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Bias Oscillator Circuit


In this instructables I am going to make an electronic circuit to erase (demagnetize) a recorded

compact cassette. This circuit is also known as ‘Bias Oscillator’. This circuit is very easy to build and you can demagnetize all the compact cassettes that you have. Let’s get started!


To demagnetize a magnetized substance it is placed inside a solenoid and and a high frequency and high voltage is applied across this solenoid and and solenoid create a high frequency alternative magnetic field on its Centre. Magnetized material is placed on the Centre of this solenoid and after sometime we decreases the voltage across the coil slightly and we make this voltage 0V in the end and magnetic flux density inside the magnetized material becomes zero. In this way we can demagnetize a magnetized material.


Demagnetization of recorded compact cassettes is similar to the demagnetization of magnetized substances but here we use a magnetic head instead of a solenoid. This magnetic head is used to demagnetized (Erase) a recorded compact cassette so this magnetic head is also known as ‘Erase Head’. Picture of erase head and its electronic symbol has included in this instructables.”

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