A newly constructed cylinder playback mechanism for all formats

by Franz Lechleitner, 1986

Österreichische Akademie der Wissenschaften, Phonogramarchiv, Wien

Since Thomas Alva Edison succeeded in preserving the human voice on a vertically cut cylinder tin foil for the first time in 1877, this recording technique has undergone rapid technical and economic development. Wax- and celluloid cylinders of different sizes flooded the market at the beginning of this century and disappeared only when the gramophone record began its triumphant progress.

The gramophone record was far more practical in many ways. It was easy and cheap to produce, had a longer playing time, and the storage space required was much smaller. With the exception of a few commercial companies, the phonograph-cylinder was used only for scientific field recording for a longer period of time.

Modern society is becoming increasingly aware of the cultural significance of historical sound documents hidden away in public and private collections. Thanks to concerted efforts previous cultural assets can be saved an preserved for future generations. This applies especially to the wax cylinder which, because of its chemical composition, is subject to an almost self-destructive aging process. This process can also be accelerated by improper storage. The playback of historical cylinder material, however, is often very difficult because of the different formats. In very few cases a sound archive is equipped with a modern playback unit, which allows to play back nor only the more common two-minute and four-minute standard cylinders with 2in diameter but also the 5in diameter concert cylinders, Pathé Saloon cylinders or Dictaphone and Columbia cylinders of 6in length. The problems actually already start with the playback of the standard cylinders with 2in diameter.

Cylinders with an inner diameter of less than 1.7in do not fit in with the Edison standard mandrel. A perfect reproduction of such cylinders requires modifications to the mandrel or to the cylinder by carefully reaming. The latter, however, implies a certain amount of risk. The sometimes not quite concentric shape of some - mainly private - cylinders due to inaccurate workmanship or improper storage is another important aspect which should not be underestimated. Historical phonographs later equipped woth a modern pickup system in most cases deliver signals which are strongly influenced by the concentricity of the cylinder itself or are not capable of tracking it at all.

The greatest difficulties are liable to occur when pushing the cylinder onto the mandrel. The cylinder may become loose and unstable during the reproduction if applied with too little pressure. This causes tracking problems and playback distorsion. On the other hand the cylinder will crack if applied with too much pressure. For the reasons mentioned before, it neither seems to be useful to modify a historical phonograph for archival transcriptions - in spite of several advantages - nor to equip a modern playback machine with a mandrel according to the historical model as the problems cannot be solved satisfactorily. For this reason we have been looking out for new solutions.

The new cylinder playback unit to be developed suitable for all common formats has to be equipped with two main features:

1. The inner pressure caused by forcing the cylinder on a mandrel had to be kept at a minimum,
2. the cylinder had to be fixed as concentric (perfectly round) as possible.

If we assume that only the playback surface of the wax cylinder had been manufactured accurately, then the cylinder had to be held in a playback position on this surface. Thus inside pressure on the cylinder was simultaneously avoided. For the prototype this was achieved by means of a concentric three-jaws-system at the starting position and of fitting rings at the end of the cylinder respectively. The fitting rings have a suitable profile and can be locked onto the driving shaft.

The three-jaws-system has an error of less than 0.1 mm (0.004in) over the whole radial range, therefore any disturbing eccentricity determined by the design will be kept within negligible limits. The driving shaft is equipped with double sliding bearings with bronze bushings on the driving side. The open end is supported by means of a tailstock with ball bearings which can be turned down.

Both the cylinder and the tone arm are DC-powered and belt-driven by means of two electrically coupled DC motors. The motor driving the tone-arm is combined with a planetary gearing system having a ratio of 165:1 which can be switched to half speed for 4 minute cylinders. Speed control takes place on the driving shaft and is equipped with a digital readout.

The tangential tone-arm works on the well-known Rabco principle; the main item consists of a Rabco ST7 carriage. For reproduction an AKG P10 pickup system is used which is selected with respect to channel symmetry and low compliance. The low compliance together with a short tone-arm increase the pick-up resonance frequency to such a degree that cylinders running off center strongly can be tracked, too. It also guarantees exact groove contact with big styli. The vertical adjustment of the tone-arm to track the different cylinder sizes is achieved ny means of putting spacing blocks under the tone-arm drive. Practical experiance has confirmed the theory that the cylinder had to be suspended at both ends. Conceiving non-concentric cylinders the sound quality is much better in comparison to the traditional suspension employing the Edison standard mandrel.

This article was originally published in:
IASA Phonographic Bulletin 45, june 1986, pp. 44-47.