JPS6141195Y2 - - Google Patents

Description

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

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. Since such a recording amplifier circuit has a built-in resistor for constant output current within the IC, the output of the amplifier circuit is sometimes too small to drive a display.

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 into which a recording signal obtained from a microphone or the like is input, 2 is a preamplifier circuit that amplifies the recording signal input to the input terminal 1, and 3 is a preamplifier circuit that amplifies the recording signal input to the input terminal 1. 4 is a bias oscillator that is activated during recording operation; 5 is a recording amplifier circuit to which the recording signal from the recording amplifier circuit 3 is applied together with a bias current from the bias oscillator 4; This is a recording magnetic head that has the function of recording the recording signal on 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 connected to each other;
A first and second reproducing amplifier circuit are BTL-connected, and are connected so that a signal level-adjusted by the variable resistor 6 is applied to the input terminal of the first reproducing amplifier circuit 7. has been done. Reference numeral 9 denotes a speaker connected between the output terminal of the first reproduction amplifier circuit 7 and the output terminal of the second reproduction amplifier circuit 8; 10 similarly denotes the first and second reproduction amplifier circuit 7;
An earphone jack 11 is connected between the output terminals of 8 and into which an earphone plug is inserted; This is a recording/playback switch that cuts off the signal path. In such a circuit, the DC potential at the output terminals of the first regenerative amplifier circuit 7 and the second regenerative amplifier circuit 8 is approximately 1/2 Vcc, where Vcc is the power supply voltage. 1
Reference numeral 2 denotes a first control transistor which is turned on by applying a DC voltage from the output terminal of the first reproducing amplifier circuit 7 when no earphone plug is inserted into the earphone jack 10, and 13 a recording/reproducing transistor. This is a second control transistor that becomes operable in the recording state by switching the changeover switch 14, and whose operation is controlled by the first control transistor 12. 1
Reference numeral 5 designates a third control transistor which is supplied with power and becomes operational when the second control transistor 13 is turned on, and which is connected as an emitter follower.The output signal of the preamplifier circuit 2 is variable at its base. The signal is applied without going through the resistor 6, and the signal is applied from its emitter 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; is,
In the recording state, the signal from the first reproduction amplifier circuit 7 or the second reproduction amplifier circuit 8 is applied to the bass by the recording/reproduction changeover switch 11. Further, the collector of the first control transistor 12 is connected to a resistor 19.
and is connected to the base of the display transistor 16 via a diode 20. Said first
A capacitor 21 connected to the base circuit of the control transistor 12 is provided to eliminate the influence of alternating current signals.

The present invention is constructed as described above, and its operation will be explained next. 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 third control transistor 15 is in an inactive state. Also, the recording/playback selector switch 14 and the resistor 1 are connected to the base of the display transistor 16.
Since the DC voltage is applied through the resistor 1
By appropriately setting the values of 8 and bias resistors 22 and 23, the power supply voltage can be checked by lighting the light emitting diode 17. In this reproduction operation state, the recording amplifier circuit 3 and the bias oscillation circuit 4 are in an inoperative state due to the action of the recording/reproduction changeover switch, and the reproduction signal reproduced by the reproduction head is input to the input terminal 1. The reproduced signal input to the input terminal 1 is sent to the preamplifier circuit 2.
After being amplified, the signal is applied to the variable resistor 6 and its level is adjusted. The signal whose level has been adjusted by the variable resistor 6 is sent to the first reproduction amplifier circuit 7.
After being amplified by the first reproduction amplifier circuit 7 and the second reproduction amplifier circuit 8, the signal is applied to the speaker 9 and is emitted. Furthermore, in such a state, 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 third control transistor 15. As a result, the third control transistor 15
becomes operational, and the signal applied to the base can be derived from its emitter, so the power signal of the preamplifier circuit 2 is transmitted to the input terminal of the first regenerative amplifier circuit 7 through the third control transistor 15. It will be input regardless of the variable resistor 6.
The signal input to the first reproduction amplifier circuit 7 is
After being amplified by the first reproduction amplifier circuit 7 or the second reproduction amplifier circuit 8, the recording and reproduction changeover switch 1
1 to the base of the display transistor 16. When an AC signal is applied to the base of the display transistor 16, the operating state of the transistor 16 changes depending on the signal level. When the operating state of the display transistor 16 changes, the current flowing through the light emitting diode 17 connected to its collector as a load changes, so that the lighting state of the light emitting diode 17 changes. Therefore, the user can recognize the level or presence/absence of the recording signal by changing the lighting state of the light emitting diode 17. 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. The output signal of the preamplifier circuit 2 is input to the first reproducing amplifier circuit 7 through the third control transistor 15 and amplified, and then applied to the display transistor 16, where the signal level is adjusted by the light emitting diode 17. 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 turned off, the second control transistor 13 is turned off, so the third control transistor 15 becomes inactive, and the resistor 19 and diode 20 are connected to the collector of the first control transistor 12.
Since a high voltage is applied to the base of the display transistor 16 through the display transistor 16, 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 reproduction amplifier circuit 7, so that the level of the signal input to the earphones is adjusted. can be adjusted by 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 there is no need for the level display operation by the light emitting diode 17, 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 signal level display circuit of the present invention, since the display is operated using the reproduction amplifier circuit, there is no need to provide a special display amplifier circuit, and the configuration can be simplified. This invention has the advantage that it is not only simple, but also that the signal level or presence/absence can be displayed without using a variable resistor to adjust the level of the reproduced signal, so the display operation can be performed reliably. has.

[Brief explanation of the drawing]

The illustrated circuit is an embodiment of the recording signal level display 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...Third control 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 receives the recording signal amplified by the preamplifier circuit and further amplifies the recording signal; and a recording amplifier that further amplifies the recording signal. In a tape recorder having a recording magnetic head for applying a recording signal from a circuit and a bias signal from a bias oscillation circuit and recording the recording signal onto a magnetic tape, the signal from the preamplifier circuit is applied and the recording signal is applied to the tape recorder. a variable resistor for adjusting a signal level; first and second reproducing amplifier circuits to which the signal level-adjusted by the variable resistor is input and connected to each other BTL;
A speaker connected between the output terminals of the reproduction amplifier circuit and the second reproduction amplifier circuit, and the signal path to the speaker is cut off when the speaker is inserted and connected in the signal path to the speaker and is on the recording side. a recording/playback selector switch; a display means to which an output signal of the first playback amplifier circuit or the second playback amplifier circuit is applied when the record/playback switch is on the recording side and displays the level thereof; and a recording state. 1. A recording level display circuit for a tape recorder, comprising switching means for inputting the output signal of the preamplifier circuit to the first reproduction amplifier circuit without passing through the variable resistor.