Where is it written that a pick-up cartridge has to utilise coils and magnets to convert the undulations of a pivoted stylus into an electrical output? Nowhere. Whether magnets are moved within a brace of coils or coils within the field of a magnet, this has simply been the most expedient technique from time immemorial. Until now... Ok, not quite until now, because the basic idea of using a vibrating stylus to modulate a beam of light falling onto a photocell can be traced back to the Philco 'Beam of Light' pick-up system from the early 1940s. More modern versions suffered from heat build-up thanks to the enclosed light source, so the performance of the photocell typically changed in the time it took to play one side of an LP.
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