JPS6040968Y2 - Tape recorder input circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the input circuit of a tape recorder in which a preamplifier device and a recording device are separated and each device has a built-in buffer amplifier.

The circuits of the preamplifier device and recording device of a conventional tape recorder of this kind are configured as shown in FIG.
The parts surrounded by two-dot chain lines on the right show block diagrams of the recording device 2, respectively.

3 is a selection switch for selecting input from the tuner 4, record player 5, and other external equipment 6, and the movable contact piece 7 of the selection switch 3 is a recording/playback selection switch (hereinafter referred to as R-P).
It is connected to a recording side terminal 12 of a switch (referred to as a switch) 8, and is also connected to a recording output terminal 9 of the preamplifier device 1.

The movable contact piece 10 of the R-P switch 8 is a variable resistor VR.
1 to the input side of a preamplifier 11, and the output side of the preamplifier 11 is connected to a main amplifier (not shown).

Further, the reproduction side terminal P of the R-P switch 8 is connected to the output side of a buffer amplifier 12, and the input side of the buffer amplifier 12 is connected to the reproduction input terminal 13 of the preamplifier device 1 via a resistor RIN1.

14 is a buffer amplifier whose input side is connected to the input terminal 15 of the recording device 2 via a resistor RIN2, and the output side of the buffer amplifier 14 is connected to the input side of the recording amplifier 16 via a variable resistor VR2. and the recording amplifier 1
The output side of the recording device 6 is connected to a recording/playback head (not shown), and is also connected to the output terminal 17 of the recording device 2.

Note that the recording output terminal 9 of the preamplifier device 1 and the input terminal 15 of the recording device 2, as well as the playback input terminal 13 and output terminal 17, can be connected with connectors or the like, respectively.

In such a conventional example, the buffer amplifier 14 of the recording device 2
The resistance value of the resistor RIN2 interposed between the input terminal 15 and the input terminal 15 cannot be reduced.

However, if the input impedance of the recording device 2 is low, the input voltage of the buffer amplifier 14 will drop, and the output voltage from the buffer amplifier 14, which has been bias-adjusted to an appropriate input, will be distorted, and the selection switch in the preamplifier device 1 will be distorted. The signal output from the movable contact piece 7 of No. 3 is transmitted through the transmission line 18.
This is because all of the signal flows through the recording device 2 side, and the level of the input signal to the preamplifier 11 decreases.

Furthermore, if the resistance value of the resistor RIN recording amplifier 16
This causes inconvenience as the recording level from the source is lowered.

Therefore, conventionally, the resistance values of the resistors RIN and RIN2 were set high (usually 47Ω or more), but the resistors RI
N1. Since thermal noise of a level proportional to the square root of the resistance value is generated from RIN2, the resistor RIN1. R.I.
As the resistance value of N2 increases, the noise increases.

In order to solve this problem, it is conceivable to configure the buffer amplifiers 12 and 14 with emitter follower circuits as shown in FIG.

That is, a resistor RIN3 and a capacitor C1 are connected in series between the input terminal 13.15 and the base of the NPN transistor 19, and a power supply (10B) electric path is connected to the base.

Further, the power supply (10B) electric path is connected to the collector of the transistor 19 and grounded via a capacitor C8.

Further, the emitter of the transistor 19 is connected to the next stage and grounded via a resistor R2.

In this way, the buffer amplifiers 12, 14 are so-called emitter follower circuits, and the input impedance during operation is high, so the resistors RIN1. The resistance value of RIN2 can be lowered, and adverse effects caused by thermal noise can be eliminated.

However, even in such a circuit, when the buffer amplifier 12 or 14 is not operating, that is, when the power supply (10B) is O, the input impedance of the emitter follower circuit becomes low. .14 and input terminal 13.15. RI'N2
Since the resistance value of the preamplifier 11 is low, this causes a decrease in the input signal to the preamplifier 11 or the recording level from the recording amplifier 16 as described above.

The present invention solves the drawbacks of the conventional example, and even if power is not supplied to the recording device 2, that is, the buffer amplifier 14
Even when the preamplifier 1 is not operating, the sound from the external input can be heard at an appropriate level, and even when the preamplifier 1 is not powered, that is, the buffer amplifier 12 is not operating, the external input can be heard. This device is designed to record sounds from outside at an appropriate level, and one embodiment will be explained with reference to FIG.

FIG. 3 is a block diagram of the circuit of the present invention, in which switches SW1.
SW2 and resistor RIN4 or RIN5 are connected in series.

The relay 20.21 is activated by turning on and off the power supply (10B) of the buffer amplifier 12.14, and the switch SW is activated only when the power supply (10B) is on.
1 or SW2 is closed, and when it is off, it is opened and brought into a non-conducting state.

Note that other constituent parts are the same as those of the conventional example, so explanations will be omitted.

According to the present invention, even if power is not supplied to the recording device 2, the switch SW2 is in an open state at that time, so the input impedance to the buffer amplifier 14 becomes infinite, and the external input to the preamplifier device 1 The signal from the preamplifier 11 is not diverted to the recording device 2, and an input signal of sufficient level is applied to the preamplifier 11, so that appropriate sound can be heard.

Further, even if power is not supplied to the preamplifier device 1, the switch SW1 is in an open state at that time, so the input impedance to the buffer amplifier 12 becomes infinite, and the recording signal of the recording device 2 is transmitted to the preamplifier device. 1, and a recording signal of a sufficient level is applied to a recording head (not shown) to enable proper recording.

Therefore, the buffer amplifier 7 consisting of an emitter follower circuit
Adopting '12,14, the buffer amplifier 12?14
It is possible to reduce the resistance value of the resistors RIN4° and RIN5 interposed in front of the relays 20 and 20.
21 and the switches SW1 and SW2 have the effect that even if one device 1 or 2 is not supplied with power, the other device 2 or 1 will not be adversely affected.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional example, FIG. 2 is a circuit diagram showing an embodiment of a buffer amplifier, and FIG. 3 is a block diagram showing an embodiment of the present invention. 1...Preamplifier device, 2...Recording device, 12.14...Buffer amplifier, 20,2
1...Relay, swl, sw2...
Switch, RIN4. RIN5...Resistance.

Claims (2)

[Scope of utility model registration request] (1) In a tape recorder where the preamplifier and recording device are separated and each device has a built-in buffer amplifier,
Means for changing the impedance in response to power on/off of the buffer amplifier is connected between each input terminal and the buffer amplifier, and when the power of the buffer amplifier is on, the impedance of the means is changed. A tape recorder input circuit characterized in that the input circuit is low and high when it is off. (2) The means for changing the impedance in response to power on/off of the buffer amplifier is a relay switch, which is closed only when the power of the buffer amplifier is on. The input circuit of the tape recorder described in item 1.