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..... ein Blick in die RCA Artikel aus 1961 hier in den RCA News:
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1. HOW THE APPROVED FM STEREO SYSTEM WORKS
   
   
2. FCC Ruling on FM Stereo Broadcasting - April 1961

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Features Replaceable Stylus For Both Stereo and Monaural Operation by J. R. SANK - Broadcast and Television Engineering

The new Universal Pickup Cartridge has been designed especially for broadcast applications. Prompted by the need for excellent quality broadcast reproduction of stereo recordings, the new cartridge is unique in that it performs in both stereophonic and monophonic applications.

The mode of operation is determined by external electrical connections to the cartridge. A replaceable stylus is a feature of the cartridge design.

The stylus plugs directly into the cartridge and is easily replaced without the need for costly and time consuming factory repairs. This plug-in feature also allows a user to buy only one type of cartridge and several sizes of economical stylus in order to take care of all record playing requirements.

Utilizing the moving-magnet principle, *1) the new universal cartridge is molded in a black plastic case with three terminal pins. The center pin is common and the outside pins are the left and right stereo outputs.

*1) Horowitz, H. "Moving Magnet Stereo" Audio May, 1959, P. 19.

In stereo use the head is connected in the usual manner with the left output going to the left equalizer and the right output, to the right equalizer. In monophonic use, the left and right outputs are paralleled.

• Anmerkung : Und das ist schon der erste Fehler in der Beschreibung. Das funktioniert so nicht wegen der Auslöschungen ganzer Frequenzbereiche.

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The cartridge plugs into the standard RCA 12-inch and 16-inch tone arms, or may be mounted on arms with standard 1/4-inch mounting centers. It features low distortion, excellent frequency response and very good channel separation.

The diamond stylus and low tracking force insure long life for both the stylus and recordings.
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The stylus assembly is mounted in a brass holder which is fastened to a convenient plastic guard, making replacement exceptionally easy. To protect against damage should the pickup be dropped accidentally, the tubular stylus arm retracts into the guard.

The inner end of the stylus arm contains a bar magnet which rotates in an elastomer pivot bearing. A wire spring, extending from the magnet, is soldered to the end of the brass stylus assembly holder.

The cartridge body contains the coils, shield, and magnetic circuit. Plug-in stylus assemblies, readily identified by color are available in three types as shown in the accompanying table.
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The 0.7 mil stylus, MI 1866-7, is for stereo applications - it must be used to play stereo recordings, but may also be used to play 1 mil standard records without appreciable change in performance.

With this stylus, stereo recordings can be reproduced for monophonic broadcasting by paralleling the left and right outputs of the pickup head. (und das ist ganz großer Mist)

The 1.0 mil stylus, MI-11866-10, is used for reproduction of standard recordings.

The 2.5 mil stylus, MI-11866-25, is used to reproduce 78 rpm records and certain old-type transcriptions cut with a 2.5 mil groove.

The 0.7 mil stylus force is 4 grams. This provides record life equivalent to that obtained with the 1.0 mil MI-11874 pickup operating at 8 grams. (Stress on the groove is inversely proportional to the square of the stylus radius.) The 1.0 and 2.5 mil stylus assemblies operate at 4 and 8 grams respectively.
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The impedance of each channel in the cartridge is essentially a 4 mh inductance. Recommended load impedance is 47 K Ohm, shunted by no more than 400 pf. A pair of BA-26A equalized preamplifiers will properly load the cartridge for stereo. A single BA-26A is used in monophonic reproduction.

The new stereo pickup has a very significant characteristic which makes it particularly suitable for broadcast use. i.e., low distortion. This may seem to be an obvious and essential requirement for any pickup. However, the methods of measurement and criteria for evaluating distortion have not been universally agreed upon. Thus, it is very difficult to find distortion data published on commercial pickups. Data contained in this article was obtained by the two-frequency method. *2) und *3)

*2) Roys, H. E. "Analysis by the Two Frequency Intel-modulation Method of Tracing Distortion Encountered in Phonograph Reproduction." RCA Review, June, 1949 - P. 254.

*3) Roys, H. E. "Distortion in Phonograph Reproduction" Journal of the Audio Engineering Society, January, 1953.

The popular concept of modern high fidelity reproduction has caused considerable emphasis to be placed on extremely smooth high frequency response in the pickup. This frequently is obtained by sacrificing (verheimlichen) low distortion performance so essential to the broadcaster.

Although moving system mass referred to the stylus tip is greatly reduced, a high frequency resonance with the vinylite record will still occur within the audible range. The smaller stylus radius (0.7 mil) required for stereophonic records has reduced the reflected stiffness of the record, resulting in a lower resonant frequency. Therefore, the highest resonance obtained in practical designs is the 15,000 cycle region.
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Many pickup designers have sought to dampen this peak by the use of mechanical resistance materials. Unfortunately, virtually all such materials do not supply true viscous damping.

They are amplitude sensitive, and contribute significant amounts of non-linear distortion, *4) depending on how much damping is required.

*4) Horowitz. H. "Moving Magnet Stereo" Audio Mav, 1959, P. 21.

The new RCA pickup employs very little damping. The elastomer part acts primarily as a bearing (ein Lager), with the wire spring supplying most of the moving system stiffness.

Lateral distortion is shown in Fig. 2. The curve shows inter-modulation distortion, which is a measure of the non-linear distortion occurring at the lower test frequency.

The RCA 12-5-39 test-record contains 400 and 4000 cps mixed 4 to 1. Harmonic distortion methods at 400 cps could alternately have been applied, but have been found to be much less practical than the intermodulation method. *3)

10% intermodulation distortion is not noticeable without a chance for direct comparison, analogous to a figure of 2 or 3% harmonic distortion.

The maximum peak level at 1000 cps on an NAB lateral disc is 21 cm/sec. Referred to 400 cps on the NAB recording characteristic, this becomes 13.5 cm/sec.

Therefore, RCA pickups have approximately a 6 db margin of safety, which allows for the frequently encountered "over-recorded" disc.

Vertical distortion of the new pickup has not been measured, as there is no standard test record. A standard vertical tracking angle has not yet been adopted by RIAA or NAB.

The angles of commercial cutting heads vary from about 19 to 30 degrees, so a compromise angle of 26 degrees was chosen for this pickup.

Frequency response and channel separation are shown in Fig. 3. These have been measured with a Westrex 1-A Stereo Test Record, with a load of 47 K plus 350 pf per channel. With the high frequency peak evident, response is maintained within ±3 db 30 to 15,000 cps due to the small moving mass.

Greatly reduced distortion has been achieved with only a small departure from flat response. Hence, superior playback quality is obtained for both stereophonic and monophonic recordings.
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Use of the new Universal Cartridge complements a complete RCA package designed to give finest sound from recordings and transcriptions. The package includes the cartridge, a selection of replaceable stylii, 12 or 16-inch tone arms, and BA-26A transistor preamplifier equalizer (das ist der Magnetsystem-Vorverstärker).

Each of these equipments are matched - both electrically and mechanically - for finest performance in both stereophonic and monophonic use.

FIG. 1. Replaceable stylus construction eliminates the need for costly repairs in this new Universal Pickup Cartridge.

FIG. 2. Lateral intermodulation distortion vs recorded level. RCA 12-5-39 Record.

FIG. 3. Frequency response and channel separation, Westrex 1-A Record.
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