Drive, He Said Part 3

Written by Bill Leebens

Part 1 of this series in Copper #92 covered idler-drive turntables; part 2 in issue #93 examined belt-drive tables. In this installment, we’ll look at direct drive turntables…and yes, they did exist before the Technics SP-10 was introduced in 1970!

I should clarify that there is a little confusion as to what, exactly, is meant by “direct drive”. As a mechanical engineer by training, the term to me means a drive system in which there is a direct coupling between the motive force (motor, powered flywheel, and so on) and the final output, without an elastomeric element like a belt or idler. This can take one of several forms including a direct shaft drive from the motor output, gear drive (including, worm, spur, bevel, and so on) and some combination of rigid drives. In the hi-fi world, for the last half-century the term refers to a turntable in which the motor and platter form an integrated assembly which turns at the exact speed required for playback.

Just to muddy the waters even further, this article will refer to both types of direct drive turntables. I’ll attempt to clarify the fine points of both types of drive mechanisms as we proceed.

Back in the early days of audio—well, I doubt if you’ll be shocked to see the name of Western Electric appear here. As we’ve discussed more times than I can cite here, WE was basically the originator of most major developments in the audio world, and comes into play here because they were involved in the origin of talking pictures—and the “talking” part was provided by discs, believe it or not.

The Vitaphone process of sound movies is famously associated with the Warner Brothers studio, staring in 1926 with a John Barrymore feature, Don Juan, which only had background music and sound effects, no dialog. The true talkies era began the next year with the next Vitaphone release, The Jazz Singer, in which Al Jolson sang, and dialog was featured in several scenes, but not throughout the film.

The Vitaphone process was entirely a creation of Bell Labs and its manufacturing arm, Western Electric. Sound was recorded on 16″ discs which ran at 33 1/3 rpm, the same as later LPs. Running at that speed (rather than the then-standard 78 rpm) the discs could match the running time of a 1000-foot reel of film—about 11 minutes. The groove spacing was such that it preserved average effective velocity, and thus maintained reasonable sound quality. The upper limit of the frequency response was about 4300 Hertz—clearly not full-range, but sufficient for articulate reproduction of speech, and most instrumental fundamentals.

The turntables were directly coupled to projectors, and the projectionist had to cue the record up at a mark on the label area—and then the record played from the inner area, to the outside, the reverse of standard record playback. As the whole rig was up in a projection booth, noise from the turntable was not a critical factor, but synchronizing sound with film was. The drive motor was coupled to the projector, and then drove the turntable through a shaft and gearing; construction was robust, to allow continuous use, as was true of the projectors.

These turntables were purely industrial mechanisms, expensive to build and maintain. I would imagine that most ended up in scrap yards after sound-on-film rendered them obsolete, by the ’30s. Given their reverse-spin and low speed, they couldn’t be adapted to playing records of the day without considerable effort—and I would imagine the noise of the mechanism would render the whole subject moot.

Turntables designed for radio station usage were also industrial devices, built to endure continuous use for years with minimal downtime. Vital characteristics were quick start-up, speed consistency, and reasonably low noise—although noise requirements were related to noise that would be transmitted through the pickup, not through the air. Compared to all but the most over-the-top megabuck turntables produced today, broadcast/transcription turntables made domestic record players look like toys. With their large, high-torque motors and squared-off consoles, the profile more closely resembled a washing machine than our standard conception of a turntable.

The header pic is a detail of one of the most popular broadcast turntables of the ’40s and ’50s, the RCA 70-D. You can see the whole drive mechanism below: a massive motor was anchored to a heavy base, coupled to and driving the turntable by means of bevel gearing, a wet clutch utilizing oiled felt supports, a driveshaft with flexible couplings, and another clutch that would prevent over-running. Above the driveshaft in the diagram, you can see the outline of a flywheel which helped insure speed consistency.


It was quite a piece of work, and a surprising number are still around today. Aside from simple playback of music records, these turntables were also used to play back transcription discs that carried program content. The format was similar to the Vitaphone discs, 16″ 33 1/3 rpm; some were even inside-start like the Vitaphone discs. Generally, two of these discs would carry a 30-minute radio program; this practice allowed radio stations flexibility in scheduling their programming, or allowed them to exist outside nationwide network links.

