Handbook for Sound Engineers

782 Chapter 22

the source impedances at the inputs. To illustrate the

method of calculating interchannel isolation, refer to

Fig. 22-31. There are two attenuations that a signal must

undergo in order to leak from one channel to an adjacent

channel. The first attenuation consists of Ri and Rin; the

second consists of Ri and Rs.

The equation for calculating isolation is

where,

Rsb is the Esb source resistance in ohms,

Rin is the A 1 closed-loop input impedance in ohms or

Reference

1. Jung, Walter G. Audio IC Op-Amp Applications, Third Edition, Carmel, IN: SAMS, a Division of Macmillan
   Computer Publishing, 1989.

Figure 22-30. Summing amplifier (active combining
network).

Ein 1

Ein 2

Ein 3

Ein 4

Ein 5

Ein 6

Ein 7

Ein 8

Ein 9

Ein 10

R 1

R 2

R 3

R 4

R 5

R 6

R 7

R 8

R 9

R 10

10 k7

10 k7

10 k7

10 k7

10 k7

10 k7

10 k7

10 k7

10 k7

10 k7

C 1

5.0 pF

Eo

R 11

10 k7

2

3

A* 1

318

+

Figure 22-31. Method of calculating interchannel isolation

for a summing amplifier.

Isolation from Ein

a

to Ein

b

Ri 1 +Rin

Rin

©¹§·---------------------

Ri 2 +Rsb

Rin

= ----------------------

Rin

Rf

AvoE

#------------

Ri 1

Rsb Ri 2

600 7 10 k 7

10 k 7

R

A1 E

+

600 7 10 k 7

Rsa Eina

Esa

Esb

Einb

O



Rin