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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a connection diagram of a conventional
equalizer switching circuit, and FIG. 2 is a connection diagram showing one embodiment of the
equalizer switching circuit of the present invention. A, B, C, D: channel, Qlly Q2 x s Qa 1 s Q 4 ■
E · · · first stage transistor, S · · · switch, Q · · · second transistor, + Vcc · · · R straight riser. Fig. 1-151-122 601 (2) Fig. 2-2
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an equalizer
switching circuit which improves its performance by reducing the number of changeover
switches, pop sound and bias leakage. Conventionally, as the equalizer switching circuit, for
example, a circuit as shown in FIG. 1 has been used. That is, the four channels (5), (B), (Q, [(1) are
switched by (1) (1)] switch by the changeover switch (S1), and the first through the condenser f
(C,) The transistor (Q,) 7) is connected to the base of the first transistor (Q1), the collector of the
first transistor (Q1) is connected via a resistor (It) to the DC power supply (-) Vc) and the second
transistor (Q, Of the second switch (SI) connected to the pace, the emitter of the first transistor
(Q,) being grounded via the resistor (k,) and operating in conjunction with the first switch (Sl)
Connected to the contact piece. On the other hand, the collector of the second transistor (Q) is
connected to the output terminal (1) through the DC power supply (-) Vc and the capacitor (C,)
through the resistor (R3), The emitter of the transistor (Q,) is connected to the first transistor (Q,
7) and is grounded via the resistor (R4), and the capacitor (C) is connected across the resistor (R,)
o ,) A; connected. In addition, terminals (2) 2 (to) of the second changeover switch (S2), (Q ', (G)',
corresponding to each channel), (I 9. q, (D) respectively correspond to Equalizers (EQ) between
(Q) ', (Q', R and the output terminal (T)), (2) 11, (EQ), (EQ,) , (EQ,) are connected respectively. In
this circuit, for example, when the first changeover switch (Sl) is set to channel CM) K, the second
changeover switch (S,) is also interlocked with the terminal φy corresponding to that channel
(5). Since the signal of channel (2) is amplified by the first and second transistors (Q1) and (Q, *)
and appears at the output terminal (7), it is set by the equalizer (EQ). The transistors (Q, 帰 還
feedback provide an output signal with the required frequency characteristics. However, in this
conventional circuit, since there are two changeover switches, the space is increased and pop
noise is generated, and since the wiring becomes long, bias leak occurs from the pattern of the
printed circuit board and the like, thereby deteriorating the performance. Furthermore, there is a
disadvantage that the circuit constant is adversely affected.
In view of the above drawbacks, the present invention provides a first stage transistor for each
channel and switches the DC power supply with a changeover switch to reduce the number of
changeover switches and to provide pop sound and) (3)) bias. It reduces leakage and improves its
performance. Hereinafter, this invention will be described in detail with reference to the drawings
showing one embodiment thereof. In FIG. 2, the input terminals of the four channels (5), @, 0.0
are respectively capacitors (C,...). (C,,), (C,,), (C ,,), through the first stage transistors (Q,,), (Q □), (Q
□), (Q ,,) of each channel The collectors of the first stage transistors (Q,,), (Q,,), (Q,,), (Q ,,)
connected to the respective channels are connected to resistors (R ++), (R,) ,), <Town 1), (R, l)
connected to their respective bases, respectively, furthermore, each capacitor (C ,,). It is
connected to the pace of the second stage transistor (Q,) via (C ,,), (C ,,), (C ,,), and the resistance
(R1,), (R □), of each channel Connected to each channel (), (), (Q, (terminal corresponding to 11,
11γ, (q ′ 叶) via (R,,), (Reason,). These terminals 、, げ, (Q ', (Q' are connected to the DC power
supply (% Vcc) through the contact piece of the changeover switch (S), and the first stage
transistor (Q, ...)). The emitters of (q □), (Q □), and (QA,) are grounded through resistors (1), (4)
bR = t), (r,), (R3,), and (RA,), respectively. ing. On the other hand, the collector of the second stage
transistor (Q) is output to the DC power supply (+ Vcc) through the other resistor (Ra +) through
the resistor (RJ through the other resistor) and through the capacitor (C5) The terminals (1) are
connected to one another and their emitters are grounded via a resistor (Ro). Furthermore, in the
dark of the first stage transistors (Q,,), (Q ,,), (Q ,,), (Q □) emitters and the output terminal ω,
each channel (end) , 0. The respective equalizers (EQ,), (EQ,), (EQI), (EQ,) are connected. In this
circuit, for example, when the switch is set to the terminal 3 in order to reproduce a signal of
channel @), only the first stage transistor (Q □) connected to the terminal side is biased or the
other first stage transistor Since (Q ,,), (Q ,,), (Q ,,) are turned off, only the signal of the channel
appears at the output transistor through the second stage transistor (Q,) t-.
Here, since the output signal is fed back to the first stage transistor (Q,) by the equalizer (EQ), an
output having a required frequency characteristic equalized by the equalizer (5)) riser (Eq) A
signal is obtained. As described above, according to the equalizer switching circuit of this
invention, the DC power source applied to the first stage transistor provided for each channel is
switched by the changeover switch, and the second stage transistor commonly used for all the
channels is used. By adding a DC power supply and feeding back to each first stage transistor by
the output イ コ ラ イ ザ equalizer for each channel, the number of changeover switches is
reduced by one compared with the conventional circuit, and the circuit constant is favorably
influenced, and the pump sound It is also possible to reduce the wiring and to reduce the bias
leakage on the printed circuit board and to improve its performance.
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