With the Wur-monica, I have found a novel way to amplify a harmonica. The Wur-monica does not have a microphone or pickup of any kind inside. Instead, the Wur-monica relies on the electro-acoustic properties of the instrument itself as a signal source. In fact, the Wur-monica is based on the same elegant principle as my beloved Wurlitzer 200A electric piano (hence the name).
How it works:
The original Wurlitzer Electric Pianos of the 1960s were gorgeous machines with a really interesting way of generating sound: instead of strings, the piano had large reeds struck by hammers (see picture). The reeds produced a signal using an ingenious electrostatic principle: the reeds were charged up to hundreds of volts, so that they formed a capacitor with the adjacent ground plate. When the reeds vibrated, this capacitance changed, pushing electrons back and forth to magically produce ethereal honks, buzzes, crunches, and chimes. If you think about it, a condenser microphone also works in much the same way (except with parallel plates instead of vibrating reeds). In a sense, each Wurlitzer piano reed is its own condenser microphone.
The Wur-monica works using the same principle as the Wurlitzer piano. Each brass reed inside the Wur-monica is mounted on a brass plate, but does not touch it. This creates a very small capacitance between the reeds and the plate. When a reed vibrates, this capacitance changes, creating a signal that can be amplified. Again, no mics, pickups, or piezos are needed -- wires are connected directly to the reeds, so that the reeds themselves produce their own electrical signal.
The main advantage of this technique is that it is immune to feedback from the speakers, because the device does not pick up airborn sound, but rather the raw vibrations of the metal parts. Of course, I'm also hoping to maybe capture a little of that crunchy, magical, soulful Wurlitzer sound in a pocket-sized instrument.
This project is only a proof of concept, so I didn't spend much time refining the circuitry, the method for mounting the reeds, or the intonation, for that matter. In fact, I only bothered to mount seven of the reeds, and one of them is still kind of wonky and shorts out the circuit if I blow too hard (you can hear it shorting in the video). Still, after only a few hours of hacking, I was pretty pleased with how the prototype looks and sounds.
Please check it out and leave me some feedback! And if you like classic devices updated with new electronics, check out my USB Typewriter instructable, too. And please vote for this project in the Pocket Sized Contest! Thanks!
Final Test (just before getting dizzy and passing out):