Turntable Motors
 

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

Turntable Motors
 

In article , 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?

Reverse the above to understand the reasoning. :-) A belt drive becomes
appopriate *because* a noisy (i.e. vibration prone) motor was chosen by the
maker. The combination of the belt and the turntable then act as a
mechanical filter.

If the motor rotated very smoothly with no vibrations then direct drive, or
an idler wheel, or some other form of more 'tight' contact between motor
and turntable would be OK.

This isn't beyond their wit. Just something they chose not to bother with.

The turntable I've used for decades doesn't have the problem. It has no
belt. Just a scorned-for-many-years direct drive japanese design. Works
fine. It has been amusing in the last few years to see older direct drives
like this start becoming 'fashionable' again with some magazine reviewers.

Slainte,

Jim

--
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Turntable Motors
 

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.

Turntable Motors
 

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.

Turntable Motors
 

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.

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'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.

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.

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?

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.

Ian

Turntable Motors
 

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

Turntable Motors
 

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

Turntable Motors
 

"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

Turntable Motors
 

"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.

Turntable Motors
 

On 06/07/2010 17:40, Jim Lesurf wrote:
In , 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?

Reverse the above to understand the reasoning. :-) A belt drive becomes
appopriate *because* a noisy (i.e. vibration prone) motor was chosen by the
maker. The combination of the belt and the turntable then act as a
mechanical filter.


Really!? What an utter shambles. Every motor vibrates - but they don't
have to physically shake the chassis they're mounted on.

Although and actually, I have done a quick search, and some of the
perhaps better motors are £50 upwards - so it is cost cutting with the
possibility of an 'upgrade' offered - £350 in one case.

Rob