Turntable Motors
 

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

Turntable Motors
 

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

Turntable Motors
 

In article , Arny
Krueger
wrote:


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

To quibble pointlessly, in principle you can have Faraday disc motors which
are 'dc'. But I have no idea if anyone has used this for a real-world motor
for anything like a turntable! Not a very practical method I guess.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Turntable Motors
 

In article , Rob
wrote:
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.

Well, you may have a 'rogue' example in need of sorting out. Can't say as I
have no idea of what is normal for your turntable. But any vibration will
"shake the chassis" to some extent. Just a question of how noticable it is,
or if it is a problem.

Can you make a recording using a test disc and check for wow, flutter, and
rumble, etc? That way you can see if it matters. Or is it clearly audible
though the speakers with the volume at a normal setting?

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Turntable Motors
 

In message , Jim Lesurf
writes
In article , Arny
Krueger
wrote:


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

To quibble pointlessly, in principle you can have Faraday disc motors which
are 'dc'. But I have no idea if anyone has used this for a real-world motor
for anything like a turntable! Not a very practical method I guess.

Slainte,

Jim

What a direct-drive turntable motor though! A nice slow homopolar disc
motor. Liquid mercury contacts perhaps and an NIB ring magnet.
--
Chris Morriss

Turntable Motors
 

"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...

Turntable Motors
 

"Chris Morriss" wrote in
message
Liquid mercury contacts perhaps
and an NIB ring magnet.

Open mercury contacts are a serious health hazard and also promote corrosion
on nearby metallic objects including contacts and fine wires.

Turntable Motors
 

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.

Turntable Motors
 

I somehow feel that aero engines and turntable motors have as much in common
as seed drills and oil drilling rigs.

I remember being rather impressed by those Phillips belt drive turntables
in the 70s. They worked very well.
However, there are a couple of very old Technics decks still running in
certain broadcasters studios with very good rumble and induced field
figures. So I agree it should be better the more it costs.
Having said that i have an SL5 with an Ortofon cart that sounds very nice,
still.

It really should not as its a cheap direct drive with a servo parallel arm!
Brian

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


"Rob" wrote in message
...
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
 

In article , Brian Gaff
scribeth thus
I somehow feel that aero engines and turntable motors have as much in common
as seed drills and oil drilling rigs.

Did you see that prog on Rolls Royce aero engines the other nite?,very
very impressive!. Its prolly still on iplayer...

--
Tony Sayer