After clearing a lot of doubts about my A/E dead guitar preamp and doing some testing Ive reached the conclusion that the undersaddle piezo is probably faulty. Looking for a replacement part Ive seen three types. A basic type seem like built in or encased in metal. A rigid (but not mettalic) type, like the Fishman acoustic matrix, usually bright coloured. And finally a braided cord type. This last one is the one I have and my question is if I need the same type or it doesnt harm to change. I would like one with the most sensitivity possible.
From your previous question (Sudden death of Fishman preamp on acoustic guitar), I'd guess that you don't KNOW if it's faulty, you're just assuming so. I still maintain that it's the church sound engineer who has the problem.
You will be looking for an under-saddle pickup - the hole will already have been drilled, for the previous pickup. Make sure you get the correct width of pickup. If your guitar has volume controls for the pickup, you need to purchase the same pickup, or at least make sure that the connections are the same. Sensitivity isn't an issue - when correctly installed, any piezo pickup will be very sensitive, and correct gain staging on the guitar and mixing console will provide the right level of output.
Before doing a search for pickups, search for a local guitar tech. A decent Fishman pickup is expensive, and if the problem is somewhere else, the cost of the guitar tech will be cheaper than replacing parts that you're not really sure about.