Re: arsclist RE: 78 Rpm Record Spindle Holes

[Graham Newton <gn@xxxxxxxxxxxxxxxxxxxxx>]

Audio101 wrote:

> As many of you know I have been working on an undersized spindle for
> the Technics SP-15 turntables for use with records that aren't centered.
> I currently have a prototype spindle assembly finished and it seems to
> work well, but I am wondering how far off the center hole can be on a
> record?

Good question... 

I thought about the merits of an undersized spindle, but I decided that a 
spindle with a removable top portion, that is, the part that protrudes above
the turntable mat, would be the better idea.  The plane of the turntable mat
is usually what the arm alignments are measured against, not counting the 
thickness variations of the records being played.  This is one reason why 
is not a good idea to build up the mat thickness when you encounter an off
center disc (which most are to one degree or another!).
A maximum thickness LP pressing (from a major producer, say RCA Victor) of 
the 60's would be the standard used for arm adjustment, and the thin LPs of
the later years productions would fall a small fraction lower, which I doubt
would affect play to any audible degree.

As far as centering is concerned, you will adjust it by moving the record
to either side of the high point after placing it roughly over the 
approximate center location.  (Anyone who can't hit approximately center 
without a center pin in place, really needs to examine what they are 
drinking or smoking!)

I do this a little more precisely with a groove microscope that is on my 
transfer turntable, but often, eye-balling it seems to get it into 
"close-enough" territory for most people.  A record weight holds everything
in place.

Look here to see it:-
http://www.audio-restoration.com/MVC-383F.JPG
Technics SP-15 turntable showing custom low resonance base, SME 3012-R arm 
and Spencer/A-O groove microscope.  The silver thing at the 11 oclock 
position, to the right of the microscope pivot, is a record weight.

> What is every bodies experiences? Can they be more the 1/16" off
> center, if so, by how much?
If you adopt the above, the maximum degree of disc eccentricity becomes a 
non-issue, although allowing for a 1/16" eccentric with a removable sleeve 
out to the standard spindle size would cover most bases  For the very 
few that don't make it, a built up mat would suffice, or bore the center 
hole of the offending disc with a tapered reamer as a last resort.



... Graham Newton

-- 
Audio Restoration by Graham Newton, http://www.audio-restoration.com
World class professional services applied to phonograph and tape
recordings for consumers and re-releases, featuring CEDAR processes.
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