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von ROBERT WAGNER - Wagner Recorder Mfg. Co. - AUDIO ENGINEERING • MAY, 1947

This article describes a new type of home recorder with many extraordinary features.
(Anmerkung : Genauer gesagt es geht um das Einpressen der Rille anstelle des Schneidens der Rille.)

FOR ALMOST TWENTY YEARS the Search has continued for some means of recording which would be readily and successfully usable by the novice, but which would be free from the limitations generally inherent in non-professional equipment.

These limitations involve the following: cost - both initial and operating - which must be kept to a minimum for such a device to have a wide popular appeal; the quality of reproduction, which should be at least reasonably comparable to commercial records; the playing time, which should be upward of five minutes per disc, with a desired maximum of fifteen minutes; and the ease of operation, to ensure that satisfactory results can be obtained by the non-professional user.

In addition to serving its principal function as a home recorder, there is an enormous field for an extremely portable instrument for the "borderline" uses, where the degree of perfection required in professional equipment is not an absolute necessity. The most important of these uses is on-the-spot recording for delayed broadcasting, and very compact equipment is of considerable advantage, provided the quality can be acceptable.
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The Wagner-Nichols Recorder is the result of these years of development, with the actual recording unit shown in Fig. 1. This unit comprises the heart of the equipment, with only a driving motor, amplifier, microphone and speaker being necessary to provide a complete system. The recording unit is 7 inches long and 5 1/2 inches high, with an overall depth of 2 1/2 inches, exclusive of the motor.

Recordings produced on this machine were considered extraordinary by those who heard the demonstrations at the recent IRE Convention in New York; a vinylite disc 3 3/4 inches in diameter and .01-inch thick records for 15 minutes with fidelity comparable to that of commercial equipment.

The principal objectives of the recorder-compactness, fidelity, simplicity, and low cost-dictate the trend which the design must follow. Cutting acetate discs requires the use of accurately ground styli, which have a comparatively short life. Constant replacement or resharpening is expensive, besides being a bother to the home recording fan, and after the novelty wears off, he is likely to consider it too much trouble to keep on using the device.

On the other hand, embossing does not wear (abnutzen) the recording stylus appreciably (nennenswert), so with a suitable record base, the life of the stylus may be considered indefinite (unendlich?).

The main disadvantage of previous embossing processes was the necessity for providing a sound groove of sufficient depth to permit adequate stylus tracking for playback. The depth required precluded the possibility of obtaining high fidelity, and limited the number of lines per inch to a maximum of about 200 per inch.

To record a full fifteen-minute program on a disc of small diameter requires a very large number of lines per
inch. On a 3 1/4" disc, the maximum usable diameter is about 3 5/8"; recording to a minimum diameter of 1 1/2" leaves a recording area only 1-1/16" wide. At a recording speed of 33-1/3 rpm, this requires that the grooves be spaced to a minimum of 470 lines per inch.

To allow a little leeway (Spielraum)over the fifteen minutes for starting and finishing off, the recording is actually done at 515 lines per inch. This figure may sound fantastic, especially so when it is remembered that this is a lateral cut, but a brief consideration of the relative dimensions may clear up an apparent discrepancy.

To begin with, 515 lines per inch means that the line spacing is just under 2 mils, and if a normal groove-land ratio of 60-40 is maintained, the groove itself is just under 1.2 mils.

This small dimension necessitates the use of a much sharper stylus point than is used tor acetate recording. A conical sapphire having a tip radius of 0.5 mil is used, with an inclined angle of 70 deg., resulting in a groove depth of 0.82 mils.

The relative dimensions are shown in Fig. 2, where {A) represents the stylus of this recorder and the resulting groove, and (B) represents the conventional stylus used for acetate recording. Since no material is removed, the embossing process deforms the surface of the disc to some extent, as indicated in (A).

This has the advantage of aiding in the tracking, since the stylus has no inclination to climb up over the banks of the adjacent groove as the disc rotates. Also, since no material is removed, the original surface of the disc is not disturbed appreciably - that is, the bottom of the groove retains the high polish which is inherent to the normal surface of the disc before recording.

When one considers that standard recording is feasible at 160 lines per inch using a stylus with a 2.0-mil radius, a reduction in radius to one-fourth of this value should permit the embossing (einprägen) of a groove having equivalent dimensions at four times 160, or 640 lines per inch. Add to this advantage the fact that the same stylus is used for recording and reproduction, so that the playback stylus follows the groove much more closely than a conventional reproducing stylus follows a cut groove.

Therefore, in spite of the seeming impossibility of such close spacing, satisfactory results are obtained at 515 lines per inch.

The embossing process has one other advantage over the cutting process in that it produces no shavings which must be removed. This eliminates the need for brushing up the shavings (gemeint ist der geschnittene Span) as they are made, or for the more elaborate vacuum system which would be prohibitive for home use. The remaining problem is that of eliminating the expense and precision required for the conventional lead screw for moving the carriage across the disc as recording progresses.

This has been solved by pre-grooving the opposite side of the disc; thus the disc itself becomes its own lead screw. A small, chisel-shaped, carbide point engages the pre-grooved bottom of the disc at a point opposite the recording stylus. A small spring, mounted on an arm which is an integral part of the carriage, presses down on top of the disc and ensures sufficient pressure for good tracking. Thus, each record is equipped with its own feed screw, and any groove spacing can be accommodated.
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 Ende seite 25 - Seite 26/27 fehlen in dem PDF von 1947
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• Anmerkung : Mit der unaufhaltsamen Einführung des Magnetophons war dieses Konzept schlagartig obsolet.

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hier die Bilder des "Press"-Recorders

Fig. 1. The complete recorder unit is shown at the right. A 15 minute recording can be made on the small plastic discs shown. The arm and spring pressing on disc assure good contact between disc and tracking point following groove cut on back of blank.

Fig. 2. Relative dimensions oi embossed groove (A) and conventional acetate groove
(6). together with recording styli used for both types.

Fig. 3. Top view and (right) underside of recorder unit shown in Fig. 1. Carriage rides on rollers and mounts tracking point, combination recording and playback head, tracking pressure spring, and Indicator.