JPH0195629A - Radio cassette recorder - Google Patents

Abstract

PURPOSE:To prevent the attenuation of a signal from being caused even in any of the radio mode and the teleco mode without requiring a changeover circuit newly by coupling a tape recorder or microphone output between an output terminal of a low pass filter circuit and an output amplifier circuit. CONSTITUTION:Low pass filter circuits 10a, 10b are operated at the radio receiver operation and gives a signal from a decoder circuit 2 to an output amplifier circuit 6, and in this case, since it is not required to insert a resistor between the filter circuits 10a, 10b and its connecting point, the output of the decoder circuit 2 is not attenuated. On the other hand, in case of a tape recorder 7 or a microphone 8, the filter circuits 10a, 10b reach a high impedance, and since no effect is given to the output of the tape recorder 7 or the microphone 8, the output of the tape recorder 7 or the microphone 8 is not attenuated. Both the outputs are not attenuated in both the radio mode and the teleco mode and any special changeover circuit is required.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a radio cassette recorder that combines a radio receiver and a tape recorder.

FIG. 3 shows a conventional circuit for selectively supplying the output of a radio decoder circuit and the tape recorder or microphone output to an output amplifier circuit in such a device.

Here, (2) is a decoder circuit of the radio (1), and its output is connected to the output terminal (3 )
(4), and a volume circuit (5) is connected to this output terminal (3) (4) via a coupling capacitor (C+) (Cz).
) and an output amplification circuit (6) as a power amplifier are connected.

A speaker (not shown) is connected to the output amplifier circuit (6). On the other hand, the output from the tape recorder (7) or microphone (8) is passed through the preamplifier (9) (a) (
b) connected to a point.

Decoder circuit (2) during radio operation (radio mode)
The stereo R and L signals applied to the output terminals (3) and (4) are supplied to the output amplifier circuit (6) through the coupling capacitor (C+) (Cz) and the volume circuit (5). On the other hand, during tape recorder or microphone operation (teleco mode), the tape recorder output or microphone output is applied to the output amplifier circuit (6) through the volume circuit (5).

■The mouth becomes "°." However, in the above conventional circuit, when the tape recorder or microphone is operating, the output level is the same as that of the radio (
There is a drawback that the resistor (R1) (R1) on the 1) side lowers the resistance. 4th to avoid this down
When resistors (R3) (R4) are added as shown in the figure, the R signal and L signal from the decoder circuit (2) are output during radio operation.
The signal level will drop.

In order to prevent a drop in the level of these two systems (radio and tape recorder or microphone output), it is possible to switch the resistor elements using a switching transistor, etc., but doing so will cause the switching circuit and control signal line to be switched. This will require a new configuration, which will complicate the configuration.

The present invention has been made in view of these points, and provides a radio/cassette recorder that does not require a new switching circuit and does not cause signal attenuation in either radio mode or telecom mode. The purpose is to provide.

In order to achieve the above-mentioned object of the invention, the present invention provides a radio/cassette recorder in which the output of a radio decoder circuit and the output of a tape recorder or microphone are selectively guided to an output amplification circuit. the first on the radio side
．． The emitter of the second transistor is connected to a common constant current source, a reactance is connected to the collector of the second transistor as an AC load, and the base of a third transistor of the emitter follower is connected to take out an output signal from the third transistor. Additionally, a low-pass filter circuit configured to feed back a predetermined amount of the emitter output of the third transistor to the base of the second transistor to obtain filter characteristics is provided, and a connection between the output terminal of the filter circuit and the output amplification circuit is provided. The tape recorder or microphone output is coupled between the two.

The Tachi-Gai filter circuit operates during radio operation and supplies the signal from the decoder circuit to the output amplifier circuit, but at that time, there is no need to insert a resistor between the filter circuit and the connection point, so the decoder circuit On the other hand, when the tape recorder or microphone is operating, the filter circuit becomes high impedance and has no effect on the tape recorder or microphone output, so the tape recorder output or microphone output is not attenuated.

