rzdz@fluke.UUCP (Rick Chinn) (01/04/84)
re: Nakamichi Dragon turntable reply by ark@rabbit.UUCP (andrew koenig)
I have actually had a few records pressed, which was a good excuse to visit
a pressing plant, and being more than a bit familiar with the process, I
must rain a bit (no pun) on your parade.
When a record is made, the groves are not "stamped" and the hole subsequently
punched. What does happen is:
If the pressing plant is using a one step process, the master disc is
plated several times (to build up a reasonable coating of nickel over
silver), then the plating is "peeled" off of the lacquer master disc
(which can now be recycled as a pizza platter). It is then placed into
a jig and rotated, while the grooves are watched. By some magic (and I
don't quite remember how), the grooves are centered with respect to the
axis of rotation, and the center hole is punched. The disc is then
placed in a press and crowned. This creates the "lip" at the lead-in
grooves which helps a record changer's arm to find the grooves. It also
helps keep the adjacent surfaces from grinding too much on a changer.
The result is a single stamper. The one step process is useful for
short runs. If there was a problem in the plating process causing a
defective stamper, you must return to square 0 and recut a new lacquer
disc.
If the pressing plant is using a two step process, the master disc is
plated, then the plating is peeled, then re-plated one more time (makes
the mother), then re-plated repeatedly (stampers). Each stamper is
punched and crowned. This process can make many stampers from each
mother. Sometimes defects from the plating process can be fixed in the
mother. This is what the biggees do.
As you can see, an error in punching the center hole in the stamper can
create many records with off-center grooves. This problem seems to be more
prevalent with 45 RPM singles than LP's.
The Nakamichi approach seems (to me) to be an elegant approach to solving a
problem caused by sloppy manufacturing. I guess the record companies aren't
too scared of us stopping our record buying habits. Personally, I can't see
spending 7 grand to play sloppy american made pressings. I vote for fixing
the problem at the source.
Rick Chinn
John Fluke Mfg. Co MS 232E
PO Box C9090 Everett WA 98043
{uw-beaver,decvax!microsof,ucbvax!lbl-csam,allegra,ssc-vax}!fluke!rzdz
(206) 356-5232dhc@exodus.UUCP (David H. Copp) (01/10/84)
I'll bet that some clever digital designer could come up with a black box that corrects the signal for the effect of an off-center center hole, and sell it more cheaply than the Nakamichi Dragon. Anybody out there up to the task?
rmd@hpcnoa.UUCP (01/19/84)
#R:tpvax:-14700:hpcnoa:30200014:000:254 hpcnoa!rmd Jan 14 15:49:00 1984 Such a device is now available and is called a CD player. Anyone who does not like digital sound is not too likely to go for a fancy digital processing technique to correct for the various effects of off-center holes on LPs. Rick Dow hpfcla!rmd
ark@rabbit.UUCP (Andrew Koenig) (01/20/84)
"Anyone who does not like digital sound is not too likely to go for a fancy digital processing technique to correct for the various effects of off-center holes on LPs." The Nakamichi Dragon turntable does not do any digital signal processing at all. Rather, it measures how far off center the record hole is and physically moves the spindle to center the record precisely..
jj@rabbit.UUCP (01/20/84)
Well, folks, let me put it this way: The Nakamichi Dragon turntable doesn't use any fancy digital SIGNAL processing on the signal. It does some computations, ONCE, to figure out the excentricity, that don't involve the signal path at all, and then does a MECHANICAL compensation. The signal path consists of two things: 1) A cartridge of your choice 2) A good, low capacitance sheilded cable to the preamp of your choice. (Not very digital now, is it?) Why is it that you assume that it's doing fancy digital signal processing? Frankly, there isn't a pitch shifting algorithm good enough for AM radio, so I wouldn't worry about correcting turntable excentricity digitally for a while. -- TEDDY BEARS ARE PEOPLE, TOO! (allegra,harpo,ulysses)!rabbit!jj