Aluminum Cutoff Kalimba and Contact Mics

Just fiddling around with some aluminum off-cuts from milling front panels.
Screwed them in to a piece of plywood and attached a few contact mics with some doublesided tape.
Run the contact mics in to an Inverting Mixer / Amplifier OpAmp Configuration.
The Input resistors are 1M and the Negative Feedback resistors are 4.7M.
That sets the gain for -4.7.
Didn’t test the voltage but i could hear it clearly on the speakers so it got the job done for playing around.