I'm needing to build an electronic stethoscope.
I'm thinking to use this piezo film because I already used a piezo disc (ceramic piezo element I suppose) 25mm large (no idea which producer, eBay purchased) plugged into a preamp of an usb audio interface (Behringer UC2020).
Very good response obtained if layed on hard surfaces, almost nothing on body even at max gain. I think preamp does not give so much gain but anyway I suppose the problem lies in the mechanical characteristics of this piezo disc: it is a metallic plate which to be bent needs a considerable amount of mechanical energy; tiny chest movements (the mechanical energy is soft) are not enough to excite the piezo material.
Now I'm wanting to go forward to a piezo film, totally another mechanical properties, but the high output voltage may became problematic (tech specs says 90V). What would you suggest?
How can I make a circuit to make the output safe? It will be plugged with a XLR connector directly in the preamp of the audio interface.