On 07/07/2010 06:31, Ian Iveson wrote:
Rob wrote:

Why do belt drive turntables, usually British, have noisy
motors? Is it really beyond the wit of
designers/manufacturers to use a quiet motor?

Beyond the means of most people to pay for, more likely.
Unfortunately the manufacturers and designers are
constrained by the way the universe tends to do its own
thing, regardless. Reminds me of the "Man can go to the moon
but can't cure the common cold" grump. If you feel that only
witlessness stands between you and pure circular motion, and
you are not witless, then make your own motor.


As I've mentioned elswhere - the 4 or 5 Thorens turntables i've had were
near enough silent. I've got an old Dual 505 which isn't bad at all. The
Xerxes was/is an expensive turntable. The motor is maybe 5% of
production costs?

Did you see the program about the production of RR aircraft
engines? Even at £ several million a shot, they still
vibrate, no matter how perfectly balanced. Circular motion
is fundamentally problematic. Do they vary the number of
blades from fan to fan through the motor, I wonder, or
concentrate the vibration at one frequency, and then filter
that out?


I have rather more sympathy for the design(ers) of aircraft engines :-)

I've just bought a Roksan Xerxes, curiosity buy, and the
motor vibrates to the point that it can be felt through
the plinth. Apparently (having been through forums etc)
this is quite normal. It's a testimony to the design that
very little of this finds its way to the platter or arm,
but why bother designing in such compromise, only to have
to design it out?

Because it's easy and cheap that way. Perhaps witless
engineers spent a fortune failing to make a perfect motor,
and then one of average intelligence had the idea of
connecting it with an elastic belt at the cost of a few
pence.

Why isn't every car a V12? Rubber bushes are a less witless
way of reducing vibration. Even more so in the case of the
turntable motor, because the primary vibration is at one
frequency, so damping is relatively simple. Is the rubber in
the mountings loaded in torsion, sheer, or compression, I
wonder? Or what about rigid mounting to a common ground?
That's the part the designers should have exercised most wit
on, if you're looking for an indication of wit.

OTOH, maybe your motor, or perhaps even a typical British
motor, uses inferior bearings or poor lubrication? If you
have noise in addition to the primary vibration and its
harmonics, rumbly or loose bearings could be the culprit.


Yes, could be. Just my experience that this tends to be a problem from
new with a number of turntables I've come across.

Just curious.

Not easy to see what you're curious about...motors,
Britishness, or the wit of engineers. Or indeed whether the
curiousness is purely rhetorical.


No, not rhetorical. It seems daft to me - compromise the operation and
design for what seems to me to be such a small cost. The power supply on
the Xerxes looks to be quite complicated, and all boxed up in wood. The
circuit board even 'floats' on rubber goo. They go to all that effort,
and then fit a noisy motor. Perhaps Thorens motors aren't available off
the shelf?

There may be less vibration if you reduce the motor drive
voltage, but then it will develop less torque. How did the
designers decide how much torque is necessary, and have the
parameters used for that decision changed since they made
it? Presumably the main consideration is variation in drag,
and hence speed stability. Does the drag caused by the
stylus contact vary substantially with the music? Do modern
stylus/cartridge combos have more variable drag, or less,
than when the turntable was designed?


it's absolutely stable in use. Paradoxically, almost, it sounds superb.
Not sure if anyone can follow my reasoning here - it's the notion that
it could sound better for a relatively small outlay at the production
and design stages.

I've not used a turntable since my sister ran off with the
Dansette, but compromises are quite interesting all the
same. I guess that's why so many over-indulgent engineers
design turntables, by the looks of what I see in magazines.


The obvious answer, to me at least, is if the motor used is noisy,
mechanically decouple from the chassis. Project and many others do this now.

Rob