This is an integrated arm-and-turntable unit using single-belt drive from a stepped motor pulley to an inside platter (under the main one), and having a three-point suspension similar to that in the AR turntable for isolation from acoustic feedback and floorborne vibrations. Speed change is accomplished by a two-pronged “fork” which, actuated by the speed selector knob, throws the belt from one step of the motor pulley to the other. The motor is a special synchronous type that is actually two motors in a single case. Their speed is determined by the frequency of the AC supply, so there is no speed adjustment.
The tonearm is made of tubular aluminum, with offsets at both the pickup end and the counterweight end. The latter holds the counterweight to one side of the axis of the arm, to compensate for the torsional force caused by the offset head. Stylus force is adjusted by sliding the counterweight back and forth, in conjunction with a removable calibration plate. The calibration plate rests on the rear of the arm, with its scale positioned to read the desired stylus force, and the counterweight is adjusted until the arm is in perfect balance. Removal of the calibration plate then unbalances the arm to provide the proper tracking force. This proved to be one of the most accurate force-setting systems we’ve seen.
The counterweight has enough range to balance any but the very lightest pickups (such as the Euphonics), which will require a small additional weight in the head. Even the heavy Ortofon pickups (footnote 1) can be accommodated without an additional counterweight, but the length of these pickups makes it difficult to install them without shorting their connecting pins to the terminals at the rear of the plug-in shell. These terminals may be bent out of the way to provide clearance.
The tonearm’s height is fixed, but there is provision for adjusting the length and the vertical angle of the plug-in shell, to provide the optimum tangency and vertical tracking angle for any pickup. The base of the tonearm is fitted with a cueing device which is viscous-damped to prevent the pickup from slamming down on the record when the cueing lever is operated rapidly. There is no bias compensation provided.
Test Results
In performance tests, the turntable proved to have exceedingly low wow, flutter, and rumble—lower in fact, than the TD-124 and about on a par with the Acoustic Research turntable. Like the AR unit, the Thorens uses a low-speed drive motor, which puts whatever motor-induced rumble there is at an inaudible below-15Hz frequency (footnote 2).
The AR’s natural rumble frequency is at 10Hz; the Thorens’ is at 7.5Hz. Both speeds on our sample TD-150 ran about 5% fast, and were unaffected by normal pickup loads. Subjectively, this 5% inaccuracy causes a barely perceptible increase in musical tempos, and raises the pitch of the music by a shade less than one semitone. There is enough torque to use one-wipe record cleaners like the Watts/ELPA “Preener,” and the use of a “Dust Bug” reduces the speed in outer grooves by about 2%. (The Dust Bug has virtually no slowing effect when working in inner grooves.)
Hum radiation was extremely low, permitting even such hum-sensitive pickups as the Ortofon SPU and SPE to be used without hum problems. The vibration suspension was judged to be only fairly effective. It was better than none at all, but even a typically bouncy floor could cause the pickup to skip grooves with every heavy footstep.
The tonearm pivots in our sample were badly out of adjustment. There was a considerable amount of free play in them and, as a result, the arm was leaning over to one side and tilting the head shell by more than 5°. We were able to adjust these to get rid of most of the play without causing an excessive increase of binding in the pivots, but we were not able to eliminate all the tilt from the head. Fortunately, Thorens supplies a number of thin spacer washers in their pickup-mounting hardware kit, so we were able to shim up one side of the head until it was parallel to the record.
There is nothing intrinsically wrong with these cone-type pivots; they just don’t seem to lend themselves to mass production. Each must be individually adjusted to within quite critical tolerances, and few production-line workers will take the trouble to do this. The result is usually a degree of sample-to-sample variability that makes the purchase of a properly-adjusted one a case of sheer pot luck.
Performance
With the pickup leveled and the tonearm pivots adjusted to minimize both play and friction, the arm behaved as any good, moderate-mass arm should. There was no evidence of problems due to pivot rattles, but we did find that the sound from the pickups we used in it was not quite as clean at a given tracking force as in, say, the SME arm. This may have been due to the lack of bias compensation on the Thorens arm, or to its moderately high vertical friction, which was measured at slightly over ½ gram. Loosening of the pivots did not significantly reduce the friction.
Some care is needed when operating the tone cueing lever. The three-point anti-vibration suspension that allows the base to vibrate without disturbing the pickup also makes it easy to jiggle the whole playing system by rough handling of the lift lever.
Conclusion
The TD-150AB, then, resembles the Acoustic Research turntable both in basic design and performance, although the AR is considerably more accurate in running speed and has shown little variability in tonearm adjustment from sample to sample. These two factors alone would tend to swing the choice toward the AR and the fact that the TD-150AB costs about $20 more would seem to confirm the choice.
The TD-150’s speed inaccuracy is due to a simple case of oversized motor pulleys, and should be easily remediable in future production models (if it hasn’t been corrected already—we tested an early sample). With this problem ironed out, the TD-150 would make an ideal turntable for the perfectionist to use with the tonearm of his choice, and we hope it will be released in an armless version for that purpose. At present, it is available only with its integral arm, although the instruction manual refers to a model TD-150B that comes without an arm, so perhaps a basic table unit is in ELPA’s future plans.
Footnote 1: For the benefit of those readers who are becoming confused by the strange spellings used in some other magazines, we point out that “f” is correct, “ph” is not.
Footnote 2: Although inaudible, it is possible for subsonic rumble to cause problems by overdriving the power amp or loudspeaker at this subsonic frequency, where power-handling ability is likely to be extremely limited. Normally, the rumble from the AR or Thorens units is well below the trouble level, but a defect in the turntable—a bent motor shaft, for instance—or an unfortunate arm-and-pickup pairing that resonates at below 10Hz could cause overloading, if in doubt, watch the loudspeaker cone (or feel It with the fingers) when playing a silent groove. If the cone vibrates continually at an inaudible frequency, you’ve got trouble.
NEXT: Manufacturer’s Comment »
COMPANY INFO
Thorens, Germany
US Distributor: American Audio & Video, A Division of JAM Industries USA, LLC
310 West Newberry Road
Bloomfield, CT 06002
(856) 596-2339
www.americanaudiovideo.com
ARTICLE CONTENTS
Page 1
Manufacturer’s Comment
Specifications
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