Some questions about the preamplifier circuit design

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Some questions about the preamplifier circuit design

Postby jeffnie » 06 Mar 2017, 09:05

Hi, I was designing a microphone pre-amplifier circuit for Wireless Noise Monitoring application.


I used an amplifier AD797AN (datasheet ) which connected to a 9V power supply. The multisim simulation of the circuit with a function generator gives the expected gain of around 7.8. But the same circuit in the breadboard with the microphone gives the gain of only around 5. Please let me know what improvements are needed in the circuit to get the expected gain of 7.8?

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Joined: 06 Mar 2017, 06:46

Re: Some questions about the preamplifier circuit design

Postby Stephane » 06 Mar 2017, 10:14


Looking at the datasheet, it seems that this amplifier is meant to be used with a negative and positive power supply. This means a very low impedance ground and the virtual ground that you create by biasing the non-inverting input at 1/2 Vcc does not meet this criteria.
One other thing: the R2 resistor is normally connected to GND or the virtual GND, not the -VS supply. Use a similar R3/R4 divider to bias the R1/R2 loop.
Or use a symmetric power supply.
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