OPA1678 datasheet(24/46 Pages) TI1

24 / 46 page

½ OPA1678

61.9 k

0.1 F

9 V

Electret

Microphone

9 V

100 k

Output

13.7 k

2.2 F

16 pF

100 k

VOUT

V+

V±

15 V

-15 V

½ OPA1678

118 k

10 k

27 nF

7.5 nF

127

47 k

150 pF

100 F

100

100 F

100 k

MM Phono Input

Output

OPA1678, OPA1679

SBOS855A – FEBRUARY 2017 – REVISED MAY 2018

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Typical Application (continued)

8.2.4.1 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 a viable choice in preamplifier circuits for moving magnet (MM)

phono cartridges. Figure 38 shows a preamplifier circuit for MM cartridges with 40 dB of gain at 1 kHz.

Figure 38. Phono Preamplifier for Moving Magnet Cartridges

(Single-Channel Shown)

8.2.4.2 Single-Supply Electret Microphone Preamplifier

The preamplifier circuit shown in Figure 39 operates the OPA1678 as a transimpedance amplifier that converts

the output current from the electret microphone's internal JFET into a voltage. Resistor R4 determines the gain of

the circuit. Resistors R2 and R3 bias the input voltage to half the power supply voltage for proper functionality on

a single-supply.

Figure 39. Single-Supply Electret Microphone Preamplifier

8.2.4.3 Composite Headphone Amplifier

Figure 40 shows the BUF634 buffer inside the feedback loop of the OPA1678 to increase the available output

current for low-impedance headphones. If the BUF634 is used in wide-bandwidth mode, no additional

components besides the feedback resistors are required to maintain loop stability.

OPA1678 Datasheet(PDF) 24 Page - Texas Instruments

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