JPH0637549A - Power amplifier unit and noise elimination circuit - Google Patents

Abstract

PURPOSE:To provide a noise elimination circuit capable of automatically eliminating a set noise such as a tone (Sharh), etc., remaining when sound volume is stopped or a residual noise, or noises that exist among plural pieces of music recorded on a cassette magnetic tape, etc. CONSTITUTION:Plural switching circuits 22 with different voltages are arranged in parallel on a switching means 23 so as to apply the voltage generated conforming to the level of an audio signal by a voltage generation circuit 21, and a cutoff frequency can be varied corresponding to the size of the level of the audio signal by a cutoff control circuit 30 comprised of capacitors C1, C2,..., Cn connected in series to the switching circuits 22, and grounded by a switching operation, and a resistor R connected commonly to the capacitors C1, C2,..., Cn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separate type power amplifier unit in which a control unit and an amplifier unit are separately provided, and a set noise such as a "shear" sound remaining when the volume control is turned down or residual noise. The present invention relates to a noise removing circuit for removing noise or noise existing between a plurality of songs recorded on a cassette magnetic tape.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 5, there is a separate type power amplifier unit 3 having a control unit 1 and an amplifier unit 2.

The control unit 1 is provided with a microcomputer 5 which electrically takes in a rotary click of the electronic volume 4. The audio signal converted by the DA converter 6 through the microcomputer 5 is input to the mute circuit 7 provided in the amplifier unit 2 through the audio signal line L1.

On the other hand, the microcomputer 5 detects when the electronic volume 4 is in the minimum volume state, and mutes the residual noise superimposed on the audio signal output from the audio signal line L1 by the mute circuit 7. Is set so as to output a mute control signal for this purpose via the mute signal line L2.

For example, if the residual noise of the audio signal input to the mute circuit 7 is 0.2 mV when the electronic volume 4 is in the minimum volume state, 0.2 mV or less with this voltage as the reference voltage. The mute circuit 7 removes the residual noise by muting.

The audio signal output from the mute circuit 7 is output to the speaker 9 via the amplifier 8.

In the power amplifier unit 3 configured as described above, in order to remove the residual noise in the mute circuit 7, in addition to the audio signal line L1 for inputting the audio signal, the mute control signal is supplied. In addition to requiring a dedicated cable for the mute signal line L2 for inputting the signal, it is necessary to provide terminals for connecting the dedicated cable to both the control unit 1 and the amplifier unit 2, resulting in a product cost. In addition, there is a problem that the working cost becomes high.

Therefore, in order to efficiently remove residual noise without providing a dedicated line between the control unit 1 and the amplifier unit 2, a mute circuit for removing an audio signal, a voltage of the audio signal, and a preset voltage are preset. It is conceivable that the power amplifier unit is provided with a control means which compares the reference voltage with the reference voltage and outputs a mute control signal to the mute circuit when the voltage of the audio signal is smaller than the reference voltage.

[0009]

However, in the power amplifier unit configured as described above, there is a possibility that the desired signal may be unnecessarily muted depending on the setting of the drive level. is there.

The present invention has been made in view of the above circumstances, and is set noise or residual noise such as a "shear" sound remaining when the volume is reduced without changing the frequency characteristic at a normal volume, or An object of the present invention is to provide a separate type power amplifier unit capable of removing noise and the like existing between a plurality of songs recorded on a cassette magnetic tape, and a noise removing circuit.

[0011]

In order to achieve the object, the invention according to claim 1 is a separate type power amplifier unit in which a control unit and an amplifier unit are provided separately, and the amplifier unit is The present invention is characterized in that it is provided with a detection means for detecting the magnitude of an audio signal and a cutoff control means set to control the cutoff frequency according to the level detected by the detection means. . According to the invention of claim 3, a voltage generating circuit for generating a DC voltage corresponding to the level of the audio signal and a switching voltage set so that the voltage generated by the voltage generating circuit is applied. Voice cutoff control having switching means in which a plurality of different switching circuits are arranged in parallel, capacitors connected in series to the respective switching circuits and grounded by a switching operation, and resistors commonly connected to the capacitors And a cutoff frequency is changed according to the level of the audio signal.

[0012]

In the above-mentioned structure according to claim 1,
In the amplifier unit of the separate type power amplifier unit in which the control unit and the amplifier unit are separately provided, the cutoff control unit controls the cutoff frequency according to the magnitude of the audio signal detected by the detection unit.

Thus, instead of completely muting the sound, it is possible to increase the high cut amount as the volume decreases and cut only the offensive "shear" sound.

In the structure according to claim 3,
A plurality of switching circuits having different switching voltages are arranged in parallel to the switching means so as to apply the voltage generated corresponding to the level of the audio signal by the voltage generating circuit, and each switching circuit is connected in series and switched. The cut-off frequency is changed according to the level of the audio signal by the audio cut-off control means composed of the capacitor grounded by the operation and the resistor commonly connected to the capacitor.

[0015]

Embodiments of the present invention will now be described with reference to FIGS.

(First Embodiment) FIG. 1 is an explanatory view of a noise removing circuit showing an essential part of a power amplifier unit of the present invention, FIG.
2 shows a waveform diagram of a main part, and FIG. 2 (a) is a part of FIG.
(B) corresponds to the part B in FIG. 1, respectively. FIG. 3 is a block diagram showing a schematic configuration of the power amplifier unit of the present invention.

In FIG. 3, the power amplifier unit 10
Is a separate type including a control unit 11 and an amplifier unit 12. Further, the control unit 11 and the amplifier unit 12 are connected by an audio signal line 13, and an audio signal is sent from the control unit 11 to the audio signal line 13.
Is output to the amplifier unit 12 via.

