Old Fashioned Record Player is mainly used for recording and playback of sound. Commonly used tape recorders are disc and cassette type. The cassette recorder has been widely used in the field of education because of its recording, playback operation is simple, cheap, excellent performance and so on. Cassette recorder according to its function can be divided into a single player, recorders, tape recorders, stereo recorders and recording deck and so on.
1. The basic structure of the recorder
The recorder is usually composed of a magnetic head, a mechanical transmission (called "movement") and a circuit. The head of the recorder is divided into recording head, playback head and erasure head three kinds of universal tape recorders often record the head and playback head into a recording and reproducing head. Mechanical transmission part of 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. The working principle of the recorder
(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, the work gap in the magnetic head with the formation of audio and change the magnetic field, when the tape close to the gap through the head , The magnetic field lines pass through the magnetic layer on the tape and magnetize it, leaving the 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 Remnant magnetic track, 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. Due to the magnetic field on the residual magnetization strength and direction are recorded with the sound signal changes, the magnetic flux within 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 nonlinear distortion, in some popular type of tape recorder 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 magnetism curve straight line, but DC bias method dynamic range is small, the noise is large. In the high-end tape recorder 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),Old Fashioned Record Player amplitude 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 supersonic 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) erase principle
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 erasure. 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.
A tape is a carrier for recording sound, consisting of a tape-based and magnetic layer. The tape base is made of a high mechanical strength of the acetate fiber material. The magnetic layer is formed by mixing a ferromagnetic metal oxide powder and a binder uniformly and uniformly coating the tape base.
1. the type of tape
According to the magnetic layer material is different, the tape is divided into the following:
(1) Fe2O3 and γ-Fe2O3 tapes. Fe2O3 is called the Normal band, marked with LN (Low Noise), also known as low noise tape. Its magnetic material is ferric oxide,Old Fashioned Record Player its high frequency characteristics are not good, suitable for recording language programs, should not record a wide range of frequency programs;
Γ-Fe2O3 tape is an improved type of ordinary belt. Marked with LH (Low noise High output), also known as "low noise high output" tape, the magnetic material is γ-shaped needle structure of ferric oxide, the magnetic particles than the "LN" type fine, In language and music recording.
(2) Cr02 tape. Cr02 with short chromium, the magnetic material is chromium dioxide. The main advantage of the chrome belt is the high frequency characteristics, wide dynamic range, suitable for recording symphonies and other dynamic range of large music programs; drawback is the hardness, the head wear large (5 to 7 times larger than ordinary), the use of this tape , The recorder must have a corresponding bias and equalization circuit adjustment selection device.
(3) iron chrome belt. It is usually marked with Fe · Cr, and the γ-Fe2O3 and Cr02 magnetic powders are successively coated on the tape base. It has both good characteristics of low-frequency γ-Fe203 and Cr02 with high frequency characteristics, wide dynamic range, low noise,Old Fashioned Record Player suitable for recording a variety of dynamic range of high fidelity music programs.
(4) Cr-γ-Fe2O3 tape. Its electromagnetic properties to meet the requirements of chromium and iron chrome belt, and high frequency performance and signal to noise ratio is more than chromium and iron chrome belt.
(5) metal belt. The magnetic material is made of nickel, iron, cobalt and other metal magnetic powder, with large output, small distortion, high frequency characteristics, and easy to saturation characteristics, suitable for high-density recording. There is also a cobalt band, its characteristics similar to the chrome belt, but the head wear is small, is used to record music high-grade tape.