JPH0316156Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to a tape recorder with a radio in which a radio receiving device and a tape recorder are combined, and particularly relates to a signal correction circuit.

(b) Prior Art Recently, tape recorders called head-on stereos, which allow you to listen to the playback sound of a magnetic tape using a head-on, have become popular. Some have built-in receiver circuits. Due to the characteristics of magnetic tape, tape recorders produce an annoying noise called hiss noise during playback operation.
There are two types of noise reduction circuits for suppressing such noise: one that corrects the frequency of the signal during recording and playback, and the other that corrects the frequency of the signal only during playback. Although the former method has excellent noise reduction characteristics, it has the problem of being expensive.
This is not suitable for inexpensive tape recorders. On the other hand, the latter method has poor noise reduction characteristics but can be manufactured at low cost, so it has been adopted in popular tape recorders, and such technology is disclosed, for example, in Japanese Patent Publication No. 15510/1973. There is something.

(c) Problems to be solved by the invention Although it is possible to suppress the hiss noise in a tape recorder with a radio by operating the noise reduction circuit mentioned above when using the tape recorder, it is difficult to listen to AM broadcasts especially when using the radio. When you are in the room, there is a lot of noise and it can be jarring. A common method for suppressing noise when listening to such radio broadcasts is to reduce the level of high frequency signals using a signal correction circuit called a tone control circuit. Incorporating this would complicate the circuit configuration and require an operating knob for control, so it was not suitable for miniaturizing tape recorders with radios. The present invention aims to provide a signal correction circuit that is improved in this respect.

(d) Means for Solving Problems The present invention includes a selection switch that switches between radio use and tape recorder use, and when the selection switch is on the radio use side, power is supplied and the switch becomes operational, and radio broadcasting starts. a radio receiving circuit that receives a signal; a preamplifier circuit that is supplied with power and becomes operational when the selection switch is on the tape recorder use side and amplifies the signal reproduced by the magnetic head; and the radio receiving circuit. A signal control transistor whose collector is connected via a capacitor to the signal path through which the broadcast signal from the preamplifier and the reproduced signal from the preamplifier circuit flow, and whose emitter is grounded; A control switch that controls the base bias of the control transistor and the selection switch are supplied with power when the tape recorder is used and the switch is in operation, and the signal is adjusted according to the level of the playback signal from the preamplifier circuit. a bias control circuit that controls the base bias of the control transistor; and a switch that is operable when the selection switch is on the radio use side and becomes conductive when the control switch is switched to make the signal control transistor conductive. It consists of a switching transistor.

(e) Effect The present invention uses a signal control transistor, which is provided to change the operating point of the bias according to the level of the reproduced signal when a tape recorder is used, and to change the frequency characteristics of the signal flowing through the signal path, to a radio. When in use, it is used to perform signal correction operations for radio broadcast signals.

(F) Embodiment The illustrated circuit is an embodiment of the signal correction circuit of the present invention. In the figure, 1 is a selection switch for switching between radio use and tape recorder use, and includes a common terminal 1a connected to a power source, a tape recorder side terminal 1t, and a radio side terminal 1r. Reference numeral 2 denotes a magnetic head for reproducing the signals recorded on the magnetic tape; and 3, when the tape recorder is in use, power is supplied through the selection switch 1 and the magnetic head 2 becomes operational, and the magnetic head 3 reproduces the signals reproduced by the magnetic head 2. 4 is a preamplifier circuit for amplifying the radio; when the radio is in use, power is supplied through the selection switch 1 to activate the radio receiving circuit; 5 is a radio receiving circuit for receiving radio broadcast signals; A signal path 7 is connected between the signal path 5 and ground, and adjusts the levels of the reproduced signal and the radio broadcast signal. a variable resistor; 8 is a main amplifier circuit into which the signal level-adjusted by the variable resistor 7 is input and amplifies the signal; 9 is a headphone jack into which a headphone plug is inserted; It includes a signal terminal 10 to which the output signal of the main amplifier circuit 8 is applied, and a ground terminal 11 that is grounded. Reference numeral 12 denotes a control switch which is switched to the opposite side from the state shown in the figure during signal correction operation, and includes a common terminal 12a, a first terminal 12b and a second terminal 1 connected to the power supply.
It is equipped with 2c. 13 is a signal control transistor whose collector is connected to the signal path 5 through a capacitor 14 and whose emitter is grounded; its base is connected to the second terminal 12c of the control switch 12 through a resistor 15; It is connected. Further, the signal control transistor 1
A diode 16 and a resistor 17 are connected in series between the base of 3 and the ground, and a capacitor 18 is also connected. 19 is supplied with power when the tape recorder is in use and becomes operational, and outputs an AC signal corresponding to the level of the reproduction signal from the preamplifier circuit 3 to control the base bias of the signal control transistor 13. The output terminal is connected to the cathode of the diode 16 via a capacitor 20. 21 has a collector resistor 22
the radio side terminal 1r of the selection switch 1 via
This is a switching transistor whose emitter is connected to the base of the signal control transistor 13, and whose base is connected to the second transistor of the control switch 12 via a resistor 23.
It is connected to the terminal 12c. In such a configuration, when the control switch 12 is switched while the tape recorder is in use, a bias current is supplied to the base of the signal control transistor 13 via the control switch 12 and the resistor 15, but the bias current is supplied from the bias control circuit 19 to the base of the signal control transistor 13. When the level of the output AC signal increases, the base bias of the signal control transistor 13 is changed via the diode 16, and in particular, the signal control transistor 13 continuously changes from a non-conducting state to a saturated state. It is configured such that its operating state changes periodically. Therefore, when the tape recorder is in use, the resistor 6, capacitor 14, and signal control transistor 13 operate as a variable frequency filter. When the control switch 12 is switched while the radio is in use, the switching transistor 21 becomes conductive, and the signal control transistor 13 is switched on via the resistor 22 and the switching transistor 21.
A bias current is supplied to the base of the signal control transistor 13, and in such a state, the signal control transistor 13 is configured to be in a saturated state. Therefore, when the radio is in use, the capacitor 14 and the signal control transistor 13 operate as a filter circuit that attenuates the level of signals above a predetermined frequency.

