Added a feedback capacitor on the first stage of the amplifier. I was having a problem with a superimposed wave on top of the high E on the guitars. Before I started this project, I made a feather wing to test out the 12mm piezo discs I used on this tuner. I did not add the filter caps on the feedback paths of the amplifier to see what would happen and it worked well so I did not include them on this project. This might be due to the LM324 frequency response being very low which is why i tried it out. No sense in filtering something out the amplifier will not amplify if that is the case. When I had seen the superimposed tone, shown on a previous post, I assumed it was due to the feeback capacitors missing. I struck the string many different ways to see if it was an overtone and could not get it to go away. I just added the capacitor and it dimished it a little but I believe this is not the problem anymore. I am able to strike the string with my fingernail and the tone is clean. Snapshot above. I strike it with a pick and the overtone returns but a little diminished. Never had seen this before but I am new to piezos. The electrets and mems microphones I used before never shown this overtone. Not sure I understand how the piezo picks it up but not a microphone considering it is a high frequency - about 2k. Anyway, I want to stay with the piezo because you can use them in noisy environments. Could add an electret with a switch but maybe on a different version of this project. So far all is working out in principle.