AN6077 INTERSIL [Intersil Corporation], AN6077 Datasheet - Page 7

• Manufacturer Part Number: AN6077
• Description: An IC Operational Transconductance Amplifier With Power Capability
• Manufacturer: INTERSIL [Intersil Corporation]

Performance
Figure 16 is a plot of the measured response of the complete
amplifier at the extremes of tone control rotation. A
comparison of Figure 16 with the computed curves of Figure
B4 (Appendix B) shows good agreement. The total harmonic
distortion of the amplifier with an unregulated power supply is
shown in Figure 17; IM distortion is plotted in Figure 18. Hum
and noise are typically 700 V at the output, or 83dB down.
FIGURE 16. THE MEASURED RESPONSE OF THE AMPLIFIER
FIGURE 17. TOTAL HARMONIC DISTORTION OF THE
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
60
55
50
45
40
35
30
25
20
15
10
10
0
2
AT EXTREMES OF TONE CONTROL ROTATION
AMPLIFIER WITH AN UNREGULATED POWER
SUPPLY
2
3 6 8
BASS CUT
100
BASS BOOST
1kHz
4
2
OUTPUT POWER (W)
FREQUENCY (Hz)
3 6 8
4-7
26kHz
6
1000
2
TREBLE CUT
16kHz
8
TREBLE BOOST
3 6 8
1kHz
2kHz
10
10K
FLAT
2
Application Note 6077
12
4kHz
3 6 8
100K
Companion RlAA Preamplifier
Many available preamplifiers are capable of providing the
drive for the power amplifier of Figure 14. Yet the unique
characteristics of the amplifier, its power supply, input
impedance, and gain make possible the design of an RIAA
preamplifier that can exploit these qualities. Since the input
impedance of the amplifier is essentially equal to the value of
the volume control resistance (250k ), the preamplifier need
not have high output current capability. Because the gain of
the power amplifier is high (40dB) the preamplifier gain only
has to be approximately 30dB at the reference frequency
(1kHz) to provide optimum system gain.
Figure 19 shows the schematic diagram of a CA3080
preamplifier. The CA3080, a low cost OTA, provides sufficient
open-loop gain for all the bass boost necessary in RIAA
compensation. For example, a g
resistance of 250k provides an open-loop gain of 68dB,
thus allowing at least 18dB of loop gain at the lowest
frequency. The CA3080 can be operated from the same
power supply as the main amplifier with only minimal
decoupling because of the high power supply rejection
inherent in the device circuitry. In addition, the high voltage
swing capability at the output enables the CA3080
preamplifier to handle badly over modulated (over-cut)
recordings without overloading. The accuracy of equalization
is within 1dB of the RIAA curve, and distortion is virtually
immeasurable by classical methods. Overload occurs at an
output of 7.5V, which allows for undistorted inputs of up to
186mV (260mV peak).
FIGURE 18. IM DISTORTION OF THE AMPLIFIER WITH AN
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
60Hz 12kHz
60Hz 2kHz
60Hz 7kHz
UNREGULATED SUPPLY
2
4
OUTPUT POWER (W)
6
m
8
of 10mS with a load
10
12
14