JPS6112576Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a recording level switching circuit for optimally recording ordinary iron oxide tape and chrome tape.

That is, since the magnetic saturation point of chrome tape, metal tape, etc. is higher than that of ordinary iron oxide tape, it is necessary to increase the recording level.

This invention uses ALC when recording these tapes.
By changing the operating point of the circuit, it is possible to record at a recording level suitable for each tape.

First, before explaining the circuit of the present invention, the circuit shown in FIG. 1 will be explained.

In Figure 1, 1 is an input signal terminal, 2 is an input resistor, 3 is a recording amplifier, 4 and 5 are diodes that rectify a part of the output signal of amplifier 3, and 6 is a rectified output from diodes 4 and 5. The control transistor 7 supplied to the base is an ALC transistor in which the emitter of the control transistor 6 is connected to the base, and there is a time constant between the base of the control transistor 6 and the emitter of the ALC transistor 7. A determining capacitor 8 is connected.
A resistor 9 and a capacitor 10 are connected between the emitter of the ALC transistor 7 and ground.

In this ALC circuit, the control transistor 6 becomes conductive in response to the level of the output signal of the amplifier 3, and the ALC transistor 7 also becomes conductive.
The input signal level of the amplifier 3 is controlled by the impedance change of the ALC transistor 7, and at this time the capacitor 8 is useful for lengthening the recovery time of the ALC.

In such an ALC circuit, when the ALC is sufficiently effective, the recording level selector switch 12 is closed to apply a control voltage (+B) to the emitter of the ALC transistor 7 through the resistor 11 in order to change the operating point of the ALC. When bias is applied to the capacitor 8, a positive pulse as shown in the diagram is generated at the moment the switch 12 is closed.
The base current suddenly flows to the control transistor 6 through the ALC transistor 6, and the impedance of the ALC transistor 7 drops rapidly.As the ALC recovery time is long, it is difficult to return to the original level, and the recording level remains unchanged for a while. There is a concern that the recording will be low and unnatural.

However, in the present invention, as shown in FIG. 2, a time constant circuit 15 consisting of a resistor 13 and a capacitor 14 is connected to a circuit for applying a bias to the emitter of the ALC transistor 7. In FIG. 2, parts that are the same as those in FIG. 1 are given the same figure numbers.

Therefore, when the recording level changeover switch 12 is open, the above-mentioned ALC operation is carried out, and the characteristic of the input level and output level on the input/output side of the amplifier 3 at this time is obtained as the curve XX' in FIG.

Next, when the recording level selector switch 12 is closed, the control voltage (+B) charges the capacitor 14 of the time constant circuit 15, so that the emitter of the ALC transistor 7 receives a pulse as explained in FIG. Since this does not occur and a bias is applied to the emitter, the voltage between the collector and emitter of the ALC transistor 7 is apparently small, and the level that makes the ALC transistor 7 conductive becomes large, which is the point at which ALC becomes effective. is Fig. 3 Y-
It looks like a Y′ curve.

As described above, the recording level control circuit of the present invention supplies a part of the output signal of the amplifier to the base of the control transistor, connects the emitter of the control transistor to the base of the ALC transistor, and connects the control transistor to the base of the control transistor. An ALC circuit consisting of a time constant determining capacitor connected between the base of the ALC transistor and the emitter of the ALC transistor.
A time constant circuit is connected to the emitter of the ALC transistor, and when the recording level selector switch is closed, a control voltage is applied to the emitter of the ALC transistor through the time constant circuit. The pulse generated at the instant of switching can be absorbed by the time constant circuit, and unnatural recording can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for explaining the present invention, FIG. 2 is a circuit diagram of the present invention, and FIG. 3 is a characteristic diagram showing the relationship between input level and output level. 3...Amplifier, 6...Control transistor, 7
...ALC transistor, 8...Capacitor,
12... Recording level selection switch, 15... Time constant circuit.

Claims (1)

[Scope of utility model registration request] An NPN type control transistor conducts when the rectified output signal of the amplifier is applied to the base, and the control transistor conducts depending on the degree of conductivity.The collector is connected to the signal line and the emitter is connected to the signal line through a resistor. and an ALC time constant determining capacitor connected between the base of the control transistor and the emitter of the ALC transistor.
An ALC circuit configured to apply a bias voltage to the emitter of an ALC transistor, characterized in that a time constant circuit is connected between the emitter of the ALC transistor and the recording level selection switch. Level switching circuit.