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building a very sensitive listening device

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As I explained in my reply to your PM, an electret mic has a fairly low impedance so the Leak2 circuit has a fairly low input impedance. But a piezo transducer is a fairly high impedance so you neede a preamp with a high input impedance like used on a guitar contact mic, a drum contact mic or a car engine sounds contact mic. The Makezine video I posted shows the schematic of a suitable jfet preamp and Google shows many preamp circuits for a piezo contact mic usually using a Jfet.
 
If i use the preamp circuit shown in the video posted by you; then, how do i merge both the circuits ? (The preamp circuit and the Leak2 circuit)
 
Remove the resistor that powers the electret mic then connect the circuits together. Maybe remove an extra coupling capacitor.
Simple.
 
I want to make a separate variable bandpass filter... so that the leak noise can be traced over a wider variable band width...
how do i go about it? Can anyone help me with the schematic?
 
I want to make a separate variable bandpass filter... so that the leak noise can be traced over a wider variable band width...
how do i go about it? Can anyone help me with the schematic?
Please learn about the basics of electronics.
The Leak2 circuit has RC lowpass filters and RC highpass filters. Change the values of the resistors for a variable bandwidth.
 
i got that... i need a separate band pass filter... can't use the same one given in Leak2 circuit... opa2134 is pretty costly.. so wanted to know if there is an alternative.
 
Hey is this circuit correct for a piezo disc in place of the electret mic ?
 

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In LEAK2, your R18 powered the 6.2V zener diode D1 that you do not have. R5 also powered the Jfet inside the electret mic from the regulated 6.2V.
Don't you know that a piezo transducer generates its own voltage and does not need R18 nor R5 for power??

Don't you know that a piezo transducer is a capacitor so C9 is not needed??

Your totalgain is about 626,000 so you will have all kinds of noise and interference and your circuit might pickup traffic vibrations on the other side of earth!
 
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