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hobbyists's
views for hobbyists |
Page first published January 8, 2004.
Servo
Control, Parallel (Linear) Tracking, Minimal Lateral Tracking Error
Edison
- Rek-O-Kut - Ortho-Sonic - -BJ - Marantz - Pierre Clément - Harman
Kardon - Garrard - Acoustical - Revox - B&O - Goldmund - Mitsubishi -
Cartridge Man - Rabco
See for the most complete manuals for SL8 and SL-8E at the end of this page.
Jump to:
Linear Tonearms
Technics
SL1100 with Rabco SL-8E Linear Tracking Tonearm and
Universal Record Stabilizing Ring (RSR) plus Universal Stabilizer Weight.
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EDISON When Emil Berliner proposed the "Grammophon", the technique
of parallel tracking was abandoned overnight. Now the radial tonearm
was the rule until several manufacturers (re-)discovered the benefits
of parallel tracking and started to design arms which would open up
the full potential of the LP record, especially of the stereo LP. |
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EXPENSIVE |
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CUTTING
LATHE |
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DIFFERENT
ANGLE If a common, pivotal arm is used, only in two instances there is zero tracking error. The tracking error results in distortion because of the time difference there are actually two readings from the groove, especially when elliptical, shibata and other fine line tips are used. The human ear is very sensitive to irregularities in the time domain of any signal, be it digital or analog. A tangential arm has the least distortion because the tracking error is minimized to practically zero: the diamond tip of the cartridge reads the two groove walls at the same time without the delay. And there is another important factor: there is no centripetal action The tangential arm does not need side thrust (bias compensation). The drawing shows an exaggeration of the mistracking of a radial arm versus the action of the cutter diamond and the reading of the groove by the diamond tip in a tangential arm. |
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REK-O-KUT
CHALLENGER DISC RECORDER The Rek-O-Kut Company proposed a portable professional disc recorder and playback phonograph for 33 1/3 and 78 rpm disc cutting. An accessory idler wheel could be mounted for cutting at 45 rpm speed. A constant speed, hysteresis motor was the driving force of the table and arm. It had interchangeable leadscrews for standard as well as microgroove recordings. The amplifier measured a frequency response of +/- 1 dB from 30 to 20.000 cycles. It had controls for bass and treble. Recordings could be made from radio tuners, tape recorders, and other signal sources. At right part of an advertisement which appeared in 1953 High Fidelity magazine. |
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ORTHO-SONIC
V/4 |
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BURNE
- JONES |
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MARANTZ An early and nice specimen of a turntable with an integrated tangential arm was the Marantz SLT-12 (when Marantz was still Marantz). It was a 2-speed turntable with a lightweight cartridge without counterweight. It was also available with a heavier arm with balance weight and universal mount for playing with other (heavier) cartridges up to 10 gr. of weight. The arm had no servo system and therefor did not always function as desired. This edited picture on the right is originally from an advertisement in High Fidelity of 1966, but the Marantz SLT-12 was already introduced in 1963. |
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PIERRE
CLEMENT Very ingenious and quite modern at the time was the tangential arm devised by Pierre Clément from France. He received a patent in 1968 from the French National Institute of Industrial Property: "Procédé et dispositif de lecture d'un disque de phonographe le long d'une trajectoire rectiligne." The use of the light bulb and the photoelectric cell has inspired many a designer. As soon as the arm moves out of the 90 degrees position, the light beam will no longer be interrupted by the small plate at the end of the arm. Then the motor will receive current and starts to turn the worm on which the carriage rides. The carriage is moved towards the spindle until the light beam is interrupted again and the arm remains at 90 degrees. See http://www.audiofolia.com/clement.php |
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HARMAN
KARDON Rabco came up with a separate arm: the SL-8 which was superseded by the SL-8E around 1969. When Rabco had been bought by the Harman Group, various turntables with tangential arms were introduced: ST-4, 5, 6, 7 and 8. When the ST-7 was hitting the market, an advertisement explained the functioning of the arm, showing a cutting lathe on one page and a ST-7 tangential turntable on the opposite page. In the Harman Kardon turntables the arm was transported with help of the turntable motor. The arm in the ST-7, and also of the ST-8, was transported by means of a rubber belt instead of the bead chain as in the SL-8 and SL-8E. |
Harman Kardon ST7 |
GARARD
ZERO 100 SB In pick up arms the pivot is designed in such a way that there is the least play and the least friction (1). The problem with the Garrard ZERO is that it has three more pivots (2, 3, and 4). These extra pivots should not add friction. Therefore they are adjusted in such a way that they have free play. |
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Garrard ZERO 100 SB | |
LENCO
SWEEPER Designing and manufacturing a tangential arm is not as simple as may seem and only thorough engineering can result in a good functioning device. Proof is the only tangential arm Lenco could come up with and then even the geometry is not right. The cleaning brush does not follow the groove correctly because it is incorrectly positioned. Nothing to please Inspector Gadget. |
Lenco's Tangential Sweeper |
