I was wondering where the cassette tape adaptors get their energy, looking at this image
there is clearly some electronics. I can't see any dynamo however. Is the energy harvested from the audio signal?
As it seems I was too fast in searching for an image. Here is an other one taken from : http://i23.photobucket.com/albums/b371/2wildthing/CassetteAdaptorInside2.jpg which shows less of electronics. Maybe the system is all passive. I was somehow assuming that still some kind of conversion had to take place, even though the audio signal and the storage on the magnetic tape is analogue.
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