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JPS5631792

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DESCRIPTION JPS5631792
BRIEF DESCRIPTION OF THE DRAWINGS The drawing is one implementation of the reproduction
equalizer circuit of this invention. An example is shown, FIG. 1 is a wiring diagram, and FIG. 2 is a
curve diagram showing the relationship between the frequency and the closed loop gain at the
time of reproduction by the MM type cartridge and the MC type cartridge, respectively. AMP ······
Equalizer amplifier, Z · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
························································································
· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · by which by using the resistor
R4 · · · DC blocking capacitor, SWl · · · first switching switch, SW2 · · · · · second switching switch.
[Detailed description of the invention] This invention provides a DC-ized reproduction feedback
system in which the negative feedback control system of the equalizer amplifier is DC at the time
of record reproduction by an MM (moving magnet) type cartridge having high output voltage
and high output impedance characteristics. By switching the input impedance and the closed '5
loop gain in the /// 2 phase tI circuit, it can be adapted also when playing back a record by the
MC (Mooching coil) type cartridge having a low output voltage OYOHI low output impedance
characteristic. The reproduction equalizer circuit, which has been In general, in a reproduction
equalization circuit which can cope with an MM-type cartridge and an MC-type cartridge by
switching one input impedance and one output impedance, respectively, an MM-type cartridge
(equalizer at the time of reproduction according to When the negative feedback control system of
the amplifier is DC, if the circuit configuration is such that the closed loop gain of the equalizer
amplifier and the negative feedback control system is simply set to one shoulder at the time of
reproduction by the MC-type cartorino gin It becomes very fat, and DC drift and ultra low-pass
noise generated by disturbances such as the inside of the equalizer amplifier and heat etc.
become very large values, and it has the disadvantage that the operation of the equalizer
amplifier and the reproduced sound are greatly affected (2 ) 18h; This device pays attention to
the above-mentioned conventional problems, and connects the resistance for gain increase at the
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time of reproduction by the MC type cartridge in parallel with the resistance for gain
determination at the time of reproduction by the MM type cartridge via the DC blocking
capacitor. Finally, the invention will be described in detail, together with the drawings showing
its embodiment. On the basis of FIG. 1, σ) is an equalizer amplifier whose input terminal is
connected to the input terminal and (AMP) is connected to the non-inverting input terminal (t) to
the input terminal α), corresponding to a DC feedback control system It is configured in the
differential input type. (SWI) is a first changeover switch for input impedance switching whose
common terminal is connected to the non-inverting input terminal r of the equalizer amplifier
(AMP), and (R1) is a first 9J switch (SWI) The first resistance connected to the MM pear type
cartridge terminal (MM) and the ground terminal dark determines the input impedance at the
time of reproduction by the MM type cartridge. (R2) is a second resistor connected between the
MCQ card (3) S'3 'of the first changeover switch (SWI), the terminal for MC (MC) and the ground
terminal, and the h1 first resistor (R1) It has a small resistance value and determines the input
impedance at the time of reproduction by the MM type cartridge.
