After trying and trying to come up with a bow wheel that could maintain effective friction on a surface while isolating the noise of the motor and mechanics from the acoustic resonating chamber, I decided to investigate making an electromagnetic bowing device, like the E-bow. Pictured above is the prototype for such a device. A physical oscillator. There are two coils around AlNiCo (Aluminum Nickel Cobalt alloy) magnetic poles, one a pickup and the other a driver. These are wired to the input and output of an audio amplifier IC and fed back into one another through the spring steel tongue (pictured here with a piezo element under it’s bridge terminating at the 1/4” jack). A digital potentiometer regulates the amount of voltage driving the circuit for dynamic control. Staccato articulation can be achieved by instantly reversing the electrical polarity of the driver to stop the vibration. The gain of the audio amplifier goes quite high, all the way to the 12V rail supplying it and reads as a square wave on a scope even at low gain settings. Because the steel tongue, like a speaker cone in a back-feeding guitar amplifier, is physically unable to jump to the +/- DC poles and has to ‘slide’ to them, a near-perfect sine wave results.