Adapt audio signal from a Microphone with a bandwidth of 20Hz-100KHz.

Hi Ivan,

The hydrofone has a preamplifier. Therefore, I think you have to feed this preamplifier first.
Then amplify and filter the signal. I want the bandwidth to be configurable. The output of the amplified signal
I want it to be with level from 0V to 3V3. I need help since I am not a great expert on this subject. The input impedance of the
Hydrophone is 2KΩ. 

The most important thing at this moment is to feed the preamplifier of the hydrophone well and know how to amplify the signal well before processing it.

Can you help me please?

Best regards,

Jota,

You're right the preamp should be powered, this is why phantom power is required. You can see this preamp as a LMV1012, the pull up resistor at the output is the phantom power.
You can then connect this output (through the coupling capacitor) to the amplifying/filtering stage.
An op amp would let you set a gain depending on the Rin and Rf values, in addition you could add feedback capacitors and this would form a Low Pass Filter and the cutoff frequency is set by Rf and Cf by the formula fc = 1/(2*pi*Rf*Cf).

As an example, let's say you use OPA1662 and input signal has 1Vpp centered at 0V. OPA1662 spec says that output voltage swing is (V-)+0.6 to (V+)-0.6, if required output voltage swing is 3.3Vpp then supply voltage must be >= 3.3+0.6+0.6 = 4.5V (if power supply voltage is 3.3V then the output swing would be 3.3-0.6-0.6 = 2.1Vpp).
The required gain would be given by 3.3Vpp/1Vpp = 3.3V/V, so the following values could be used: Rin = 2k, Rf = 6.6k.
Then the feedback capacitor for 100kHz is obtained Cf = 1/(2*pi*Rf*fc)  =1/(2*pi*6.6k*100k) = 241.144 pF so lets say Cf = 270pF
The resulting circuit would be as the following figure:

Gain must be modified if input voltage swing or power supply voltage are different than this example.
I hope this helps you as a starting step.

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

Hi Ivan :)

Thank you very much for your help.

I attach images of the montage I want to make. Highlight the feeding part of the preamplifier formed by MLZ2012M100WT coil, filter capacitors for noise. I want to feed the preamplifier to 1.5V and the impedance of the hydrophone is 2KΩ. You could give me your opinion on this part.
I'm going to test the assembly of the TL072 because it's available to me right now. The difference with OPA1662 or OP1642 can be noticed. I'm going to ask for both and carry out the assembly that you indicated to me to see how it works but I would like to know your opinion.

Kind Regards,

Jota Formoso.

Hi Iván,

Thanks for your answer.

I would like to know your opinion to know if to use the OPA1662 or the OP1642, it is better or the difference would be noticed much. I have never used these components and since they are specific for audio, I would like to know if the difference is noticeable compared to the TL072.

Best Regards,

Jota Formoso.

Hi Ivan,

I think I'm making progress in the design. But I have another question, which I find difficult to solve. I want
put the part of control and acquisition of data with a microcontroller. My question is, if it is necessary to design a filter in the GND,
that is, isolate the noise and differentiate between analogue GND and digital GND. Which is the best option.

Kind Regards and thanks,

Jota Formoso

Hi Ivan,

I think I'm making progress in the design. But I have another question, which I find difficult to solve. I want
put the part of control and acquisition of data with a microcontroller. My question is, if it is necessary to design a filter in the GND,
that is, isolate the noise and differentiate between analogue GND and digital GND. Which is the best option.

Kind Regards and thanks,

Jota Formoso