JPS58177505A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the noise level of a reproduction output by impressing a less bias current than a normal bias current when there is no input signal. CONSTITUTION:The output of an oscillator 5 for AC bias current generation is applied to a sound recording head 12 through a variable attenuation network 6, amplifier 8, and capacitor 4. The variable attenuation network 6 varies the attenuation of the output of the oscillator 5 by variation in the internal resistance value of a control element Q with a control signal applied from a control circuit 10 to vary a bias current value. When there is not signal from a sound recording amplifier 2, the positive voltage of a bias power source E is applied to the control element Q, which turns on to attenuate the oscillation output of the oscillator 5 greatly. When an input signal is applied to the control circuit 10, it is amplified and then rectified and smoothed to generate a minus DC voltage and the bias voltage E is canceled in accordance with the level of the generated voltage to vary the control voltage to the control element Q; and the attenuation of the oscillation output is reduced to increase the AC bias voltage to a normal value.

Description

[Detailed Description of the Invention] The present invention relates to a magnetic recording and reproducing device, and particularly aims to improve the noise level of the reproduced output by applying a bias current lower than the normal bias current when there is no input signal. The purpose is to

In general, in the AC bias recording method, the signal level recorded on the magnetic tape (hereinafter expressed as the level of the playback output signal obtained from the magnetic tape) depends on the change in the AC bias current value superimposed on the signal current during recording. "Output level"
) The amount of distortion, frequency response characteristics, noise characteristics, etc. change. The tendency of change in the output level of the recording signal obtained when a signal with a constant signal level is recorded on a magnetic tape by changing the AC bias current value is expressed by the AC bias current value on the horizontal axis and the output level distortion rate on the vertical axis. When represented by the curve C1°C2 in FIG. 1, the output level becomes a mountain-shaped one showing a maximum value at a certain AC bias current value.

Further, the minimum point of the distortion factor is shifted from the lowest position of the output level toward the side where the AC bias current is increased. In this way, the minimum point of the distortion factor is shifted from the maximum position of the output level to the part where the AC bias current value is large, so normally,
When setting the AC bias current of an AC bias recorder, focus on the distortion rate, and make sure that the AC bias current value is higher than the AC bias 'current value corresponding to the maximum output level when recording midrange signals. In most parts, the output level is set to a value that is approximately 0.5 to 1d8 lower than the maximum value.

In FIG. 1, a curve C1 is an example of a characteristic curve of AC current value versus output level when a signal with a certain level in the midrange (for example, a frequency of 40 of (Z signal)) is recorded on a magnetic tape. The point A1 in the figure is the output level point of the mid-range signal corresponding to the above-mentioned normal AC/(Iasumi style setting value) A. Also, the curve C2 corresponds to the mid-range output level of the curve C. This is an example of the distortion characteristic curve, which is 0.5 to
1dFP.

AC corresponding to the falling point A1) (Iasumi Nagaraiko A
indicates the minimum. To reduce the AC bias current value,
It is well known that this method has not been used in the past because it increases the distortion rate of low frequency signals.

Conventionally, it has been common knowledge that the AC bias current value is selected to be large within a range that achieves reduction of distortion of low frequency signals.

FIG. 2 shows an example of audible band noise characteristics when signalless recording and reproduction is performed on a magnetic tape without applying an input signal. Curve d represents the bias current IA
Or the noise characteristics when recording and reproducing without a signal with IB, the curve ~ is the noise characteristic when recording and reproducing without a signal with a bias current of 7 (Ias value - 10d15) of curve d1,
A curve d3 shows an example of noise characteristics when recording and reproducing without a signal is performed with a bias current of 12 odJs or more of the bias value of the curve d1. Note that this curve d3 exhibits the same noise characteristics as those obtained when a tape erased with a demagnetizer (referred to as a pulse erase tape) is reproduced.

