why isn't this homemade (badass) STOMP BOX not working??

[sleesaw]

Hi, I made myself a stompbox that's similar to this one:
http://www.youtube.com/watch?v=0BM0WNtJzcs

And I'm wondering why it's not working! I happen to have jazz bass pickups laying around and I'm using those. Is that the problem? Do I need an older license plate (made from a different formed steel or something?). Anything will help! Please let me know your thoughts! I plug it in and theres a slight hum, but I can't get the pickups to react. Thanks!!!

[Mark Hammer]

1) Magnetic pickups will need something vibrating within a reasonable distance. Hold those same pickups 4" above guitar or bass strings, and you won't hear much. So, make sure your height is adjusted suitably. Unfortunately he doesn't really show the actual license-to-pickup distance from the side so it's hard to judge.

2) Magnetic pickups need something that is magnetically conductive vibrating near it, whether ferrous or otherwise. A vibrating aluminum license plate is not likely going to do very much of anything. You might be better off getting yourself a piece of galvanized steel. Less mojo than a license plate, but you'll be able to hear it.

3) Clever idea, actually. Part of what's missing from most piezo-embedded-in-wood foot-stompers is the resonance and drum-head-like decay. Here, the license plate (or whatever you end up using) has some membrane-like qualities, that let it vibrate for juuuusssst a little longer. A bit like what a plate reverb sorta does, except with much less bandwidth, and a much faster decay.

[sleesaw]

thanks for the input!
yeah that's the problem I'm having, not knowing the distance between the plate and pickups. I just don't seem to be getting any response no matter what I do. there is a 'buzzing' so I know it's connected. also, he doesn't show that it's grounded in any way. I'm guessing that's necessary. PLUS there's some comments on that video where people are saying it works, and some that it doesn't work. The poster never responded to the comments though.. UGH.
Am I better off ditching the bass pickups and just using a cheap piezo transducer from radio shack for like 2 bucks?

[eschertron]

The pickup-to-plate distance will be a big factor. If the pickup fields follow the inverse-square law (probably not exactly, but close for this setup) then a signal from a 1/4" pickup to plate distance can be almost 10 times as that from a 1" distance. you probably want a distance similar to the string to pickup distance on the pickups' original bass guitar.
Make sure that the pickups are wired appropriately - ie, not out of phase - or you might be canceling out the signal you do get. Also, tap the pickup with something iron (screwdriver, nail, etc) and verify that you have a HOT signal coming out of your electronics. If you are having problems with the wiring, post a schematic of what you have, and the friendly forum denizens will help with that.

[Justin Thomas]

+1 for wiring... What pickup are you using, too? He said for the one he demoed that there was a bass pickup, but when he showed the construction he said he used "two bass pickups," but it seems that it might have been a single P-bass pickup? Actually why not just yank the guts straight out of a P-bass? No wiring confusion! Keep poking and stick around here - it'll get working.

[Mark Hammer]

Given that arranging for the distance between the pickup polepiece/s and the license plate to be optimal can involvea fair amount of taking apart, and puttig back togother, may I suggest the following: use somethng else to bring the membrane properties of the license plate closer to the pickup. Indeed, what you use may not only be closer to the pickup, but also more appropriate in terms of materials than what the license plate is made of.

So, pop a couple holes through the license plate and select a suitable type of ferrous bolt that will be held against the license plate by a nut on each side of the plate. Mount a couple of them above the pickups, hopefully not protruding so high above the license plate that they hurt your foot, and when you hit the plate the bolts will behave like strings do; vibrating just above the pickups. Once you have the height adjusted optimally, you may want to dab a bit of glue where they attach to the plat to secure them and damp them a tad.

[Steve Conner]

Did you check that a magnet will stick to the license plate? If it's not magnetic, the pickups won't pick it up. You could try something else like the lid of a paint can.

[Mark Hammer]

That's why I suggested some kind of ferrous bolt to attach to the license plate. If the bolt can provide some "magnetic tug", then the composition of the license plate is - pardon the pun - immaterial.