I promise that this is the last one for today! It's also the smallest of the three I've made and housed in an old, wooden, cream cheese box. One isn't enough, you say? Of course not! As long as I had the components out, though, I figured I'd make a few of them. Who knows when one will need a bizarro effect?
This version of the rumbler has one humbucking pickup which senses three springs, a volume control, and has an open portion of the "spring box" to allow easy access to the springs themselves. I've used a cheese grater as a "control plate" as well as a surface to ground the pickup to and serve as a "soundboard" to interact with. In the clip you can hear me using a brush and mallet on it as well as using the stick end of the mallet to "twangle" the springs and get that "groan" effect.
The jack is a Switchcraft unit and I've reinforced the box where it needs to be.
Here you can see how the springs are anchored. The three below the pickup (the chrome bit hanging down from the grater) give it plenty of natural "reverb" and output while the two visible are easy to mess with.
The pot is an Alpha 500k.