REVOX Revox too developed turntables with tangential arms: B 790, B 791, B 795 and B 291, all with a direct drive motor. But since the arm was very short, it was only suitable for the high compliance moving magnet cartridges which were en vogue in the 1970's: ADC, Stanton, Pickering, Shure, Goldring. |
Revox
B 795 turntable with the ultra short 'Linatrack' arm, |
ACOUSTICAL
TANGENT ARM |
Acoustical "Tangent", predecessor of the Bang & Olufson series. |
BANG
& OLUFSEN Bang & Olufsen used tangential tracking since 1974 first in the Beogram 4000 and they refined the technique of parallel tracking each time they came up with a new model. There were many series of integrated turntables like the Beogram 3000 (the successor of the earlier 3000 which was a Thorens TD124), 1102, 4002, 5005, 6002, 8000 and 9000. At right Beogram 4002. |
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MITSUBISHI BALANCED
PLATTER
THREE BELTS AND ONE THREAD VERTICAL
POSITION
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The
clever engineering of the belt drive Mitsubishi with |
PIONEER To give a new boost to the sales of turntables, knowing that the Compact Disc would soon be introduced, many manufacturers came up with newly designed tangential turntable. In 1980 Pioneer presented a very clever tangential arm system for their PL-L-1000. The arm is transported electronically by the interaction of magnets and a long coil: electromagnetic suspension. Exactly like the Maglev train (Magnetschwebebahn), a technique initiated by the German engineer Hermann Kemper in 1922. |
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TECHNICS Also Matsushita launched a series of tangential turntables: SL-5, 6, 7 and 10. In these turntables the arm was incorporated in the lid. At right the SL-10 which was introduced in 1980. |
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GOLDMUND Like
B&O, Goldmund does not use micro switches as Rabco does, but applies
detection by a photocell. Today there are many designers of tangential (=parallel tracking) tonearms which can be fitted on a variety of turntables. |
Goldmund
T3F Automatic Tonearm with 2 separate motors |
In
the DIY department there is Poul Ladegaard's air bearing arm which
keeps inspiring many a hobbyist to build a tangential arm. MUSIC
MAKER CONDUCTOR |
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It is marketed by HIAudio in the UK. On the web site it says: 'Forget the issues of cartridges mounted on carriages on wheels, or high pressure air pumps through ceramic bearing housings'. It is amazing in this age, in which the digital format is constantly reinvented, that the sound reproduction of analog recordings is brought to an even higher level. The arm has no servo system. The arm base rests on a thin cushion of air and this does not generate friction. The arm just moves by itself when following the groove. |
The Cartridge Man's Conductor Tonearm. |
HIGH
END / HIGH PRICE |
HiAudio's Martin Bastin-Garrard 401 The Cartridgeman's Conductor arm and Music Maker III cartridge. |
The Rabco SL-8 / SL-8E
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Rabco
Arm Wands
It
is not clear whether the SL-8 had a one piece arm as a drawing in a
magazine review showed. Could be that the two part design was omitted
in the drawing. Whatever. The arm is a two part adjustable arm, the
connector being the third element.
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The measurements are given for those owners of Rabco arms who want to restore an original arm tube or reconstruct an alternative for modified arm wands while using the original connector. |
How to go about if you want to make an armwand which has less mass and would better suit the cartridge you use better as far as weight and sound are concerned? There are several suggestions for using balsa wood. But just pure balsa is in my opinion not suitable. It is soft and therefor less firm. My experiments have shown that the combination of aluminum strips and balsa make an arm or armwand stronger and does influence the frequency characteristic and transient response in a positive way. I do not guarantee that the suggestion pictured in the drawing at left gives the results you desire. But the drawing indicates a possibility and shows along what lines you could think. The amount of aluminum (large width or narrow, weight and thickness) determines the effectiveness and the final sound quality and dynamics. So some experimentation should be done. | |
At left is an image of the arm wand proposed by David Shreve built of two layers of balsa and a magnesium block which holds the nylon threaded bar. - Picture Copyright David Shreve. | |
This drawing explains the construction of the arm wand proposed by David Shreve. It is made of a thin upper layer and a thicker base of balsa wood. The lift wire has to be adjusted carefully. The original connector is omitted and makes place for a magnesium block with threaded rod of nylon. - Drawing Copyright David Shreve. |
Rabco Manuals
EXTENSIVE DOCUMENTATION If you own a Rabco SL- 8 and/or SL- 8E I can provide
I can provide these in neat, well printed copies. The Service Manual contains all descriptions, instructions for disassembling and reassembling the arm, adjusting the arm, repairing the electric / electronic circuits for the SL-8 and 8E. Instructions are given both in descriptions and drawings.
The cost of shipment is not included. It varies per country. Click here to send a mail for more info. Drawings,
pictures and edited images on this page
Copyright
Rudolf A. Bruil
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Technics SL1100 with Rabco SL-8E and Universal Record Stabilizing Ring (RSR) plus Universal Stabilizer Weight.
© Rudolf A. Bruil. Page first published January 8, 2004.
The
Rabco came well packed in a large box with the Serial number written on the
top.
At right the relatively short but in length adjustable arm can be seen, the
wooden strip (shim) and two triangular wooden parts
to be used when the Rabco SL-8 or 8E will be mounted on a Thorens TD-150 or
TD 125 or later model of which the armboard is too short to accommodate the
arm
without being obstructed by the plinth.
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