JPS6144319Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a monitor circuit for a tape recorder. Conventionally, as shown in FIG. 1, a built-in condenser microphone 2 to which an operating voltage (+B) is applied via a time constant circuit 1 during use, and a reproduced output from a magnetic head 3 are sent to a preamplifier 4 and a line amplifier 5. A first amplification system 8 amplifies the signal and outputs it to a speaker 7 via an output amplifier 6, and a microphone input from an external microphone (i.e., a microphone input from an external microphone jack 9 into which the external microphone plug is inserted). It is amplified by an amplifier 10 and a buffer amplifier 11, and then output to a speaker 7 via an output amplifier 6.
The built-in condenser microphone 2 is provided with a second amplification system 12 that outputs an output to
During recording, the microphone input is supplied to the magnetic head 3 via the external microphone jack 9, the preamplifier 4 as a pre-amplifier of the first amplification system 8 , and the recording amplifier 13, and also supplies the microphone input to the magnetic head 3 through the external microphone jack 9, the preamplifier 4 as a pre-amplifier of the first amplification system 8, and the next-stage amplifier of the first amplification system 8 . A cut-off voltage (+B) was applied to the transistor 14 of the line amplifier 5 via the time constant circuit 15 to put the amplifier 5 in an inoperable state and make it impossible to monitor the speaker. Note that FIGS. 2a, b, and c show the microphone input amplifier 10,
This is an explanatory diagram of the operating state of the line amplifier 5 and the built-in condenser microphone 2, and the resistor 16 of the time constant circuit 1 provided on the built-in condenser microphone side.
The charging time constant determined by and capacitor 17 is:
When switching from the tape playback state to the recording state using the built-in condenser microphone 2 (point A in FIG. 2), the line amplifier 5 is switched so that the built-in condenser microphone 2 becomes active after the line amplifier 5 becomes inactive. Time constant circuit 1 installed on the side
The charging time constant is set to a value larger than the charging time constant determined by the resistor 18 and capacitor 19 of No. 5. Furthermore, when the recording state by the built-in condenser microphone 2 is canceled (point B in FIG. 2), the built-in condenser microphone 2 first becomes inactive, and then the line amplifier 5 becomes active.
The discharge time constant determined by the capacitor 17 of the time constant circuit 1 and the internal resistance of the built-in capacitor microphone 2 is smaller than the discharge time constant determined by the capacitor 19 and resistor 20 of the time constant circuit 15 provided on the line amplifier side. This is what has been set. However, in such a conventional circuit, when the recording state of the built-in condenser microphone 2 is canceled and the built-in condenser microphone 2 is still in the operating state (near point C in FIG. 2), the recording/playback selector switches S ₁ to S ₄ are turned off. Since the input signal is switched from the recording R side to the playback P side, the microphone input from the built-in condenser microphone 2 is amplified by the second amplification system 12 via the external microphone jack 9 and the recording/playback switch _S2 , and then output to the output amplifier. speaker 7 through 6
There was a possibility that the so-called howling phenomenon would occur, albeit momentarily. The present invention has been developed in view of these points, and one embodiment thereof will be described below with reference to the drawings. Note that parts that are the same as those in the prior art will be given the same drawing numbers and their explanations will be omitted. That is, as shown in FIG. 3, the circuit of the present invention includes the base of the transistor 21 of the microphone input amplifier 10 as a pre-stage amplifier of the second amplification system 12 and the capacitor 19 of the time constant circuit 15 on the line amplifier side.
are connected through a diode 22 and a resistor 23, and when recording with the built-in condenser microphone 2, a cut-off voltage is also applied to the transistor 21 of the microphone input amplifier 10 as a pre-stage amplifier of the second amplification system 12 through a time constant circuit 24 . (+B)
is applied to put the amplifier 10 into a non-operating state. Incidentally, FIGS. 4a, 4b, and 4c are explanatory diagrams of the operating states of the microphone input amplifier 10, line amplifier 5, and built-in condenser microphone 2, respectively, of the circuit of the present invention. Therefore, according to the circuit of the present invention, when the recording state by the built-in condenser microphone 2 is canceled, the microphone input amplifier 10 as a pre-stage amplifier of the second amplification system 12 is connected to the microphone input amplifier 10 for a certain period of time (i.e., the capacitor Since the built-in condenser microphone 2 can be inactivated for a period of time (the discharge time constant determined by the resistor 23 and the discharge time constant determined by the resistor 23), the recording/playback selector switch S ₁
~Even if _S4 is switched from the recording R side to the playback P side,
Capacitor 19 and resistor 23 of the time constant circuit 24
By setting the discharge time constant determined by
There is no possibility that the microphone input from the built-in condenser microphone 2 will be outputted to the speaker 7 via the external microphone jack 9, the recording/playback switch _S2 , and the second amplification system 12 . That is, there is no possibility that the built-in condenser microphone 2 will cause howling when the recording state of the built-in condenser microphone 2 is canceled. In this embodiment, the charging and discharging time constants of the time constant circuit 24 on the microphone input amplifier side are set to the same values as the charging and discharging time constants of the time constant circuit 15 on the line amplifier side. It is not limited to this. As described above, the circuit of the present invention includes a built-in condenser microphone to which an operating voltage is applied during use, a first amplification system that amplifies the reproduced output from the magnetic head and outputs it to the speaker via the output amplifier.
A second amplification system is provided for amplifying the microphone input from the external microphone and outputting it to the speaker via the output amplifier, so that the playback output from the magnetic head and the microphone input from the external microphone are mixed during tape playback. , when recording with the built-in condenser microphone, the microphone input is supplied to the magnetic head via the external microphone jack and the preamplifier of the first amplifier system, and
In a tape recorder in which a cut-off voltage is applied to the transistor of the next-stage amplifier in the amplification system so that the amplifier is in an inoperable state and speaker monitoring is disabled, when recording with the built-in condenser microphone, the transistor of the previous-stage amplifier of the second amplification system is also affected. A cut-off voltage is applied through a constant circuit to put the amplifier in an inoperable state, and when the recording state by the built-in condenser microphone is released, the preamplifier in the second amplification system is inactivated for a certain period of time through a time constant circuit. Since the built-in condenser microphone is in the operating state and configured so that the microphone input from the built-in condenser microphone is not output to the speaker via the external microphone jack and the second amplification system, the built-in condenser microphone There is no possibility that howling will occur due to the microphone, and this effect has extremely high practical value in increasing the product value.

