Audio Engineering

Preamplifi ers and Input Signals 227

If such networks are connected across an inverting gain block, as shown in Figures
7.63(a) and 7.64(a) , the resultant frequency response will be shown in Figures 7.63(b)
and 7.64(b) , since the gain of such a negative feedback confi guration will be

Gain a

b



Z

Z

assuming that the open-loop gain of the gain block is suffi ciently high. This is the design
basis of the Baxandall type of tone control, and a fl at frequency response results when
the impedance of the input and output limbs of such a feedback arrangement remains in
equality as the frequency is varied.

Figure 7.59 : Layout and frequency response of a simple bass-cut circuit (high pass).

Ein Eout

0V

(a)

C 1

R 1

0

Frequency

 3

6 dB/octave

(b)

Output (dB)

Figure 7.60 : Layout and frequency response of a simple treble-cut circuit (low pass).

Ein Eout

(a)

C 1

R 1

0

Frequency

 3

Slope

6 dB/octave

(b)

Output (dB)