Mine is not separate but is largely decoupled from the plinth by the use of a Pete Wriggle VTA adjustor. Arm is held on table by its own weight and not bolted on. See the Wriggle web site for pictures and more info. Seems to work well.
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Depends on how strict you mean by "strict distance relationship between
the arm pivot and the spindle center?" I have a separate 15lb armpod
and I tested the theory that alleged movement. I aligned my cartridge
according to the Mint lp protractor, used the set up for x amount of time and
then put the Mint back on: no movement that I could see with that tool. If
someone wants to argue that with better tools I would be able to detect the
movement, then fine. But that's a moot point as far as I'm concerned. IMO, the
weight of the pod and the type of coupling feet (spikes in my case) one uses
should prevent any gross movements. I have a lighter 8lb pod that doesn't
appear to move either, but I never tested that one.
OK, thanks gents.
If one uses coupling/decoupling spikes on both the
motor assembly and the arm/cart assembly, and the
spikes go into something "soft",i.e., a piece of wood,
the SAME piece of wood, that is, then I can see that
the spindle-pivot distance can be maintained.
The question of both assemblies being vibrationally
isolated from each other, in this instance, is topic
for a different post.
My interest here is primarily how to maintain the
spindle-pivot distance (while observing motor-cart
isolation). Two big weights could possibly drift apart,
or the dog's tail could move one of them, etc.
Banquo, it's comforting to read that you've had
good luck with your setup.
For example, one could not place the two assemblies
in a box of sand, or on a big lump of clay even.
Possibly I'm making too much out of this issue.
I'm seriously considering such a project, and I want some
certainty the design will work once I start spending.
If you have a very heavy and very stable outboard arm pod, and if the turntable is also weighted down, and if both are supported on the same perfectly flat and very stable surface, then it can be made to work and hold the alignment, as Banquo and others have done.
But it is NOT really a great idea to isolate the tonearm pivot point from the turntable, I and others maintain. There is a case to be made that the tonearm at its pivot must move in unison with the bearing and platter, in response to spurious external stimuli (a large truck passing by, an airplane flying low, a big fat guy walking around on the floor above), because the stylus will read any difference in motion between the two as a signal that will be overlaid onto the audio signal. Such a phenomenon is not desireable. The reason that a set-up such as the one I describe above can work well is precisely because it does favor coupling.
Each of my armpods is made of cast bronze and weighs 30 lbs sitting on 3 spikes. ARMPODS
They simply don't move without me physically lifting one of the spikes.
This is not a new idea.....see DaVinci's turntable system?
Henry, Your solution and the Da Vinci turntable system both comply with the conditions I outlined above in my first paragraph. So I am sure both work very well. However, I don't agree "in principle" with mounting a tt chassis on a compliant footer (e.g., AT616 or the like) whilst the arm is mounted on a totally noncompliant pod, because such a set-up would permit relative motion between tonearm pivot and platter/bearing. But we've been through this before; no need to butt heads over it again.