Although it may seem novel because of its rarity, using light to read the undulations engraved in LP grooves and photoelectric cells to convert them into voltages is a relatively mature technology. The Japanese were already experimenting with optical cartridges in the 1960s, and periodically since then various iterations of this idea have popped up on the market.
Indeed, it wasn’t all that many years ago that I reviewed the ELP Laser Turntable, which used beams of laser light (five of them, precisely aimed at various spots on the shoulders and the bottom of a record groove and controlled by a large mirror) as a “stylus.” Those beams of laser lights were then reflected off the grooves to optical sensors and transformed by the ELP’s photoelectric circuitry into equalized line-level signals. The advantages of this system were manifold: Since there was no stylus, there was no stylus wear; moreover, because of its laser-based, groove-depth sensor, the ELP was said to be able to read warped or damaged records more effectively than mechanical styli.
While it may seem counter-intuitive given its CD-like use of light, there was nothing “digital” about the ELP Laser Turntable. The system worked rather more like Laserdisc players (remember them?), reading analog data rather than a series of zeros and ones, and simply (or not so simply) turning them into currents. There was no analog-to-digital or digital-to-analog conversion at any stage of the process.
Despite its undeniable ingenuity, the ELP did have a problem that, for me, proved intractable. To wit, the laser stylus had no way of distinguishing between data and, well, dirt. Unless a record was immaculately cleaned (and even then), the lasers would read and amplify any specks of dust and grime embedded in the grooves as if they were part and parcel of the musical signal. Now it’s true that conventional mechanical styli also “see” this detritus as they track grooves, but because of their mass they tend to push such dust and dirt ahead of them like snowplows (until, of course, enough crap collects on the stylus to induce mistracking). As a result, the “sound” of dirt doesn’t register as distinctly via conventional playback as it did via the ELP, which, with really worn records, produced a kind of crunching noise in the background.
Comes now the latest iteration of optical playback: DS Audio’s new DS-W1 “Nightrider” cartridge. A “re-creation” of a 1960s design that is considered a classic in Japan, the Nightrider uses state-of-the-art technologies developed by Japanese photo-optics specialist Digital Stream Corporation (the co-inventor, along with Microsoft, of the optical mouse) that simply weren’t available when the original was built. For the purpose of comparison, the primary thing that sets the new Nightrider apart from something like the ELP is that it uses a conventional Shibata diamond stylus attached to a conventional boron cantilever, rather than beams of laser light, to read the grooves. As a result, it doesn’t have the ELP’s problem of distinguishing dirt from Debussy—a major advantage.
Of course, the Nightrider’s Shibata stylus also has considerably more mass than the ELP’s near-massless beams of light, though DSC claims that the entire Nightrider stylus/screen apparatus—for which see below—has less moving mass than the ELP’s mirror-guided system. Be that as it may, compared to a conventional moving-coil or moving-magnet cartridge, in which the stylus/cantilever has to leverage heavy coils and magnets at its back end, the Nightrider is spectacularly lightweight. Housed in a machined aluminum body that contains no magnets or coils, it weighs in at a mere 6.5 grams and tracks between 1.3 and 1.7 grams, with 1.5 grams said to be optimal.
Here’s how the Nightrider works: The cartridge uses a light source (a miniature LED) that is powered by the included equalizer/power supply (which replaces your phonostage) via the tonearm cables and internal tonearm wiring. The record-groove vibrations transmitted by the stylus/cantilever modulates this LED light via a moving screen, and the modulated light is picked up by a photoelectric sensor. This photodiode converts the light into an electrical signal, sending it back through the tonearm cabling to the equalizer/power supply unit, which amplifies the signal into a RIAA-equalized line-level output. Unlike the ELP, there are no lasers in the Nightrider. As with the ELP, there is nothing digital about the DS-W1. It is an entirely analog device.