Harman/Kardon ST-7

1 9 7 6 1976
1 9 7 8 1978

Ravishingly bare but exquisitely styled turntable from when Harman/Kardon hadn't yet engulfed half the audio brands on planet Earth.

Its main feature, however, was imported from a brand recently acquired by Dr Sidney Harman for its then fairly small Group : the tonearm was indeed a variant of the famed (but unknown) RABCO.

The ST-7 was built at Rabco's factory for H/K and the latter even added a sticker under it naming all the people involved in the engineering and design :

Dipen Guha : development engineer
Yasuhiro Okuda : industrial designer
Frank Baudille : project engineer
Irwin Katz : electrical engineer
Frank Holetsky : mechanical engineer
Len Rosenblatt : production engineer
Robert Brady : director of engineering
"and the people at Haman/Kardon, Plainview, Long Island, U.S.A."

Not something you see nowadays nor that was seen back then elsewhere !

The big difference between the original Rabco and the H/K version being that Harman simplified its mechanical design... a lot.
Instead of being powered by a battery and having its own autonomous movement, the Rabco version in the ST-7 is moved by a belt hooked to base of the main bearing.

The tonearm's carriage is rests on a dual-axis gimbal and - "In the vertical axis the tonearm is supported by a tracking roller which rolls against the tracking shaft.
When the tonearm is tangent to the record groove the tracking wheel is biased in angle so that the carriage travels toward the platter center at approximately 0.17" per minute. This corresponds to the average velocity of the stylus used for cutting the groove of the master disc.

As the tonearm attempts to pivot in angle to track pitch variations, the angle of the tracking roller axis changes relative to the cylinder axis. This change in direction of the tracking roller accelerates or decelerates the motion of the carriage to track the pitch of the groove.

The correction is continuous, self-adjusting, and automatic.

It is simple, elegant, fairly easy to build and it works.
And unlike today's rabid buyouts, H/K was elegant enough to keep the Rabco name on the tonearms of the H/K turntables.

The rest of the ST-7 is visibly built by hand and in small numbers : aluminium slabs for the enclosure, mechanical arm lift and simple PCBs with two ICs (two !).

The tonearm has its balancing weight on the arm's wand and a tracking adjustment control set at the back of the main carriage - see here for a .pdf of the ST-7's owner's manual which describes very precisely how to unpack, setup and use an ST-7. And why. And how to adjust tracking, and how to use the restrictor, and how to clean the main roller guide, and how to everything. It also has a very detailed drawing showing (and explaining) the mechanical system here driving the RABCO.

The ravishing -again- speed selector is styled as that of the Sony PS-X7, only it is here transparent and backlit with a color code : red for stop, blue for 45rpm and green for 33 1/3rpm.

Of course, after the Beatrice Food sale and Shin Shirasuna episode, no such humanly-engineered fiddly cuties were to come out of H/K anymore.

Although I had a couple of worthwhile images, I never could find a proper catalog to bring the ST-7 online.
Göran Karlsson came to the rescue and included in his donation a set of very nice H/K swedish catalogs - with an ST-7 in them.

Harman/Kardon ST-7, image 1 Harman/Kardon ST-7, image 2 Harman/Kardon ST-7, image 3
Harman/Kardon ST-7 specifications
Title Value
Tracking error :
Skating force :
Vertical friction (*): 0
Lateral friction (**): 0
Effective tonearm mass : 6g
Stylus overhang : 0
Wow & flutter : 0,04% (NAB, wtd.)
0,09% (DIN-B)
Turntable rumble : - 68dB (DIN-B)
Hum : - 76dB (DIN 45544, tonearm in)
Speeds : 33 1/3 & 45rpm
Pitch control : ± 5,5%
Speed constancy : ± 0,3%
Motor : Brushless DC with Hall effect
Drive : precision ground belt
Platter : diecast aluminium (1,1kg)
Dimensions : 41,9 x 15,7 x 41,3cm
Weight : 10kg.
* Zero vertical friction is achieved by a rolamite bearing utilizing counter-rotating
metal bands which generate self-cancelling forces and permit no sliding contact between
moving elements.
** No relative rotation exists between stylus and driven end of tonearm.
Harman/Kardon ST-7 : 1 topic
(last updated topic shows up first)
  • A little more Harman/Kardon ST-7 info                             (1)last updated by MisterFishey - 04/11/2011, 22H54
page online since : april 2010
page updated : april 2010
page type : LGT / KNB
page weight : 639.17 Kb / 458.84 Kb

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