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Applications Information
(Continued)
Figure 4 shows the effect of changing C
and C
in the oppo-
site direction to C
/2, 2C
respectively giving reduced control
ranges. The various results corresponding to the different C
t
and C
values may be mixed if it is required to give a particu-
lar emphasis to, for example, the bass control. The particular
case with C
b
/2, C
t
is illustrated in Figure 5
Restriction of Tone Control Action at High or Low
Frequencies
It may be desired in some applications to level off the tone
responses above or below certain frequencies for example
to reduce high frequence noise.
This may be achieved for the treble response by including a
resistor in series with C
. The treble boost and cut will be 3
dB less than the standard circuit when R=X
C
.
Asimilar effect may be obtained for the bass response by re-
ducing the value of the AC bypass capacitors on pins 5
(channel 1) and 16 (channel 2). The internal resistance at
these pins is 1.3 k
and the bass boost/cut will be approxi-
mately 3 dB less with X
at this value. An example of such
modified response curves is shown in Figure 6 The input
coupling capacitors may also modify the low frequency re-
sponse.
It will be seen from Figure 2 and Figure 3 that modifying C
t
and C
for greater control range also has the effect of flatten-
ing the tone control extremes and this may be utilized, with
or without additional modification as outlined above, for the
most suitable tone control range and response shape.
Other Advantages of DC Controls
The DC controls make the addition of other features easy to
arrange. For example, the negative-going peaks of the out-
put amplifiers may be detected below a certain level, and
used to bias back the bass control from a high boost condi-
tion, to prevent overloading the speaker with low frequency
components.
LOUDNESS CONTROL
The loudness control is achieved through control of the tone
sections by the voltage applied to pin 7; therefore, the tone
and loudness functions are not independent. There is nor-
mally 1 dB more bass than treble boost (40 Hz–16 kHz) with
loudness control in the standard circuit. If a greater differ-
ence is desired, it is necessary to introduce an offset by
means of C
t
or C
b
or by changing the nominal control voltage
ranges.
Figure 7 shows the typical loudness curves obtained in the
standard
application
circuit
(C
b
=0.39 μF).
at
various
volume
levels
Figure 8 and Figure 9 illustrate the loudness characteristics
obtained with C
b
changed to C
b
/2 and C
b
/4 respectively, C
t
DS005142-7
FIGURE 4. Tone Characteristic (Gain vs Frequency)
DS005142-8
FIGURE 5. Tone Characteristic (Gain vs Frequency)
DS005142-9
FIGURE 6. Tone Characteristic (Gain vs Frequency)
DS005142-10
FIGURE 7. Loudness Compensated Volume
Characteristic
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