Consumer Electronics

MAGNETIC PLAYBACK

All methods of recording and reproduction rely on a sequence of reversible processes with sound vibrations at one end of the sequence and a lasting change produced in some other property at the other end.

During playback the magnetised tape recording is moved at the same speed past the poles of the magnet and induces a field in the magnet. This, in turn, induces a current in the windings, which can be amplified to reproduce the original sounds, as shown in Fig. 10.2. In practice, all these changes are superimposed on a very high frequency current of about 80 kHz, which acts as a carrier wave for the low-frequency vibrations.

The amplitude of the voltage across the head coil depends on the rate of change of flux in the core assuming ...