JPH0119476Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a karaoke device with an FM receiver.

FIG. 1 shows part of a conventional karaoke device with an FM receiver. The output of the FM receiving section 1 and the output of the cassette deck section 9 are mixed by a mixer 10 to obtain a karaoke output with mixed audio at an output terminal 11. The configuration inside the FM receiver section 1 is the same as that of a normal FM receiver, and the front end section consists of an RF amplifier 3, a mixer 4, and a local oscillator circuit 5, and the FM demodulation circuit 7 performs FM demodulation via an IF circuit 6. The resulting signal is introduced into the audio signal mixer 10 via the muting circuit 8. Further, a control signal that detects the presence or absence of a carrier wave is sent to the muting control signal terminal M of the FM demodulation circuit 7, and this signal controls the muting circuit 8, and when there is no carrier wave, the output of the muting circuit 8 is cut off. do. Here, the output of terminal M is resistor 1
Smoothing is performed by a time constant circuit consisting of 5 capacitors 17 and 16. The capacitor 17 serves to pass high frequency components leaking to the terminal M, and the large capacitor 16 serves to smooth the audio signal component appearing at the M terminal and convert the control signal to DC. The audio signal component appearing at this M terminal is almost non-existent when the modulation depth is shallow, but as the modulation depth becomes deeper, the IF
It becomes larger as it exceeds the passband width of the circuit. If the modulation depth is less than 100% as stipulated by the Broadcasting Act, the IF circuit will
A bandwidth of 180KHZ is sufficient, but the modulation degree of wireless microphones often exceeds 400% when used in karaoke etc.
630KHZ or higher is required. It is difficult in practice to provide an IF circuit with such a wide bandwidth because the selectivity decreases and it becomes susceptible to interference. For this reason, a capacitor 16 is inserted to remove the signal component of the muting control signal terminal to increase the time constant.

However, in karaoke, etc., it is often necessary to turn off the carrier wave output of a wireless microphone, and the very loud pop noise that occurs when it is turned off delays the operation of the muting circuit due to a large time constant. Therefore, there is a drawback that pop noise is not removed.

The present invention aims to eliminate such drawbacks.

FIG. 2 shows an embodiment of the present invention. In the figure, parts that operate in the same way as in FIG. 1 are designated by the same numbers and their explanations will be omitted. 12' is a voltage variable local oscillator circuit, 13 is a negative feedback circuit, 14 is a switch circuit, mixer 4, IF circuit 6, FM demodulation circuit 7,
An FM negative feedback loop is formed by the negative feedback circuit 13 and the local oscillator circuit 12'. Capacitor 16 in FIG. 1 is removed.

In the above configuration, the modulation degree of karaoke is
400%, stipulated in the so-called Broadcasting Act.
If you configure an IF circuit with a bandwidth equivalent to 100% modulation, and apply approximately 11 dB of FM negative feedback, equivalently
This means that the IF passband width has been expanded to 630KHZ.
Therefore, the selectivity is not degraded and no audio signal component is generated at the muting control terminal. Therefore, there is no need to smooth the audio signal component, there is no delay in the operation of the muting circuit, and it is possible to cut off pop noise when the wireless microphone is turned off. The audio signal component appearing at the muting control signal terminal M varies somewhat depending on the circuit configuration or variations in the mixer 4, IF circuit 6, FM demodulation circuit 7, etc., so the amount of FM negative feedback depends on the modulation level at which the audio signal component appears. It may be increased or decreased. The switch 14 is controlled by the dotted arrow to cut off the negative feedback signal when no cassette tape is attached to the cassette deck section 9. Therefore, when receiving normal FM broadcasts, if you remove the cassette tape, you can listen to the FM broadcasts without applying negative FM feedback.

As described above, according to the present invention, in a karaoke apparatus that transmits singing voices using a wireless microphone, the generation of pop noise can be extremely reduced even if the wireless microphone is frequently turned on and off, and its practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional example, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. 1...FM receiving section, 12'...Local oscillator, 1
3... Negative feedback circuit.

Claims (1)

[Scope of utility model registration request] a wireless microphone, an FM receiving section that receives an FM modulated wave transmitted by the wireless microphone and demodulates it to obtain an audio signal, and a recording/playback section;
means for mixing the output of the FM receiving section and the output of the recording/playback section and outputting the mixture to an output terminal;
It detects that the level of the intermediate frequency signal in the receiving section is below a predetermined level, and uses this detection output to
In the karaoke apparatus, the FM demodulated audio signal is supplied to the local oscillation circuit of the FM receiver via a switch circuit. An FM receiving section characterized in that it has an FM negative feedback means for feeding back, and a control means for controlling the switch circuit on and off depending on whether or not the karaoke is being used, and these means apply the FM negative feedback when the karaoke is being used. Includes karaoke equipment.