Many DIY TT seem to go the high mass route, have any of you gone the opposite way and gone for lightweight materials?
I am at the moment making a simple high(ish) mass plinth useing a LP12 bearing, sub platter and motor but will have a go at a lightweight design next. Aerolam is to expensive to have a play with so I will probably make up a constained layer plinth useing some sort of foam, (not done much research at the momment).
Any thoughts on the platter? Weight is preferable for speed stability but would a heavy platter negate any advantage of a light plinth?
Paul.
I am at the moment making a simple high(ish) mass plinth useing a LP12 bearing, sub platter and motor but will have a go at a lightweight design next. Aerolam is to expensive to have a play with so I will probably make up a constained layer plinth useing some sort of foam, (not done much research at the momment).
Any thoughts on the platter? Weight is preferable for speed stability but would a heavy platter negate any advantage of a light plinth?
Paul.
Actually it isn't the weight but rather the moment of inertia which is important.
In a translational system you have Newtons famous equation F=MxA, where F is the force needed to accelerate a given mass M at a given acceleration A. Similarly, in a rotational system you have T=JxAA, where T is torque, J is the moment of inertia and AA is the angular acceleration. J depends on both the mass and the distribution of the mass.
You could have a very light platter with a large outer rim and still obtain a high moment of inertia for rotational stability.
Regards,
Ray
In a translational system you have Newtons famous equation F=MxA, where F is the force needed to accelerate a given mass M at a given acceleration A. Similarly, in a rotational system you have T=JxAA, where T is torque, J is the moment of inertia and AA is the angular acceleration. J depends on both the mass and the distribution of the mass.
You could have a very light platter with a large outer rim and still obtain a high moment of inertia for rotational stability.
Regards,
Ray
In my case increasing the diameter of the platter is not an option, purely for asthetic reasons. I like my turntables small and unasuming, just a personal thing.
A turned heavy ring around the circumferance of the platter would put the weight where it would do most good while still keeping the overall weight down. Perhaps I would also need to look at the motor if I were to go on a weigh saving diet. A motor with more of a flywheel effect than the generic Airpax/Premotec motor from the Linn?
Paul.
A turned heavy ring around the circumferance of the platter would put the weight where it would do most good while still keeping the overall weight down. Perhaps I would also need to look at the motor if I were to go on a weigh saving diet. A motor with more of a flywheel effect than the generic Airpax/Premotec motor from the Linn?
Paul.
EC8010 said:
True. My Kenwood KD 650 has just such a platter. If I pull the platter off, support it at the centre with as few fingers as will balance it, and give it a good rap, it will ring for quite some time. Place the rubber mat on top, however and it makes barely any noise with very quick decay. I'm not knocking on the mat here; the platter is 13" leaving a good half inch of bare aluminum to hit. When I put the platter back on the plinth and try a knock test, it just makes a dull thud like MDF. Can't say as it's a problem I've ever noticed when playing records on it
I guess if ringing was a concern, you could make the platter out of something that won't resonate. Wood with a lead hoop on the perimeter? Rubber platter with some sort of rebar truss inside to keeep it rigid? Asphalt?
Max
I believe the only way to have a light platter only 12" and still maintain a high moment of inertia is having some sort of flywheel in your system - either within the motor, or external. Actually, a flywheel turning at a high speed adds to the MOI much more effectively then just making the platter heavier - as MOI is related to the square of Omega (tangential speed), but only has a linear relationship with the mass.
Ofcourse, the upside of any high MOI system is it's speed stability at steady state, where as the down side is the motor's ability to correct the platter's speed if need arises (say stylus drag, for example)
-T
Ofcourse, the upside of any high MOI system is it's speed stability at steady state, where as the down side is the motor's ability to correct the platter's speed if need arises (say stylus drag, for example)
-T
Hmm... I think a seperate, belt driven flywheel would be a bad idea. Imagine a light platter with transients in stylus drag: it will slow down easily, but the flywheel will not. This will cause the belt to bunch and the platter to pulse. It seems you'd be adding complexity with no gain in performance over a standard belt drive setup.
