JPH064401Y2 - Recording / playback switching circuit for tape recorder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a recording / reproducing switching circuit of a tape recorder.

(B) Conventional technology The simple recording / playback switching circuit of a conventional tape recorder is equipped with a playback amplifier and a recording amplifier, and the recording / playback head is connected to the input side of the playback amplifier or the output side of the recording amplifier via the recording / playback selector switch. It is supposed to be connected.

In such a circuit, the reproduction signal at the time of reproduction is led to the recording / reproducing head → reproducing terminal of the recording / reproducing changeover switch → reproducing amplifier → recording amplifier → recording terminal of the recording / reproducing changeover switch.

(C) Problems to be solved by the invention In the recording / playback switching circuit having the above-mentioned signal system path,
When the playback signal level during playback is high, the signal leaks from the recording terminal to the playback terminal side through the inter-terminal capacitance of the recording / playback switching switch, is input to the playback amplifier again from the playback terminal, and the loop gain becomes 1 or more. Then, there was a problem of causing an oscillation phenomenon.

In order to prevent such oscillation, it is necessary to cut the output of the recording amplifier or the power source of the recording amplifier during reproduction, and it is necessary to specially provide a switch means for this purpose.

(D) Means for Solving the Problems In view of the above-mentioned problems, the present invention is to prevent a signal leak at the time of reproduction by using an ALC circuit connected to a recording amplifier. Alternatively, a recording / playback head is selectively connected to the input side of the playback amplifier or the output side of the recording amplifier through the recording terminal, and the playback amplifier, the recording amplifier, and the recording terminal of the recording / playback selector switch are connected during playback. In the recorder, the time constant circuit connected to the output side of the recording amplifier and the first and second electrodes are connected between the input side of the recording amplifier and the ground.
An ALC circuit composed of a transistor to which the charging potential of the capacitor for determining the time constant of the time constant circuit is applied is provided in the electrode, and is interlocked with the recording / playback changeover switch between the control voltage source and the ALC circuit. A shorting type control switch is provided, and during reproduction, the capacitor is charged from the control voltage source via the control switch to make the transistor conductive, and the input signal to the recording amplifier is muted, and at the start of recording. A recording / playback switching circuit of a tape recorder, wherein the capacitor is instantly discharged by the shorting operation of the control switch to instantly bring the transistor into a non-conducting state.

(E) Operation According to the recording / reproducing changeover circuit of the present invention, a constant control voltage is supplied to the ALC circuit connected to the recording amplifier through the control switch during reproduction when the recording / reproducing changeover switch is switched to the reproducing terminal. The ALC circuit mutes and mutes the input side of the recording amplifier.

Then, at the start of recording when the recording / reproducing changeover switch is switched to the recording terminal from this reproduction, the control switch performs a shorting operation to instantly discharge the electric charge charged in the time constant determining capacitor of the ALC circuit.

After the recording / playback selector switch is switched to the recording terminal, the capacitor is charged by the rectified voltage according to the output signal of the recording amplifier, and the ALC circuit operates as ALC.

(F) Embodiments Embodiments of the present invention shown in the drawings will be described below.

(1) is a reproducing amplifier, (2) is a recording amplifier, (3) is a recording / reproducing selector switch, and (4) is an input of the reproducing amplifier (1) through a reproducing terminal (P) of the recording / reproducing selector switch (3). Side or recording / playback head connected to the output side of the recording amplifier (2) through the recording terminal (R) of the selector switch (3), (5) is a tape terminal
(Ta) and radio terminal (Ra) tape / radio changeover switch, (6) is a recording / reproduction changeover switch which is switched in conjunction with the recording / reproduction changeover switch (3), and a reproduction terminal (P) is the reproduction amplifier. It is connected to the output side of (1), and the recording terminal (R) is connected to the microphone (8) through the microphone amplifier (7).

( 9 ) is connected to the output side of the recording amplifier (2) and is a rectifier
(10), time constant determining capacitor (11) and resistor (12), NP
In an ALC circuit including an N-type ALC transistor (13), the charging potential of the capacitor (11) is applied to the base (third electrode) of the ALC transistor (13), and the collector (first electrode) is a recording amplifier ( It is connected to the input side of 2) and the emitter (second electrode) is grounded. (14)
Is a control voltage supply circuit having a control switch (15) that is switched in conjunction with the recording / playback changeover switches (3) and (6), and the control switch (15) is a shorting type playback terminal.
(P) is connected to the base of the ALC transistor (13), the recording terminal (R) is grounded, and the movable terminal is connected to the control voltage source (+ B) via the resistor (16).

