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Reference Section -Jack Homes on Linear Tracking Turntables
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70s Audio - Receiver Wars
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Amplifier Distortion, DC Offset and You
 
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Jack Homes on
Linear Tracking Turntables
 

Jack Holmes - Linear Tracking Turntables
Jack Holmes is an experienced audio guy. He is also an active participant in our 70sAudioMindset discussion group. Here are some of his thoughts on Linear Tracking Turntables.
Rick,

I've thought a great deal about why most of the linear tracking arms /tables that I have heard sound dreadful. I think it is due to the same reasons that cheaper pivot arm tables sound bad but to an even greater degree due to the complexity of the servo motor controls on the vast majority of linear arms.

The reasons are undamped internal resonances of the arm combined with excessive "play" or sloppiness in the bearings both vertically and horizontally. Combine these problems with a resonating lightweight platter and minimal isolation (no sub-chassis) and you get a cacophony of resonances so large that the sound coming out of the cartridge is a total distorted mess.

In the worst designs, the cartridge /stylus is so confused that it is unable to track the groove at any decent modulation level such that mistracking is often and severe. I have owned three B&O (Bang and Olufsen) linear tracking tables and all had this problem. One had the MMC 20 CL cartridge, one had a MMC 20 EN and the other had the MMC 1. All pretty decent cartridges that when mounted in a good pivot arm /table sound good and track very well, yet when mounted in the B&O linear tracking units, frequently mistracked and in general sounded bad.

To show you the degree that I believe these resonances affect the sound, about a year ago I purchased an old (1965) Weathers synchronous turntable with the Weathers wooden tone arm off eBay. When the unit arrived, I disassembled it and thoroughly cleaned the unit, oiled the main spindle bearing and motor. I mounted a NOS (New Old Stock) Pickering AT-3 cartridge in it and re-wired the arm /cables.

For those that don't know it, the weathers arm was a solid piece of mahogany wood and the bearings both vertically and horizontally were heavily silicon damped and have essentially no "play" in them. Additionally, the horizontal bearing of the Weathers arm sits tightly into a 1 1/2 inch diameter larger rubber grommet. There is no direct mount of the arm to the table plinth. The arm is held in that large rubber cone shaped grommet. I think that isolates the arm from any resonances being transmitted from the plinth. The platter of the Weathers is a very thin stamped sheet metal. I placed a sorbothane mat on the platter to stop its resonances.

Also for those that don' t know, the Pickering AT-3, it was basically a bottom of the line design that had a spherical stylus and tracked at 2 to 4 grams. I set the tracking force at 2.75 grams and then hooked this table up to my main system. WOW!!!!!

You could not believe the sound that came out of that table. That old table sounded better than most tables I have had on my system. No mistracking, I mean none. Extremely silent groove noise (ticks, pops, etc.), astounding bass response and smooth detailed highs, albeit, slightly rolled off at the very extreme highs above 12 kHz due to the Pickering cartridge, but just a tad.

Now, just as a point of reference, I am comparing this versus my Oracle Delphi with an SME III arm and a Grado Sonata cartridge. That old Weathers was a delight to listen to. I am convinced that it was that arm that made that table sound so spectacular. Thoroughly damped and controlled resonances.

By the way, at the same time that I had the Weathers, I also had a Thorens TD-125 MkII with the factory TP-12 tonearm.  I mounted a Grado Prestige Gold in it. The Weathers trounced the Thorens. Again, it was the arm. The TP-12 has a lot of play in the bearings and many internal resonances. The Thorens TD-125 is a good table though, very heavy platter, good isolated subchassis, deserves a better arm.

Anyway, that's my thoughts on the whole linear tracking arm question. By the way, if you look at the really good linear arms such as the Emminent Technology and a couple others, you will see a great deal of effort expended to control resonances and eliminate "play" in the bearings.

Jack
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