture shows one of many disasters which can befall a stylus -- or more specifically, its cantilever.
Fractured cantilever
Fractured stylus cantilever from a consumer-level record deck.
The next page deals in detail with the elliptical diamond stylus and the level of wear which leads to mistracking of the record.

  The Microscopy of Vinyl Recordings
 Part 4 - The Elliptical Stylus and Stylus wear
 The Elliptical Diamond Stylus
elliptical stylus from front
Pictured on the right is an elliptical stylus from an Ortofon FF10XE magnetic cartridge (once common on consumer-level record decks) showing the way the stylus is mounted in the cantilever arm. The diamond part of assembly is only the conical tip. This is bonded to a metal shank which is glued into a hole made in the cantilever.

The cantilever itself is a tiny thin-walled aluminium tube which has been pressed flat at the very end (out of focus in this picture) to accommodate the stylus. The resin used to glue the stylus can be seen at the top of the picture.

The stylus tip has been cleaned for this picture by careful stroking with a cotton bud moistened with saliva. The buildup of debris around the base is typical of a stylus which has been in use for some time and exerts no effect on sound or performance. The degree of wear shown in the following micrographs was sufficient to cause a slight buzzing distortion in loud passages, particularly in heavily modulated records of choral and piano music at a stylus tracking force of 1.5 grams. For less demanding recordings, no audible mistracking could be detected.

 The Elliptical Contour
The reasons for adopting an elliptical stylus profile are that whilst the broader radius across the width of the groove determines the height at which the stylus rides in the groove, as it did with the older spherical stylus, the smaller radius of that part of the stylus in contact with the wall of the groove enables more accurate tracking of the high frequency modulations of the groove.

Various refinements on the elliptical stylus principle have been developed, and are well explained and illustrated in this link to the Needle Express website FAQ page. The objective of all the design types is to increase the area of contact between the stylus and the wall of the groove in a vertical direction. The high cost of these styli is a consequence of the careful grinding and polishing required to achieve the required profile, and the very exacting task of mounting the stylus in the cantilever so that the narrow axis of the ellipse is perpendicular to the line if the groove. This cost is offset somewhat by the reduced rate of wear on both stylus and records.

The standard elliptical tip is made by first grinding the diamond to a conical shape having a spherical tip with a radius equal to the curvature across the major axis of the finished elliptical stylus. Narrowing the tip to form the ellipse is achieved by grinding a flat surface on the front and the back of the tip so that the profile is now "elliptical" when viewed looking directly at the tip along the axis of the cone. The front flat surface can be clearly seen in the above picture and below, far right.

Elliptical Contour 1
Elliptical Contour 2
Four views of the same elliptical stylus (Ortofon FF10XE): x80
In the row of illustrations above, all shot at the same magnification, the difference in stylus profile from the side and from the front can be clearly seen. The stylus is broader across the width of the groove than along its length. This observation reliably identifies an elliptical stylus. However, even when the stylus has had sufficient wear to affect its tracking in the loudest passages of the record, the change in stylus profile is almost impossible to see, even at much higher magnification. Indeed, the exact extent of stylus wear can be a difficult thing to determine regardless of the optical devices at the investigator's disposal. The challenge is to position and illuminate the stylus so as to highlight the worn areas on the sides of the stylus profile.
 Patterns of Stylus Wear
In the pictures below, the stylus is seen from directly above with the cartridge flipped over onto its back. The first picture is lit from top and bottom, with the lights arranged to reflect in the polished surfaces formed on the sides of the stylus profile which result from wear caused by the walls of the record groove.
Wear flats on stylus
Stylus wear pattern.
Top Image: Worn stylus showing wear surfaces from contact with groove walls.
Bottom Image: The same stylus under more general illumination. Both pics x200.
L: wear caused by contact with the left-hand wall of the groove.
R: wear caused by contact with the right-hand wall of the groove.
Relative motion of the record groove is from left to right in both pictures.
The second picture has been lit to give a general view of the stylus showing the front and rear flats which produce the elliptical shape as seen from above. The wear has occurred assymmetrically, with that part of the stylus which bears against the right-hand wall of the groove (as seen looking towards the cartridge,with the centre of the record to the left) showing more wear than the side bearing against the left-hand wall.

This is probably due to the fact that the stylus cantilever has undergone a rotation in relation to the cartridge body, so that the stylus does not track the groove in a dead vertical orientation (as seen from the front). This results in a larger contact area with the right-hand wall of the groove, as can be seen from the larger area of wear.
Having too high a setting of the bias (anti-skating) adjustment of the tone arm would also be consistent with this wear pattern.

Since the conventions of disc recording dictate that the right stereo channel is recorded in the wall of the groove closest to the edge of the record, and the left channel in the wall closest to the centre, it is clear from the micrographs that it is the right audio channel which is being subjected to excess force. Whether the differential wear pattern seen is due to stylus misalignment or to excess bias will determine which of the two channels will provide the first audible evidence of mistracking.

 Record Wear
Even though the tracking force of the stylus above is only 1.5 grams, this force is applied to such a small area that the pressure on the walls of the groove can be surprisingly high.
Measurement of the wear surfaces at higher power using an eyepiece micrometer gives a figure of 20 µm for the average width of the worn areas. Neglecting factors such as the elastic deformation of vinyl, the distribution of forces in a V-shaped groove and the accelerations at the stylus tip during tracking, simple calculation based on these figures gives a stylus pressure of 240 grams per square mm, or 340 pounds per square inch. The transient pressures exerted by a stylus tracing a heavily modulated groove during playback will of course be much greater, but beyond my ability to calculate.

The pressure exerted by a new (spherical or standard elliptical) stylus is even greater than the figure calculated above, as the area of contact of the new stylus tip with the walls of the groove will be less.
As areas of wear develop with use, the pressure (and therefore the damage to the walls of the groove) decreases, rapidly at first, then more slowly as the surfaces increase in area. This would suggest that really precious records should only be played with a new stylus after it has been used for a few hours to play less valuable vinyl.
The need to polish a stylus in this way is much less with the special profile elliptical stylus types (Shibata, fine-line, microline, etc.) as these have already been shaped to achieve optimum contact with the groove wall.

Eventually a point is reached where the worn surfaces are so broad that the stylus can no longer accurately trace the higher frequencies or more extreme modulations of the recorded groove, especially those towards the centre of the disc. As this condition is approached, mistracking becomes audible, and the stylus must be replaced.

As a footnote to all these observations on record wear, I have to say that of the many thousands of records which I have examined, purchased and played over the years, only a very few were unlistenable on account of record wear, and these were from the earliest days of vinyl when the manufacturers advised collectors to play them with a pickup "of not more than 8 grams". All other rejected discs were unplayable due to accumulated crud in the grooves and physical abuse to the record surface. I have many records which are the best part of fifty years old, and as smooth and quiet as the day they were pressed.

I can only hope that my CDs last as well.

©www.micrographia.com

About the Author
Micrographia is for those who use microscopes in their investigations of the world around them. It is for students and teachers of (especially) fresh water biology in their search for creature identification and illustrative material, for both amateur and professional light microscopists seeking to extend the performance of their instruments and to record the images they produce ..... and for anyone at all who feels like a browse through a minutely detailed world of small animals, small plants, and small things.
 


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