Magnetophon’s Public Demonstration: A Recorder Working with Coated Tape

Magnetophon’s appearance in 1935 combined two industrial technologies. AEG in Berlin provided tape transport, magnetic heads, amplifiers and other hardware. IG Farben’s former BASF works in Ludwigshafen developed the tape base and magnetic coating, with Friedrich Matthias involved. Magnetic powder on paper tape had supplied an earlier approach but broke readily. A dependable tool required consistent backing, binding and coating.

Early tape used cellulose acetate film coated with carbonyl iron powder fixed by a binder. Unlike a steel-tape recorder, it separated the flexible backing that carried tension from the particles that stored magnetization. Later iron-oxide formulations differed from the material used in 1935.

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In spring 1935, AEG adopted a three-motor transport. One maintained steady tape speed at the working position, while two managed the supply and take-up reels. Excessive tension could tear the film; insufficient tension produced loops. Starting, stopping and rewinding required coordinated braking. Mechanical stability contributed to recording quality alongside the amplifier.

Both separately cased equipment and cabinet versions existed that year under the Magnetophon name. Familiar identifiers such as K1 were applied retrospectively. The cased version comprised separate transport, amplifier and loudspeaker units. Tape traveled at approximately one meter per second. Long reels permitted sustained recording while size, heat and operational demands remained substantial.

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A microphone and amplifier supplied a signal varying with sound. The recording head left corresponding magnetic states in the moving coating. During playback, changes in the moving tape’s magnetic field generated a signal in the playback head, amplified into audible sound. Reuse required erasing the previous recording. Storage depended on magnetization rather than grooves carrying a visible sound pattern.

Eduard Schüller’s ring head provided a smooth contact surface better suited to thin, vulnerable tape. Erasing, recording and playback already had separate heads in the 1935 machine, although their arrangement did not constitute the mature immediate off-tape monitoring system of later machines. Coating consistency, contact with the head and stable transport all affected the signal.

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Visitors at the Berlin radio exhibition in August 1935 could hear newly recorded sounds. Matthias’s report to the factory on 4 September records commercial interest in bulk orders, telephone and radio connections, news gathering, dictation and prerecorded music. These were observations and proposals following the exhibition, rather than evidence of widespread adoption of every use.

A fire during the exhibition destroyed the displayed equipment. AEG rapidly made replacement machines and continued demonstrations. The public appearance showed an operating system while raising further manufacturing, reliability and user requirements.

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Broadcasters valued reusable tape, editing and long recording time, but background noise and distortion from early direct-current bias limited demanding music recording. A 1936 recording of Thomas Beecham and the London Philharmonic in Ludwigshafen explored practical use without establishing that early tape sound had comprehensively surpassed discs.

Around 1940, Reichs-Rundfunk-Gesellschaft engineer Walter Weber effectively applied high-frequency alternating-current bias in a laboratory environment led by Hans Joachim von Braunmühl. The high-frequency current acted together with the audio signal at the head, markedly improving noise and distortion. There had been earlier precedents in magnetic recording; Weber’s contribution made it a usable broadcast process. That mature performance belonged to later development, beyond the 1935 demonstration machine.

References: [1] [4]