Ortofon MC 100U Phono cartridge Review

Ortofon’s MC 100U is the least expensive model in the company’s line of Ortophase cartridges. It is a low-mass, moving-coil cartridge whose standard 1/2-inch mounting centers allow it to be mounted in virtually any headshell. Like the other models in the line, the MC 100U was designed for optimum phase response, not necessarily the flattest frequency response—hence the designation “Ortophase.” Ortofon’s research into why moving-coil (MC) cartridges often sound different from moving-magnet (MM) cartridges suggested that high-frequency phase shift plays a major role in these subtle sonic effects. The moving system (the stylus and cantilever) of every cartridge resonates at some high frequency, usually (but not always) above the audio range. An unsuppressed resonance produces an output peak at the resonance frequency, a peak that often affects a wide range of frequencies on either side of it. A stylus/cantilever resonance, like all resonances, is accompanied by a shift in the signal’s phase that can reach as much as 180 degrees at the resonance frequency and often extends down into the audio range.

Most cartridge designs use electrical or mechanical damping to reduce the amplitude of the stylus resonance. When mechanical damping is used, it is usually applied to the internal moving parts by means of rubber-like elastic materials. Some MC cartridges use no damping, however, and the result is a large response peak above or at the top of the audio range, accompanied by an appreciable rise in output at the upper audible frequencies. Such accentuated high-end response is responsible for much of the sense of “air” and “definition” attributed to some moving-coil cartridges.

After extensive listening tests of basically identical cartridges having different amounts of stylus damping, Ortofon concluded that phase shift in the audio range is a more serious drawback than a rising amplitude response. The undamped system tested had a pronounced high-end rise, but its phase shift was restricted to a narrow range of ultrasonic frequencies. Ortofon’s designers found that this combination produced the best imaging and overall feeling of realism despite the excessive brightness. When the damping was adjusted to flatten the frequency response, the phase shift extended down into the audio frequencies, and the stereo imaging was degraded. The optimum result, Ortofon says, was obtained with partial damping, which left a moderate high-frequency rise but greatly reduced the phase shift in the audio range. The Wide Range Damping (WRD) system that resulted from this research is a key feature of the Ortophase line.

The WRD system consists of a tiny metal disc sandwiched between two rubber discs, with the stylus cantilever passing through their centers. At low frequencies the double rubber mount allows the cantilever to move freely through large excursions. At higher frequencies, the compliance of one of the rubber discs decouples the innermost portion of the cantilever, reducing the effective tip mass and improving the high-frequency tracking and response. The damping provided by the discs is designed to produce a rise in response starting at around 15,000 Hz and peaking at approximately 30,000 Hz, with a reduced phase shift in the audio range.

The mass of the MC 100U cartridge is a very low 2.3 grams. Since most tone arms cannot be balanced with such a light cartridge, the MC 100U comes with a removable 3-gram weight in its top (mounting) surface. The total 5.3-gram mass, though still less than the weight of most moving-magnet cartridges, can be balanced by virtually any tone arm. If your arm doesn’t need the extra weight, you can easily remove it to take advantage of the MC 100U’s very low intrinsic mass.

One reason for the cartridge’s small size and mass is that its coils are surrounded by a powerful samarium-cobalt ring magnet, which creates a symmetrical magnetic field. The aluminum-alloy stylus cantilever is tipped with a nude elliptical diamond stylus.

The Ortofon MC 100U is a low-output cartridge that requires a step-up transformer or pre-preamplifier in order to drive a standard moving-magnet cartridge input. Ortofon offers two suitable transformers, the T-10 and the T-20. The T-10 supplied with our test cartridge (and shown in our photographs) is a very compact unit, measuring 3-1/2 x 1-1/2 x 3/4 inches. As with most moving-coil cartridges, the stylus is not user-replaceable. Each cartridge comes with a small but accurate stylus-force gauge. Prices: MC 100U, $250; T-10 transformer, $150.

