JPS6131369Y2 - - Google Patents

Description

[Detailed explanation of the invention] This invention relates to a volume adjustment circuit used in small tape recorders, etc. Specifically, the volume adjustment is achieved by synergistic effect with the bias supply circuit of the electronic switch circuit using a CMOS inverter that switches between recording and playback. It is related to circuits.

Conventional variable resistors used to adjust the volume of audio equipment such as small tape recorders cut out direct current components to prevent noise generated when the resistors are sliding or fixed. Therefore, a capacitive element was installed before and after the variable resistor. This caused problems such as an increase in the number of parts. This invention provides a noise-free variable resistor circuit using an electronic switch circuit whose direct current can be ignored.

This invention will be explained below with reference to the drawings. The audio signal from the microphone 1 becomes the output signal of the recording amplification section 2, is supplied to the head 5 via the equalizer 3 and the bias oscillation circuit 4, and is magnetically recorded on the tape 6.
In order to monitor this audio signal, a portion of the output signal is guided to an electronic switch section 8 using an OMOS inverter. Next, regarding the playback system, tape 6
The amplifying section 7 reproduces the signal from the head 5 as the head 5 moves.
The signal is then guided to the electronic switch section 8. Here, this electronic switch is composed of two CMOS inverters, and in order to maintain the switching function, there is a variable resistor 9 having a bias resistor function to apply a bias voltage between the common sources. In the drawing, the power is supplied from the positive power source, but it may be supplied from the negative power source. Next, to explain the feature of this invention, in the above-mentioned CMOS inverter, when the transistor of one channel, N or P, is on in its switching operation, the other transistor connected in series has a high resistance that is almost infinite. is in the off state. Therefore, the condition is equivalent to that where almost no direct current flows through the variable resistor 9 and is cut off by a capacitive element. Either recording or reproduction signal is selected by this electronic switch and appears between the terminals of the variable resistor 9, the volume is adjusted by adjusting the movable terminal 9', and the signal is input to the power amplifier. This power amplifier 10 drives a speaker 11 or provides a signal to an earphone connected to a monitor jack 12 during a reproduction operation.

Also, during recording operation, the configuration is such that a signal is provided only to the monitor jack.

As explained above, the volume adjustment circuit according to this invention does not use a capacitive element for DC blocking and also has the function of supplying bias voltage to the electronic switch section, so it can be used in tape recorders, especially small ones that can be stored in pockets. This is effective for thin products.

[Brief explanation of the drawing]

The figure is a circuit diagram of a tape recorder showing the configuration of the volume adjustment circuit of this invention. 2... Recording amplification section, 7... Playback amplification section, 10...
. . . power amplifier section, 8 . . . electronic switch section, 9 . . . variable resistor.

Claims (1)

[Scope of utility model registration request] An electronic switch section that selectively connects the output of the recording amplification section and the output of the reproduction amplification section to the input of the power amplification section, and a variable resistor is installed between the input of the power amplification section and the output of the electronic switch section. 1. A volume adjustment circuit, characterized in that the variable resistor adjusts the volume and supplies a bias voltage to an electronic switch section.