I'm now a member after having stumbled upon a lot of great information in the archives. I'm also pretty close to novice when it comes to electronics, and I have some questions if anyone doesn't mind helping me out a bit.
I'm starting on a piezo project, with the eventual goal of it being a reasonably good quality hydrophone. This group is one of the only places I've come across a bit of a secret - that piezos are inherently balanced, and one needs only connect pos/neg to XLR pins 2/3 respectively and to connect pin 1 to the "chassis" if it exists (e.g., conductive tape, insulted from piezo).
This project is an attempt to address typical challenges in working with piezos, especially when used as hydrophones. It goes like this:
-A (eventually submerisble) shielded piezo element connected (with short-length, lightweight cable, no plugs/jacks) to (eventually submersible) dual balanced I/O buffer circuit, taking the high impedence balanced input and delivering a low Z balanced output.
-The power supply to the buffer is provided by a 9V battery in an "interface box" above the surface.
-The "interface box" contains basically only the battery for the buffer circuitry and possibly coupling capacitors to provide a "local" unbalanced output for quick monitoring (with a portable amp) in addition to the balanced output (running inside to the studio).
In case that's unclear, I've made a basic illustration:
I have looked at some buffer designs linked here before (such as Scott Helmke's piezo mint-box and Don Tillman's preamp cable), but the need for a balanced in, balanced out dual buffer raises a question - for a novice like me with limited equipment, would it be more sensible to use a dual op-amp based design (e.g., a 5532) than to try to match FETs by ear?
Also, to avoid getting into phantom power-ish designs, the 9V from the passive box to the buffer would be run on a seperate cable in parallel to the lowZ balanced signal from the buffer. Since the audio is balanced, I assume the problems of running power parallel to an audio signal are minimized. Am I correct on this?
Lastly, any general assessment-type comments would be much appreciated.