I have wired a disc piezo and a rod piezo in parallel through a simple active (9V) endpin Jack preamp. I tested it before installing, by tapping them on the table. The disc piezo cane through strong. The rod piezo was faint. I plugged a different rod piezo (by itself) into the preamp, and its signal was strong (as loud as the disc had been).
I thought maybe I had messed the first rod up when wiring it and the disc together. So I took the second rod piezo (the one that tested strong by itself) and soldered it and the disc in parallel, then plugged them into the preamp. This time I took extra care in wiring and soldering them. I am absolutely certain I have wired them correctly, in terms of negative and positive, with no shorts. Same result. The disc signal is loud, but the rod signal is faint.
Is there something about the different signal strengths of discs and rods that makes a rod come through quieter than a disc when wired in parallel through the same preamp?
I don’t know if these details make any difference to the question, but the disc is somewhat oversized (2 inches metal diameter), and the disc is wired with slightly thicker gauge wire than the rod (which is wired via the standard shielded wire with the woven outer shield/ground).
That’s a great idea. I will attach the disc piezo all the way up at the neck and body junction.
Also, I didn’t really factor in the fact that rod piezos are made to function under compression, not merely vibration. When I tested them, I simply tapped the disc and rod on the table or flicked them. Perhaps that isn’t really a proper test of what signal the rod will produced when compressed under the saddle.
In any event, it sounds like a rod simply generates less signal than a disc. Next time, maybe I’ll install a blend pot between them to see how that works.