this is actually from a request from a guy called Jim (sorry don't know your last name) who wanted a peizo preamp because they are so expensive. they are essentially just a high impedance preamp
and you could probably use this for other things like hiZ microphones and whatever.
there is a gain control on this and it uses an op-amp that is able to function as a single rail op-amp which cuts down the component count which is always useful when you need to hide this inside a guitar cavity or something.
