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ARSCLIST  July 2005

ARSCLIST July 2005

Subject:

Re: Turntable Reverse Rotation

From:

Eric Jacobs <[log in to unmask]>

Reply-To:

[log in to unmask]

Date:

Tue, 19 Jul 2005 13:34:30 -0700

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (97 lines)

Here's what I use for reverse play of 12-inch discs, which might give
you some ideas.

I use a Simon Yorke S7 which I've configured for up to 20-inch disks
and as low as 24 RPM rotation.  Although I can't get to 16.66 RPM, the
final pitch correction can be handled in the DAW, especially if you use
a high sampling rate and long word.  My speed is accurate to 0.01 RPM
(NIST calibrated no less), so pitch correction can be super accurate.
I can actually measure speeds accurately to 0.001 RPM, but my turntable
speed is not that stable when playing coarse grooves (stylus drag) -
and that's with a 25 lb platter.

The motor has been modified for forward and reverse playback.  This
is pretty easy to do if your AC synchronous motor is wired for this
option.  I'm not a motor expert, but I was able to open up my turntable
motor assembly, identify the OEM supplier of the motor and its part
number, and then called the manufacturer to find out how to reverse
the rotation.

On the tonearm side, I use an air-bearing linear tracking tone arm to
handle metal parts and other reverse playing material.  The linear
tracking arm has two benefits: (1) no tracking distortion, and (2) no
skating forces are generated.  It works very well for damaged material
where skipping might be a problem for pivoted arms.  I can work my way
through most skipping problems with a pivoted arm, but sometimes I'm
adjusting tracking forces in 0.05 gram increments to finally capture
that skipped groove (along with a host of other techniques).  But
linear tonearms are tempermental in other ways, like set-up and what
type of turntable they are mounted to.

Unfortunately the linear tonearm has a 7.375" pivot-stylus distance, so
it can't handle the 16" discs.  It also doesn't have enough travel to
handle the wider groove area.  I'm not aware of any linear tracking
arms that have enough capacity for a 16-inch disc.  Custom making such
an arm would be cost prohibitive for most people as well as an
engineering challenge - doubtful the arm would be right on the first
try.

For reverse play with a pivoted tonearm, I know that both the Simon
Yorke and perhaps the Nottingham unipivot arms can be special ordered
in this configuration in a 12-inch arm.  However, you're going to be
in for a long lead time and these arms are not going to be cheap.

A gimbal bearing design arm (SME, Rega, etc.) is going to be very
difficult to redesign/manufacture for reverse play.  So unipivot arms
are really going to be your best bet.  Other unipivot arm makers are
VPI and Graham - but I don't know how open they are to custom work.

You might try to DIY with a stock unipivot arm.  The problems to solve
will be cartridge mounting (which might be easy with a slotted
headshell), and antiskate (which needs to be reversed somehow).

I'd be curious to know what you end up trying and how well it worked.

Eric Jacobs
The Audio Archive


-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]]On Behalf Of Kevin P. Mostyn
Sent: Monday, July 18, 2005 1:48 PM
To: [log in to unmask]
Subject: [ARSCLIST] Turntable Reverse Rotation


I am working on a project of transferring a collection of 16" lacquers, a
number of which have suffered water or humidity damage, due to poor storage
conditions.

One of them is a glass base disc of the Koussevitzky 2/27/1943 world
premiere broadcast of the Roy Harris Symphony #5. One side of the disc is
playable; the other side is delaminating. A portion of the lacquer has
started to peel off, but is still attached. I have had some success with
re-affixing peeling lacquer in the past, but unfortunately, differential
shrinkage has set in, and the partially peeled off section does not quite
align with the unpeeled section. The method of re-attaching the peel is
temporary and not strong, and I would appreciate any hints on a permanent
method.

While I can readily deal with the clicks and clunks this will cause, I am
reluctant to try to play the side, as the normal rotation of the disc and
stylus would "go against the grain" of the peel, and the stylus would try to
lift the peel off the glass. I would probably have a greater chance of
success in playing this side if I could play the disc while it is rotated
counter-clockwise, and at 16 2/3 rpm.

Has anyone here ever done this? Of course, the arm will have to be
re-mounted, and there will be a problem with the offset geometry, but I'm
willing to suffer the tracking angle distortion if I can play this disc. I
do have an aircheck of this performance, but the sound on this disc is
rather better, and without the severe pitch problems of the aircheck.

Any advice would be greatly appreciated. Thanks!

Kevin Mostyn

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