Audio Engineering

230 Chapter 7

In the Clapham junction type system, so named because of the similarity of the possible
frequency response curves to that of railway lines, a group of push switches is arranged
to allow one or more of a multiplicity of RC networks to be introduced into the feedback
loop of a negative feedback type tone control system, as shown in Figure 7.66 , to
allow individual 3-dB frequency adjustments to be made, over a range of possible
frequencies.





Zb

Za

Ein Eout

Rin R 2 R 1

C 1

0V

(a)

Figure 7.64 : Active RC treble-cut or bass-lift circuit.

Gain

Rin

R 1 R 2

1

2 πR 2 C 1

1

2 πR 1 C 1

Frequency

GainRR^1

f 1 f 2 in

Output (dB)

(b)