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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of one example of a
conventional input circuit in a record reproducing apparatus, and FIG. 2 is a circuit diagram of
one embodiment of a manual power switching circuit according to the present invention. 1 и и и и и и
и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и output terminal, S1> ... shunt
resistor, R2yR3 ииииии ceramic for Atsuteneta resistance, R4 ииииии RIAA Ikora, organizer resistance, C0
ииииии low frequency blocking capacitor, C2, C3 иии и и и DC blocking capacitor, C4, C5 и и и и и и и RIAA
equalizer condenser, Ql и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и drive
transistor, Q2 и и и и и и и impedance variable transistor, R5 и и и и и и и Fixed resistance, R6 to R8 и и и и и и
и и и и и и и и и и и и и collector resistance, vR1, vR2 и и и и и и и и volume setting volume resistance, PL и и и
high Lot lamp, Rc ... и CdS cell. Fig. 1-5 = Actual opening 50-. 122202 (2) Fig. 2-1-1
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic
input switching circuit of a record reproducing apparatus, in which the outputs of a magnetic
pickup car (1) 2) one cartridge and a one monolithic pink up cartridge are switched and applied.
An object of the present invention is to provide a circuit capable of automatically switching input
circuits according to the level of cartridge output. There are a magnetic type and a ceramic type
in the player knob up cartridge in the stereo record reproducing apparatus, and recently there
are many cases where the reproducing terminal has an input terminal for the magnetic ic in
addition to the input terminal for the ceramic type cartridge. It is coming. FIG. 1 shows only one
channel of the input circuit in the conventional reproduction apparatus of this type. In the figure,
l is an input terminal of a signal from the pickup cartridge, 8. Reference numeral l82 denotes an
input selector switch. The switch S1.5 ? is interlocked, and switches between contacts 1 and b
when the cartridge is of the magnetic type, and manually switches to an image of t-connection
with the contact C when the cartridge is of the ceramic type. When the switch 81 + S2 is
connected indirectly between the contacts a and b, the output of the magnetic cartridge (2) is cut
off by the capacitor C1 from the magnetic cartridge and the shunt resistance R1 and the DC
blocking capacitor C2 are cut off. Through to the equalizer amplifier 2. The characteristics of this
amplifier 2 are appropriately determined by the RIAA equalizer capacitor C4 ░ C5 and the
resistor R4. The amplified signal is further outputted from the output terminal 3 after passing
through the DC blocking capacitor C5. Meanwhile, the switch 8. In the state where +82 contacts
and between c, the output from the ceramic cartridge is attenuated by the attenuator resistor
R2rR3, and after the reproduction volume balance is taken, it is added to the equalizer amplifier
2 as described above. Because the magnetic type and the ceramic type have different output
levels and frequency characteristics, the cartridge output is added to the equalizer amplifier
through separate input circuits. However, since such a switching circuit is provided on the input
side of a high gain circuit, there are many various problems, and there are many uneconomical
problems in terms of cost. A minimum of 2 circuits and 2 contacts (3) are required, ? Click noise
is large at switching, and there is a drawback such as easy to receive inductive ham. If the above
switching method is not adopted, the characteristics of the magnetic and ceramic types adversely
affect each other, and two input terminals are required per circuit. The
Furthermore, in the case where a ceramic input circuit is provided downstream of the magnetic
equalizer, there are disadvantages such as the need for a rotary switching circuit, and the need
for a circuit having a high input impedance or a high gain. there were. The present invention
eliminates the disadvantages of the conventional circuit as described above, and one embodiment
will be described below. Usually, the output level of the ceramic cartridge is about 30 dB larger
than that of the magnetic type at IKI (z). Furthermore, at 100 KHz, when the output of the
ceramic cartridge is received with high impedance, the output level difference between the two
cartridges is about 43 dB, taking into account the RIAA recording characteristics of the magnetic
store. Therefore, the system input circuit can be electrically switched by detecting this output
level difference (1). In general, the dynamic range for the reference output of the cartridge is as
dBe degree, so it is possible to provide an operating boundary line between the ceramic cartridge
and the magnetic cartridge at about -35 dB of the maximum output. However, in this case, since
the output levels of both cartridges approach in the region higher than I KHz, it is necessary for
the detection circuit of the output level difference to cut an input signal having a frequency of 1
KHz or more. If switching is performed by detecting the output level difference, for example,
even if a ceramic cartridge is used, the signal level drops in the non-modulated band between
record songs, and switching to a magnetic type input circuit generates noise and hum. Therefore,
it is also necessary to drop the cartridge output to the ground when there is no signal. FIG. 2
shows a circuit diagram of one embodiment of the circuit according to the present invention
constructed on the basis of the above principle. In FIG. 2, when no signal from the cartridge is
applied to one input terminal 1, page of the drive transistor Q1 is shown. This transistor Q is
turned off since no input is input to the first (5) gate. Therefore, a current flows from the tens
Btm through the resistor R8, the pilot lamp PL, the volume resistor 2, and the resistor R9 to the
ground, and the pilot lamp PL is turned on. For this reason, the impedance of the
photoconductive element provided close to the pilot lamp PLK, for example, the Cd8 cell Rc
becomes nearly zero. That is, when the cartridge output is zero as in the record music, the input
terminal 1 is grounded through the DC blocking capacitor C and the CdS cell Rc, and the scratch
noise can be eliminated. Incidentally, they are bias resistors of R6 ░ R and R811 transistor Q.
