Handbook for Sound Engineers

886 Chapter 25

Figure 25-65. Loop filters.

RCR C

R C R

C. Introducing loss to temper the Q to usability.

A. Three-inverter loop (stable).

B. Introducing 180° phase shift via two integrators.

across integratorResistive loss

(Bi-quad) C

90° 90°

Vin

C

R R

10 k 7

10 k 7

10 k 7 10 k 7

10 k 7

2.4 k 7 2.4 k 7

47 k7Antilog

150 pF

18 nF 18nF

F. State-variable filter with single pot Q adjust.

D. CAPS – variable filter, Q determined as for state variable.

Vin

Vin

Vin

Vo

Vo

Vo

C

Proportional phased

feedback (state variable)

E. Ganged potentiometer simultaneously altering Q and input attenuator.