Oh! I forgot to explain that entirely. As for the CA3140 circuit, I'd love to usean op amp with full wave rectifying function already built in, but I'd have to end up using 8 separate ones, however it could make things easier in the end, I'll test out two configurations using the CA3140 method, and then use the LM324 to also try out the diagram in Figure 6 from earlier.
Also with the full wave rectification - I need this because both sides of the waveform produced by the piezo are important to me. The first peak is the most important to me, and sometimes the peak is negative. However a half wave rectifier is canceling out this signal!
The project itself is dependent on Time Delay between 4 piezos on the same drum skin. This time delay happens in the order of less than a millisecond, but is still noticeable when using an oscilloscope to compared such data.
**broken link removed**
If you look at the readings on the graph, you can see that one peak from a piezo arrives before the rest, followed by two at relatively the same time, followed by the one on the opposite side of the drum.