JPS60170006A - Bias oscillating device of magnetic sound recorder or the like - Google Patents

Abstract

PURPOSE:To ensure the supply of a prescribed bias at and after a time point when a power supply is applied by actuating a control element put in parallel into a resistance which supplies a DC bias to an oscillation transistor when the power supply is applied. CONSTITUTION:An oscillation transistor 1 is provided together with a switch 4 for reproducing/sound recording changeover and a control element 5 which is put in parallel into a resistance 2 as well as a resistance 7. A capacitor 9 is charged satisfactorily by a resistance 8 when the switch 4 is set at the reproduction side. Then the switch 4 is changed to the sound recording side with application of a power supply of an oscillator. Thus the charging is stopped for the capacitor 9. The element 5 is actuated by the electric charge of the capacitor 9 via a resistance 6 and has reduction of its synthetic impedance since it is put in parallel into both resistances 2 and 7. As a result, the DC bias to be applied to the transistor 1 is increased. This increases the oscillation output of the transistor 1. Thus it is possible to supply a prescribed bias immediately after application of a power supply by setting the value of the resistance 7 at a proper level.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a bias oscillation device for supplying a recording bias to a magnetic recorder or the like.

Configuration of conventional example and its problems Figure 1 is a circuit diagram of a conventional bias oscillation device, where 1 is an oscillation transistor, 2 is a resistor for supplying DC bias to the oscillation transistor 1, and 3 is for adjusting the oscillation output. The variable resistor 4 is a switch for switching between playback and recording.

Here, when the switch is switched to the recording side, the oscillation circuit 10
oscillates and supplies recording bias to the recording head.

According to the above-mentioned conventional configuration, there is a difference in the oscillation output between immediately after the oscillation device turns on the radio waves and after a certain period of time has elapsed, generally as shown by the solid line in FIG.

This, f'1. depends on the temperature characteristics due to self-heating of the oscillation transistor 1. Since the recording bias to the recording head is generally adjusted to a steady value, in the case of a conventional circuit, a recording bias lower than the specified bias is supplied when the power is turned on. Moreover, when the temperature around the indoor heating tube is low, the value becomes even lower. In this case, as is well known, as a characteristic of magnetic tape, if the recording bias becomes lower than a specified value, the recording level will drop and recording distortion will suddenly worsen, making it impossible to make good recordings.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems, and an object thereof is to provide a bias oscillation device that has a simple structure and is devised so that a constant bias is supplied from the time the stain source is turned on. .

Structure of the Invention The present invention operates a control element inserted in parallel with a resistor for supplying an iN current bias to an oscillation transistor of a bias oscillator when the power is turned on, thereby controlling the recording head from the time the power is turned on. It is constructed so that a prescribed recording bias can be supplied, and the operation of the control element is stopped after a certain period of time has elapsed.

Description of examples FIG. 2 shows an embodiment of the present invention.

In Figure 2, 1f''i oscillation transistor, 2 is a resistor for supplying JIAc bias to oscillation transistor 1, 3 is a variable resistor for adjusting the oscillation output, and 4 is for switching between playback and recording. A switch 5 is a control element inserted in parallel with the resistor 2 together with a resistor 7. A resistor 8 charges the capacitor 9. 6 is a resistor.

The operation of this embodiment configured as described above will be explained below.

When the switch 4 is on the reproduction side, the capacitor 9 is sufficiently charged by the resistor 8. The switch 4 is switched to the recording side, and the power to the oscillation device is turned on.

At this time, charging of the capacitor 9 by the resistor 8 is stopped. The control element 5 is operated via the resistor 6 by the charge stored in the capacitor 9, and is inserted in parallel with the resistor 2 together with the resistor 7, so the combined impedance is lowered and the DC bias to the oscillation transistor 1 is increased. Become,
The oscillation output will increase. Therefore, by selecting an appropriate value for the resistor 7, it becomes possible to supply a specified bias immediately after power is turned on. Also, when the switch 4 is on the recording side, the charging of the capacitor 9 is stopped, so the amount control element 5 consisting of the resistor 6 and the capacitor 9 with a time constant time operates, and after that time, the control element 5 will no longer operate, and DC bias will be supplied via resistor 2. By the above-described operation, the specified recording bias is supplied immediately after the power is turned on, as shown by the broken line 2 in FIG.

Note that the resistor 2 may be provided at the position shown in FIG. 4, and the control element 6 may be connected in parallel with the resistor 2.

Effects of the Invention As described above, according to the present invention, the recording bias supplied to the recording head is the specified recording bias immediately after the power is turned on, making it possible to perform stable recording immediately after the power is turned on. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional bias oscillation device, FIG. 2 is a circuit diagram of a bias oscillation device according to an embodiment of the present invention, and FIG. 3 is a diagram showing the time course of recording bias according to the conventional and the above embodiments. FIG. 4 is a circuit diagram of a bias oscillation device in another embodiment of the present invention. 1...Oscillation transistor, 2...Resistor, 4
...Switch, 6...Control element. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure 2 Figure 3 Figure □ Time Figure 4

Claims (1)

[Claims] By operating a control element inserted in parallel with a resistor for supplying DC bias to the oscillation transistor of the bias oscillation device when the power is turned on, the bias oscillator is operated.