I just tried my first rod-piezo, mounted under the saddle of the bridge. I was rather underwhelmed. The sound was just fine, a bit more mellow than my usual disc type piezo, but the volume was so soft that I had to crank my 15 watt amp to 11 with full gain to hear it at all.
I swapped it out for a disc and was back in bussiness.
Is it typical to use a preamp with rod piezos? Or did I just get a bad one? Maybe there is some trick to mounting inside the bridge that I am unaware of?
In my opinion,a rod piezo is superior to a disc.It sounds to me that it might not be connected properly or more likely,it's not seated properly under the saddle.Make sure the saddle is firmly making contact with the rod along it's full length and check your soldering.As for preamps,they do help,especially with discs but I've never found it absolutely essential to use one.I use a rod piezo on my one string diddley bow which I plug straight into my amp and as long as I don't raise the roof with the volume,i get no feedback whatsoever.....
Rod piezos are in my opinion far superior to the disks.
You need direct contact with a rod piezo, and that's where your problem arises.....there needs to be good pressure form the strings onto the rod.
I insert rods directly under the bridge so that the string pressure down on the bridge presses against the rod.
The way I do it:
Build the bridge piece, then slot a trench along the top of this.
Drill a hole at one end of the bridge piece for the lead to the piezo rod to go through.
Drop the rod into the bottom of the trench, then drop a piece of corian on top of the rod, the same length as the trench......that becomes the bridge piece the strings mount on, so the string pressure pushes down on the corian strip, which in turn pushes down on the rod piezo.
You'll never go back to the disks once you have a rod piezo set up properly....great sound with almost no box sound.