On 06/07/2010 22:08, mick wrote:
On Tue, 06 Jul 2010 16:52:16 +0100, 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?

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?



I thought the Xerxes had a DC motor and a fancy power supply?


I think it's AC. The power supply looks to be a a lot of components -
not sure what they do!

All AC motors will vibrate to some extent. It's because they have to have
a finite number of poles, causing the armature to "step" between them.
The inertia of the armature reduces this somewhat, but it's always there
- it doesn't matter when or where the turntable was made. The more poles
the better, but there is a limit to how many can be usefully
manufactured. Thorens used to use 16 poles IIRC, and Linn used 24 poles.


I had a Thorens TD125 - virtually silent, about 25 years old that one.
never had a Linn.

The motor is (should be!) mechanically isolated from the system via
rubber bushes and the drive belt (or capstan wheel on older units). How
well this is done affects how much it matters. Sometimes the motor is
mounted directly onto the plinth, so the vibration is easily felt but
doesn't affect playing.


Yes, I accept the measures taken to isolate a motor. But why build in a
motor that vibrates to such an extent? I would have thought the
vibrations would affect playing, albeit to a small extent if the attempt
to isolate works. On the Roksan there's a series of plinths and rubber
blobs, and a cutout on the top plinth to channel vibration.. It seems to
work. But the stylus is still mechanically *coupled* to the motor
through the turntable chassis.

Having said all that, the motor should be almost silent. If it isn't then
there is probably a problem somewhere. Check for hardening of the
mounting bushes or something touching the motor casing.


Yes, I'll have a proper look at some point. The motor mounting looks
fine and 'compliant'. There's no play in the motor shaft or pulley.

You can reduce the vibration at the expense of motor torque by reducing
the voltage fed to the motor. Typically, a motor will run down to about
75 to 85 volts (no matter what it says on the label), but the increase in
start-up time becomes noticeable.


Indeed - some people have fiddled with the power supply. I'd just point
out that the 'loud' motor is a designed in aspect of the turntable.
Thorens manage to fit near-silent motors, and direct drive Japanese TTs
I've had are just about silent (as Brian says). Systemdek, Rega, Pink
Triangle, and Revolver don't/didn't.

The obvious guess answer to my question is cost, and a probable
dislocation between design and production. I can't see a designer
specifying a noisy motor. Whether that's correct or not, don't know.

Rob