I built this circuit:
It is based on this design for a single-supply non inverting amplifier:
When I tested my output waveforms with earphone A I got normal results:
When I used earphone B, I got abnormal results:
Blue - Vout Red -Vin
I suspect this has something to do with earphone B pulling more current than earphone A, and the op-amp upper current restriction, though I am not too sure yet.
Why do you think the waveforms of voltage behaves this way?