NE5517, NE5517A, AU5517
Stereo Amplifier With Gain Control
Modulators
Figure 24 shows a stereo amplifier with variable gain via
a control input. Excellent tracking of typical 0.3 dB is easy
to achieve. With the potentiometer, R
P
, the offset can be
adjusted. For AC-coupled amplifiers, the potentiometer
may be replaced with two 510
W
resistors.
Because the transconductance of an OTA (Operational
Transconductance Amplifier) is directly proportional to I
ABC
,
the amplification of a signal can be controlled easily. The
output current is the product from transconductance×input
voltage. The circuit is effective up to approximately 200 kHz.
Modulation of 99% is easy to achieve.
+V
CC
10kW
V
IN1
R
IN
1k
R
P
+V
CC
15kW
3
+
11
NE5517/A
R
D
−
4
I
ABC
1
R
L
10kW
5.1kW
8
INT
+V
CC
V
OUT1
30kW
V
C
R
C
10kW
V
IN2
R
IN
1k
R
P
+V
CC
15kW
R
D
−
13
14
15
NE5517/A
12
6
+
I
ABC
16
−V
CC
10
9
R
L
10kW
R
S
−V
CC
INT
V
OUT2
+V
CC
Figure 24. Gain-Controlled Stereo Amplifier
R
C
30kW
V
IN2
SIGNAL
I
ABC
+V
CC
11
3
2
NE5517/A
−
10kW
4
R
L
10kW
6
−V
CC
R
S
−V
CC
INT
+
5
7
1
I
D
15kW
V
OS
V
IN1
CARRIER
1kW
INT
+V
CC
8
V
OUT
Figure 25. Amplitude Modulator
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