piezo transducer for EDrum

I am planned to build a project from the following link:
https://edrum.info fromt his link I made my PCB circuit.. with a slight changes I made the circuit to work fine with naked crytal(without any cover or others).. and I made a cover to my piezo crystal as attcahed in the photo, this was with a wooden piece cutted into round and piezo covered with a rubber(since I am going to hit the crystal with hand I chosed rubber that will make less pain to my fingers) but now the problem was I am not able to get signals from the crystal what I made with even a gain of 11 I fixed for the amplifier...
I can't suspect the crystal since the same setup was working fine with SPD-20 module( I bought from Roland) with my fingers...
I am not able to get any signal fromt the amplifier when I use it in my EDRUM project but the same crystal setup working fine with Roland SPD-20 module... what i lack from Roland module... should I increase the gain higher than this or something else I should make... I can't change the setup of crystal because it fits perfectly for my project and since it is working with accurate sensitive with Roland SPD-20 module...
Kindly poitn me where was the problem... All suggestions are welcomed in any degree...

Try a gain of 100. Any buffered CMOS gate with 1M feedback and cap to 10k series to inverting gate should work with AC coupled out.

Even an electret mic would work.

Is it acceptable that a gain can be raised to 100...???
can you pls elaborate about electret mic....???

I tested with even gain of 1000, where I am missing I don't know, should I look at the ADC part instead of looking at amplifier part... since the circuit works fine for others...???
What was the logic used in SPD-20 to boost the signal to that much level... the same drum pad was working fine the spd-20 board with sensitive... but when I hit too much hard also it is not capable to detect the signal....??? Pls help in getting this work with Piezo crystals....

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The circuit diagram is **broken link removed**
and the Roland SPD-20 board is using some other technique to boost the signal....

I am getting a full range change of 0.500 mV to 0.530 mV change if I set a gain of 200 that is the difference is 0.030mV whicch is too low for my PIC ADC resolution...

Kindly do needfull

What levels do you get out of rectifier channel Vdc, with no sound and full sound? If not 0, 1V respectively , then we can go from there.

workign with 5V Vdc input for MC, 8V Vdc for OP-Amp... I need to check in the amplifier part alone... atleast if I get 1V diference then it will be fine... since I need to take three levels of input from piezo(light, medium and hard hit) shall I increase the voltage to op amp from 8V to 15V and try will that have an effect...???

If I hit on the piezo directly I am getting the signal difference upto 1V with gain of 10 but with the cover that what I made was not able to get even when the gain was 1000... But the same setup was working fine with that module... I am totally confused and stuck where and what I miss....