Lab Tests

After removing the 3-gram weight from the MC 100U, we mounted the cartridge in the low-mass arm of a high-quality turntable. The recommended tracking force of 1.5 grams was used throughout our tests. We made all cartridge measurements through the Ortofon T-10 transformer; during listening tests we also used our regular MC transformer, which sounded identical to the T-10.

The output of the cartridge (through the T-10) while playing the 1,000-Hz, 3.54-cm/s standard-level tones on the CBS STR 100 test record was about 5.3 millivolts, with the channel levels matched within 0.25 dB. Since the transformer steps up the voltage by a factor of forty, the actual cartridge output was about 0.12 millivolt (120 microvolts). The frequency response, again measured with the STR 100 record, was flat within ± 1 dB up to about 9,000 Hz but rose to + 5 dB at 20,000 Hz (see graph). The channel separation, about 30 dB in the midrange, was still a thoroughly adequate 17 dB at 20,000 Hz. We also measured the frequency response with the JVC TRS-1007 test record, which showed a smaller high-frequency rise—to +2.5 dB in the range from 10,000 to 20,000 Hz.

Our subjective tracking tests immediately set the MC 100U apart from many of the other MC cartridges we have used. For years, an MC cartridge could be expected to have low compliance, hindering the tracking of high-level bass recordings, and often an undesirably high vertical tracking force (2 grams or more) as well. The MC 100U is rated to track at a very reasonable 1.5 grams, and it does a first-rate job at that force. It played the very high-level 32-Hz sections of the Cook Series 60 test record with no difficulty, and it performed equally well with the 30-cm/s 1,000-Hz tones on the Fairchild 101 record. Even the 300/315-Hz test tracks on the German HiFi #2 and the DIN 45549 records were played cleanly at the 70-micrometer level.

The MC 100U’s tracking distortion, measured with the Shure TTR-102 and TTR-103 test records, confirmed its excellent tracking ability. The intermodulation distortion was a low 2 to 3 percent up to a recorded velocity of 16 cm/s and a reasonable 9 percent at 27 cm/s (many cartridges, especially MC types, mistrack totally at this level). High-frequency tracking was excellent, with the TTR-103’s 10.8-kHz tone bursts yielding a distortion range from 0.5 percent at 15 cm/s to 0.7 percent at 30 cm/s. These figures are close to the lowest we have measured from a phono cartridge and may reflect the intrinsic distortion of the test record.

The 1,000-Hz square waves of the CBS STR 112 test record showed only a single overshoot and a moderate amount of low-level ringing, a considerably better result than we have observed with most other relatively undamped MC cartridges. The vertical stylus angle was 20 degrees as rated. In our low-mass tone arm, the low-frequency resonance of the stylus/arm combination was around 13 Hz, making the combination virtually immune to the most severe record warps as well as to external jarring or impact (which can cause difficulties when the resonance frequency falls much below 8 or 9 Hz, an unlikely possibility with the very light MC 100U).

Comments

We could not confirm—or contradict, for that matter—Ortofon’s claims for the superiority of the Ortophase design over other, more conventional approaches, but listening to a variety of records established that the MC 100U is in every respect a very fine-sounding cartridge. It did not seem in the least “bright,” in spite of the undeniable high-frequency emphasis. Its overall sonic balance was exemplary, and in our tests it did not exhibit many of the usual MC qualities— very crisp, excessively sizzling highs and the like—that are considered virtues by some and aberrations by others (including me).

The MC 100U’s output level makes a step-up device a must unless your preamplifier has a really good low-noise, high-gain MC input, but the tiny Ortofon T-10 makes it unnecessary to find some place to put a large or heavy transformer. The T-10 also proved to be unusually resistant to hum fields, another common problem with moving-coil step-up transformers.

Even if we cannot unequivocally confirm Ortofon’s thesis on the importance of audio-range phase shift (we have not had the opportunity to hear a demonstration of its reality), we can affirm that the MC 100U is an excellent cartridge. Besides its fine performance, its very low mass should go a long way toward making a phono system immune to record warps and other gross mechanical stimuli. An MC cartridge with all this and sweet, uncolored sound at a relatively moderate price—who could ask for more?

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