Friedrich Engel
Iron oxide γ-Fe2O3

Hardly any successful applications having been found for magnetic sound recordings by the mid-1920s, it needed an innovation by the remarkably versatile Salzburg inventor Fritz Pfleumer (1881–1945) to bring a fresh breeze into the stagnating development.1 Instead of using steel wires and tapes (heavy, expensive and difficult to repair), he suggested using a special paper coated with a fine distribution of iron powder.2 This magnetic tape was lightweight, cheap to make and, if it broke, could be repaired using a little adhesive. Pfleumer built a first “tape recorder” with which he hoped to convince the press and industry of his method. After a few unsuccessful attempts, Pfleumer found a powerful supporter in the person of Geheimrat Hermann Bücher, the then head of AEG. A contract was concluded in November 1932 by which AEG developed the mechanical part of what was soon to be known as the magnetophon, while the powerful I. G. Farbenindustrie Aktiengesellschaft’s Ludwigshafen works agreed to work on the magnetic tape. It was here that, between 1932 and 1935, the first magnetophon tape was made, using cellulose acetate as base tape with a coating of carbonyl iron powder as recording material.

AEG magnetophon K4: magnetic heads. 1938The machine and the tape were presented to the public in 1935, and were a huge success. However, its technical complexity led to it being marketed not, as initially intended, as a machine for the people but instead as a high-quality dictation machine for industry and the public administration. And since the quality of the system was insufficient for music recordings, success was relatively modest, nor did it improve with the next generation of machines. However, the one institution that did recognize the advantages of the magnetophon despite its faults was the German radio service, the Reichs-Rundfunk-Gesellschaft (RRG), in Berlin. Having persuaded the developers to make certain improvements, it ordered 20 magnetophons for stationary use (mains powered) and 20 mobile machines (battery powered). A mains-powered version, the K4, was announced by AEG in 1928 and supplied from spring 1939. Despite the high price (deck RM 2930, extra amplifier RM 550, loudspeaker RM 80 and dynamic microphone RM 150), the company immediately had difficulty meeting demand, mainly a result of the many priority orders by the German military.

The K4’s music reproduction quality was roughly on a par with that of industrial records, a consequence in particular of the third magnetic tape recipe developed by I. G. Farben, which also went into production in 1938. It was only in 1970 that a rival (chromium dioxide, CrO2) was developed that could challenge the iron oxide γ-Fe2O3 “magnetophon tape Type C.”

Magnetophon AEG K4: magnetic tapeThe magnetophon’s advantages were obvious. Playing time was far longer than that of the record, the tape could be cut and edited, it was cheap, could be erased and re-recorded, it was less susceptible to breakage and lighter than a stack of records that would play for the same length of time. In addition, the K4 was the first to allow the user to hear the recorded tape almost simultaneously. Like its predecessors, it was fitted with three magnetic heads, one to record the signals, one to play them back and one to erase the tape. The magnetophon designer Eduard Schüller found a way to use the playback head to hear what had just been recorded by the recording head. This check meant that it was possible to assess the quality of the recording without delay, an inestimable advantage for all kinds of uses. This made the K4 the first full tape recorder. The qualitative development that was to ensure that the magnetophon would be the preferred recording method for almost every situation was made in 1940 at the RRG by Walter Weber, who (re)discovered the idea of “high-frequency pre-magnetization,” which at a stroke ensured that the magnetophon achieved the hitherto best recording quality.


1 Cf. Friedrich Engel, Gerhard Kuper, Frank Bell, Zeitschichten – Magnetbandtechnik als Kulturträger, Potsdam 2008.

2As magnetically active “sound record carrier,” to quote his patents DE 500 900, FR 669.443, GB 333,154, NL 42 477 and CA 306,485.