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?

Just curious.

Rob

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
Filtering everything posted from googlegroups to kill spam.

I know this is probably sacrilege, but direct drive motors seem to be one
of the quietest and it surely cannot be that hard to design them to not go
in jerks as the early ones did, and not to have big induction fields, except
at switch on.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"mick" wrote in message
...
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
Filtering everything posted from googlegroups to kill spam.

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

"Rob" wrote in message
...
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.


Was it a DC Pink Triangle?
Both my PT1s have been almost silent and vibration free.

D

On 07/07/2010 12:28, David wrote:
wrote in message
...
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.


Was it a DC Pink Triangle?
Both my PT1s have been almost silent and vibration free.


Not sure, they were both very early models - but to be fair, the LPT was
pretty good, the PT Too less so, but still fine if audible. The LPT was
superb.

I am (fairly) uniquely neurotic about such things. One of the first
things I do is couple the stylus to the plinth, and then the platter
(belt removed) to see what's getting through. It's one of those 'how
hard can it be?' feelings. We should have one state provided turntable
and be done with it. That's what I'd do. It'd be useless, but the motor
would be quiet ;-)

Rob

"mick" wrote in message

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.


All motors are in some sense AC motors. If you apply pure DC to the armature
coils of a motor, it will be locked down solid.

So called DC motors have commutators, which are in essence electromechanical
DC-to-AC converters.

So-called brushless motors simply cut to the chase and replace the
electromechanical commuator with a multiphase solid state inverter.

Therefore, all DC motors are effectively AC motors and they will similarly
all vibrate to some extent.

The spectrum of noise from motors has a few dominant sources. One is at the
motor's rotational speed, and another is at the motor's rotational speed
multiplied by the number of poles.

The primary means of isolating the turntable platter from these vibrations
is a number of mechanical low pass filters. One is formed by putting the
motor on compliant mounts and another is formed by the drive belt and the
flywheel effect of the turntable platter.

On 07/07/2010 12:47, Arny Krueger wrote:
wrote in message

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.


All motors are in some sense AC motors. If you apply pure DC to the armature
coils of a motor, it will be locked down solid.

So called DC motors have commutators, which are in essence electromechanical
DC-to-AC converters.

So-called brushless motors simply cut to the chase and replace the
electromechanical commuator with a multiphase solid state inverter.

Therefore, all DC motors are effectively AC motors and they will similarly
all vibrate to some extent.


There's endless chatter on 'net about relative merits.

The spectrum of noise from motors has a few dominant sources. One is at the
motor's rotational speed, and another is at the motor's rotational speed
multiplied by the number of poles.

The primary means of isolating the turntable platter from these vibrations
is a number of mechanical low pass filters. One is formed by putting the
motor on compliant mounts and another is formed by the drive belt and the
flywheel effect of the turntable platter.


And have a motor that's as quiet as possible. Or mechanically isolate
the motor completely. I would have thought.

Rob

"Rob" wrote in message

On 07/07/2010 12:47, Arny Krueger wrote:
wrote in message

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.


All motors are in some sense AC motors. If you apply
pure DC to the armature coils of a motor, it will be
locked down solid. So called DC motors have commutators, which are in
essence electromechanical DC-to-AC converters.

So-called brushless motors simply cut to the chase and
replace the electromechanical commuator with a
multiphase solid state inverter. Therefore, all DC motors are effectively
AC motors and
they will similarly all vibrate to some extent.

There's endless chatter on 'net about relative merits.

And this differs from other audio subjects how? ;-)

The spectrum of noise from motors has a few dominant
sources. One is at the motor's rotational speed, and
another is at the motor's rotational speed multiplied by
the number of poles. The primary means of isolating the turntable platter
from these vibrations is a number of mechanical low pass
filters. One is formed by putting the motor on compliant
mounts and another is formed by the drive belt and the
flywheel effect of the turntable platter.

And have a motor that's as quiet as possible.

Slow is good from a noise perspective.

Or mechanically isolate the motor completely. I would have
thought.

That's that I meant by mechanical low pass filter...

On 07/07/2010 20:51, Arny Krueger wrote:
wrote in message

On 07/07/2010 12:47, Arny Krueger wrote:
wrote in message

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.


All motors are in some sense AC motors. If you apply
pure DC to the armature coils of a motor, it will be
locked down solid. So called DC motors have commutators, which are in
essence electromechanical DC-to-AC converters.

So-called brushless motors simply cut to the chase and
replace the electromechanical commuator with a
multiphase solid state inverter. Therefore, all DC motors are effectively
AC motors and
they will similarly all vibrate to some extent.

There's endless chatter on 'net about relative merits.

And this differs from other audio subjects how? ;-)

The spectrum of noise from motors has a few dominant
sources. One is at the motor's rotational speed, and
another is at the motor's rotational speed multiplied by
the number of poles. The primary means of isolating the turntable platter
from these vibrations is a number of mechanical low pass
filters. One is formed by putting the motor on compliant
mounts and another is formed by the drive belt and the
flywheel effect of the turntable platter.

And have a motor that's as quiet as possible.

Slow is good from a noise perspective.

Or mechanically isolate the motor completely. I would have
thought.

That's that I meant by mechanical low pass filter...


Ah, got you, thanks.