The amplifier unit 12 is roughly composed of a buffer amplifier 14, a mute circuit 15, and an amplifier 16.

The mute circuit 15, as shown in FIG.
Detection circuit (detection means) 20 for detecting the frequency of the audio signal (voice signal) output from the buffer amplifier 14.
And a cutoff control circuit 30 (cutoff control means) that cuts off a frequency determined to be noise among frequencies corresponding to the level detected by the detection circuit 20.

The detection circuit 20 includes a voltage generation circuit 21 for generating a DC voltage corresponding to the level of the audio signal, and a plurality of different switching voltages set so that the voltage generated by the voltage generation circuit 21 is applied. And a switching means 23 in which the switching circuits 22, 22 ... Are arranged in parallel.

The voltage generating circuit 21 includes a buffer amplifier 14
From the current conversion circuit 21a for converting the AC voltage output from the DC voltage into the DC voltage, and the inverting circuit 21b for inverting the waveform of the DC voltage converted by the current conversion circuit 21a into the waveform shown in FIG. Become.

The switching circuits 22, 22 ... Have diodes D1, D2 ... Dn and diodes D1, D2.
Transistors T1, T2 ... Tn connected in series to Dn
And consists of. The switching means 23 is set to be in a high cut (maximum interruption value) when the signal becomes a non-signal (or below a certain level).

When the output from the inverting circuit 21b is small, the diodes D1, D2 ... Dn are sequentially turned off.
Then, the speaker 17 outputs a voice.

On the other hand, when the output from the inverting circuit 21b is large, as the output increases, the diode D1 and the diode D2 correspond to the output level.
... The diodes Dn are turned on in this order,
The transistors T1, T2 ... Tn are turned on in a state in which a predetermined amount of shift-up (for example, 0.7 V) is performed corresponding to the diodes D1, D2 ... Dn.

The cutoff control circuit 30 includes each transistor T
1, a plurality of capacitors C connected in series to T2 ... Tn
1, C2 ... Cn, and a resistor R commonly connected to the capacitors C1, C2 ... Cn.

Then, a certain switching circuit 22 is turned on.
In this state, by this switching operation, the capacitors C1, C2 ... Cn are grounded correspondingly, the audio signal of a certain frequency band judged as noise is cut off, and the noise is not output from the speaker 17. There is.

(Second Embodiment) By the way, the noise removing circuit (mute circuit 15) of the present invention is not limited to the hardware implementation as shown in FIG. It is also possible to adopt a configuration as shown in.

The noise removing circuit 45 shown in FIG. 4 detects a frequency of an audio signal (voice signal) output from the buffer amplifier 14, and a frequency corresponding to the level detected by the detecting circuit 50. A cutoff control circuit 60 that cuts off a frequency determined to be noise.

The detection circuit 50 includes a current conversion circuit 51 for converting the AC voltage output from the buffer amplifier 14 into a DC voltage, and an A / D converter 52 for converting an analog signal from the current conversion circuit 51 into a digital signal. , A / D converter 5
2 and a control circuit (CPU) 53 that outputs a signal in accordance with the digital signal output from the device 2.

The cutoff control circuit 60 includes capacitors c1 and c
2 and a resistor r commonly connected to the capacitors c1 and c2, and a transistor t1 which is turned on in response to an output signal from the control circuit 53 and is connected in series to the capacitor c2. When it is determined that the noise is generated, the transistor t1 is turned on to remove the noise.

[0031]

As described above, according to the present invention, the set noise and residual noise such as "shear" sound remaining when the volume control is turned down or the cassette magnetic tape can be achieved without changing the frequency characteristic at the normal volume. It is possible to automatically remove noises existing between a plurality of recorded songs.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a noise removing circuit of the present invention.

2A and 2B show waveform charts of a main part, FIG. 2A corresponding to a part of FIG. 1 and FIG. 2B corresponding to a part of FIG.

FIG. 3 is a block diagram showing a schematic configuration of a power amplifier unit of the present invention.

FIG. 4 is an explanatory diagram of a noise removing circuit according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a schematic configuration of a conventional power amplifier unit.

[Explanation of symbols]

 10 power amplifier unit 11 control unit 12 amplifier unit 20 detection circuit (detection means) 21 voltage generation circuit 22 switching circuit 23 switching means 30 interruption control circuit (interruption control means)

Claims (3)

[Claims] 1. A separate type power amplifier unit in which a control unit and an amplifier unit are provided separately, wherein the amplifier unit is a detection unit for detecting the magnitude of an audio signal, and the detection unit detects the detection unit. A power amplifier unit, comprising: a cut-off control unit set to control the cut-off frequency according to a level. 2. The detecting means is different in a voltage generating circuit for generating a DC voltage corresponding to the level of the audio signal and a switching voltage set so that the voltage generated by the voltage generating circuit is applied. A switching circuit in which a plurality of switching circuits are arranged in parallel, wherein the cutoff control means is connected in series to each of the switching circuits and is grounded by this switching operation, and is commonly connected to the capacitors. The power amplifier unit according to claim 1, wherein the power amplifier unit comprises a resistor. 3. A voltage generating circuit for generating a DC voltage corresponding to the level of an audio signal, and a plurality of switching circuits having different switching voltages set so that the voltage generated by the voltage generating circuit is applied. A switching means arranged in parallel; a capacitor connected in series to each of the switching circuits and grounded by a switching operation; and a voice interruption control means having a resistor commonly connected to the capacitor, A noise removal circuit characterized in that the cutoff frequency is changed according to the level of an audio signal.