An Excerpt from “Acoustic Research Inc: The Golden Years” by Roy Allison
For a year and a half, while [Ed] Villchur was working on the AR-3, he had an outside engineer designing a turntable. It had always been his intention for AR to offer a complete high-fidelity system. That turntable project had come to nothing, and as soon as the AR-3 was launched, he turned his attention to a turntable design done in-house.
Again he reduced the problem to basic principles. It was obvious, on reflection, that relative motion between the tonearm spindle and the turntable platter had to be minimized to prevent rumble-both horizontal and vertical motion, since the new stereo pickup cartridges were sensitive to vertical motion as well as lateral. Solution: do what Stromberg-Carlson had done in its turntable, mounting both arm and platter spindle on a rigid bearing plate isolated from the base, and do it better if possible.
Stability and isolation were accomplished by using a three-point damped spring-mount system for the bearing plate, with a very low resonance frequency and with the springs located at equal load points. Isolation from the drive motor was to be accomplished by a rubber belt between the drive pulley and the platter. The pickup arm had to be lightweight, with a damped descent, an offset and overhung pickup head for minimum tracking angle error, and balanced completely except for an adjustment to achieve the proper stylus force. It also needed geometry that placed the stylus in the same horizontal plane as the arm’s vertical pivot, to minimize warp-wow.
It was far easier to state these requirements than to implement them. Along the way, finding a satisfactory belt manufacturing process proved to be a major headache. To achieve nearly perfect dimensional uniformity in a simple cast rubber belt was impossible-until an extra-thick belt was put on a machining mandrel and frozen to rigidity while being ground to spec. It was also discovered, after some frustration in achieving adequate isolation, that the rubber in production belts had to be completely free of acoustic resistance from additives, as the prototype belts had been.
The arm and platter spindle bearings were originally bored to specified ID in cast Delrin-a new plastic at the time, claimed to have all the properties you could desire for use in bearings, including dimensional stability. The stability claim was somewhat exaggerated, to put it mildly. After a month or so, the ID would close in and seize the spindle.
Along came Mitchell Cotter, who said that the supplier had not properly annealed the castings and that he had a facility to anneal and re-bore them. He was given the go-ahead to do a fairly large quantity. And what do you know: after a month or so the reworked bearings contracted and seized the spindles. That problem was fixed by putting steel jacketed Babbitt-metal inserts into the Delrin, but it took time.
The first turntables were shipped to dealers in 1961. They were a completely assembled package except for the pickup cartridge: the drive/platter system mounted on a finished wooden base, tonearm, power and amplifier cables, turntable mat, overhang plate, stylus force gauge transparent dust cover. The initial price was $58, on which the company lost money. It was sub-sequentially raised in steps, in 1972 it was still only $90.
The turntable quickly gained profitability, and AR sold hundreds of thousands of them. Although it was the least expensive quality turntable on the market, many reviewers and consumer organizations rated it the best-with one exception. Stereophile thought it was good, but said that the spindle was too big. In fact that was an incorrect call; the spindle diameter was precisely what industry standard specified.
“Reprinted, with permission by Amateur Audio Press, from Multi Media Manufacturer, Volume 1, Issue 1, (January/February), 2004, p. 22. © Copyright 2004 by Audio Amateur Corporation, P.O. Box 876, Peterborough, NH 03458, USA. All rights reserved.”