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?

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.

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.

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.

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.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
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