Next, when the ? force of the ceramic cartridge is applied to the input terminal l, this output
signal is applied to the base of the transistor Q, via the DC blocking capacitor C7 and the volume
resistor I. The volume resistor VR is used to adjust the level of the cartridge output, and the
capacitor C6 is inserted to cut the high frequency component such as 700 Hz in the cartridge
output. The above signal (6)-) 2 to which the signal is applied and the transistor Q perform tube
amplification, and the voltage between the collector and the emitter drops, so that the pilot lamp
PL is turned off. Therefore, the impedance of the Cd8 cell Rc becomes extremely large. Transistor
Q at the same time. Since the potential of the collector of 0, that is, the point 0 increases in the
positive polarity direction, the transistor 1 for variable impedance changes from the cutoff state
to the on state. Therefore, the impedance between the collector and the emitter of the transistor
Q drops extremely, and becomes almost% value when the resistor R5 is inserted between the
input terminal 1 and the ground. If the value of the resistor R5 is selected to be ?, the level of
the input signal is attenuated to a broad width, and the low frequency characteristic drops. Next,
when a low level bias from the magnetic cartridge is applied to the input terminal l, the transistor
Q is in an amplification state, but the voltage between its collector and emitter does not drop
extremely, so the pilot lamp PL Light. In this case, the value t of the volume resistance 2 is
adjusted to adjust the brightness of the pilot lamp PL and to adjust the distance between the
lamp PL and the CdS cell (7) -hel Rc, thereby adjusting the impedance of the Cd8 cell Rc. By
changing the impedance, the impedance seen from the input terminal 1 to the input circuit is set
to a threshold of about 50 ?. Thus, according to the present invention, the input impedance of
the input circuit can be automatically switched to a low impedance in the case of a ceramic
cartridge and to a high impedance in the case of a magnetic cartridge. Further, the frequency
characteristic of the output from the magnetic cartridge can be corrected by hM according to the
RIAA characteristic curve of the equalizer amplifier 2. Incidentally, in order to cause the abovementioned operation like O, it is mandatory to add the human power in-dance of the equalizer
amplifier 2 in advance, and the transistor Q7. There is also a need to increase the human
impedance of the drive circuit of f, ?. Since the cartridge ? output has a large level difference in
the low region in the nest, a low frequency F waver is formed by the gerium resistance R R and
capacitor C4, and the first frequency of 700 Hz or less in the above output is taken out,
According to the magnitude of the signal, the transistor Q2 is recommended to be switched off
(8) 1)!
Each constant is selected so that it can be produced. As described above, in the input automatic
switching circuit according to the present invention, the resistor and the impedance variable
transistor are inserted in series between the input terminal of the signal from the cartridge and
the ground, and the photoconductive element is connected in parallel with this series circuit. To
change the impedance of the photoconductive element according to the voltage between the
collector and the emitter of the transistor driven by the low frequency component of the input
signal, and to change the impedance according to the collector potential of the drive transistor.
Since it is configured to control the impedance of the transistor, when the input signal is zero, the
input terminal and the ground are short-circuited, so that the scratch noise between the songs
can be eliminated, and the ceramic cartridge When a high level signal is applied from the input,
the input impedance drops and the magnetic cart Tsu when a low level signal from the di is
applied less noise for switched automatically switching as the input impedance becomes higher
sheet, etc. that can make easily the operation and has a number of features. ????
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