OPA1678 Datasheet, PDF (24/41 Pages) Texas Instruments – Low-Distortion Audio Operational Amplifiers

OPA1678, OPA1679
SBOS855 – FEBRUARY 2017
www.ti.com
8.1 Other Applications
The low noise and distortion of the OPA167x series make the devices well-suited for a variety of applications in
professional and consumer audio products. The examples shown here are possible applications where the
OPA167x provides exceptional performance.
8.1.1 Phono Preamplifier for Moving Magnet Cartridges
The noise and distortion performance of the OPA167x family of amplifiers is exceptional in applications with high
source impedances, which makes these devices an excellent choice in preamplifier circuits for moving magnet
(MM) phono cartridges. Figure 38 illustrates a preamplifier circuit for MM cartridges with 40 dB of gain at 1 kHz.
MM Phono Input
R1
47 k
15 V
C1
150 pF
+
V+
±
V±
½ OPA1678
VOUT
R2 -15 V R3
118 k
10 k
C5
R5
100
100 F
Output
R6
100 k
R4
127
C4
100 F
C2
27 nF
C3
7.5 nF
Copyright © 2017, Texas Instruments Incorporated
Figure 38. Phono Preamplifier for Moving Magnet Cartridges
(Single-Channel Shown)
8.1.2 Single-Supply Electret Microphone Preamplifier
The preamplifier circuit shown in Figure 39 operates the OPA1678 as a transimpedance amplifier which converts
the output current from the electret microphone's internal JFET into a voltage. The gain of the circuit is
determined by resistor R4. Resistors R2 and R3 bias the input voltage to half the power supply voltage for proper
functionality on a single-supply.
9V
R1 _{13.7 k}
C1
Electret
Microphone
2.2 F
9 V _R2
100 k
C3
16 pF
R4
61.9 k
9V
0.1 F
±
+
½ OPA1678
Output
R3
100 k
C2
2.2 F
Copyright © 2017, Texas Instruments Incorporated
Figure 39. Single-Supply Electret Microphone Preamplifier
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