Hi, guys,
I made some tests with my reverse engineered MiSi preamp using a signal generator. The preamp is not at fault at all. I include a screenshot of my scope in its "spectrum analyzer" mode (actually, it is fft with a spectrum analyzer interface). It shows the first harmonic that comes out from the preamp to be around 40.8dB down. This is too weak to be heard. Moreover, its frequency is an exact double of the main signal! This means, even if our ear were able to hear it, it would be in complete unison with the main tone! But what we hear coming from the guitar is a far cry from unison. And the installation method we used is not at fault also, as the original MiSi unit, installed exactly the same way creates no noises. So, the only culprit remains - chinese piezo. We ordered another type, hope to get something better.