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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 -- 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
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 |
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 |
Turntable Motors
Brian wrote:
I somehow feel that aero engines and turntable motors have as much in common as seed drills and oil drilling rigs. Seed drills don't rotate AFAIK. Aircraft turbines and turntable motors are multipole drivers used in situations where vibration management is crucial, and noise is an annoyance. Vibration analysis is similar, in that there are stators and rotors, each with a number of poles, and forces upon them that vary depending on their relative positions, which change as they rotate. Car engines have multiple cylinders and in some respects demand similar consideration, including the option for sprung and damped mountings. I mentioned the possibility of using a different numbers of blades through a turbine because the option to use a different number of rotor and stator elements, with a non-integer ratio, in an electric motor would result in quite different vibration characteristics, because peak forces wouldn't coincide. Design engineers are generally not witless, but rather make informed decisions, in these cases about how much vibration is worth eradicating, and how much can be managed. They may be misinformed, of course, about market requirements, and constrained by the cost and availability of parts and materials, but engineering is engineering, and vibration analysis is pretty well understood. Seems to me that this particular turntable occupies a niche in which functional simplicity is considered a key feature. If it sounded bad I could understand the criticism. You can't spoil the ship for a ha'porth of tar if the sheep is of a variety that doesn't need tarring. OTOH, you won't satisfy a buyer who judges a sheep on the quality of its tarwork. 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. Vertically integrated mainstream manufacturers can make their own optimised motors and/or electronic controllers cheaply and not sell them to anyone else. They're the ones to go to if you want a mainstream product. Niche products from small manufacturers are more likely to be quirky and unreliable, or horribly expensive. It really should not as its a cheap direct drive with a servo parallel arm! Does that mean the cartridge isn't floating? If so, and rigid mounting to a common ground makes the whole caboodle shake in unison, then the shaking won't matter much, maybe. Ian |
Turntable Motors
tony sayer wrote:
Did you see that prog on Rolls Royce aero engines the other nite?,very very impressive!. Its prolly still on iplayer... Watch out, Arny's a spy. Worth watching just for the blade containment test, I thought. Must have been heartbreaking for the poor welder. Remember the RB211? The one with carbon fan blades that failed the chicken test. AFAIR, RR's recovery was assisted by the state. Now they have those very impressive inflated composite sandwiches that Arny's not supposed to know about. That Boeing Dreamliner has alarmingly floppy wings, I thought. Good for decoupling vibration perhaps, but those huge engines droop so close to the runway it looks like they could easily suck up something harder and heavier than a chicken. Hopefully they learned from the Concorde disaster. These days, although British engineers are highly regarded, there aren't many British manufacturers to employ them. When Forgemasters recently had their state loan stopped, they were instead encouraged to sell themselves abroad to raise the cash. I don't necessarily mind that in itself, but it doesn't fit well with the kind of patriotism that is demanded of us for football, wars, and repaying the "national" debt, whatever that is, and whoever we owe it to. "British engineering" seems such a quaint concept now. If the turntable in question is actually of British design and manufacture, then hats off to 'em for heroically paddling against the current, even if they do shake a bit. Ian |
Turntable Motors
"Ian Iveson" wrote in
message news:vdvZn.183542$Hs4.127292@hurricane tony sayer wrote: Did you see that prog on Rolls Royce aero engines the other nite?,very very impressive!. Its prolly still on iplayer... Watch out, Arny's a spy. Correct connection at one degree of separation: My father made his name as an expert toolmaker during WW2 as part of the team that started up production of Rolls Royce Merlin aircraft engines at Packard Motor Car Company, here in Detroit. RR sent detailed plans for the engine but nada about how to tool up or assemble it. My dad helped "spy out" those little details. For his efforts my father was given a journeyman's credentials without ever serving an apprenticeship, which of course was a very valuable reward at the time. |
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