Audio-Technics AT155LC Phono cartridge Review

The Model AT155LC heads the Audio-Technica line of “Vector Aligned” stereo cartridges. It has a high-efficiency magnetic structure based on the toroidal-coil design introduced a couple of years ago in the company’s AT24 and AT25 cartridges. This “para-toroidal” design eliminates soldered wires between the coils and the terminal pins (the coil wires themselves extend to reach the pins), and the coil cores are extended and shaped to serve as pole pieces. An integral mu-metal shield installed between each channel's coils gives improved audio separation between the two channels in addition to its hum-shielding properties.

The well-known Audio-Technica dualmagnet design uses two small rod magnets mounted just forward of the cantilever pivot at right angles to the cantilever and to each other. The reduction of electrical and magnetic circuit losses in the generating system of the AT155LC helps to give it an unusually high output voltage for a high-quality cartridge. It is rated at 5 millivolts at a 5-cm/sec velocity. The rigid beryllium cantilever is fitted with a nude-mounted, “linear-contact” square-shank diamond stylus.

Recommended tracking force is 0.8 to 1.6 grams. The easily replaceable stylus assembly includes a hinged stylus guard.

There are four less expensive models in the Vector Aligned series; they use the same coil and magnet structure as the AT155LC but have different body materials and stylus and cantilever designs. The AT155LC, which comes with an individually run frequency-response curve, is priced at $225. The ATN155LC replacement stylus is $100.

Laboratory Measurements

The Model AT155LC was tested in the tone arm of an Onkyo CP-1130F record player. The low-mass arm (11 grams) and 8.1-gram cartridge mass interacted with the cartridge’s highly compliant stylus to resonate at 8.5 Hz. This is near the low end of the optimum range of arm-resonance frequencies. (The ATI 55LC’s weight of 8.1 grams, compared with the 6.5 grams of its sister cartridges in the series, is apparently the result of using a die-cast metal body instead of—presumably—a lighter plastic body. However, no difficulties were experienced from this source.)

The recommended load for the AT155LC is 47,000 ohms and 100 to 200 picofarads (pF). Our tests were made with a 180-pF load shunting 47,000 ohms. We also checked the frequency response of the cartridge with several values of capacitance, confirming the manufacturer’s ratings but also showing that no reasonable load capacitance will have a serious effect on the cartridge’s performance. Up to 14.000 Hz, the response changed by no more than ± 1 dB with capacitance changes from 180 to 450 pF. It is more important to use the correct resistance load, since a higher terminating resistance results in a sizable response peak at about 15,000 Hz.

With the CBS STR 100 test record, the frequency response of the AT155LC was within ± 1 dB from 40 to 20,000 Hz. Channel separation was maintained strongly over the full range, although we noted the differences in left- and right-channel separations that are typical of the test record. Since a close match between the geometry of the cutter and the playback cartridge is important for maximum separation, we also checked the cartridge with the AT-6605 test record. The separation was 16 to 24 dB at 20,000 and 30,000 Hz and some 27 to 30 dB in the midrange.

Its flat response in the audio range encouraged us to measure the AT155LC with the JVC 1005 test record at higher frequencies. This yielded even more spectacular results, the response being almost identical for the two channels and within ± 1 dB from 1,000 to 40,000 Hz. Midrange channel separation was about 25 dB, and it was 15 dB or better up to the record’s limit of 50.000 Hz.

Although our preliminary tracking tests showed that the AT155LC could handle almost any commercially released music record at a force of 1 to 1.2 grams, we preferred to use a 1.5-gram force (it is axiomatic that any cartridge will give its best performance when operated close to its maximum rated force). At 1 gram, the AT155LC tracked the 60-micrometer level of the German HiFi No. 2 test record, but at 1.5 grams it was able to play the 90-mi-crometer level, a feat of which few cartridges are capable.

The tracking distortion, measured with Shure TTR-102 and TTR-103 test records, was low. The IM distortion hardly changed over the full range of the test bands on the TTR-102, from 1.5 per cent at 7 cm/sec to 3.2 per cent at 27 cm/sec. The former reading is close to the residual distortion on the record, and the latter shows that the cartridge is not close to mistracking, or even distorting significantly, at a level far above that likely to be found on music records.

The cartridge output was 4.85 millivolts at a 3.54-cm/sec velocity and the channel levels were matched within 0.36 dB. The measured vertical-tracking angle was 20 degrees. The response to the 1,000-Hz square wave on the CBS STR 1 12 record showed a single sharp overshoot, but otherwise there was no significant ringing or other shape alteration.

Comment

Subjective tracking tests of the AT155LC, using Shure's “Audio Obstacle Course” records, were consistent with our measurements. The cartridge was able to play every level of every band on both records without audible mistracking, although there was a trace of “hardness” on the highest level of the bells section in the Shure ERA IV test record (a sign of incipient mistracking).

Clearly, the Audio-Technica AT155LC excels in just about every area of cartridge performance, and it came as no surprise to find that it was as silky smooth and “forgettable” when playing music as its measurements would suggest. We would have difficulty describing the "sound” of the cartridge, since it contributes so little of itself to the final sonic quality. Good records often sound superb when played with the AT155LC, and records with sonic deficiencies are immediately recognizable for what they are. Previous Audio-Technica cartridges we have used have been uniformly excellent, and the AT155LC continues in that tradition. In a growing competitive field of very fine cartridges, it manages to more than hold its own.

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