To every person who has read the "Technical Information" box on the jacket liner notes of an LP record, the names Scully, Presto, Neumann, Westrex, Grampian, HAECO, Pultec, Langevin, Fairchild, Altec, Capps, Transco, Audio-Devices, Soundcraft and others may be familiar, almost household names.

These were all manufacturers of equipment and supplies that touched the process of making phonograph records, from the stage of being converted from a "master" to a release pressing intended for home playback.

THE LACQUER CHANNEL

It all starts with the disc recorder or "lathe" as it is often referred to... a precision piece of equipment designed with a slowly rotating feed screw mechanism and carriage to uniformly move a cutting head across the radius of the disc. The accurately shaped cutting stylus, mounted in the head, cuts a VERY precise spiral groove across a flat lacquer coated aluminum disc spinning at an exact speed of 33-1/3, 45, or 78.26 revolutions per minute, the standard phonograph operating speeds. Scully, Presto and Neumann are probably the best known manufacturers of disc recording lathes.

There were instances of early recordings (mostly acoustical) that played at speeds as low as 60 rpm, and as high as 90 rpm, but by the time electrical recording replaced acoustical, standard speeds were adopted.

THE CUTTING HEAD

Installed on the lathe, the cutting head is simply a phonograph pickup in reverse, that is, feed audio in and get mechanical motion out. Other than its greater size, the specially shaped cutting stylus, and the feed screw mechanism which moves the head across the record to make the spiral groove, the internal workings are very similar. A great deal of literature has been written about the cutting stylus, its shape and the resulting groove cut by it, many written by engineers Frank and Isabel Capps, whose company produced many of the innovations in disc recording styli over the years, not the least of which was the Capps (ANM) Antinoise Modulation Stylus and the Cappscoop stylus which provided a further 3 dB reduction in noise for stereophonic records.

THE RECORDING STYLUS

Contrary to what you might think, diamond IS NOT a good material for a cutting stylus, but IS excellent as a reproducing stylus. The recording stylus is one of, if not THE most important component of the recording process, and was probably first used by Edison in 1877.

Home cutting styli were often made of a steel alloy called Stellite because it was inexpensive to manufacture, and although cutting styli have been made of other materials, most cutting styli for professional use are made of corundum, commonly known as sapphire.

Because of its lack of grain, crystalline structure and cleavage, sapphire may be ground to very accurate dimensions and angles, while retaining a very fine cutting edge. These properties are of prime importance in manufacturing a recording stylus. Believe it or not, a sapphire recording stylus will outlast a diamond and produce superior recordings.

A small sapphire rod is ground with a flat face and mounted in an aluminum shank to make it easier to install and remove the stylus from the cutting head as the need arises. The end of the sapphire rod is ground to a point with a rounded tip, and extending upwards from the tip, along the flat edge, are tiny burnishing facets that polish the groove as it is cut, producing a quieter groove. These facets are critical since, if ground incorrectly, they will affect not only the signal to noise ratio but also the high frequency response of the recording. High quality recording demands that the stylus noise be typically in the range of 57 to 60 dB below a recorded 1kHz reference level of 7 centimeters.

For microgroove recordings (16-2/3, 33-1/3 and 45 rpm), the recommended cutting stylus tip radius is .00025 inch or less, and for coarse groove recordings (33-1/3 rpm transcriptions and 78 rpm) the recommended radius is .0015 inch. You can see why a 78 played with an LP stylus sounds so bad! For coarse groove recording, the stylus was often mounted with a slight mechanical bias toward the center of the record. This ensured the thread of cut lacquer material or "chip" would be thrown toward the center of the disc thus avoiding fouling the stylus tip.

In both LP and coarse groove recordings, the included angle (that's the angle formed by the groove walls) is 88 degrees plus or minus 5 degrees. The top of the groove is supposed to measure not less than 4 mils across, for a recording to be played with a 2.5 mil stylus, and in the case of LP's played with a 1 mil stylus, no less than 2 mils across at the top.

A tremendous improvement in cutting "fine groove" records occurred with the introduction of the hot stylus. This is no more than a winding of 6 or 7 turns of "Nichrome" resistance wire around the shank of the stylus, near the tip. Connected to a power supply with adjustable current and metering, is used to bring the cutting stylus to a carefully controlled even temperature. The hot stylus momentarily softens the lacquer surface of the recording disc while the groove is being cut. The lacquer thus offers less resistance to the cutting process, the cut is smoother with less distortion, and the necessity for diameter equalization is virtually eliminated, being reduced to about a 2dB difference between the outside to inside of a disc.