The present invention is constructed as described above, and its operation will be explained next. First, the operation of the tape recorder when the selection switch 1 is in the illustrated state will be described. When the tape recorder is in use, power is supplied to the preamplifier circuit 3 and bias control circuit 19 through the selection switch 1. In this state, when a reproduction operation is performed, the tape recorder enters a reproduction operation state and the signals recorded on the magnetic tape are reproduced by the magnetic head 2. The reproduced signal reproduced by the magnetic head 2 is input to a preamplifier circuit 3, amplified, and then applied to a variable resistor 7 through a resistor 6. The reproduced signal applied to the variable resistor 7 is level-adjusted and then input to the main amplifier circuit 8 where it is amplified. The playback signal amplified by the main amplifier circuit 8 is applied to the signal terminal 10 of the headphone jack 9 , so if a headphone plug is inserted into the headphone jack 9 , the magnetic tape can be played back by the headphone. You can hear the sound.
The reproduction operation of the tape recorder is performed in this manner, but the noise reduction operation will be explained next. When the user performs a noise reduction operation, the control switch 12 is switched to the opposite side from the illustrated state. When the control switch 12 is switched to the opposite side from the state shown, a voltage is applied to the base of the switching transistor 21 via the resistor 23, but since no voltage is applied to the collector, the switching transistor 21 is in a non-operational state. It is in a conductive state. Therefore, in this state, a bias current is supplied to the base of the signal control transistor 13 through the control switch 12 and the resistor 15. When the level of the signal reproduced by the magnetic head 2 is low, that is, when the hiss noise becomes harsh, the level of the AC signal output from the bias control circuit 19 is low, so the diode 16 does not conduct, and the signal control circuit 19 does not conduct. transistor 13 is deeply biased and in saturation. Therefore, the hiss noise amplified by the preamplifier circuit 3 is bypassed through the capacitor 14 and inputted to the main amplifier circuit 8 at a low level, so that it does not cause discomfort to the listener. When the level of the signal reproduced by the magnetic head 2 is high, that is, when the hiss noise is masked by the signal and does not become harsh, the level of the AC signal output from the bias control circuit 19 becomes high, so the diode 16 becomes conductive. The base bias of the signal control transistor 13 becomes shallow, and when it exceeds a predetermined level, the signal control transistor 13 becomes non-conductive. When the signal control transistor 13 is in a non-conducting state, the capacitor 14 is disconnected from the signal path 5, so the level of the reproduced signal amplified by the preamplifier circuit 3 is not attenuated. It will be input to the main amplifier circuit 8. The bias control circuit 19 changes the base bias of the signal control transistor 13 in accordance with the level of the signal reproduced by the magnetic head 2, and as a result, the level of the signal input to the main amplifier circuit 8 changes in accordance with the frequency. death,
A noise reduction operation is performed in this circuit. Although the tape recorder operates in this manner, the radio receiving circuit 4 is in an inoperative state because no power is supplied to it in this state.

