CS-880H,HG,U,UC
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meaning that the characteristics change. A t a scale position lower
than the volume control's tap position, the loudness characteris
tics are provided regardless of the strength of the sound level
and, in contrast, even when the sound level is low, the effect is
impaired by the control's scale position.
However, the DSL system judges the strength of the sound
level by electrical means and features a configuration which
produces dynamic super loudness characteristics.
5-2.
DSL Circuit Configuration
The D SL circuit comprises the equalizer circuit which produces
the D SL characteristics, the detector circuit which judges the
strength o f the sound level and the control circuit which sup
presses the D SL characteristics when the sound is high.
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CIRCU IT
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1
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Fig. 13
5-2-1. Equalizer Circuit
An ordiany direct-coupled amplifier feedback circuit (T-type
bridge circuit) is provided with time constants, and its character
istics generated.
Tow T-type bridge circuits are connected in series and the time
constants are divided into the left side for bass [R361, 359,
C359,361 ] and right side for treble.
The characteristics of each of the twin filters connected to pins 3
and 8 of IC351 (TA7137P) are attenuated by frequency f,
determined by constants R1, R2 and C1.
RI
OUTPUT
5-2-2. Detector Circuit
The level of this circuit is set by the frequency division ratio of
two resistors.
5-2-3. Control Circuit
This circuit is the same as an A LC circfflt used for normal record
ing although it differes in that its attack time and recovery time
are extremely short.
Because of the boosted level, the output must be not distorted.
When a signal exceeding a certain fixed level is fed out, it is
taken out by the Q49 emitter, the IC7 A LC circuit functions and
the input of pin 2 is controlled.
+ 8
IC 7
Fig. 16
The D SL circuit with the above-mentioned configuration is
mixed with a main amplifier. The ICI (AN7146) input has a
differential amplifier configuration, and when a flat signal enters
transistor Q1 at one side of the differential amplifier from the
volume control, a flat signal also enters the D SL circuit simul
taneously. Q2 is basically a negative feedback pin but when the
output (signal with D SL characteristics) of the D SL circuit is fed
into the Q2 input, differential operation is provided by Q1 and
Q2.
The D SL block input transistor Q47 is used to invert the phase.
As a result, the phase is inverted at the D SL block input and
output sides and so the differential operation of Q1 and Q2
becomes a mixing operation. Meanwhile, the feedback from the
output inside IC7 does not change and negative feedback opera
tion results.
When the signal level is low in Fig. 13, there is a high degree of
mixing by Q1 and 02 inside IC1 so that the D SL feeds out a
strong signal, and the bass nad treble are greatly boosted. How
ever, when the signal level is high, the D SL block output is
suppressed, the amount of mixing by Q1 and Q2 inside IC I is
reduced, and since the Q2 input is reduced to a fraction, almost
all of it becomes the signal fed in from Q1.
The resistor inserted across the ground and O FF side pin of the
D SL ON/OFF switch functions to compensate for the difference
in the volume when the switch is selected.
Fig. 14
Fig. 15
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