[78-L] Turning the tables

[Michael Biel]

Yes this is a good point.  I certainly agree that rising and falling of
the record surface can set up bouncing and resonance of the tone arm and
cartridge, and this can be caused by a warped record (naturally or with
pennies underneath) as well as a tilted table.  The Shure V-15 has a
long cantilever, and I feel that these are more likely to have this
problem.  That is one of the reasons I used an Audio Empire cartridge in
the 60s for microgroove because it had a very short cantilever.  The
same is true of the Stanton 500 and other carts used for 78s.  It is
shorter than what the Shure M44 and SC35 have.  You watch those things
bounce two or three times for every bounce the record forces.  When this
happens there is a subsonic frequency added to the audio as well as
fluttering of the pitch because the stylus is possibly moving a bit
forward and back with each lowering and raising of the cartridge.  One
raise and lower per rev due to the uneven platter can result in four or
five bounces of the cartridge. 

Mike Biel  mbiel at mbiel.com 


-------- Original Message --------
From: DAVID BURNHAM <burnhamd at rogers.com>
M. Biel wrote:
 I think that rather than some of the other potential problems David
Burnham mentions it probably was a defective unit that JD had received,
especially since he says that others he had looked at from that brand
did not have a rising and falling turntable during rotation which is
what he said this one had.  That ALWAYS is a defect, and has nothing to
do with acoustic feedback from the speakers

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Dr. Biel is correct, the rising and falling of the turntable when it's
rotating is certainly a defect, but I was addressing the flutter in the
sound of the recording, and this wouldn't be caused by the uneven
turntable.  Just so I could put in my two cents worth of expertise here,
I just played an Lp with two pennies under the edge of the record;  this
is on a turntable with a linear tracking arm and a Shure V15 type V
cartridge.  While the arm rose and fell significantly on every
revolution the sound was unaffected.  Of course there could be a problem
in the turntable drive motor which could cause flutter but such a
problem would be obvious before you even play a record because there
would be a vibration felt on the motor board and there would be no need
to play the record on another player to compare it as JD said he/she
did.  Acoustic feedback will cause a flutter, often at a frequency so
low that the sound of the feedback itself can't be
 heard.   db