Some practices die hard: at radio stations I worked at in the ’70s, some syndicated weekly programs were still distributed on LPs. I recall listening to the Wolfman Jack show in what was supposed to be our recording studio.

We’re getting far afield from an examination of turntable drive mechanisms, although how tables were used definitely influenced their design. Most major radio station/transcription turntables of the ’40s and ’50s had mechanisms similar to that of the RCA, so we’ll move on from that subject. By the LP era, most broadcast turntables were idler drive with torquey motors (think of the Garrard 301/401, various EMTs, Gates, Sparta, Gray, and others)— less elaborate and less-costly than the monster turntables of the earlier era. Another factor was that the turntables designed for mono reproduction often had a rumble spectra that made them unacceptably noisy for playback of 45/45 stereo discs.

And so it goes.

For the last half-century, if you mention “direct drive turntable”, the Technics SP-10 is what first comes to mind. Developed at Matsushita (parent company for Panasonic and its upmarket/professional sub-brand Technics) and released in 1969 or 1970, depending on which source you believe, the SP-10 was a true transcription deck like the 301/401, designed to be dropped into a broadcast console, and sold without a tonearm. Many were used in broadcast studios worldwide, even at the BBC, often paired with SME 3009 arms.

From Technics' own historical website. They say release was in 1970---who am I to argue? Take THAT, Wikipedia!
Direct drive tables might seem straightforward, mechanically, but the good ones go to great lengths to ensure smooth, consistent speed without motor cogging.

The fundamental principle of modern direct drive tables is that the platter assembly actually becomes part of the motor assembly, rather than linking to it by an external coupling. Initially in the ’70s and early ’80s, direct drive turntables were heavy-duty, precision built devices, many of which were designed for continuous broadcast use. These days, the top Technics, Denon, JVC, and EMT direct drives from that era are often repackaged into custom, heavy bases to improve their stability and lower the noise floor.

As turntables fought a losing battle in the late ’80s and early ’90s, direct drives became cheapened and commonplace, often built with motor assemblies that quickly wore out or were noisy and unpleasant to listen to. Use of lightweight platters reduced the smoothing flywheel effect provided by a heavy platter—and the reputation of direct drive tables suffered. Audiophiles turned to belt-drive tables, in the post-Linn era.

Ironically, the underground revival of idler wheel turntables revived interest in better direct drive tables. The “jump factor” provided by idler wheel tables was also provided by the better direct drives, and as elderly Thorens, Garrard, and EMT tables became prohibitively expensive, attention turned to salvaged SP-10s and other broadcast models.

Within a few years, demand was such that few of us can now afford an early, high-quality direct drive table, either. Sheesh.

Development continues in direct drives. A few years ago, the $100k Continuum Caliburn turntable favored by Michael Fremer became the poster child for new, hyper-performance direct drive turntables. Since then, a number of models have appeared from Brinkmann and many others. Recently, American manufacturer VPI celebrated their 40th anniversary with the HW-40 turntable, designed by founder Harry Weisfeld. It features a sophisticated motor assembly and control circuitry reminiscent of the Caliburn, at the relative-bargain price of $15,000.

The hefty coil and rotor assemblies of the VPI HW-40's direct drive motor. Add a 25-pound platter, and you've got a beast.

You can read an interesting white paper on the HW-40’s design, here.

Modern direct drive tables vary in their quality of execution, and the details of the coil and rotor assemblies, and the speed-control circuitry. For the most part, such discussions fall more into the realm of electrical engineering than mechanical design—and for me, that makes them boring. Feel free to poke around in the world, at models from Bergmann, the PBN Groovemsaters (which utilize vintage Denon direct drive chassis), Thrax Audio, Continuum, and others.

In the next installment, we’ll look at oddballs, unclassifiables, and loose ends. Think of it as a pickup pot pourri.

Back to Copper home page

1 of 2