Write current control circuit for audio recording

A write control circuit for audio signals in a video recorder having an audio signal processor for signal processing a received audio signal in order to record the received audio signal and a video signal processor for signal processing a received video signal in order to record the received video signal, said circuit having a normal recording mode in which both the received audio and video signals are simultaneously recorded on a recording medium and the level of the received audio signal is limited to a predetermined level for recording on the recording medium, and an exclusive audio recording mode in which only the received audio signal is recorded on the recording medium, said circuit comprising:

• mode setting means for setting one of the normal recording mode and the exclusive audio recording mode under control of a user;
• a bias control circuit for adjusting the received audio signal output from said audio signal processor to decrease the level of the received audio signal in the normal recording mode so that the level of the received audio signal is no larger than the predetermined level, and for adjusting the received audio signal to allow the received audio signal to reach an optimum level in said exclusive audio recording mode;
• wherein said bias control circuit includes muting means for muting the received video signal output from said video signal processor when the exclusive audio recording mode has been set by said mode setting means, said muting means being operatively connected between said mode setting means and said video signal processor;
• wherein the output of said audio signal processor is connected to a resistor which is switchably connected to a ground potential, and wherein said bias control circuit comprises first switching means for switchably connecting said resistor to the ground potential, said bias control circuit switching off connection between said resistor and the ground potential in said normal recording mode, thereby controlling an audio signal output from said audio signal processor at said optimum level, and second switching means for switchably connecting the output of said video signal processor to the ground potential, thereby muting the received video signal output from said video signal processor;
• further comprising current control means for controlling current of said audio signal output from said audio signal processor, said current control means being operatively coupled to said first switching means;
• wherein said first switching means comprises a first transistor and protecting means for protecting said first transistor from excess current;
• and
• wherein said first transistor of said first switching means is a field-effect transistor.

A write control circuit for audio signals in a video recorder having an audio signal processor for signal processing a received audio signal in order to record the received audio signal and a video signal processor for signal processing a received video signal in order to record the received video signal, said circuit having a normal recording mode in which both the received audio and video signals are simultaneously recorded on a recording medium and the level of the received audio signal is limited to a predetermined level for recording on the recording medium, and an exclusive audio recording mode in which only the received audio signal is recorded on the recording medium, said circuit comprising:

• mode setting means for setting one of the normal recording mode and the exclusive audio recording mode under control of a user;
• a bias control circuit for adjusting the received audio signal output from said audio signal processor to decrease the level of the received audio signal in the normal recording mode so that the level of the received audio signal is no larger than the predetermined level, and for adjusting the received audio signal to allow the received audio signal to reach an optimum level in said exclusive audio recording mode;
• wherein said bias control circuit includes muting means for muting the received video signal output from said video signal processor when the exclusive audio recording mode has been set by said mode setting means, said muting means being operatively connected between said mode setting means and said video signal processor;
• wherein the output of said audio signal processor is connected to a resistor which is switchably connected to a ground potential, and wherein said bias control circuit comprises first switching means for switchably connecting said resistor to the ground potential, said bias control circuit switching off connection between said resistor and the ground potential in said normal recording mode, thereby controlling an audio signal output from said audio signal processor at said optimum level, and second switching means for switchably connecting the output of said video signal processor to the ground potential, thereby muting the received video signal output from said video signal processor;
• wherein said second switching means comprises a transistor and means for protecting said transistor from excess current;
• and
• wherein said transistor of said second switching means is a field-effect transistor.

A write control circuit for audio signals for improving a signal-to-noise ratio in an exclusive audio use write mode of a hi-fi video tape recorder having an audio mixer for mixing two audio channels in stereo into a single audio signal and a video mixer for mixing luminance and chrominance signals into a single video signal, said circuit comprising:

• muting means for muting said video signal output from said video mixer, said muting means being switchably connected between said video mixer and ground potential;
• write current control means for controlling output current of said audio mixer being supplied to a recording head, said write current control means being connected to an output of said audio mixer;
• path control means switchably connected between said write current control means and said ground potential so as to permit said write current control means to control the output current of said audio mixer;
• and
• a mode switch for controlling said muting means, when in said exclusive audio use write mode, to mute said video signal by connecting said muting means to said ground potential, and for controlling said path control means to operate in the exclusive audio use write mode by not forming a path between said write current control means and said ground potential, thereby allowing said audio signal to be supplied to said recording head without attenuation, said mode switch further controlling said path control means to form the path between said write current control means and said ground potential when the hi-fi video tape recorder is not in said exclusive audio use write mode so that the audio signal is attenuated to a predetermined level prior to being supplied to said recording head to prevent mutual interference between the audio and video signals.