Traveling beyond the world of pickup magnets to an optical galaxy for musicians.
I wrote a column touching on optical pickups a few years back ["Piezo and Optical Bass Pickups," October 2012], but every once in a while a new or upgraded concept enters the stage that warrants digging deeper. So, to refresh, what sets optical pickups apart from standard magnetic pickups?
Early LightWave pickup systems came with a huge circuit board that didn't leave much wood on the backside.
Photo by Milo Stewart Jr.<p>Until recently, all available optical pickups were built for "transmission" mode, which is an arrangement where the source and sensor are on opposing sides of the string. What the sensor "sees" is the varying amount of shade from the vibrating string. Sounds simple, but the problem here is the positioning and calibration of the elements. As the string vibrates, there shouldn't be a complete coverage of light on the sensor. The result would be comparable to common clipping and you can't simply blow up the sensor's area to allow for more amplitude since your signal-to-noise ratio goes down significantly. The amplitude limits are why these pickups are often positioned close to—or even built into—the bridge and fully covered to shield them from ambient light. Worth noting is that even though the pickup elements are actually rather small, the large-ish covers required for shielding can get in the way when palm muting.</p><p>Light can sense all kinds of magnetic or non-magnetic string materials, so it's easy to switch between roundwound, flats, or even nylons, but this still often requires different setups. In transmission mode, you'll need to recalibrate whenever you're switching string gauges or readjust the bridge to optimize source and sensor usage. That said, the LightWave system's internal circuitry nowadays can support this setup process with LEDs that shine when the bridge sensors are correctly adjusted.</p>A second optical-pickup construction and design arrangement is called "reflection" mode, which we'll discuss next month. Reflection mode <em>does</em> make some of the aforementioned transmission-mode drawbacks easier to deal with, but the arrangement also comes with a load of new drawbacks of its own.