232 Chapter 7
Because the ideal solution to this requirement—that of employing a group of parallel
connected amplifi ers, each of which is fi ltered so that it covers a single octave band of
the frequency spectrum, whose individual gains could be adjusted separately—would be
excessively expensive to implement, conventional practice is to make use of a series of
LC-tuned circuits, connected within a feedback control system, as shown in Figure 7.68.
This gives the type of frequency response curve shown in Figure 7.56. As can be seen,
there is no position of lift or cut, or combination of control settings, that will permit a fl at
frequency response because of the interaction, within the circuitry, between the adjacent
octave segments of the pass band.
50 Hz6K8 6K8 6K8 6K8 6K8 27 K 22 K22 pF
0.015μ 0.033μ 0.068μ 0.15μ
‘Cut’‘Cut’Treble‘Lift’‘Lift’0V1 K5Hz3 kHz7 kHz14 kHz33 K 33 K33 K33 K33 K22 K14 kHz1K5Hz7 kHz3 kHz560Eout33 K33 K33 K22 K3 n3 3n3680 p330 p1n5220 K 220 K220 K220 K220 KOffOffOffOff220 K220 K220 K330 p680 p1n50V Bass0.15μ 0.068μ 0.033μ 0.015μ100 μEin400 Hz 200 Hz 100 Hz 50 Hz22 K 22 K 22 K 22 K 6K8 22 K 6K8 22 K 6K8 22 K 6K8100 Hz 200 Hz 400 HzFigure 7.66 : Clapham junction tone control.