Micro Seiki MB-38 Turntable Review

The MB-38 is the first fully automatic, belt-driven turntable from Micro Seiki. The full-size, cast nonferrous platter, which weighs 2 pounds including its rubber mat, is driven by a light rubber belt around an inner drive rim that is smaller in diameter than the platter itself. The motor speed is electronically controlled for 33-1/3- and 45-rpm operation. Stroboscope markings are cast into the outside of the rim for both speeds and for power-line frequencies of 50 and 60 Hz, and they are illuminated from below the motorboard by a neon lamp-and-prism arrangement.

A separate motor controls the tone arm (for cueing, arm lift and descent, automatic indexing to the beginning of a record, and automatic shutdown after play). According to Micro Seiki, the MB-38 also features what they call an “exclusive oil bath bearing system,” presumably for the platter bearing. The tone arm is a low-mass straight tube whose offset cartridge mount can be removed by loosening a thumbscrew. A plastic jig aids in setting the cartridge position for minimum tracking error. The threaded counterweight carries the usual tracking-force scale, and an antiskating dial, arm-lift lever, and locking arm rest are on the arm base.

The MB-38 is furnished on a rosewood-finish wooden base with a hinged clear-plastic cover. The entire unit is supported on four softly sprung feet. The principal operating controls (everything except the arm-lift lever) are on the front of the base, where they are accessible with the cover lowered. The power switch is at the left, near a small speed knob that gives a vernier speed adjustment. Four slender, flat pushbutton switches along the front top edge of the base set the arm indexing diameter for either 12-or 7-inch records, select the operating speed, engage the auto repeat function, and initiate the start or reject cycles.

Normally the start/reject button is the only operating control. A light touch on it starts the record turning, moves the arm over the lead-in groove, and lowers it gently to the playing surface. After play, the arm rises and returns to its rest, and the motor shuts off. Full manual control of the arm is also possible. Red LEDs on the control buttons show their status at all times.

Laboratory Measurements

We operated and tested the Micro Seiki MB-38 with an AKG P25MD cartridge installed in its arm. Using the supplied mounting jig for the cartridge installation, we measured a maximum tracking error of 0.25 degree per inch for radii between 2-1/2 and 6 inches. The actual vertical force was within 0.05 gram of the indicated value between 0.5 and 2.5 grams after an unaided visual balance of the arm. When we reset the counterweight for exact reading at 1 gram it was equally exact at other force settings.

The effective arm mass (less cartridge) was a low 11 grams, and the combination resonated in the near-ideal range of 10 to 12 Hz. Apparently there was little damping in either the arm or the cartridge, since the amplitude of the arm movement at resonance (with the Shure ERA IV record) was very large. The capacitance of the tone-arm and signal-cable wiring was 143 picofarads from each channel to ground and 8 picofarads between channels. The arm cueing was good (free of drift) if the lift lever was handled carefully and if the antiskating dial was not set higher than the vertical tracking force. The arm tended to bounce and shift its lateral position when raised rapidly with the cueing lever. The calibration of the antiskating system was good, giving approximately correct skating compensation when the dial was set to match the applied tracking force.

The automatic operating cycles of the MB-38 were relatively rapid, with 6.5 seconds elapsing between start and the beginning of play and 6 seconds from the end of play to the shutdown of the player. The vernier speed control had a range of +4, —6 per cent and required a slight readjustment when switching from one speed to the other. The turntable rumble was —34 dB unweighted and —55 dB with ARLL weighting. The rumble was mostly in the range of 5 to 25 Hz, with smaller peaks at 40, 60, and 70 Hz. The flutter was ±0.1 per cent weighted peak (DIN) and 0.08 per cent weighted rms (JIS), with most of the flutter being at rates under 10 Hz; there were smaller components at 15 to 20 Hz.

The acoustic isolation of the base appeared to be quite good. However, recent changes in our test equipment prevent us from making a close quantitative comparison between the base transmission of the MB-38 and turntables tested previously. We did note that its major acoustic/mechanical sensitivity was between 20 and 30 Hz, with narrow lower-level responses at 80, 300, and 1,200 Hz.

Comment

Although the Micro Seiki MB-38 is a very good record player with no significant faults, for its level of performance it is also rather expensive. One of its best features is the low-mass tone arm, whose geometry seems to have been optimized for minimum lateral-tracking-error distortion and whose other calibrated parameters of vertical tracking force and antiskating compensation are also as nearly ideal as our measurments can determine.

The operation of the MB-38 is simple and foolproof, although we would have preferred to be able to turn on the turntable (say, by lifting the arm, as on many other units) and cue the arm manually from the start instead of having to go through the automatic cycle. We usually avoid subjective styling judgments, but we must admit that this is a handsome piece of equipment. It presents a more “furniture-like” appearance than most of the more clinically styled record players from other manufacturers.

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