Therefore, as shown in the figure, the recording / playback selector switches (3) (6),
During playback when the control switch (15) is switched to the playback terminal (P), the ALC transistor (13) is passed through the control switch (15).
A constant control voltage (+ B) is supplied to the base of the transistor, the transistor (13) becomes conductive, and the input side of the recording amplifier (2) is muted through the collector / emitter. Therefore, the playback signal from the recording / playback head (4) is amplified by the playback amplifier (1) and guided to the output amplifier, is not input to the recording amplifier (2), and is the recording terminal of the recording / playback selector switch (3). The leakage phenomenon from the (R) to the playback terminal (P) does not occur. At this time, the time constant determining capacitor (11) is charged with a predetermined potential.

Next, at the start of recording when the recording / playback selector switches (3) (6) and the control switch (15) are switched from the playback terminal (P) to the recording terminal (R) in such a playback state, the capacitor (11 The electric charge charged in () is instantaneously discharged by the shorting operation of the control switch (15) (that is, the instantaneous contact between the reproducing terminal (P) and the recording terminal (R)).

As a result, the ALC transistor (13) which has been in the conductive state until now becomes the conductive state in an instant, the recording input signal is amplified by the recording amplifier (2) and the level is controlled by the ALC transistor (13), and the recording / reproducing head (4) is Be led to.

Thus, at the start of recording, the electric charge previously stored in the capacitor (11) for ALC operation can be instantly discharged, so that the ALC transistor (13) responds to the recording signal level with an appropriate time constant. Can be operated with.
At the start of recording, if the charge stored in the capacitor (11) is not sufficiently discharged, the transistor (13) remains conductive and the input signal to the recording amplifier (2) is muted. As a result, the recording start timing is delayed. However, in this embodiment, the charge of the capacitor (11) is instantly discharged at the start of recording, so that the timing of recording start is not delayed.

(G) Effect of the invention As described above, the invention is the ALC of the recording amplifier during reproduction.
Since the circuit can be operated to mute the playback signal that enters the recording amplifier, signal leakage between terminals occurs in the recording / playback selector switch that selectively connects the recording / playback head to the playback amplifier and the recording amplifier. It is possible to prevent the oscillation phenomenon.

Then, the capacitor for the ALC operation is instantly discharged at the start of recording by the shorting operation of the control switch interlocked with the recording / playback changeover switch. Therefore, the ALC operation at the start of recording is responded to the recording signal level. It can be executed with an appropriate time constant.
Also, the timing of recording start will not be delayed.

[Brief description of drawings]

The figure is a schematic circuit diagram of the present invention. (1) …… playback amplifier, (2) …… recording amplifier, (3) (6) …… recording and playback selector switch, (4) …… recording and playback head, ( 9 ) ……
ALC circuit, (11) ... Capacitor for determining time constant, (14) ...
… Control voltage supply circuit, (15) …… Control switch.

Claims (1)

[Scope of utility model registration request] 1. A recording / reproducing head is selectively connected to an input side of a reproducing amplifier or an output side of a recording amplifier through a reproducing terminal or a recording terminal of a recording / reproducing changeover switch to reproduce the reproducing amplifier, the recording amplifier, and the recording amplifier. In a tape recorder to which the recording terminal of the recording / playback switch is connected, a time constant circuit connected to the output side of the recording amplifier,
An ALC circuit is provided which includes a transistor to which the first and second electrodes are connected between the input side of the recording amplifier and the ground, and a charge potential of the time constant determining capacitor of the time constant circuit is applied to the third electrode. A shorting type control switch interlocking with the recording / reproducing changeover switch is provided between the control voltage source and the ALC circuit, and during reproduction, the capacitor is charged from the control voltage source via the control switch to turn on the transistor. The input signal to the recording amplifier is muted by making it conductive, and at the start of recording, the capacitor is instantaneously discharged by the shorting operation of the control switch, and the transistor is instantaneously made non-conductive. A recording / playback switching circuit of a tape recorder characterized by the above.