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electret mic amplification using TL071 op amp

David Gold
Prodigy 100 points
Other Parts Discussed in Thread: TL071, INA217, TINA-TI

Hello everybody,

I have a 2-wire electret microphone ( Panasonic wm-62 ), and I want to amplify the signal by about 100 or even 1000 ( the signal is a few mV ) and send the output to an ADC.

I also have a TL071 op amp.

The frequency range which I'm covering is 1Hz - 5000Hz ( I need to keep the information in the low frequencies, not reject them ).

The mic is powered by a battery through a 2.2k resistor, and the output of the mic is AC coupled with a 0.1uF capacitor.

I have 2 questions :

1.How should I hook up the circuit from mic to op amp?

Should I use just the classic non-inverting scheme ( picture above ) or should I add resistors and caps in order to bias the op amp somehow?

The input impedance of this op amp is 10^12 ohms ( from the datasheet ), so the cuttoff frequency of the RC HPF that is formed at the input of the amp is extremely low, which is good for me.

2. Does the application needs the use of an instrumentation amp? or should an op amp suffice?

Thank you,

David.

  • 0
    TI__Guru 64140 points

    David,

    As was the case of INA217, you MUST always provide a DC bias to the input terminals; therefore, you may not capacitively coupled the non-inverting input as shown in your schematic - this would cause a charge built up across the input cap (due to IB) and result in the output collapsing against one of the supply rails.  

    Below please see schematics and simulation results with proper biasing of the op amp for dual (top) and single (bottom) supply applications.   I have also attached the TINA-TI schematic so you may use it for your own simulations.

    TL071 circuit.TSC
  • 0
    TI__Guru**** 152056 points

    David,

    Try a Google search for "tl071 electret microphone" and select images. Many circuit examples will be found. The input capacitor and bias resistors (needed to set proper common mode range) will set the lower input cutoff frequency. Increase R and C in examples to get down to 1 Hz.