Old Fashioned Record Player is mainly used for recording and playback of sound. Commonly used tape Old Fashioned Record Players are disc and cassette type. Cassette Old Fashioned Record Player for its recording, playback is simple, cheap, excellent performance, in the field of education has been widely used. Cassette Old Fashioned Record Player according to its function can be divided into a single player, Old Fashioned Record Players, tape Old Fashioned Record Players, stereo Old Fashioned Record Players and recording deck and so on.
1. The basic structure of the Old Fashioned Record Player
The Old Fashioned Record Player is usually composed of a magnetic head, a mechanical transmission (called "movement") and a circuit. The head of the Old Fashioned Record Player is divided into recording head, playback head and erasure head three kinds of universal tape Old Fashioned Record Player often record the head and playback head into a recording and reproducing head. Mechanical transmission part by the drive mechanism, brake mechanism and a variety of functional operating mechanism. The circuit part consists of recording, playback amplifier, super audio oscillator and some special function circuit.
2. How the Old Fashioned Record Player works
(1) recording principle
Old Fashioned Record Player's recording and playback is an electro-magnetic conversion process. Recording, the audio signal is amplified and sent to the head coil, it will produce alternating magnetic flux in the head of the magnetic head in the work of the magnetic gap formed with the magnetic field changes, when the tape close to the gap through the head , The magnetic field lines pass through the magnetic layer on the tape, magnetizing it, leaving a remanence. As the tape moves at constant speed, the polarity and strength of the tape are left with the continuity of the change in the audio signal Remanence tracks, so that the acoustic signal in the form of remanent magnetization, as shown in Figure (a) below. When the magnetic tape is recorded at the same speed as the recording tape, the magnetic field of the magnetic field on the magnetic tape will pass through the magnetic head Core made of closed magnetic circuit. The magnetic flux and the direction of the magnetic tape are changed with the recorded sound signal, the magnetic flux in the head core also changes accordingly, resulting in the coil corresponding to the magnetic flux changes in the induced electromotive force.
(2) bias recording principle
Ferromagnetic material is magnetized, even if the removal of external magnetic field, ferromagnetic material still retains a certain magnetic, called remanence. The greater the magnetic field strength, the greater the remanence. However, the magnetic field on the tape and the gap in the magnetic field strength is not a linear relationship, but the occurrence of significant distortion, that can not accurately reflect the original signal.
In order to overcome this non-linear distortion, in some popular type of tape Old Fashioned Record Player in the use of DC bias recording, that is, in the recording signal to add a DC bias current leaving the audio signal to the working point of the residual line to the residual line, DC bias method dynamic range is small, the noise is larger. In the high-end tape Old Fashioned Record Player is commonly used in the AC bias mode, that is, in the audio signal superimposed on a higher than the highest frequency of audio signals more than 5 times (often 45 ~ 100kHz), the amplitude of 5 to 25 times the super-audio oscillation current ( See Figure (2)), so get a comprehensive signal as shown. If the supersonic current is selected, the ultrasound signal is distorted, but its envelope, that is, the distortion of the audio signal curve is very small, thus solving the problem of recording distortion. AC bias method has the advantages of high sensitivity, small noise, large dynamic range and good fidelity.
(3) the principle of wiping
The erasure is to degauss the tape and remove the remanence from the tape. At present, more use of the method is the exchange of wiping. AC wipe, also known as super audio erase. The basic structure of the wiping head is the same as the recording and reproducing head, except that the working gap width is about 10 times that of the recording head. When the sound is sounded, the super-audio oscillator provides a super-audio current to the wiper head coil, resulting in a magnetic field at the head gap at a sufficient number of turns. Super-audio magnetic field in the wipe the head gap before the symmetrical division, the strongest gap between the two sides gradually weakened, as shown. When the tape is moved closer to the wiping head, the magnetic field on the tape is gradually strengthened by the magnetic field, the remanence gradually increases, reaching the gap, the maximum residual magnetic density, thus obscuring the original magnetic remanence. When the tape continues to run, leaving the gap, the magnetic field strength gradually weakened, when the magnetic field strength reduced to zero, the magnetic field on the magnetic field density is reduced to zero. So the tape on the original record of the track is completely erased.