[Vintage-Audio] Re Super Thin Dynaflex

[wolfbob]

In 1947, just in time to play the then new microgroove 33 1/3 RPM records 
Zenith came out with the "Cobra Arm" turntable with a 1 mil needle and 1 
gram of tracking. It used a special pickup that changed the frequency of a 
2.5 MHz oscillator by causing a capacitor in the head to change value as a 
function of the needle position. They called it a "variable reluctance" 
pickup possibly because of Weathers patents.

There were also a number of optical pickups that did not contact the 
recording surface at all. I never saw one work, however.

Another issue is that on stereo recordings the L-R signal is recorded as a 
vertical excursion. The tone arm/stylus must be capable of staying in the 
groove with loud low frequency signals from one channel. The sum channe L+R 
is lateral and for recordings requiring large signals they invented the so 
call variable-width groove or "Dynagroove" so that they didn't have to 
compress so much to keep the tone arm tracking.

My pet peave is in compression. Even with dynagroove they still mash the 
signal during mastering. It is much worse on cassette and unbearable on what 
they do to CDs (for no good reason other than they do).

WBob


----- Original Message ----- 
From: "Robert Nickels" <w9ran at oneradio.net>
To: "Vintage home and professional audio equipment from 1975 back" 
<vintage-audio at mailman.qth.net>
Sent: Friday, July 25, 2008 6:24 PM
Subject: Re: [Vintage-Audio] Re Super Thin Dynaflex


> Duane Fischer, W8DBF wrote:
>> At what point in time did the record changer and turntable companies 
>> change the tracking weight from 3 grams+ to about 1 gram?
> This is an interesting question Duane, because I've been working on a 
> turntable that it is said paved the way for this transition.  I refer to 
> the Weathers turntable, which was based on the Capacitance Or FM Cartridge 
> developed by Paul Weathers at his comany, Weathers Industries of 
> Barrington, NJ in the 1950s.  Let me quote (somewhat edited by me) from a 
> website I found that discusses this topic rather well:
>
> His theory was, the less work the stylus must do, the more accurate the 
> pickup can be. In magnetic, dynamic and piezo-electric pickups the 
> electric signal is generated by the motion of the stylus itself, which 
> requires a certain minimal bulk. Even with the most careful engineering a 
> vertical pressure of four to eight grams was necessary to make such 
> pickups work properly, and the moving mass of the stylus must remain a 
> measurable quantity. If you could design a pickup in which the signal 
> voltage was already there, and the motion of the stylus would merely 
> modify it, then you would approach the perfect pickup.
>
> Literally hundreds of patent applications have been filed on such designs, 
> and a few such pickups have actually been manufactured. The most 
> successful of them is the Weathers, which is called a "capacitance" pickup 
> or an "FM" pickup because the stylus causes frequency deviation of an 
> oscillator that is demodulated to produce the audio signal.  The Weathers 
> pickup consist of a fixed metal plate  and a parallel free-floating plate 
> separated by a tiny air gap. The floating plate is attached to the stylus. 
> As the stylus traces the wiggles in the groove of a spinning record, it 
> causes the floating plate to flutter toward and away from the charged 
> plate.  This capacitive change is demodulated to produce left and right 
> channel audio.
> The author of the website cites several advantages of the 
> Weathers..."Since it tracks at a pressure of only one gram, it wears both 
> records and styli much more slowly than any other pickup available at the 
> time.  The moving mass of the stylus has been reduced to the point where 
> it is scarcely measurable, which means that the frequency response is 
> practically unlimited - the Weathers has tested out to 30,000 cycles."
>
> I can't verify all this but I can say that the Weathers I have sounds 
> good, thankfully after all the years the stylus is intact, which I'm sure 
> is pure unobtainium today.  Ironically, a surplus dealer in Omaha has a 
> few similar turntables (not all in working condition) if anyone would like 
> to take a look: http://www.surplussales.com/Equipment/Audio.html  (the 
> separate basswood tone arm and demodulator unit for sale for $350 are 
> identical to mine).
>
> The simplicity of the tonearm itself is striking - it's nothing but a 
> piece of basswood with a basic gimbal mount attached.  The tonearm rest 
> uses a magnet to hold it in place.   The stylus connects to the headshell 
> via two pairs of slide-in spring contacts, an there's another set of 
> similar contacts where the cartridge leads attach to the electronics.  The 
> FM demodulators are each contained in an aluminum can (looks like an IF 
> can) that is potted with some waxy goop, and plugs into six PC terminals. 
> That's a lot of series connections that have to all work in order to get 
> output, but I think cleaning and fighting intermittents has produced a 
> working unit.  The drive mechanism is also unique - nothing more than a 
> tiny synchronous motor and a soft rubber drive wheel driving the inside 
> surface of the very light aluminum turntable.  It's a unique design 
> throughout - even the power is turned on and off by a lever that tilts a 
> sealed mercury switch.
>
> So that's my answer to the 1 gram trackin question - Paul Weathers did it 
> first and the rest figured it out later.
>
> 73, Bob W9RAN
>
>
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