This is probably the simplest vibrato circuit I've run across. It is based on Tim Escobedo's Wobbletron circuit, but it uses a LED/LDR instead of a JFET for the variable resistance element and the LFO is totally different.
It's definitely on the subtle side of vibe. It's more pitch bendy than it is tremolo-y, and it's hard to hear the effect on low LFO speeds.
This version has a single control: Rate. The LFO depth is set by trimmer, because the sweet spot is very small. There is also an optional switch that adjusts the speed range of the LFO to go from normal to high-speed ring mod and mild octave-down tones.
Just to be clear: This is NOT a Uni-Vibe clone or workalike.
It's simple and subtle, but sounds pretty good I think.
Here is a sound clip I recorded (I was playing the dark, so don't mind the couple clams I hit):http://soundcloud.com/effdub/wobble-vibe-v1-demo
I am working on a more robust version that is deeper and a bit pitchier (and has more parts), but I thought people would enjoy this one as a really simple build or a springboard for a new circuit.
Anyone should feel free to make layouts for this.
Bill of Materials:
LDR1 light = ~100R / dark = ~3M (probably anything will work here)
D1 LED (normal diffused LED works fine)