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In Reply to: You are assuming stuff.... posted by tubesforever on September 11, 2006 at 08:58:56:
No Rega arm uses an eccentric counterweight.The Graham is a very noteworthy unipivot which doesn not use an eccentric counterweight.
And yes, the eccentric C/W when used with a Rega arm causes a nonlinear change of the VTF.
The mass of the C/W at stylus height means nothing. The arm has fixed bearings and cannot tip sideways.
Follow Ups:
... relative to the pivot, which is located in the 'tower', well above the center of mass of the arm-tube and C/W.
it is concentric with the armwand and the bearing oint is at that same location.Do you have one? Take it apart, I have.
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It has nothing to do with the counterweight like with the Hadcock for instance where it does double duty.
Not the plane of the bearings.
when the sylus goes up in the air the VTF changes. when the sylus dips the VTF changes. with a dropped counterwieght the theory is that the changes in VTF are beneficial in that they keep the stylus from digging in and rising off the record. Some contend otherwise.So with a dropped counterweight the beneftis you are looking for and claimning that you get come directly from, among other things, changes in VTF.
As the cartridge rises it forces agasint the intertia of the dropped counterweight which keeps it down. When the cartridge dips, the inertia of the counterweight does not let it fall 'quickly' thus, and for all time, VTF be helping. The benefits are derived from a transitory imbalance.
all this is becuase the counterweight IS dropped and that is does rise above and below that level of the sylus.
I didn't make up any of this up and it ain't original to me. It is merely how I understand things mith my tiny head.
Now, I am going down to the other end of the bar and finishing my drink.
"when the sylus goes up in the air the VTF changes. when the sylus dips the VTF changes. with a dropped counterwieght the theory is that the changes in VTF are beneficial in that they keep the stylus from digging in and rising off the record. Some contend otherwise."Exactly so. What advocates of the solid underslung weights are not taking into account that an arm tracing a disc is a 'dynamic' system, not a 'statically balanced' one.
IMO the sonic benefits of an uderslung weight are not to do with tracing (at least, in a Rega) but with with balancing/stabilizing the load on the two vertical bearings, i.e. stabilizing the whole beam assembly in the 'roll' plane (that aircraft terminology again). I believe this benefits the way the bearings transmit audio-band vibration to the pillar and hence to 'ground'.
Were thet spaced well apart in a yoke, rather than pressed into short stubs in the Rega's tube, it wouldn't be a problem.
is this what you are saying? stablility[less noise] = wide apart bearing sets.
Symmetry is important to vinyl replay I think, especially stereo.If the bearings supporting the 'beam assembly' (cart., tube, counterweight) are spaced (equally) well away from it's centre of mass, they 'take the weight' equally and will behave in a more ... linear (?) way when they inter-react with the yoke, the arm-pillar, the arm-baord or plinth, the equipment stand .......................
Tires wider apart make for more stable secure traction. The outrigged weights may compensate somewhat in this regard, sort of like the bar a tightrope walker uses.
The outrigger weights act in two ways. My guess is that they absorb the vibrations and resonances of the vertical bearings. Second they add unsprung mass to the arm itself so it increases mass without increasing effective mass of the tonearm.
They are not attached to the arm, just the bearing/yoke assembly, so they add zero mass to the arm.i can't speak to them absorbing resonance from the bearings but their purpose, mass qua mass, is to add that mass outward on a horizontal plane to create, litteraly mass/inertia to slow down the arms movement along that plane, or to stablilize the arms back and forth movement.
Why? When the cartridge is 'excited' by the groove it will over-react [think Grado here in the extreme] and cause the arm to react as well. Some think this is good in that the arm is nible and allowing the cart to 'do it's thing.' But, stopping that arm from reacting is the point. Keeping that arm stable but fluid keeps that cartridge/stylus riding smoother/deeper into the groove. The cartrdige should move and send that energy up then cantilever into the coils, etc. Hold that cart still and stopping the arms reactive movement stops feedback to the cart. NO WIGGLING. Keep that arms steady to keep the cart steady so that the sylus/cantilever can react to the grooves ONLY means ... a higher level of fidelity[truth in movement], dynamics[deeper in the groove], detail, able to calmly reproduce subtle changes in the groove.
Can you see that picture?
I would describe this modification as akin to the balance beam a tightrope walker uses. Well sort of.But locating the two largest masses, namely the cartridge and the C/W at the very extremes of the "stick" contributes to the same type of stabilization. The idea of the C/W close to the pivot is counterintuitive.
The bearings are in the armtube not the yoke so they can be adjusted more easily for preload.Just because some guy has time on his hands and has created Gandystein's Monster doesn't mean it is all sound engineering. There is alot of NIH going here and there.
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I didn't come here for an argument, Garth, just some considered input.It should be obvious how important 'symmetrical' behaviour is in a tonearm playing a stereo source. Imaging?
I don't know why you're even taking issue with my stating that the cost-compromise design of the Rega included a far-from optimal way of pivoting the arm-tube (for all the arm's many other virtues, which make it such a playground for inventive tweakers).
Was that it offset the angle of the vertical pivot to the angle of the tonearm.Technically this is done to minimize the torsional effect of the counterforce to the stylus.
so symetry is not always the best method. Sometimes offseting angles are better....
And offset counterweights is still up in the air!
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The spacing of the bearings is I feel irrelevant.
Movement? I said nothing about "movement". Re-read the post.The spacing of the bearings is I feel irrelevant.
The reason to move bearings outboard is because they do vibrate, and it is best to decouple the vibration from the arm wand as much as possible.The distance is not an issue. The resonance and vibration is an issue.
And dropping the mass of the counterweight below the plane of the stylus just creates the same mistracking issues as a counterweight above the plane of the stylus, just the opposite force is applied.
The best model I have seen is with the counterweights median mass at the exact plane of the stylus. BTW I love how Graham does his arm. with the opposing magnetic structure for damping and stabilization. Pure genius.
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