How to choose an upgraded tonearm.

Thank you pindac. I hadn’t heard of Stand Alone Tonearm Pods before. I’ve started looking into them to see what I can find out. Interesting idea,

Mike

In relation to my suggestions, a further investigation might uproot some of the pro/con material to be discovered about a Stand Alone Pod, the following might clarify why some of the discussion takes place.  

There is a die hard element in the use of Vinyl and LP Replays, that objects to the idea of using a Pod, the concern is usually seen that maintaining a consistency to the Spindle > Pivot distance is compromised when adopting this method.

I have not at any time seen this as being a concern, and have seen TT's that are at risk of compromising the dimensions for this critical Geometry due to the Plinth Materials chosen to be used by the Manufacturer.

If the TT and Pod are both mounted onto a very stable material, that does not swell in differing environments, this material will serves as a Sub Plinth.

There are many out there, I have trialled many types, and most recently have been very impressed with a material called Panzerholz when used on a system I am familiar with.

When both TT and Pod are securely seated on the Sub Plinth, the Sub Plinth will not contribute to creating micro dimensional movements impacting on Geometry of the Spindle > Pivot distance.

There is then the risk that the materials used for producing the TT's Chassis or Plinth is made from materials that are not stable, and micro dimensional movements can occur.

Unfortunately if this is the case, the conventional method to mount a Tonearm will be impacted on with the same influence, and in differing environments dimensional changes can occur.

The use of materials with properties that are very stable for the Chassis / Plinth are the only method that ensures the rigid coupling philosophy for a TT > Tonearm interface having a chance of a success, when keeping with the required tolerances that allow for the design to be called a rigid coupling .

As my knowledge of the critical mechanical interfaces on TT's has grown.

My experience of TT's which have had an unknown amount of usage hours behind them when encountered, has been to discover many TT's, I have been able to manually inspected the Spindle Bearing, has shown a high percentage have a detectable sideways movement on the Platter Spindle, that in some cases can be made to rattle.

I have my own thoughts on how such a condition can develop, but that is a separate subject.

This sideways movement condition on a Spindle will when functioning during a replay put any of the above concerns out of the Ball Park, as these are no longer micro dimensional changes, but eccentric rotations and speed fluctuations.

The Tonearm Pod is in my view a totally acceptable method to mount a Tonearm when compared to how many other TT's function in relation to the Spindle > Pillar distance being maintained.

There is no reason why the correct methods when adopted are any lesser than other more common options used to maintain the critical Geometry.

The Tonearm Pod can also be a design that offers increased options and allows for differing Base Plate Materials to be used, that will further allow for a selection of a preferred interface materials to be discovered, and ultimately end up with a Bespoke assembly to suit an individuals unique preferrence. 

If a Detachable Head Shell Tonearm design is also considered, the New Tonearm can be tried with differing Headshell Materials, which will further enable a opportunity to discover a Bespoke and preferred interface for your Cart' of choice.

The Detachable Head Shell will all so enable a Speedy exchange of the Preferred Cart' to a Head Shell that has a Cart' mounted, that is a of a lesser concern, which can be used to preserve the life of the Cart' of choice.

A little food for thought, Your Tonearm in use at present could? become an improved Tonearm if mounted on the Pod, as the separation from the TT's imparted energies might suit its overall function for the better.  

@ skyscraper I hope you are not feeling as limited as you were when the thread commenced

The Rega RB3000 tonearm mounted on the RP 10 is available as a separate item at a very reasonable price. It is not neutral balance and has it's vertical bearings are above record height. With a perfectly flat record none of this is a problem. Unfortunately there is no such thing. Even with vacuum clamping there are undulations in the record's surface that the tonearm has to negotiate without causing the cantilever to deflect. Such deflections cause wavering of the sound as the relative speed of the vinyl changes. This happens to some degree even if the tonearm tracks the record perfectly but a poorly designed arm makes this worse. It is built in wow and flutter. The reason vacuum clamping turntables with great arms sound better is better speed consistency, less wavering. This is more important then wow and flutter specs is todays better turntables. 

Tonearms, regardless of specific design points are captive to the laws of physics. Effective mass and cartridge compliance determine resonance. Effective length determines tracking error - especially important when using Shibata or other thin-line stylus designs. Bearing design is at the heart of the conflicting tonearm design requirement of infinite mass, which gives the stylus a firm platform to work against, minimizing loss of dynamics and zero friction allowing the arm to move freely as it tracks across the vinyl. What shortcoming in your current rig do you feel are addressed by a new arm?

The major argument against mounting the tonearm on an outboard pod is not the fact that pivot to spindle distance is subject to variation, if the pod is inadvertently moved in relation to the spindle, although that certainly is a major secondary consideration.  The major argument against is that the separated pod will likely exhibit differences in resonance properties in relation to the spindle and bearing; this will cause minute relative movements of one vs the other.  You don't want that. You want the tonearm pivot, spindle, and bearing to be together in a closed system.  That said, there are a few outboard pods with sufficient inherent mass that they work OK, if also in contact with a subchassis that is shared with the TT chassis.  There was a ridiculously lengthy thread on this topic, started by Halcro.  Search on the keyword "Copernicus", if you want to revisit it.

Can someone show me the math or physics that says the tonearm pivot must be in the plane of the LP surface?  The idea sounds "right", but I am trying to visualize why.  I start with the principle that certainly the center of mass of the counter-weight should be in the plane of the LP surface, but I'm not sure how we get to the pivot.  There are oodles, probably a vast majority, of tonearms where the pivot is not in the plane of the LP surface.  Many of them are terrific tonearms.