Spindle oil

El, eplain to me how your arm can keep from cogging over to catch up when the groove spacing is wider than average. You can't. If the arm is moving at a constant speed and the groove's relative motion toward the spindle is faster, the arm has to either make periodic corrections or keep getting further and further behind. Either we're talking about 2 different things or one of us is wrong.

These aren't the "problems of slipshod design." They are the issues that any arm has to deal with. I'm not saying that your system might not be the best solution to the problem, but to deny that it exists is ludicrous.

Sean, I don't think my example of an off center record is extreme. El tells us his sylus won't deviate from the center line more than .006 inches. That is less than 1/128 of an inch, about the width of the markings on my ruler. Not much. I just tried a number of random records and several of them were easily moving back and forth more than 1/128 of an inch.

Since it pivots it can track deviations up to the .006 limit without any correction. After that it is either making corrections or it is deviating more than .006 inches. You can't have it both ways.

Herman & El: You guys are discussing something in specific that i'm not really super fond of i.e. servo-driven linear tracker. Based on past experiences, i still believe that such a design has the potential to be better than most conventional pivoted designs.

Having said that, my thoughts are that the servo-driven mechanism is still going to be closer to the center of the groove more of the time than ANY pivoted arm over the duration of the LP. We already know that a pivoted arm can only be "centered" twice on an LP. We also know that this figure is based upon optimal cartridge installation / alignment.

With that in mind, how often do you think that the stylus is going to be centered on a pivoted arm as the off-center record yaws back and forth? On top of that, you have the inertial mass of the arm following that rotational irregularity, supported only by the cantilver of the cartridge up front and the bearing at the back of the arm. This not only causes the arm to follow that motion with NO form of correction, you're introducing more horizontal deflection into the stylus than should be there. My guess is that under these conditions, the stylus of a pivoted arm would be centered a big fat "ZERO" times on a record like this. That's because even when the arm gets to the point where the stylus should be centered, the stylus is probably going to be being pitched about sideways as the record wobbles around its' rotation.

Now how often do you think the linear tracker is going to be out of the center of the groove? Not only can the arm measure and correct for this ( to some extent ), but the arm starts off with the stylus following the grooves rather than pivoting across them? Before answering that, ask yourself how a record is originally cut i.e. with a pivoted arm or with a linear tracking cutting head? Now factor in how that cutting head is driven i.e. with a servo-driven motor.

If common sense has any input into your thought process, the law of averages will tell you that it is with the "inferior" servo-driven linear tracker, flaws and all. Pivoted designs came about because they were FAR more cost effective and easier to design and produce, not because they worked better. Sean
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PS... Most of the early motorized linear trackers put the money into the mechanics of the table's arm, meaning that the rest of the table i.e. the attention to motor vibration and the platter suspension were highly compromised. The fact that many of the motors driving the platter were also driving the arm compounded the vibration problem, which was already poor to begin with.

Guys...I guess you still don't "get" the concept behind the Sony arm. Perhaps my explanation was not the best.

The gist of the thing is that the Sony arm IS A PIVOTED ONE. What moves with the linear motion servo is the pivot point. Even if the servo were to "cog" (which it doesn't for reasons I have explained) this would only cause the arm angle (tracking angle) to vary by some tiny amount, at a frequency too low for any sonic effect to be audible. There are no sideways forces on the stylus from the servo.

Herman...perhaps it would help if I drew an analogy to driving a car in steady moving traffic on the interstate. You press the accelerator to a certain point which moves you along with the traffic. Sometimes you ease up a bit, or press down a bit so as to vary the speed according to local conditions. If you are a good driver (servo) these corrections are so gradual that your passengers never notice. In similar manner, the Sony arm smoothly varies the pivot point movement speed, but it never stops or reverses direction, which is what I think you mean by cogging. Because the arm is always moving in the same direction, at nearly constant speed, friction direction reversals, which can destabilize to fine control servo, do not happen.

Sean...The arm tracking is a completely separate servo. Actually, If I remember right the TT has five (count em!) microprocessors. Platter motor control, Fast arm movement, Fine arm movement (while playing the record), vertical arm control (biotracer), and one more to run the show.

I'm a terrible driver

El: I know how the Sony arm works and understand how it is allowed to pivot at the rear i.e. it isn't "anchored" at the rear like the older HK / Rabco motor driven designs. Having said that, even the HK / Rabco has enough "slop" in the arm assembly to allow a certain amount of lee-way should sidewall thrust come into play.

As such, i was trying to keep the discussion somewhat "universal" in scope and not just concentrate on that one specific product. There were many other mechanically driven linear trackers out there and that is what i was talking about. After all, the comment pertaining to "why aren't these designs more common in the industry now if they were so good then" was previously used. I was trying to respond to that and at the same time, keep things current with the comments being made about your Sony. Hard to be both specific and general at the same time without some form of confusion arrising : )

Herman: Maybe the Bose servo-suspension is what you need in your car : ) Sean
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