JPS6317111Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a tape recorder, and particularly to a recording circuit.

2. Description of the Related Art Recently, tape recorders, particularly tape recorders with a radio, which are configured in combination with a radio receiver, have become popular. Such a tape recorder is equipped with a level display circuit that displays the level of the recording signal during recording operation, but the level display circuit is a display that displays the output signal of the recording amplifier circuit that supplies the recording signal to the recording magnetic head. It is common that the voltage is applied to the voltage and the level is displayed. Furthermore, most of the amplifier circuits that make up modern tape recorders are integrated circuits (ICs), and recording amplifier circuits are no exception. In such a recording amplifier circuit, a resistor for a constant output current is built into the IC, so that the output of the amplifier circuit is sometimes so small that it cannot drive a display. Also,
When recording with a microphone built into the tape recorder, it is important to know what kind of sound is being recorded and howling occurs when the motor is driven by the speaker built into the tape recorder. It was impossible.

The present invention has been developed in view of these points, and will be described in detail below with reference to the illustrated embodiments. In the figure, 1 is an input terminal to which a playback signal from a magnetic head for playback is input during playback operation, and a recording signal obtained from a built-in microphone etc. is input during recording operation, and 2 is a playback signal or recording signal input to input terminal 1. 3 is a recording amplifier circuit that amplifies the recording signal from the preamplifier circuit 2 during recording operation; 4 is a bias oscillator that is activated during recording operation; 5 is the recording amplifier This is a recording magnetic head to which a recording signal from a circuit 3 is applied along with a bias current from a bias oscillator 4, and has the function of recording the recording signal onto a magnetic tape. 6 is a variable resistor to which the signal from the preamplifier circuit 2 is applied and adjusts the level of the signal; 7 and 8 are first and second reproducing amplifier circuits connected BTL to each other; The input terminal of the first reproduction amplifier circuit 7 is connected so that a signal whose level is adjusted by the variable resistor 6 is applied thereto. 9 is a speaker connected between the output terminal of the first reproduction amplifier circuit 7 and the second reproduction amplifier circuit 8; 10 is a speaker connected between the output terminal of the first reproduction amplifier circuit 7 and the second reproduction amplifier circuit 8; An earphone jack 11 is connected between the output terminals and into which the earphone plug is inserted, and is connected within the signal path to the speaker 9, and when switched to the recording side, connects the earphone jack 11 to the signal path to the speaker 9. This is a recording/playback switch. In such a circuit, the DC potential of the output terminals of the first reproducing amplifier circuit 7 and the second reproducing amplifier circuit 8 is approximately 1/2 Vcc, where Vcc is the power supply voltage. Reference numeral 12 indicates the first reproduction amplifier circuit 7 when the earphone plug is not inserted into the earphone jack 10.
The first control transistor 13 turns on when DC voltage is applied from the output terminal of the transistor and turns off when the earphone plug is inserted. and a second control transistor whose operation is controlled by the first control transistor 12. 15 is the second
When the control transistor 13 is turned on, power is supplied to it and it becomes operational, and it is a bypass transistor connected as an emitter follower, and the output signal of the preamplifier circuit 2 is passed through the variable resistor 6 to its base. applied without
The emitter is connected so that a signal is applied to the input terminal of the first reproducing amplifier circuit 7. 16 is a display transistor whose emitter is grounded and whose collector is connected to a light emitting diode 17 for display operation; in the playback state, a DC voltage is applied to the base from the recording/playback switch 14 via the resistor 18; In the recording state, the signal from the first reproduction amplifier circuit 7 or the second reproduction amplifier circuit 8 is applied to the base by the recording/reproduction changeover switch 11. Further, the collector of the first control transistor 12 is connected to the base of the display transistor 16 via a resistor 19 and a diode 20. A capacitor 21 connected to the base circuit of the first control transistor 12 is provided to eliminate the influence of alternating current signals.

