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Old 14th Nov 2012, 7:27 pm   #56
GP49000
Hexode
 
Join Date: Mar 2012
Location: Sonoma County, California, USA.
Posts: 405
Default Re: Garrard record player deck identification.

Zero Tracking Error: the Garrard Zero 100

Garrard tackled the issue of tracking error with their famous Zero 100 automatic turntable. It was based on the "large chassis B" models like the SL95B. Its most obvious advance was its tonearm, designed to adjust its offset angle as it played across the record. This was done with a headshell that pivoted , the pivoting controlled by an auxiliary arm attached to the headshell and to a fixed point near the tonearm's main pivot.

The idea wasn't new (the B-J...Burne-Jones...arm from the 1950s used the same idea), but the execution differed from early attempts. Most commentary attributed this to improvements in bearing technology, but there was a significant difference in the geometry...the location of the auxiliary arm and the pivots.

Both the B-J and Garrard solutions were in the form of a tetragon (four-sided shape) but there was a fundamental difference in that the B-J placed its stylus tip midway between two pivot points; the Garrard placed it directly under the main headshell pivot point. This difference was sufficient so that Garrard was issued patents on its design in Europe and in Canada. In the USA, it was found to be similar to prior Patent 2983517 and a patent was not granted. Illustrations showing the similarities and differences among the three designs are provided below.

Some have thought that the Zero 100 headshell rotates such that it always remains in the same position, like a parallelogram. It doesn't, and that is what is clever and different about it: it rotates in counter-synchronism with the tracking error generated by its curved path across the record, nulling out that error. Also, unlike the earlier efforts at similar designs, the Zero 100's tonearm is designed SHORTER than a conventional arm, so as to have no overhang (the distance the stylus would extend past the spindle, were the arm to be placed there). This was a requirement of the design because it places the tracking error all in one direction, whereas conventional arms' tracking error varies in both directions from their two null points.

Another new invention in the Garrard Zero 100 was the magnetic antiskating system. Others had used magnets for antiskating previously, but Garrard's differed from the others in that its adjustment was done by a critically shaped shield of magnetically permeable material that selectively blocked the magnetic field and also shaped it, so that antiskate would vary properly across the record. Garrard was granted worldwide patents on this design.

There were other advances in the Zero 100 from the SL95B on which it was based. The Zero 100, for the first time in Garrard automatics since the RC98, had adjustable speed. It was based on a tapered motor pulley and an idler wheel bracket that could be adjusted by the user to operate at different diameters on that tapered pulley. This was the same variable-speed system that Dual and others had already been using. The Zero 100 also had an illuminated strobe built-in, to aid the user in properly setting the speed. The motor was the same Synchro-Lab induction-synchronous as had powered the higher-priced Garrard automatics for the prior four years.

Tracking weight was set without springs; the user would balance the arm first, using the counterweight that moved along its shaft when rotated, a less-expensive way of providing fine adjustment that was introduced first on the SL72B; then the user would then slide a precision brass weight along a calibrated scale on the tonearm's front shaft, thus unbalancing the arm by the correct amount to apply tracking weight.

For the first time on a Garrard automatic multiple-play model, the short, single-play spindle rotated with the platter and the record; the prior version had a rotating collar on a fixed spindle.

Slots in the C3 cartridge slide and an adjusting lever on the front of the headshell provided for precise mounting of the cartridge so its stylus tip was directly under the main headshell pivot, as required by the Zero Tracking Error arm; and for setting the correct vertical tracking angle for either single record play, or halfway up a stack of records.

Functionally the Zero 100 operated exactly the same in both record-changing and single record play as its predecessors.

Underneath there were some improvements in the automatic trip mechanism, further reducing its already very low friction and moving mass, thus resulting the resultant drag on the tonearm to trigger the automatic workings. These improvements could be retrofitted to the other models built on the same chassis, and were probably incorporated by Garrard in their production; I have seen a late SL72B with the Zero 100 automatic trip parts. A new lower-friction main tonearm bearing from an outside supplier of precision bearings, designed-in during research and development of the Zero 100, had already been introduced with the SL95B and its sibling models.

Styling of the Zero 100 was entirely different from the SL95B, which remained in the line, and the other Garrards. It was built on a chassis that was painted pure white, not black as were the others. A stylish, clear plastic housing carrying the magnetic antiskate system surrounded the tonearm's pivots at the rear; the tab controls, the counterweight on the tonearm, and the tonearm rest were finished in brushed brass.

There was criticism of the Zero 100 as to the additional bearing friction and mass that the Zero Tracking Error tonearm introduced, at a time when ultra-high compliance, absolute minimum tracking weight, and low tonearm mass were popular among hi-fi enthusiasts. Sellers of competitive products which could not match the zero tracking error tonearm, claimed that tracking error had already been made almost insignificant in conventional tonearms and that its further reduction was not worth the compromises in friction and mass. That was "salesman talk," but the pivoting headshell did cause some reliability issues, in that in a significant number of samples, the very thin tonearm wiring would fracture from continual flexing as the headshell pivoted. A redesigned wiring harness was introduced; it was retrofittable to those units with the earlier harness and it did help cure the problem, along with special instructions to technicians in the field as to how it was to be installed. The Zero 100's C3 cartridge clip did nothing to cure the problems with intermittent contacts that had been an issue with the earlier C2 clip, and which would plague Garrards as long as the various cartridge clips were used.

B-J tonearm patent drawing, showing its geometry
Garrard Zero 100 arm geometry
US Patent 2983517, showing similarity to Zero 100
Garrard Zero 100 in USA solid wood base
Garrard Zero 100 tonearm detail
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