1 time■ An embodiment shown in the drawings will be described below.

In Figure 1, on the radio (1) side, the decoder circuit (2
) on the output side of the low-pass filter circuit (10a) (10
b), and this filter circuit (10a) (f
In this embodiment, the output terminals (3) and (4) are connected to the output terminals (3) and (4), and the output amplifier circuit (6) is configured in the same manner as in Fig. 3. .

The filter circuits (10a) (10b) are connected to the first . Second transistor (Ts) (T
Constant current source transistor (T2) with common emitter of I)
A capacitor (C
8) is connected, and the base of the third transistor (T,) of the emitter follower is connected, and an output signal is taken out from the third transistor (T?), and a predetermined amount of the emitter output of the third transistor (T,) is connected. is configured to feed back to the base of the second transistor (TI) to obtain filter characteristics, and the first transistor (T, )
The output signal or R signal of the decoder circuit (2) is applied to the third transistor (T?) via the level shift transistor (TI), and the emitter of the third transistor (T?) is connected to the output terminal (3) or (4). In Figure 2, the transistor (rs) (
T&) constitutes a current mirror circuit. The principle of this low-pass filter circuit is described in Japanese Patent Application Laid-open No. 55-4.
5224, so I will not discuss it here.

Since the filter circuits (10a) and (10b) are provided on the radio (1) side, it goes without saying that the radio (1)
A power supply voltage (+Vcc) is applied by the operation of . Therefore, when radio (1) is deactivated, (+Vcc)
is cut out, each transistor of the filter circuit (10a) (10b) is turned off, and the filter circuit (10a) (1
0b) itself becomes a high impedance. Therefore, it does not affect the level of the signal given from the preamplifier (9).

In this embodiment, the filter circuits (10a) (10b)
is configured as a 50μs low-pass filter, but this value is based on the constant current value (10
) and the capacitance value of the capacitor (C1).

In the above embodiment, the second level shift transistor (T1
), the output signal of the decoder circuit (2) is input to the first transistor (T3), and the third transistor (T7
) is fed back to the base of the second transistor (T, ) via the second level shift transistor (T*). This has the advantage of improving voltage reduction characteristics and lowering the power supply voltage (+Vcc) to a relatively low value, but these transistors (r+) (
is) and the level shifting current sources (11) and (12) are not necessarily required, and the configuration of the filter circuit is not limited to the form shown in the drawings, but may be modified in various ways without departing from the gist of the present invention. Changes are possible.

As described above, according to the present invention, in the radio mode and the teleco mode, the outputs are not attenuated by the circuit for the other, and no special switching circuit is required. effective.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of the main parts of a radio/cassette recorder embodying the present invention, and FIG. 2 is a circuit diagram of the main parts thereof. FIGS. 3 and 4 are circuit diagrams relating to conventional examples. (1)---Radio, (2)---Decoder circuit. (6) --- Output amplifier circuit, (7) --- Tape recorder. (8)...-Microphone. (10a) (10b) -Low pass filter circuit. (T,)...first transistor. (T4) --- Second transistor. (T7) --- Third transistor. (C3)...Capacitor (reactance element).

Claims (1)

[Claims] (1) In a radio/cassette recorder in which the output of a radio decoder circuit and the output of a tape recorder or microphone are selectively guided to an output amplifier circuit, the emitters of the first and second transistors are common on the radio side. A reactance is connected as an AC load to the collector of the second transistor, and the base of a third transistor of the emitter follower is connected to take out an output signal from the third transistor, and the emitter of the third transistor is connected to the constant current source of the second transistor. A low-pass filter circuit configured to feed back a predetermined amount of output to the base of the second transistor to obtain filter characteristics is provided, and the tape recorder or microphone is connected between the output terminal of the filter circuit and the output amplification circuit. A radio/cassette recorder characterized in that outputs are combined.