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Analogue's ultimate strength over digital lies in
the fact that a laser swamps low-level signals in the groove.
Faithful analogue retrieval is down to measuring
movements smaller than the wavelength of light.
So the maxim, "keeping in the groove" easy to say,
is not quite so easy to achieve - even in the 21 century.
First there was the AC motor. Because it cogged a
soft belt had to be used when driving the platter.
The DC motor, with far less vibration, heralded
improvements. So much so that in Pink Triangle's Anniversary, the unique
mounting of a motor directly on the sub-chassis proved possible and yielded
considerable benefits. Motor selection was crucial: An (expensive), precision,
ironless rotor design was the DC motor of choice – one that no AC motor can
ever hope to match.
But all that was fifteen years ago! What have
people been doing? Or have we reached perfection? Sadly no.
For bearings to work there must be a gap. Compared
to groove dimensions, engineering tolerances are large.
"That shouldn't matter", I hear you cry, "Platters work gyroscopically…don't they?"
Ah. Would that were true. As the motor drives the
platter it constantly tugs the bearing (in its gap) in one direction. No longer
gyroscopic now, the unstable platter teeter-totters constantly, bicycle style,
as it vainly struggles to stay upright. This instability works against us in at
least three ways
– In fact at this point it could be said we have
actually lost the battle…:
First: This teetering distance (bearing play)
intrudes directly into the audible domain! Not a good start.
Second: The platter motion is not stable. This
instability is left for the poor unsuspecting motor to deal with. The trouble
is that due to the belt, correction by the motor is always out of synchronicity
with the platter. Again this is audible. It affects pitch and rhythmic accuracy
Third: All this wiggling increases wear that we
hear as rumble!
Pretty yukky and
definitely not funky! We need a stable, linear drive. Enter Vector (pat pend)…
Vector is a novel and unique use of three
asymmetrically positioned pulleys, one driven and two passive. These support
and balance the force around the bearing, like a ballerina being supported as
she pirouettes.
Vector's triple pulley support arrangement frees
the platter from the need to self-correct and it now rotates uniformly,
reducing demands on the motor. So current varies less. We can return to the
idea of gyroscopic motion and surprise, surprise pitch resolution is noticeably
enhanced. Perhaps the war isn't lost!
(Three pulleys are the minimum to achieve
stability, for by contrast, a motor and one passive pulley only balance along a
straight-line direction leaving the platter free to "rattle" side to side.
Vector's asymmetric geometry is the result of having one motor driving with two
passive anchors. The alternative of three motors acting to the centre is
entirely out of the question – real life practical motors will always be
fighting each other – a really bad idea!)
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