Handbook for Sound Engineers

Tubes, Discrete Solid State Devices, and Integrated Circuits 339

frequency bandwidth of 0–10 kHz, the maximum gain
of the op-amp in Fig. 12-40 is 100. To have lower
distortion, it would be better to have feedback at the
required upper frequency limit. To increase this gain
beyond 100 would require a better op-amp or two
op-amps with lower gain connected in series.

Differential Amplifiers. Two differential amplifier

circuits are shown in Fig. 12-41. The ability of the

differential amplifier to block identical signals is useful

to reduce hum and noise that is picked up on input lines

such as in low-level microphone circuits. This rejection

is called common-mode rejection and sometimes elimi-

nates the need for an input transformer.

Figure 12-39. Stability enhancement techniques.

A

+

+

+

V+

Rin

Cf**

C 1 *** (3–10 pF typical)

C 1 *

A

V

Rf

Cs

Rf

Ro‡‡

R 1

A‡

Cf

Cs

=

Rf

Rin

(3–0 pF typical)

A. Power-supply bypassing.

*Low-inductance short-lead capacitors—0.1 μF stacked

film preferred. For high-speed op amps, connect C 1

and C 2 directly at supply pins, with low-inductance

ground returns.

C 1 may be larger. If A is

unity-gain compensated.

B. Compensation of stray input capacitance.

CL

***XC 1 =

R 1

10 @ft of A

‡A is compensated for unity gain

‡‡Ro 50–200 7

C. Compensation of stray output capacitance.

C 2 *

Input

Input

Output

Input Output

Input Output

Figure 12-40. Typical open loop gain response.

Figure 12-41. Differential amplifiers.

103

104

102

101

100

105

10

1 100 101 102 103 104 105 106 107

Frequency—Hz

Voltage gain

C 1

C 2 R 3

R 4

R 1 R 2

Ein

2

(^3) +
(^6)
Ein
C 1
C 2 R 3
R 5
R 1 R 2
Ein
2
(^3) +
(^6)
Ein
RL
R 6
R 4
V+
V+
V
A. Basic differential amplifier.
B. Single supply differential amplifier.