The reproduction operation of the tape recorder is performed as described above, but next, the operation of listening to radio broadcasting will be explained. The operation of listening to a radio broadcast is performed by switching the selection switch 1 to the radio use side, which is the opposite side from the state shown in the figure. When the selection switch 1 is switched to the opposite side from the state shown in the figure, the power supply to the preamplifier circuit 3 and the bias control circuit 19 is cut off, and the power is supplied to the radio receiving circuit 4, so that the radio receiving circuit 4 is in the operating state. become. The broadcast signal received by the radio receiving circuit 4 is applied to a variable resistor 7 through a signal path 5. The broadcast signal applied to the variable resistor 7 is level-adjusted and then input to the main amplifier circuit 8 where it is amplified. The broadcast signal amplified by the main amplifier circuit 8 is applied to the signal terminal 10 of the headphone jack 9 , so that the user can listen to the radio broadcast signal through the headphone. The operation of listening to a radio broadcast signal is performed in this manner.Next, the operation when the reception condition is poor and there is a lot of noise will be explained. When a signal correction operation is performed in such a state, the control switch 12 is switched to the opposite side from the state shown. When such a switching operation is performed, a bias voltage is applied to the base of the switching transistor 21 via the control switch 12 and the resistor 23, so that the switching transistor 2
1 becomes conductive. When the switching transistor 21 becomes conductive, a bias current is supplied to the base of the signal control transistor 13 through the resistor 22 and the collector-emitter path of the transistor 21, and the signal control transistor 13 becomes conductive. Therefore, signals of a predetermined frequency or higher among the broadcast signals output from the radio receiving circuit 4 are bypassed through the capacitor 14, and no harsh noise signals are input to the main amplifier circuit 8. . Therefore, the radio broadcast signal listened to by the headphone does not cause any discomfort to the listener.

In this embodiment, the tape playback signal and the radio broadcast signal are listened to through a headphone, but they can also be configured to be listened to through a speaker. Further, although the case where the present invention is applied to a monaural type radio tape recorder has been described, it is of course possible to implement the present invention to a stereo type radio tape recorder having left and right channels. The bias control circuit 19 controls the operation of the signal control transistor 13 according to the level of the reproduced signal, but the bias control circuit 19 controls the operation of the signal control transistor 13 according to the level of the signal having a predetermined frequency or higher in the reproduced signal. If configured to operate, the noise reduction operation can be performed in a more natural manner.

(g) Effects of the invention The present invention uses a signal control transistor that is provided to change the bias operating point according to the level of the reproduced signal when a tape recorder is used, and to change the frequency characteristics of the signal flowing through the signal path. Since it is used to correct the radio broadcast signal when the radio is used, the circuit configuration is simplified. Also, when the radio is in use, the bias control operation of the signal control transistor that performs the signal correction operation is performed by a switching transistor that is controlled by a control switch provided for performing the noise reduction operation of the tape recorder. Therefore, the signal correction circuit can be incorporated without making any mechanical changes, and the present invention has a very large effect when implemented in a small tape recorder with a radio.

[Brief explanation of the drawing]

The illustrated circuit is one embodiment of the signal correction circuit of the present invention. Explanation of main drawing numbers, 1...Selection switch, 2...
Magnetic head, 3... Preamplifier circuit, 4... Radio receiving circuit, 5... Signal path, 8... Main amplifier circuit, 1
2... Control switch, 13... Signal control transistor, 14... Capacitor, 19... Bias control circuit, 21... Switching transistor.

Claims (1)

[Scope of utility model registration request] A radio-equipped tape recorder equipped with a selection switch for switching between radio use and tape recorder use, wherein when the selection switch is on the radio use side, power is supplied and the radio receiver circuit receives a radio broadcast signal. , when the selection switch is on the tape recorder use side, power is supplied and the tape recorder becomes operational, and a preamplifier circuit amplifies the signal reproduced by the magnetic head; and a broadcast signal which is the output signal of the radio reception circuit; A variable resistor is connected between a signal path through which a reproduced signal, which is an output signal of the preamplifier circuit, flows and ground, and adjusts the level of the signal, and a signal whose level is adjusted by the variable resistor is applied. a main amplifier circuit that amplifies the signal, a control switch that is switched during the signal correction operation, a collector connected to the signal path via a capacitor, and an emitter that is grounded; A signal control transistor whose operating state is continuously changed from a non-conducting state to a saturated state, and when the selection switch is on the tape recorder use side, power is supplied and the signal control transistor becomes into an operating state, and the signal from the preamplifier circuit is switched on. a bias control circuit that controls the base bias of the signal control transistor according to the level of the reproduction signal; and a bias control circuit that is operable when the selection switch is on the radio use side and becomes conductive when the control switch is switched. , a switching transistor that supplies a base current that saturates the signal control transistor, and changes the base bias of the signal control transistor according to the level of the playback signal when the tape recorder is in use, and also 1. A signal correction circuit for a tape recorder with a radio, characterized in that when in use, the signal control transistor is brought into a saturated state by conduction of the switching transistor.