The working principle of the tape recorder
The tape recorder is mainly composed of a microphone, a tape, a recording and reproducing head, an amplifier circuit, a speaker, and a transmission mechanism. Its working principle is as follows:
1. Recording principle
During recording, the sound causes the microphone to generate an induced current – audio current, which changes with the sound. After being amplified by the amplifying circuit, it enters the coil of the recording head. Since the audio current passes through the coil, a magnetic field that changes with the audio current is generated at the gap of the magnetic head. The tape moves close to the gap of the magnetic head, and the magnetic powder layer on the tape is magnetized. , so the magnetic signal of the sound is recorded on the tape.
2. Principle of sound playback
Sound playback is the reverse process of recording. During playback, the tape passes through the gap of the playback head, and the changing magnetic field on the tape causes an induced current to be generated in the head coil, and the change of the induced current is the same as the linear magnetic signal, that is, the audio current is generated in the coil, and this current is amplified. After that, it is sent to the speaker, and the speaker restores the audio current to sound. In the tape recorder, the two functions of recording and playback are completed by a single magnetic head. When recording, the magnetic head is connected with the microphone; when playing, the magnetic head is connected with the speaker.
3. Principle of erasing
Erasing, also known as degaussing, is to remove the AC residual magnetism recorded on the tape. There are two types of erasures: DC erasure and AC erasure.
DC erasing is to let a certain intensity of DC current pass through the erasing head to generate a one-way strong magnetic field. When the tape passes through the erasing head, the magnetic tape is magnetized to saturation, covering all the original information . Because the DC erasure will leave saturated remanence on the tape, which leads to the increase of DC noise during playback, so the AC erasure is widely used at present.
Communication erasure is also known as superaudio erasure. When erasing, the coil of the erasing head has a super-audio current of tens of KHz, and a magnetic field that changes with the super-audio current is generated at the gap of the head. This magnetic field is much stronger than the magnetic field of the audio signal on the tape. When the gap of the audio magnetic head is repeatedly magnetized by alternating magnetic field from weak to strong, the remanence gradually increases, and when it reaches the center of the gap, the remanence is the largest and reaches a saturation state, thus covering the original remanence on the tape. After passing the center line, the strength of the alternating magnetic field gradually weakens, so that the residual magnetism on the tape gradually decreases to zero, so that the residual magnetism originally recorded on the tape is completely erased.