[Brief explanation of the drawing]

FIG. 1 is a conventional circuit diagram, FIG. 2 is an explanatory diagram of its operating state, FIG. 3 is a circuit diagram of the present invention, and FIG. 4 is an explanatory diagram of its operating state. 2... Built-in condenser microphone, 3... Magnetic head, 4... Preamplifier, 5... Line amplifier, 6... Output amplifier, 7... Speaker, 8 ...
First amplification system, 10...Microphone input amplifier, 12
...Second amplification system, 24 ...Time constant circuit.

Claims (1)

[Scope of utility model registration request] A built-in condenser microphone to which operating voltage is applied during use, and a first microphone that amplifies the playback output from the magnetic head and outputs it to the speaker via an output amplifier.
It is equipped with an amplification system and a second amplification system that amplifies the microphone input from the external microphone and outputs it to the speaker via the output amplifier, and mixes the playback output from the magnetic head and the microphone input from the external microphone during tape playback. let them do it;
When recording with the built-in condenser microphone, the microphone input is supplied to the magnetic head via the external microphone jack and the pre-stage amplifier of the first amplification system, and a cut-off voltage is applied to the transistor of the next-stage amplifier of the first amplification system to disable the amplifier. In a tape recorder in which speaker monitoring is disabled as an operating state, a cut-off voltage is also applied to a transistor of a pre-stage amplifier of the second amplification system via a time constant circuit to place the amplifier in an inoperable state when recording with the built-in condenser microphone. Then, when the recording state by the built-in condenser microphone is released, the preamplifier of the second amplification system is made inactive for a certain period of time through a time constant circuit, and the microphone input from the built-in condenser microphone is connected to the external microphone jack and the second amplifier. A monitor circuit for a tape recorder characterized in that it is configured so that the output is not output to a speaker via an amplification system.