The pickup coil in a hearing aid is named Telecoil because its early form was to pick up a magnetic field from coils within a telephone.
The pickup coil remains a single winding over the toroid (Fig. 8).
To do a complete job would of course require two rings and three pickup coils.
These are to facilitate the winding of the pickup coils.
The signals generated in the pickup coils are not neat rectangular pulses although their amplitudes very with the external field.
The finished transducer includes a second pickup coil at right angles to the first.
By example: a full pickup coil may be 10,000 turns of wire and the "Tap" may be at 8000 turns.
The vibration of the strings produces a signal in the pickup coil.
This coil functions as the audio pickup coil.
The audio pickup coil is connected to a telephone receiver which converts the varying current to sound.
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