OPA1641 Datasheet, PDF (26/31 Pages) Texas Instruments – High-Performance, JFET-Input AUDIO OPERATIONAL AMPLIFIERS

OPA1641, OPA1642, OPA1644
SBOS484C – DECEMBER 2009 – REVISED DECEMBER 2015
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Typical Application (continued)
Because there are multiple combinations of passive components which satisfy these equations, a spreadsheet or
other software calculation tool is the easiest method to examine resistor and capacitor combinations.
A_LF
1 ^{R3 R2}
R₄
1000(60dB)
(5)
Capacitor C4 forces the gain of the circuit to unity at dc in order to limit the offset voltage at the output of the pre-
amplifier circuit. The high-pass corner frequency created by this capacitor is at:
F_HP
1
2SR₄C₄
(6)
The circuit described here was constructed with 1% tolerance resistors and 5% tolerance NP0/C0G ceramic
capacitors without any additional hand sorting. The large value of C4 typically requires an electrolytic type to be
used. However, electrolytic capacitors have the potential to introduce distortion into the signal path. This circuit
was constructed using a bipolar electrolytic capacitor specifically intended for audio applications.
8.2.3 Application Curves
The deviation from the ideal RIAA transfer function curve is shown in Figure 40 normalized to an ideal gain of
40 dB at 1 kHz. The measured gain at 1 kHz was 0.05 dB less than the design goal, and the maximum deviation
from 100 Hz to 20 kHz was 0.18 dB. The deviation from the ideal curve may be improved by hand-sorting
resistor and capacitor values to their ideal values. The value of C4 may also be increased to reduce the deviation
at low frequency.
A spectrum of the preamplifier output signal is shown in Figure 41 for a 10 mV_RMS, 1-kHz input signal (1-V_RMS
output). All distortion harmonics are below the preamplifier noise floor.
0.5
0
-0.5
-1
-1.5
10
100
1000
Frequency (Hz)
10000
C006
Figure 40. Measured Deviation from Ideal RIAA Response
0
-20
-40
-60
-80
-100
-120
-140
-160
10
100
1000
Frequency (Hz)
10000
C010
Figure 41. Output Spectrum for a 10 mV_RMS, 1 kHz Input
Signal
9 Power Supply Recommendations
The OPA164xare specified for operation from 4.5 V to 36 V (±2.25 V to ±18 V); many specifications apply from
–40°C to +125°C. Parameters that can exhibit significant variance with regard to operating voltage or
temperature are presented in the Typical Characteristics.
26
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