The present invention is constructed as described above, and the operation of the circuit thus constructed will now be described. First, the playback operation when the recording/playback selector switches 11 and 14 are in the illustrated state will be described. In such a reproducing operation state, since no power is supplied to the emitter of the second control transistor 13, the second control transistor 13 is in an off state and the bypass transistor 15 is in an inactive state. Further, since a DC voltage is applied to the base of the display transistor 16 from the recording/playback switch 14 via the resistor 18, the resistor 18 and the bias resistor 2
By appropriately setting the values of 2 and 23, the power supply voltage can be checked by lighting the light emitting diode 17. In this playback operation state, the recording amplifier circuit 3 and bias oscillator 4 are inactive due to the action of a recording/playback switch (not shown), and the playback signal played by the playback magnetic head is input to the input terminal 1. be done. Said input terminal 1
The reproduced signal input to the amplifier circuit 2 is amplified by the amplifier circuit 2, and then applied to the variable resistor 6 to adjust its level. The signal whose level has been adjusted by the variable resistor 6 is input to the first reproduction amplifier circuit 7, and after being amplified by the first reproduction amplifier circuit 7 and the second reproduction amplifier circuit 8, the signal is sent to the speaker 9. is applied to emit sound. Also, in such a situation,
When the earphone plug is inserted into the earphone jack 10, the signal to the speaker 9 is cut off, and the reproduced sound can be heard through the earphone.

Although the reproduction operation is performed as described above, the recording operation will be explained next. In the recording operation state, the recording amplifier circuit 3 and the bias oscillator 4 are in operation, and the recording/reproduction changeover switches 11 and 14 are in a state opposite to that shown in the figure. First, a case will be described in which a recording operation is performed without inserting an earphone plug into the earphone jack 10. In such a state, a bias current flows from the output terminal of the first reproduction amplifier circuit 7 to the base of the first control transistor 12, and the first control transistor 12 is turned on. When the first control transistor 12 is turned on, the second control transistor 13 is forward biased and turned on, supplying power to the bypass transistor 15. As a result, the bypass transistor 15 becomes operational, and the signal applied to the base can be derived from the emitter, so the output signal of the preamplifier circuit 2 is passed through the bypass transistor 15 to the first reproducing amplifier circuit. It is input to the input terminal of 7 regardless of the variable resistor 6. The signal input to the first reproduction amplifier circuit 7 is amplified by the first reproduction amplifier circuit 7 or the second reproduction amplifier circuit 8 and then passed through the recording and reproduction changeover switch 11 to the base of the display transistor 16. is applied to The display transistor 16
When an AC signal is applied to the base of the transistor 16, the operating state of the transistor 16 changes depending on the signal level. The display transistor 1
When the operating state of the light emitting diode 6 changes, the current flowing through the light emitting diode 17 connected to the collector as a load changes, so that the lighting state of the light emitting diode 17 changes. Therefore, the light emitting diode 17
The user can recognize the level or presence/absence of the recording signal by changing the lighting state of the recording signal. In such a recording operation state, the recording signal input to the input terminal 1 is amplified by the preamplifier circuit 2 and the recording amplifier circuit 3, and then applied to the recording magnetic head 5 together with the bias signal from the bias oscillator 4. recorded on magnetic tape. Further, the output signal of the preamplifier circuit 2 is input to the first reproducing amplifier circuit 7 through the bypass transistor 15 and amplified, and then applied to the base of the display transistor 16 to change the signal level by the light emitting diode 17. Or presence/absence is displayed. Since the recording signal level display operation is performed regardless of the position of the variable resistor 6, the display operation can be performed reliably.

