DS Audio Grand Master Cartridge and Grand Master Equalizer
It seems like it was only yesterday that I rave-reviewed DS Audio’s Master1 phono cartridge and Master1 EQ unit, at the time DS’s most advanced entries in that tiny new niche of analog playback—the optical cartridge (oc). While we’ve grown used to regular game-changing advancements in digital audio (MQA and streaming being the latest), analog is a different story. Since Ortofon’s patent of the moving coil circa 1946, Norman Pickering’s invention of the moving-magnet cartridge with user-replaceable styli and (along with Joe Grado) the moving-iron cartridge circa 1948, and Columbia’s introduction of the long-playing record in 1949, there haven’t been many game-changers in the world of vinyl. This is not to say that improvements weren’t made in cartridges throughout the latter half of the twentieth century and the start of the twenty-first; just that those improvements have tended to be refinements of previous designs. So, the advent of something truly new (and in many respects, better) is something to write home about—which is what I’m doing now.
How Optical Cartridges Work
Unlike CD or SACD players, there is nothing digital about optical phono transducers. All DS Audio cartridges use conventional diamond styli to read the modulations engraved in a record’s grooves. Where they differ from conventional magnetic cartridges is in the way they turn those tiny modulations into electrical signals. Unlike mm, mi, and mc carts, oc’s don’t transmit vibrations to an assembly of coils and magnets for conversion into voltages. Instead, they translate that constant stream of jiggles and jogs into variations in the intensity of light from an LED built into the cartridge body, the brightness of which is altered by a thin, lightweight “shading plate” mounted to the cantilever, close by the stylus. Each jiggle or jog causes this shading plate to move in concert with the stylus, blocking some of the light from the LED, and, thereby, changing the strength of its beam. This continuously varying stream of LED light and shade is subsequently read by high-precision photoelectric sensors (also built into the cartridge), which convert it to continuously varying voltages for each channel. Those voltages are equalized by one of DS Audio’s dedicated EQ boxes, which must be purchased with the cartridge, before being sent to your preamp or integrated amp. (DS offers quite a variety of these EQ boxes at substantially different price points, all of which will work with any DS cartridge.)
Why go to all this trouble when magnets and coils have worked pretty darn well for the past one hundred years? Because, says DS, magnets and coils generate magnetic resistance to the movement of the stylus, impeding tracking; they are also relatively heavy devices, whose internal mass has to be leveraged by the cantilever, further encumbering the stylus. A light beam isn’t magnetic, so it generates no resistance to stylus movement; plus, unlike magnets and coils, a light beam is virtually weightless, so inertia and moving mass are reduced to nearly zero.
As I said in my review of the Master1, eliminating magnets and coils appears to have many audible advantages—not the least of which are dead-quiet background silences, without a hint of RF or hum (provided that the tonearm is properly grounded), the elimination (at least in theory) of the inevitable treble peakiness of moving-coil cartridges, and a bass response that (once again in theory) can extend down to 1Hz. (There are also drawbacks to optical transducers, which I’ll come to in a moment.)
A Bit of Optical History
Calling the optical cartridge “new,” as I did a few paragraphs ago, isn’t exactly the case. The idea of using light to generate voltages in a phono cartridge dates all the way back to 1941, when Philco introduced its “Beam of Light” transducer, which employed a lightweight sapphire stylus (as opposed to the massive steel styli of the 78 era) mounted on a mirror to modulate the beam from a miniature bulb and reflect it into an “electric-eye” photodetector. Toshiba re-introduced this idea in the 1970s with its C-100P optical cartridge, which also used a small filament lamp as a light source.
Unfortunately, both the Philco and the Toshiba systems were prone to failure, chiefly due to the heat generated by the bulbs of their lamps (and the necessity for factory-replacement of those bulbs when they burned out, which was soon and often). With advances in the LED and photoelectric-sensor technology used in computer-era optical “mice,” Tetsuaki Aoyagi, a young Japanese engineer with the Digital Stream Corporation (which, alongside Microsoft, co-developed the optical mouse), had the happy idea of adapting these cool-running, high-precision, high-reliability, miniaturized devices for use in a new Toshiba-like phono cartridge. (Indeed, “Aki,” as Aoyagi calls himself, sought and received the help of the C-100P’s designer, Hamaguchi Kazuo, for this project.) Suddenly, heat and the wear and tear it exercised on the wiring of oc’s were no longer problems. Neither was bulb failure. Inertial mass was also tremendously reduced. And the accentuation of high frequencies (an unavoidable side effect of any velocity-reading system like that of a conventional magnetic phono cartridge) was theoretically eliminated.