THE LACQUER DISC

Over the years, since the days of wax, recording blanks have been called by various names including "instantaneous discs", lacquers", "acetates", "soft-cuts" and others. If there is a "proper" name, it is probably "lacquer" because of the fact that they are lacquer coated with a compound of cellulose nitrate, and acetate had little to do with it, although it has become a common name for a lacquer coated disc, and many professionals still use the term "acetate". Habits are hard to break.

The term "waxing," still persists to this day, even though actual wax is as out of date in disc cutting as the horse and buggy is to the automobile. In the "bad old days" of recording, there was no magnetic tape and the recordings had to be cut originally on huge thick blocks of warmed, essentially beeswax. Modified versions of the old solid block of wax were in use until not long before World War II.

With the acceptance, in the early to mid thirties, of the much more satisfactory lacquer-cutting process, wax went the way of the Dodo bird. Thus, the final product before "processing" became a single lacquered disk onto which the actual recording grooves were cut.

If you are old enough to ever have made an instantaneous recording, those one-of-a-kind records that studios, department stores, vending machines and the like made for you on the spot, you have seen a lacquer disk. It is made of metal (although the very cheap ones had a paper base), usually aluminum, coated with a thin layer of black, smooth, shiny lacquer. For professional master work, the lacquer surface must be perfectly even... just like a black mirror, and as a matter of fact, you can actually see a good reflection of yourself in a lacquer!

Different grades of "blanks" were offered by the manufacturers, distinguished by the evenness of coating and thickness of the metal itself. Simply put, all the discs of a given grade started through the manufacturing process the same way, but subsequent inspection determined the quality level that the disk met before it was shipped out of the plant... a "double face master" being the highest level sold for the highest price. A disc with a blemish on one side, but otherwise master grade would be a "single face master" and sell for less. More blemishes and defects produced lower quality levels that sold for less and less down to the level of the home recording user. Needless to say, for the making of commercial pressed records or radio transcriptions there was only one standard - the best that can be had for the purpose.

THE DISK CUTTER

A high quality professional disc recording lathe system is very impressive, to say the least... accurately controlled to produce grooves that lie precisely even, next to each other, and such that the depth of the groove being cut will remain uniform and exactly as set, throughout the recording.

The mastering engineer controls all aspects of the overhead cutting mechanism, which extends from the outside edge, across the record, to the center pin, like a bridge over water, and from which the recording head with its stylus is lowered to the record surface. The spiraling grooves are cut by moving the head very slowly, across this bridge, usually by a type of screw feed. Think about a home phonograph playing a record, where the arm follows or "tracks" the pre-set grooves in the record. A disc recorder working upon a blank disk, has no such thing to guide it's motion, and so it must be mechanically moved by a special mechanism to cut spiral grooves. Provisions are made to allow speeding up the mechanism to make the faster spirals at the beginning and end of the record, as well as disengaging the feed-screw drive to permit making a "lock" groove at the end of the record. In earlier days, or with less automated professional equipment, the mastering engineer usually did this by turning a small hand operated crank to speed up the spiraling process.

The record grooves are very small, measuring on the order of 2 mils (thousandths of an inch) for microgroove and about 5 mils for coarse groove recordings (transcriptions and 78's). So that the mastering engineer can look at and measure this tiny area, professional disc recording systems come with attached calibrated microscopes, that can be swung over the groove while the record is being cut. Through the microscope a good mastering engineer can quickly determine if the cut is smooth and of the right depth with the grooves far enough apart so as not to interfere with each other. (Sometimes the pattern of one groove, cut too close, may distort the wall of an adjacent groove, giving a strange almost ghostly "echo" that can be heard just before the first sound or after the last sound on some records.)

THE CHIP

The continuous thread of cut material that the stylus throws off as the groove is made is called by a few names... chip, swarf, thread and probably a few others, although "chip" was probably the most common. Most home disc recording enthusiasts ran afoul of this exasperating byproduct. On occasion, it would throw itself nicely to one side and lie flat on the disk in neat rows out of harm's way, but far more often, if not attended to, it would entangle itself on each turn with the chip cut on earlier turns. Catching under the stylus, it quickly builds a rat's nest of tangled material which ruins the cut since, while recording, you cannot lift the stylus away from the record in order to clear it without interrupting the recorded sound and the groove itself. "Chip" accumulates static electricity as it is cut from the groove, and it sticks obstinately to anything and everything in sight, but mostly to the uncut lacquer surface that the cutting head is moving towards! A dry paint brush was usually used to push the chip well out of the way of the advancing cutter head.