Handbook for Sound Engineers

Attenuators 777

and one end connected to the load, Fig. 22-20. The

volume control should be a high impedance with respect

to the source so it will not load it, and the load imped-

ance should be a high enough so as not to affect the

control. The output voltage is calculated with the

following equation:

(22-47)

where,
R 1 is the upper section of control,
R 2 is the lower section of control,
Z 2 is the load impedance.

If the load impedance is high compared to R 2 , the

equation is simplified to

(22-48)

The attenuation is

Figure 22-19. Impedance characteristics of a 600: ladder
type attenuator.

Figure 22-20. Simple volume control.

800

700

600

500

400

300

200

0

70

60

50

40

30

20

10

0

Steps counterclockwise rotation

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Impedance–Ohms

Decibels

Attenuation

Output

Input

R 1

Zin R

(^2) Vout
Source
Load

• 
  


• 
  

  Vout Vin
  R 2 Z 2
  R 2 +Z 2

  
  

  ©¹
  §·
  R 1
  R 2 Z 2
  R 2 +Z 2
  +©¹§·------------------
  = ------------------------------------
  Vout Vin
  R 2
  R 1 +R 2

  
  

  ©¹
  = §·
  Figure 22-21. Method of varying the response of a simple
  potentiometer.
  R 1
  Input
  R 2
  Output

  
  


• 
  


• 
  

  Input
  Output

  
  


• 
  


• 
  

  Input
  Output

  
  


• 
  


• 
  

  Linear
  potentiometer
  Linear
  potentiometer
  Linear
  potentiometer
  C. Two shunt resistors connected
  at each side of the wiper.
  A. Shunt connected from
  the wiper to the ground.
  B. Second potentiometer ganged with
  the straight-line potentiometer.