(2) is a feedback circuit element connected between the output terminal of the equalizer
amplifier (AMP) and the inverting input terminal (-), is composed of a resistor and a capacitor,
etc., and has frequency characteristics that determine the RIAA characteristics of record
reproduction doing. (R3) is an eighth resistor for determining the gain connected between the
inverting input terminal (-) of the equalizer amplifier (AMP) and the ground terminal, and the
eighth resistor (R3) and the negative feedback by the feedback circuit element (Z) The control
system determines the gain at the time of reproduction by the MM cartridge. C ′ ′ 1W 2) is a
second changeover switch for gain switching interlocked with the first changeover switch (swl),
and the MMu cartridge terminal (MM) is in an open state. (C) is a DC blocking capacitor
connected to the dark of the common terminal of the second changeover switch (sw2) and the
inverting input terminal of the equalizer amplifier (AMP), (R5) is the switching of the second
shadow (4) 2 A fourth resistor for gain increase connected between the MC type cartridge
terminal c'1 (C) of the switch (SW2) and the ground terminal, having a resistance smaller than
that of the eighth resistor (R3), and an impedance circuit The element -r (Z) and the eighth and
fourth resistors (R3) and (R4) determine the gain at the time of reproduction by the MC type
cartridge. (R5) is a fifth resistor connected between one end of the capacitor (C) and the ground
terminal, for removing noise due to charging / discharging of the capacitor (C) ○, eighth and
fourth resistors (R3), (R4) It does not affect the reproduction gain determined by (0) is an output
terminal derived from the output terminal of the equalizer amplifier (AMP). Next, the operation of
the embodiment will be described with reference to FIG. When playing back a record with the
MM type cartridge, the first and second changeover switches (SWI) and (SW2) are respectively
switched to the MM pear cartridge terminal (MM), and the feed puncture circuit element (Z) and
the third resistance Negative feedback control consisting of (R3) and (5)? The frequency
characteristics of the closed loop constituted by the negative feedback control system and the
equalizer amplifier (AMP) become like a convex line indicated by A in FIG. The gain G is usually
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about 55 to (iQ dB). At the same time, when the record reproduction is performed by the MC
type cartridge, the first and second changeover switches (SWI) and (SW2) are respectively
switched to MC type cartridge terminals (MC :) as shown.
Therefore, for the MC type cartridge having a low output voltage and a low output impedance
characteristic, an input innobiance is determined by a second resistor (R2) having a smaller
resistance value than the first resistor (R1). Further, the frequency characteristic of the closed
loop constituted by the equalizer amplifier (AMP) and the negative feedback control system is
like a convex line shown by B in FIG. That is, since the portion surrounded by the broken line in
FIG. 1 is AC-structured by the DC blocking capacitor (C), the DC gain is equal to that at the time
of reproduction by the MM9 cartridge as shown by G of the second L′ ′ 4. , Equalizer (6))) A
pump (AMP), a negative feedback control system and O, and it is φ'hM / + /-7 °. Negative
feedback control that is AC-structured by the fourth resistor (R4) for increasing the gain (R4) and
seven feedback circuits (Z) to DC gain during playback. The reproduction gain of the closed loop
by the system is added, and the hatched portion in FIG. 2 is one minute above the gain at the
time of reproduction by the MC type cartridge, compared to the reproduction by the MM type
cartridge. G 'is about 20 to 3 QdB. If, in FIG. 1, the common terminal of the second changeover
switch (EW2) is directly connected to the inverting input terminal (-) of the equalizing amplifier
(AMP) without passing through the DC blocking capacitor CC). In this case, although the negative
feedback control system holds DC, its DC gain becomes very large at about 75 to 99 dB, and DC
drift and extremely low frequency noise become very large values as described above. In FIG. 2,
fo is a cant-off frequency determined by the capacitor (C) and the fourth resistor (R4), fl. f2. f3 is
a constant frequency determined by the feedback circuit element (Z) according to the (7) t ···
RIAA characteristic. As described above, according to the reproduction equalizer circuit of the
present invention, the negative feedback control system of the equalizer amplifier, which includes
the feedback circuit element for RIAA characteristic determination and the gain determination
resistor at the time of reproduction by the MM に よ る card source, is DC converted to MM A
first selector switch for switching the input impedance of the equalizer amplifier according to the
type of cartridge and the M09 cartridge, and a second selector switch for interlocking the first
selector switch with a gain determining resistor at the time of reproduction by the MC type
cartridge By connecting in parallel to the gain determining resistor via the overflow blocking IE
capacitor, the DC gain at the time of reproduction by the MC type cartridge is the same as at the
time of reproduction by the MM type cartridge. Stable equalizer amplifier without increasing
noise It is possible to obtain a good reproduced sound is possible or be operated.
Moreover, the resistance for gain gain ,! 18) Makes the gain increase necessary for reproduction
with MC type cartridge compared with reproduction with MM type cartridge from
Reproduction gain of closed loop with a negative feedback control system AC structured with
feedback loop element 18) be able to.
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