JPS6030855Y2 - Tape recorder monitor circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a monitor circuit for a tape recorder, and is designed to smoothly switch the speaker monitor circuit in accordance with the insertion and removal of an external microphone.

Conventionally, as shown in FIG. 1, when using a built-in condenser microphone 1, an operating voltage B is applied to the built-in condenser microphone 1 via a changeover switch 2, and a cut-off voltage B is applied to a transistor 4 of an output amplifier 3.
was applied to the amplifier 3 to disable the speaker monitor, thereby preventing howling caused by the built-in condenser microphone 1 and the speaker 5.

. When using an external microphone (not shown), the selector switch 2 is switched from terminal 3 to terminal 4 in conjunction with the insertion/connection operation of the external microphone to cut off the voltage applied to the built-in condenser microphone 1 and the transistor 4. It was possible to monitor the speakers.

However, in the circuit configuration in which the external microphone is inserted or removed, the rise or fall of the cut-off voltage cut off or applied to the base of the transistor via the changeover switch becomes rapid, and the speaker There was a risk that more popping noise would occur.

The present invention was developed in view of this point, and uses an extremely simple circuit configuration to prevent the pop noise that occurs when inserting and removing an external microphone, and to ensure smooth switching of the speaker monitor circuit. It is.

A circuit embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows a schematic wiring diagram of the monitor circuit of the present invention.

11 in the figure is a movable contact 11 and a fixed contact 12.13
A voltage element B is always applied to a movable contact 11 of the changeover switch 10, and a built-in microphone and a resistor JUTt, which will be described later, are applied to one fixed contact 12.
Transistor T1 of output amplifier 15 via time constant circuit 14 consisting of R2 and capacitor C1 and diode D1.
The base a of is connected.

Reference numeral 16 denotes a built-in condenser microphone to which the operating voltage B is applied from the fixed contact 12, and the microphone jack 11 whose output side is grounded via a voltage dividing resistor R3.
The fixed contact 18 connects the always connected movable contact 19 of the microphone jack to the preamplifier 21 via a coupling capacitor 20.

Further, the output side of the preamplifier 21 is connected to a recording magnetic head 22.
and is connected to the output amplifier 15.

Therefore, when an external microphone (not shown) is not inserted and connected to the microphone jack 17 through its plug, the movable contact 11 of the changeover switch 10 is connected to one fixed contact 12, and the external microphone is connected to the microphone jack 17 through its plug. When inserted and connected via the plug, the movable contact 11 of the changeover switch 11 is connected to the other fixed contact 13.

The time constant circuit 14 controls the cut-off voltage 10 B applied to the base a of the transistor T□ by the changeover switch 11, which is switched in conjunction with the insertion/removal operation of the external microphone. The values of resistors R1, R2 and capacitor C1 are set so that the discharge time constant determined by R2 and capacitor C1 is delayed and the voltage is gradually cut off, and when the external microphone is removed, the charge time constant determined by resistor R1 and capacitor C1 is applied slowly. It is set.

The present invention is constructed as described above, and its operation will be explained below.

In Fig. 2, when recording is being performed using the built-in condenser microphone 16 without inserting and connecting an external microphone to the microphone jack 11 through its plug, the selector switch 10 is connected as shown in the drawing, and the output A cutoff voltage of 1 B is applied to the base a of the transistor T□ of the amplifier 15, and an operating voltage of 1 B is applied to the built-in condenser microphone 16.

Therefore, the output amplifier 15 is in an inactive state, and speaker monitoring cannot be performed when the built-in condenser microphone 16 is used.

Therefore, there is no risk that the built-in condenser microphone 16 will pick up the sound emitted from the speaker 23 and cause howling.

Next, when an external microphone is inserted and connected to the microphone jack 11 via its plug and the external microphone is used to record, the signal from the built-in condenser microphone 16 is connected to the fixed contact 1 of the external microphone jack 11.
8 and the movable contact 19, the output is no longer sent to the preamplifier 21, and the movable contact 1 of the changeover switch
1 is switched to the fixed contact 13 side, and the operating voltage 1 B is no longer supplied to the built-in condenser microphone 16.

and the base B1 of the transistor T1 of the output amplifier.
The cutoff voltage 10B applied to the time constant circuit 1
4, the signal is cut off with a gradual fall delayed by a certain period of time.

Therefore, when using an external microphone, the output amplifier 15
operates, and the output signal from the external microphone is monitored by the speaker via the preamplifier 21 and the output amplifier 15.

Even when the external microphone is removed, the time constant circuit 14 applies the cutoff voltage to the base B of the transistor T1 of the output amplifier with a certain time delay and a gradual rise.

Therefore, the base voltage of the transistor of the output amplifier will not change suddenly when the external microphone is inserted or removed, eliminating the possibility of pop noise coming from the speaker when the monitor circuit is switched due to the insertion or removal of the external microphone. I can do it.

As described above, according to the device of the present invention, when using the built-in condenser microphone, a cut-off voltage is applied to the transistor of the output amplifier via the time constant circuit, and the output amplifier is rendered inactive, making it impossible to monitor the speaker. This makes it possible to prevent sudden changes in the base voltage of the transistor when switching the speaker monitor circuit due to the insertion and removal of an external microphone, thereby eliminating pop noise caused by sudden application or interruption of the cutoff voltage. The effect is of great practical value.

[Brief explanation of the drawing]

FIG. 1 is a schematic wiring diagram of a conventional monitor circuit, and FIG. 2 is a schematic wiring diagram of the monitor circuit of the present invention. 10... Selector switch, 14... Time constant circuit, 15... Output amplifier, 16...
・Built-in condenser microphone, 17...Mic jack, T□...Transistor, 10B...
...W.

Claims (1)

[Scope of utility model registration request] When using the built-in condenser microphone, an operating voltage is applied to the built-in condenser microphone via the selector switch, and a cut-off voltage is applied to the transistor of the output amplifier to disable the amplifier and make it impossible to monitor the speaker, allowing use of an external microphone. In a tape recorder with a built-in microphone, in which the changeover switch is switched in conjunction with the insertion/connection operation of the external microphone, and the voltage applied to the built-in condenser microphone and the transistor is cut off to enable speaker monitoring, A monitor circuit for a tape recorder, characterized in that a cutoff voltage is applied to a transistor of an output amplifier via a time constant circuit consisting of a resistor and a capacitor.