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I was wondering where the cassette tape adaptors get their energy, looking at this image

enter image description here http://car-mods.wonderhowto.com/how-to/hack-your-cars-cassette-deck-into-wireless-bluetooth-music-player-0139843/

there is clearly some electronics. I can't see any dynamo however. Is the energy harvested from the audio signal?

Edit:

As it seems I was too fast in searching for an image. Here is an other one taken from <code>http://i23.photobucket.com/albums/b371/2wildthing/CassetteAdaptorInside2.jpg</code> 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.

If you find better tags, feel free to add them.

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    \$\begingroup\$ -1 for not telling us where you got that picture, and for not reading the information on the site it came from. \$\endgroup\$ – Dave Tweed Nov 21 '14 at 12:31
  • \$\begingroup\$ Usually taking power from the audio minijack, or the usb connector \$\endgroup\$ – GR Tech Nov 21 '14 at 12:45
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Standard cassette tape adapters have no active circuitry. The audio signal is simply wired directly to the tape head, like this...

enter image description here

Your image shows an adapter which has been hacked to include the circuit from a Bluetooth stereo headset. It is described here...

How to Hack Your Car's Cassette Deck into a Wireless Bluetooth Music Player

There is no harvesting involved. A small Lipo battery is probably hiding under the pcb, similar to this...

enter image description here

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  • \$\begingroup\$ Notice: There are two SMD resistors (1K each) and two SMD capacitors on the head it's PCB. \$\endgroup\$ – Codebeat Aug 13 '19 at 18:32
  • \$\begingroup\$ Yes, they compensate for the frequency response of the tape head. \$\endgroup\$ – Bruce Abbott Aug 13 '19 at 22:27
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Consider that a real audio-cassette is "nearly" passive; the motion of the magnetic field on the tape past the coils in the read head produces a tiny, tiny signal which is amplified by the circuitry in the player.

For the common audio-cassette adapter that plugs into an MP3 player or other source, the headphone-level signal is more than strong enough to produce a signal at a similar level. Most inexpensive headphones are entirely passive, after all.

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A microphone input provides a little power because it must be compatible with an electret microphone with a built-in one-FET amplifier. I guess thus little power will be enough for the tapehead-to-microphone amplifier you show.

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  • \$\begingroup\$ This is irrelevant to the question asked, as there is no microphone input or microphone amplifier involved here. This is strictly an output device. \$\endgroup\$ – Chris Stratton Jan 20 '18 at 17:34
  • \$\begingroup\$ It connects to a mic input. \$\endgroup\$ – Wouter van Ooijen Jan 20 '18 at 22:49
  • \$\begingroup\$ No, it doesn't. It connects to a speaker/headphone output and inserts into a tape deck which it stimulates with the magnetic head in the stock model, or a power source and receives bluetooth data in the hacked one. To connect to a mic input it would need to be tape deck, not a fake tape. The only mention of microphones anywhere on this page is in your posting. \$\endgroup\$ – Chris Stratton Jan 20 '18 at 22:56

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