How Does a Wurlitzer Electronic Piano Work?
With the lid of this Wurlitzer 140b off, you can clearly see the keyboard’s mechanical action. The reeds and the harp are also partially visible in this photo, particularly in the treble section where the dampers are abbreviated. In this model, the amplifier is located at the back (where the wires at the back left lead).
All Wurlitzer electronic pianos - from the model 112 to the Wurlitzer 200a - are more or less built the same. There are subtle differences in the mechanical action and the amplifier, but they all follow the same basic principles.
When you hit a key on the Wurlitzer electronic piano, a felt-tipped hammer rises and strikes a metal reed. The reed vibrates to a certain pitch, which is determined by the weight of a lump of solder at the end of the reed. A pickup converts the vibration into an electrical signal, which is finally amplified by the onboard amp and sent to a speaker.
Here’s how it works in a little more detail:
The mechanical action. Wurlitzer was primarily an acoustic piano company, so the mechanical action is actually well-designed and pretty comfortable to play. It uses a simplified piano action that is meant to strike reeds instead of piano strings. Regulating screws allow the user to make periodic adjustments to the mechanical parts in order to ensure that all keys play consistently across the keyboard.
The pickup. The Wurlitzer’s pickup is an electrostatic pickup. Just like a magnetic pickup found in a guitar, an electrostatic pickup converts adjacent vibration into an electrical signal. But unlike a guitar pickup, an electrostatic pickup requires a polarizing voltage to function. So, the Wurlitzer amplifier sends 180v to the input, which is high enough for the pickup to reproduce the entire swing of he reed without introducing distortion.
An electrostatic pickup is basically a capacitor: the pickup and the reed are the conductive plates, and the air between them is the insulator. The movement of the reed changes the capacitance of the pickup, which induces a signal voltage across it. This is very similar to the way a condenser microphone works.
The amplifier. Because the pickup requires 180v to function, the Wurlitzer requires its own custom-designed amplifier. (Typical keyboard and guitar amps are different because they don’t send high voltages straight to the input jack.) Other than that, though, Wurlitzer amplifiers are similar to other audio amplifiers. For the most piano-like result, they are designed for clean signal reproduction. Some models additionally have an aux output so that they can be connected directly to other amplifiers or recording devices.
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