Chapter 7

Moving-Magnet Disc Inputs

The Vinyl Medium

The vinyl disc as a medium for music delivery in its present form dates back to 1948, when Columbia introduced microgroove 33 rpm LP records. These were followed soon after by microgroove 45 rpm records from RCA Victor. Stereo vinyl did not appear until 1958. The introduction of Varigroove technology, which adjusts groove spacing to suit the amplitude of the groove vibrations, using an extra look-ahead tape head to see what the future holds, allowed increases in groove packing density. This density rarely exceeded 100 grooves per inch in the 78 rpm format, but with Varigroove 180–360 grooves/inch could be used at 33 rpm.

While microgroove technology was unquestionably a considerable improvement ...

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