Hitachi HT-68 Turntable Review

The Hitachi HT-68 two-speed direct-drive turntable uses a “Unitorque” motor said to have a constant (nonpulsating) torque characteristic that results in very low rumble and flutter levels. The rotation of the brushless, slotless, and coreless d.c. servomotor is controlled by a quartz-crystal oscillator, giving it a speed accuracy of 0.003 per cent at 33 V3 and 45 rpm. The cast-aluminum-alloy platter (with its rubber mat) weighs about 2 pounds.

The inner surface of the straight stain-less-steel tone-arm tube is chemically treated to damp its mechanical resonances. The HT-68 is furnished with a Hitachi MT-35 dual-magnet cartridge, but the detachable plug-in shell accommodates all standard cartridges having 1/2-inch mounting centers and weighing between 4 and 9 grams. The arm’s automatic operation is handled by a separate d.c. motor, so that record rotation is completely unaffected by tone-arm movement.

The HT-68 employs a photosensor system to detect the presence and size of a record on the turntable. This is done by means of small holes at 90-degree intervals around the platter and mat (at diameters of about 5>/2 and 11 inches), illuminated from above by a light near the turntable rim. As the platter rotates, light reaches a photocell beneath it through any holes not covered by a record. This information is used to determine turntable speed and the tone arm’s indexing diameter (the arm will not leave its rest unless a record is present). At the end of play another optical sensor initiates the arm return and shut-off cycle.

All operating controls of the Hitachi HT-68 are located on its top front edge, where they are accessible with the clear plastic dust cover lowered. Very-light-touch pushbuttons are used for power switching, speed selection, repeat-play mode, and the tone arm’s up/down (cueing) function. LED indicators next to the last three momentary-contact buttons show when they are engaged. A large flat plate serves as the start/cut switch, initiating and terminating a playing cycle on alternate operations. The player, of course, shuts off automatically at the end of a record, and it can be operated manually by lifting the tone arm from its rest (which starts the motor).

The HT-68 is mounted on a silver-colored plastic base molded of a compound that is claimed to minimize vibration transmission to the pickup and record, thus reducing acoustic-feedback tendencies. It is supported on four softly sprung mounting feet. The turntable specifications include 0.025 per cent wow-and-flutter (wrms), a tone-arm tracking error of less than 2 degrees, and a lead-wire capacitance of 140 picofarads. The adjustable counterweight has a tracking-force scale calibrated from 0 to 3 grams at intervals of 0.1 gram.

The Hitachi HT-68 record player is 17-1/8 inches wide, 14-3/8 inches deep, and 4-1/4 inches high. It weighs 13.2 pounds. The price, including the Hitachi MT-35 cartridge, is $259.95.

Laboratory Measurements

Although the MT-35 cartridge was not being evaluated, we did measure its frequency response, tracking at the recommended 2 grams. With the CBS STR 100 test record the response was flat to 6,000 Hz, rising to + 6 dB in the 15,000-Hz region. Output level averaged 4.16 millivolts with a 3.54-cm/sec groove velocity. The cartridge could track up to the 70-micrometer level on the German Hi-Fi Institute HiFi:2 record.

The tracking-force scale calibration of the HT-68 arm was quite inaccurate on our sample. When the arm was initially balanced horizontally according to instructions, the actual force was typically 0.5 gram higher than the scale setting. When we rebalanced the arm for a correct reading at a typical operating force (1 to 2 grams), the error was 0.2 to 0.5 gram at all other settings. While the error was always in the safest direction (upward), we strongly recommend that this tone arm be set up with a separate stylus-force gauge.

The tracking error of the arm was within its 2-degree rating, and even when stated correctly (as a function of playing radius), it was less than 0.33 degree per inch over almost the entire record and a maximum of 0.67 degree per inch at a 3-inch radius. The antiskating compensation (adjusted by a small dial next to the base of the tone arm) was correct when set to match the actual (not indicated) tracking force. The capacitance of the tone arm and cable wiring was lower than rated, about 100 picofarads per channel. The combined effective mass of the arm and cartridge we used was 18 grams, suggesting that the arm’s effective mass was in the vicinity of 12 grams, typical of many modern arms.

The weighted-rms flutter was 0.1 per cent, and the weighted-peak reading was ±0.13 per cent. The flutter energy spectrum was principally confined to the range under 10 Hz. The rumble was —30 dB unweighted, and with ARLL weighting it was — 58 dB. Although the rumble spectrum for the most part was randomly distributed, there were small but distinct peaks at a number of discrete frequencies such as 10, 15, 30, and 80 Hz. The speed, being quartz locked, was accurate and invariable. The automatic cycle times of the HT-68 were relatively short, 6 to 7 seconds for either the start or stop operation. The arm cued up in less than 1 second and lowered in about 4 seconds. The lateral drift during the arm’s descent, a result of the antiskating torque, caused about 3 or 4 seconds of the record to be repeated each time the arm was raised and lowered.

The isolation afforded by the base mounting was slightly better than average at audio frequencies (with the major transmission occurring at 40 to 50 Hz), and it was considerably better than most turntables at infrasonic frequencies. The record player was nearly immune to most ordinary jarring applied to itself or to the supporting shelf (its most sensitive frequency was about 12 Hz, comfortably located between the audible range and the very low frequency of a physical impact).

Comment

The only respect in which the Hitachi HT-68 record player proved wanting was in the accuracy of its stylus-force adjustment calibration. With any record player it is desirable to check the tracking force with a separate gauge, such as Shure’s inexpensive and accurate SFG-2, and that practice would remove any ambiguity as to tracking-force accuracy.

The measured flutter and rumble of the HT-68 are well below the point of audibility under normal listening conditions. Although our flutter measurements did not match Hitachi’s figures, it is only fair to point out that commercially available flutter test records do not generally have the degree of flatness and concentricity required to obtain flutter measurements under about 0.05 per cent. In fact, we have not been able to get readings below 0.07 per cent with our various test discs. Possibly Hitachi uses a special record, or even measures the motor servo-control signals, to obtain its 0.025 per cent rating.

We especially appreciated the HT-68’s single start/stop control, since it eliminated the possibility of accidentally pressing the wrong button (which has happened to us with some players where the two functions were handled by separate but adjacent buttons). In all, the HT-68 proved to be a very quiet (mechanically) and smoothly performing record player whose highly accessible controls could be operated without risk of jarring the player. This could be attributed to its better-than-average isolation from external vibrations at both audible and infrasonic frequencies.

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