[78-L] 78-L a shuddering stylus

[JD]

> Date: Fri, 14 May 2010 07:10:46 -1000
> From: Malcolm Rockwell <malcolm at 78data.com>
> Subject: [78-L] a shuddering stylus
> To: 78-L Mail List <78-l at klickitat.78online.com>
> Message-ID: <4BED8416.60806 at 78data.com>
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>
> Has anyone else besides me noticed a little shudder of their tone arm
> once a revolution on some pressings? It's especially prevalent at the
> outside edge of indy 1950s issues, but not limited to them and can cause
> the stylus to jump out of the groove in some instances. In fact I
> recently received an RCA-Victor record with this problem. It seems to
> disappear the closer to the center of the disc the groove is.
> I believe it's due to an unbalanced (or badly lubricated) lead screw, or
> possibly a bad bearing at the outer end of the lead screw on the disc
> cutter.
> Any other ideas?
> Mal
>

If your tone arm iadjustments and tracking force are properly set and this 
symptom persists you may have a resonance problem between the arm and disc. 
The Dual 608 turntable (single play, three speed, long out of print) was 
able to address this problem via a separate adjustment of the arm 
counterweight. The Shure "ERA IV" test Lp (TTR115) had several tracks to 
test for resonance. Unlike some of the non-existent or imaginary problems 
and tweaks that latter era Voodoo hi-fi loonies have focused upon this could 
be a real problem and the Shure disc could demonstrate it vividly. The 
resonance damping adjustment on the Dual 608 worked perfectly. On some of 
the Shure tracks the arm would vibrate violently. Adjusting the damper would 
cause the vibrations to disasappear. Some months ago I mentioned having 
tried a so-called "DJ" turntable ( a cheesy copy of the excellent and proven 
Technics) of a well known brand. Luckily, one of the first LPs I played on 
it (a classical Mercury Living Presence) began with a clarinet solo. I 
immediately heard what sounded like flutter. I knew darn well that there was 
no flutter on the Lp and verified that by playing it on my Technics SLQX 300 
and my old Empire. I concluded that what I was hearing was an artifact of a 
poorly designed arm exhibiting a resonance effect. That turntable did not 
exhibit real flutter on other recordings but did have
 other major problems that I soon discovered (unusually high rumble for a 
direct drive and an off-kilter platter). Needless to say it went right back 
to the dealer and I decided to avoid similar TTs in the future.
So, I suspect from your description (assuming correct adjustments) that 
resonance is the likely culprit. The first thing you should try after 
verfying that arm & cartridge adjustments are properly set is to play the 
"problem" discs on another turntable of known quality.  Good luck!!!
JD