The normal recording operation is performed as described above, but next, the operation when the earphone plug is inserted into the earphone jack 10 and the recording operation is performed will be explained. When the earphone plug is inserted into the earphone jack 10, the first reproduction amplifier circuit 7
Since the bias applied to the base of the first control transistor 12 from the output terminal of is cut off,
The first control transistor 12 is turned off. When the first control transistor 12 is inverted to the OFF state, the second control transistor 13 is also inverted to the OFF state as the first control transistor 12 is inverted, so that the power supply to the bypass transistor 15 is cut off and the bypass transistor 15 becomes inactive. The collector of the first control transistor 12 connects the display transistor 16 through a resistor 19 and a diode 20.
A high voltage is applied to the base of the display transistor 16, and the display transistor 16 is turned on regardless of the presence or absence of a recording signal. Therefore, in such a state, the level of the output signal from the preamplifier circuit 2 is adjusted by the variable resistor 6 and applied to the first regenerative amplifier circuit 7, so that the level of the signal input to the earphones is adjusted. It can be adjusted with the variable resistor 6. When performing a recording operation by inserting an earphone plug into the earphone jack 10, the recording signal can be monitored by the earphone, so the level display operation by the light emitting diode 17 is not necessary, and the light emitting diode 17 indicates that the tape recorder is in operation by lighting it.

In this example, the case where a light emitting diode is used as the indicator is explained, but it is of course possible to use a lamp or a mechanical meter, and it is also possible to use a light emitting diode instead of a single light emitting element. It can also be configured with

As explained above, according to the recording circuit of the present invention, the reproduction amplifier circuit is used to operate the display, so there is no need to provide a special display amplifier circuit, and the configuration is simplified. Instead, when the earphones are not used, the level or presence/absence of the signal is displayed without using a variable resistor to adjust the level of the reproduced signal, so the display operation can be performed reliably. In addition, when using earphones, the signal is guided to the earphones through a variable resistor, so it is possible to perform a monitor operation with adjustable volume, and the bias of the transistor that performs this switching operation can be connected to the BTL Since the bias is obtained from the output terminal of the amplifier circuit and the bias is controlled by inserting the earphone plug into the earphone jack, the configuration is simple and the practicality of the present invention is very high.

[Brief explanation of the drawing]

The illustrated circuit is one embodiment of the recording circuit of the present invention. Explanation of main drawing numbers, 2... Preamplifier circuit, 3...
Recording amplifier circuit, 6... variable resistor, 7... first
Reproduction amplifier circuit, 8...Second reproduction amplifier circuit, 9
... Speaker, 10 ... Earphone jack, 11, 14 ... Recording/playback switch, 12
...First control transistor, 13...Second control transistor 15...Bypass transistor, 16...Display transistor, 17...Light emitting diode.

Claims (1)

[Scope of utility model registration request] A preamplifier circuit that amplifies a recording signal obtained from a microphone or the like, a recording amplifier circuit that further amplifies the recording signal amplified by the preamplifier circuit, and a recording signal and bias oscillation from the recording amplifier circuit. In a tape recorder having a recording magnetic head for recording the recording signal onto a magnetic tape while a bias signal from the circuit is applied, a variable resistor is applied to the signal from the preamplifier circuit and adjusts the signal level. , first and second reproducing amplifier circuits to which a signal level-adjusted by the variable resistor is input and are BTL connected to each other; the first reproducing amplifier circuit and the second reproducing amplifier. a speaker connected between output terminals of the circuit; an earphone jack connected in parallel to the speaker and cutting off a signal path to the speaker when an earphone plug is inserted;
a recording/playback switch which is inserted into a signal path to the speaker and cuts off the signal path to the speaker when the switch is on the recording side; and the first playback amplifier when the recording/playback switch is on the recording side. Display means to which the output signal of the circuit or the second reproducing amplifier circuit is applied and displays its level;
It is biased by the DC voltage obtained from the output terminal of the first reproducing amplifier circuit or the second reproducing amplifier circuit and turns on, and when the earphone plug is inserted into the earphone jack, the bias is cut off. and a control transistor that is controlled by the control transistor and that when the control transistor is in the on state, outputs the output signal of the preamplifier circuit to the first regenerative amplification without passing through the variable resistor. It consists of a bypass transistor that is input to the circuit.
When the earphones are not used in a recording operation state, the bypass transistor inputs the output signal of the preamplifier circuit to the first playback amplifier circuit without passing through the variable resistor, and the display means displays the signal level; A tape recorder characterized in that when the earphones are used, the output signal of the preamplifier circuit is inputted to a first reproduction amplifier circuit via a variable resistor, so that the recording signal is monitored by the earphones. recording circuit.