222 Chapter 7
The effect of these is to modify the frequency response of the system, at the HF end, as a
result of signal currents passing through these capacitances. The choice of a low value for
R 1 is desirable to minimize this problem.
The use of the gain control to operate an on/off switch, which is fairly common in low-
cost equipment, can lead to additional problems, especially with high resistance value
gain control potentiometers, in respect to AC mains “ hum ” pick up. It also leads to a
more rapid rate of wear of the gain control in that it is rotated at least twice whenever the
equipment is used.
7.18.2 Tone Controls
These exist in the various forms shown in Figures 7.52–7.56 , respectively, described as
standard (bass and treble lift or cut), slope control, Clapham junction, parametric, and
graphic equalizer types. The effect these will have on the frequency response of the
equipment is shown in the drawings, and their purpose is to help remedy shortcomings
in the source program material, the receiver or transducer, or in the loudspeaker and
listening room combination.
To the hi-fi purist, all such modifi cations to the input signal tend to be regarded with
distaste and are therefore omitted from some hi-fi equipment. However, they can be
useful and make valuable additions to the audio equipment, if used with care.
100Gain (dB)30 200 201 K 10 K 20 kHz
Frequency
Figure 7.52 : Bass and treble lift/cut tone control.