Applications Information
OBTAINING MODIFIED RESPONSE CURVES
The LM1036 is a dual DC controlled bass, treble, balance and
volume integrated circuit ideal for stereo audio systems.
In the various applications where the LM1036 can be used,
there may be requirements for responses different to those of
the standard application circuit given in the data sheet. This
application section details some of the simple variations pos-
sible on the standard responses, to assist the choice of opti-
mum characteristics for particular applications.
TONE CONTROLS
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Summarizing the relationship given in the data sheet, basi-
cally for an increase in the treble control range Ct must be
increased, and for increased bass range Cb must be reduced.
FIGURE 3. Tone Characteristic (Gain vs Frequency)
Figure 4 shows the effect of changing Ct and Cb in the oppo-
site direction to Ct/2, 2Cb respectively giving reduced control
ranges. The various results corresponding to the different Ct
and Cb values may be mixed if it is required to give a particular
emphasis to, for example, the bass control. The particular
case with Cb/2, Ct is illustrated in Figure 5.
Figure 1 shows the typical tone response obtained in the
standard application circuit. (Ct=0.01 μF, Cb=0.39 μF). Re-
sponse curves are given for various amounts of boost and cut.
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 Ct. The treble boost and cut will be 3 dB
less than the standard circuit when R=XC.
A similar effect may be obtained for the bass response by
reducing 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 kΩ and the bass boost/cut will be approxi-
mately 3 dB less with XC 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.
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FIGURE 1. Tone Characteristic (Gain vs Frequency)
Figure 2 and Figure 3 show the effect of changing the re-
sponse defining capacitors Ct and Cb to 2Ct, Cb/2 and 4Ct,
Cb/4 respectively, giving increased tone control ranges. The
values of the bypass capacitors may become significant and
affect the lower frequencies in the bass response curves.
It will be seen from Figure 2 and Figure 3 that modifying Ct
and Cb 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 output
amplifiers may be detected below a certain level, and used to
bias back the bass control from a high boost condition, to
prevent overloading the speaker with low frequency compo-
nents.
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 difference
is desired, it is necessary to introduce an offset by means of
Ct or Cb or by changing the nominal control voltage ranges.
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FIGURE 2. Tone Characteristic (Gain vs Frequency)
Figure 7 shows the typical loudness curves obtained in the
standard application circuit at various volume levels (Cb=0.39
μF).
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