I recently removed the strings to have a look at the bridge, and saw that the piezo elements make direct contact with the bridge feet, but are embedded in foam on the side that contacts the body. Kozmikyak, or anyone else, ever try removing the foam to see how the sound changes? I imagine that the body's vibration would come through better, but the foam must be there for a reason...maybe the pressure from the bridge is too much, or there is a buzz without the foam? Maybe electrical tape instead of foam? I'm planning to experiment with this in a couple of weeks.
The standard pickup installation is a pair of piezo discs wired in-phase (meaning both red wires to one side of a jack, both black wires to the other side). The pickup elements are a bit fragile on the side that contains the solder bumps for the wires--put too much pressure on that portion of the pickup and things can go wonky.
The last three pickup installations I've done have been of similar design. I do remove the foam, but I use varying degrees of damping/stress relief.
The configuration that worked best for a _HUGE_ fundamental-heavy bass tone was to use those neoprene washers one can find in a hardware store. On the side of the pickup without the solder bumps, I made a disc of this material the same size as the pickup disc. On the other side, with the solder bumps, I cut out a slot of the neoprene disc right where the solder bumps would be. If you get a thick neoprene washer you can even fold a pickup-sized disc in half, and use a fingernail scissors to trim a slot _halfway_ through the thickness. I super glue the pickup discs to the neoprene and put bits of double-sided tape in the bridge slot to keep them from shuffling around while trying to install the bridge.
This worked great for bass sounds, but was not sufficient for my lead arco tones; it dampened too much high end. My next attempt was using very thin squares of maple. I put one slice of maple on top of the pickup and one on the bottom. I used a Dremel tool to carve a little slot into the wood square where the solder bumps would be on the pickup. Once again, super glued together. I'm not talking about huge slices of wood, but I did have to shave down the bottom of my bridge substantially to do this. I had a luthier on hand locally to carve me a new bridge in case this experiment failed. Luckily it did not.
The result was a bit _too_ high-endy for my taste, at least arco. So my final experiment used balsa wood veneer. I ordered 1/16" thick strips of balsa wood, and did my pickup sandwich. Except this is so thin that I could just use the Dremel cutting disc to cut a slot all the way through a sheet of balsa where the solder discs would be, and just put another sheet of the balsa over that sheet. Once again, super glued together. This seemed about right to my ear.
I have the best luck with the pickup pair if the elements are located as far from the middle of the bridge slot as possible, but your taste might vary. If you use the double sided tape to keep things in place while installing the bridge, and you make sure to solder the wires leaving lots of slack, you can experiment with placement; however, without modifying the bridge your placement options are limited.
I don't know that I'd recommend going down the path of pickup mods for giggles. I had a specific reason for what i wanted to do; I wanted a simultaneous set of arco pickups and pizz pickups, so I could footswitch between them. But keeping that in mind, you're likely to get a reasonable tone no matter what you do with the "stock" pickup elements. Stress relief and dampening of high frequencies are the main points I ran into.
Jesse was so kind as to tell me what pickup elements he uses. They're not fancy, but with proper preamp they sound rather nice. I'll not mention the part here, lest he get a flood of requests to support non-standard configs. But if you ask him nicely, he's likely to accommodate you.
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