ADC Astrion Phono cartridge Review

The Astrion is ADC’s “top of the line” cartridge, combining advanced design features with hand assembly and test procedures. Like most other ADC cartridges, the Astrion is an induced-magnet transducer. A newly developed “Orbital Pivot System” reduces the moving mass of the stylus system compared to that of some other designs. No armature wires or adhesives are used in the Astrion pivot, which employs a precision armature fitted to a compliant suspension block.

The stylus cantilever is a laser-etched solid-sapphire rod whose high stiffness-to-mass ratio (compared to other materials used for this purpose) minimizes flexing problems and helps to place the stylus resonance well above the audio range (25 kHz or higher). The stylus jewel is a nude-mounted diamond with a square shank for precise orientation of the shaped tip. That shape is ADC’s “line-contact” design with hand-polished radii of 0.25 x 1.5 mils.

The ADC Astrion is designed to track at forces between 1 and 1.4 grams (nominally 1.2 grams). The frequency response is specified as 20 to 20,000 Hz ± 1 dB. The channel separation rating is 30 dB at 1,000 Hz and 20 dB at 10,000 Hz, and the tracking ability is stated to be 30 cm/sec from 3,000 to 10,000 Hz and 21 cm/sec from 400 to 3.000 Hz.

The ADC Astrion presents an unusual appearance, with a gold-finished shielded body enclosed in a clear-plastic mounting. It has an integral hinged stylus guard. The cartridge is packaged in a clear plastic box within a velvet-like cloth bag with a drawstring closure. A similar, smaller bag contains a screwdriver, stylus cleaning brush, and mounting hardware. A cardboard overhang gauge simplifies setting the stylus position for zero tracking error at a 2.6-inch radius.

In addition to being individually assembled, each Astrion cartridge is serially numbered, and the titles of the specific test and music records used in its final inspection and listening test are written in the instruction booklet, which is signed by the inspector. An automatic reminder to have the stylus checked every 500 hours of operation is sent by ADC to the registered owner of an Astrion. If the cartridge is sent back to the factory for this inspection, it will be returned with a new frequency-response curve. Price: $245.

Laboratory Measurements

The ADC Astrion, installed in an ADC low-mass magnesium headshell, was mounted in a medium-mass (S-shaped) tone arm for testing. The vertical force was set at 1.2 grams. The cartridge load was the recommended 47.000 ohms in parallel with 300 picofarads (pF). The effect of other capacitance values was also measured.

The frequency response and crosstalk were measured with the CBS STR 100 test record. The frequency response was an almost perfectly straight line, sloping slightly downward with increasing frequency (the 20.000-Hz output was about 2 dB less than the midrange level). The peak-to-peak irregularities in the response curve did not exceed about 0.5 dB, however, making the Astrion one of the smoothest and “flattest” cartridges we have yet tested. Further checks with JVC and B&K test records showed the usual differences between records, with the former being flatter to 10,000 Hz and falling off more rapidly above that frequency, while the latter was almost perfectly flat to 18,000 Hz.

A lower load capacitance (170 pF) resulted in a very slight upward tilt in the high-end response (about +1 dB at 20,000 Hz compared to the 10,000-Hz level), and a high load of 400 pF raised the output in the midrange by about 1 dB and rolled it off to about — 3 dB at 20,000 Hz. We judge that the effects of load capacitance would be negligible in most listening situations.

The channel separation was 25 dB in the midrange, increasing to a maximum of 30 to 35 dB at 6,000 Hz and falling to 10 or 12 dB in the 15,000- to 20,000-Hz range. The output of the cartridge was moderately high—about 4.25 millivolts—with the two channels matched within 0.4 dB. The measured vertical stylus angle was a relatively high 30 degrees.

In our tracking tests, the Astrion was able to play the high-level, low-bass tones on one of our test records and the 70-micrometer level of the German Hi Fi Institute test record at 1.2 grams. Increasing the force to the rated maximum of 1.4 grams improved the latter capability to 80 micrometers and enabled the cartridge to play the 30 cm/sec 1.000-Hz tones on another record without visible waveform distortion (there was some peak clipping at the lower force). From these tests, we conclude that 1.2 grams is a perfectly satisfactory operating force for this cartridge and that increasing it to 1.4 grams is unlikely to make any worthwhile improvement in the sound quality.

Subjective listening tests with the Shure “Audio Obstacle Course” records (at 1.2 grams) showed that the Astrion could play through level four of every band on either the ERA III or ERA IV record without difficulty. However, the highest level of most of the selections on these records produced some audible strain—evidence of incipient mistracking, although we never heard any definite “hard" mistracking.

The tracking distortion was measured at middle frequencies with the Shure TTR-102 test record (intermodulation distortion with frequencies of 400 and 4,000 Hz). The distortion was in the 1 to 2 per cent range for velocities under 20 cm/sec, increasing rapidly above 22 cm/sec with a 1.2-gram force and above 25 cm/sec with a 1.4-gram force. High-frequency distortion was measured with the shaped 10.8-kHz tone bursts of the Shure TTR-103 test record. The distortion readings rose from 0.7 to 2.7 per cent as the velocity increased from 15 to 30 cm/sec. This is fairly typical performance for a good phono cartridge.

The square-wave response of the cartridge with the CBS STR 112 test record showed a couple of cycles of low-level, well-damped ringing on the leading edge of the 1,000-Hz square wave, but its shape was otherwise excellent. The low-frequency resonance in the fairly massive arm (about 26 grams including the 5.7 grams of the cartridge itself) was at about 8 Hz.

Comment

As might be expected from its ruler-flat frequency response and excellent inter-channel symmetry, the ADC Astrion was an unusually neutral-sounding cartridge. Some cartridges, because of a peaked or rising high-end response, may have a crisp or slightly bright sound. Others, with an elevated output in the lower midrange, may be noted for their warmth (or “presence,” if the output emphasis is at a sufficiently high frequency). The ADC Astrion has none of these qualities, so that when we played the best records at our disposal through speakers noted for their lack of coloration, the end result was the kind of music one can enjoy for hours on end without being reminded that it originates on a record.

A few cartridges can track higher recorded velocities in certain frequency ranges than the Astrion, but we doubt that it will ever be overtaxed by any record other than the few special test records we used for the tracking tests (these records, designed to stress a cartridge beyond its normal limits, have higher velocities than those of commercial music pressings). The Astrion’s combination of high output, virtual independence of output load conditions, extreme flatness of frequency response, and uniformity of crosstalk response is noteworthy. Together with its low tracking pressure (its special tip shape distributes the already small tracking force over a wider area of the groove wall than the usual elliptical stylus), these factors make it one of today’s better cartridges and one of which ADC can justifiably be proud.

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