Added Feedback Capacitor

A project log for Clipper - A Clip on Tuner for Musical Instruments

Minimalist LED strobe style clip on instrument tuner using a SAM D11C and a piezo sensor with LED readout.

rrace001rrace001 08/25/2019 at 21:010 Comments

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.