As shown in Fig. 3, when the bias current is reduced and no signal is recorded and reproduced on the magnetic tape, the noise is improved by 6 dp near 1KH2 and by 6dβ above 500H2. , which was designed in consideration of the above-mentioned no-signal input, reduces noise by lowering the bias current by more than 120 dβ from the normal bias current value when no signal is input, and at the same time returns to the normal bias when a signal is input, reducing distortion. It is possible to record and reproduce signals without deteriorating the rate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording/reproducing apparatus of the present invention will be described below with reference to drawings of embodiments. FIG. 4 shows an embodiment of the present invention. In FIG. 4, 5 is an oscillator for generating AC bias current, and the output of this oscillator 5 is sent to an amplifier 8 via a variable attenuation network 6. The output of the amplifier 8 is applied to the recording head 12 via the capacitor 4 as an alternating current bias current. The variable attenuation network 6 described above includes resistors R1, R2,
The signal is supplied from the oscillator 5 to the amplifier 5 and the amplifier 8 by a change in the internal resistance value of the control element Q, which changes in response to a control signal applied to the control element Q from the control circuit 10. By changing the amount of attenuation for the oscillation output,
The AC bias current value applied to the recording head 12 is changed. Also, 1 is an input terminal, 2 and 3 are recording amplifiers,
7 is a bandpass filter, and the control circuit 10 includes a recording amplifier 2.
An input signal is applied from the output 6 through a bandpass filter 7. The control circuit 1o described above includes an amplifier 11, a capacitor C1,
Diode d1. d2. It consists of a resistor R3, a capacitor C2, a resistor Ra, a bias power supply E, etc., and when no signal is applied from the recording amplifier 2 through the bandpass filter 7, the positive voltage of the bias power supply E is variable attenuated through the resistor R4. In addition to the control element Q in the network 6, it is made conductive, and the oscillation output given from the oscillator 5 to the amplifier 8 is greatly attenuated so that the alternating current bias current given to the recording head 12 is reduced; When an input signal is applied to the control circuit 10 via the bandpass filter 7, it is amplified and then passed through the capacitor C1 to the diode d1. d2 and smoothed by the circuit of resistor R3 and capacitor C2 to generate a negative DC voltage, and according to the magnitude of the negative DC voltage, the positive voltage of bias voltage E is canceled to control the variable attenuation network θ. By changing the control voltage applied to element Q and thereby increasing the internal resistance of control element Q7, amplifier 8
, the amount of attenuation for the applied oscillation output is decreased 712,- and the AC bias current applied to the recording head 12 is increased to a normal bias value. Here, the control element Q is an NPN transistor, but a semiconductor element such as a PNP transistor or a field effect transistor may also be used. The signal is amplified by the recording amplifiers 2 and 3 and subjected to necessary compensation, and then superimposed on the AC Iasumi current applied via the capacitor 4 and applied to the recording head 12, where it is magnetically recorded on tape. Therefore, when there is no input signal, the AC bias current value supplied to the recording head 12 during recording is -20 dβ lower than the standard bias current for the magnetic tape due to the action of the control circuit 10 and the variable attenuation network 6 described above. The following bias current is applied.

Specifically, in order for the above operation to be performed well, it is necessary that the response time of the control circuit 1o is appropriate. Therefore, it is desirable that the output impedance of the amplifier 11 of the control circuit 1o and the control circuit 10 of the capacitors C1 and C2 have a short attack time and a long recovery time.

As explained in detail above, according to the present invention, the AC bias current superimposed on the signal current during recording is increased (this is the reference bias value) at the time of signal input where distortion becomes a problem in the signal to be recorded and played back, When there is no signal input, the noise component is reduced so that the noise component when there is no signal approaches the pulse erase tape noise, so when there is a signal input, it can be recorded well without an increase in distortion using a simple device, and the signal can be recorded. This has the advantage that recording can be realized that prevents an increase in residual noise when there is no input.

[Brief explanation of the drawing]

Figure 1 is a characteristic quantity diagram showing an example of bias and distortion characteristics.
2 and 3 are characteristic curve diagrams showing an example of recording and reproduction noise characteristics, and FIG. 4 is a block diagram showing an embodiment of the present invention. 2.3... Recording amplifier, 5... Oscillator, 6... Variable attenuation network, 7... Bandpass filter, 8... Page 9: Amplifier, 10: Control circuit.

Claims (1)

[Claims] A magnetic head for recording audio frequency signals on a magnetic recording medium, a bias oscillator for supplying bias current to the magnetic head, and a bandpass filter for detecting audio frequency signal components to be recorded by the magnetic head. a control circuit that rectifies the output of the filter to generate a control signal, and an audio frequency that is provided between the bias oscillator and the magnetic head and that is to be recorded in response to the control signal from the control circuit. A magnetic recording/reproducing device comprising a variable attenuation circuit network that controls a bias current to a large value only when a signal is input, and to a small value when unattended.