Max
Max
Hey look, it's been done!
Check out this site for a low inertia platter with a flywheel attached:
http://digilander.libero.it/bellocaddo/turntablesgalleryRZ.htm
scroll down to Yamamura Churchill
Max
Check out this site for a low inertia platter with a flywheel attached:
http://digilander.libero.it/bellocaddo/turntablesgalleryRZ.htm
scroll down to Yamamura Churchill
Max
The new Pabst motor Audionote uses now is synchronous or asynchronous, they look alike. Noone can tell from the pixes.
Anyway, i am not feeling too comfortable with a TT using three asyncronous motors with a slightly different speed slip .... neither with a TT using three syncronous motors with a slightly different pulley diameter or z position .... huge amounts of energy stored in each motor and all of them trying to wrestle with the other two ones.
In the past, i did extended listening with a Voyd TT, to my ears it sounded best when only one motor was engaged, the belt pulling to one side, messing up the suspension, but i didn't care, i liked it best that way. So my listening experience is aligned with my engineer's prejudices
Anyway, i am not feeling too comfortable with a TT using three asyncronous motors with a slightly different speed slip .... neither with a TT using three syncronous motors with a slightly different pulley diameter or z position .... huge amounts of energy stored in each motor and all of them trying to wrestle with the other two ones.
In the past, i did extended listening with a Voyd TT, to my ears it sounded best when only one motor was engaged, the belt pulling to one side, messing up the suspension, but i didn't care, i liked it best that way. So my listening experience is aligned with my engineer's prejudices
dice45 said:The new Pabst motor Audionote uses now is synchronous or asynchronous, they look alike. Noone can tell from the pixes.
Anyway, i am not feeling too comfortable with a TT using three asyncronous motors with a slightly different speed slip .... neither with a TT using three syncronous motors with a slightly different pulley diameter or z position .... huge amounts of energy stored in each motor and all of them trying to wrestle with the other two ones.
In the past, i did extended listening with a Voyd TT, to my ears it sounded best when only one motor was engaged, the belt pulling to one side, messing up the suspension, but i didn't care, i liked it best that way. So my listening experience is aligned with my engineer's prejudices
Why not just run one motor with two little pulleys along for the ride? Or how about, god forbid, direct drive?
Max
direct drive?
we'll just pretend you never said that
seriously, though, I've owned at least 10 different TT during the past 35 years, and only 2 were DD ( Dual 701 and Kenwood KD500) A Rega Planar 2 (P2 in today's parlance) would probably outperform them
I've heard 3 different models of AN tables; the smaller 2 based on the Systemdeck design, and 2 examples of the 3 motor Voyd based design. Yep they sound great, but as Dave and I have said before, any DIY worth this salt could assemble a complete system for less than one of the sales taxes on the TT3 alone, much less the tonearm / cartridge
For those interested in serious investment in analog front end (but not Ivor's or Peter's retirement fund), the Teres is a very sweet sounding unit. Of course it doesn't subscribe to the low mass school of platter design
maxro said:
we'll just pretend you never said that
seriously, though, I've owned at least 10 different TT during the past 35 years, and only 2 were DD ( Dual 701 and Kenwood KD500) A Rega Planar 2 (P2 in today's parlance) would probably outperform them
I've heard 3 different models of AN tables; the smaller 2 based on the Systemdeck design, and 2 examples of the 3 motor Voyd based design. Yep they sound great, but as Dave and I have said before, any DIY worth this salt could assemble a complete system for less than one of the sales taxes on the TT3 alone, much less the tonearm / cartridge
For those interested in serious investment in analog front end (but not Ivor's or Peter's retirement fund), the Teres is a very sweet sounding unit. Of course it doesn't subscribe to the low mass school of platter design
maxon rules (atleast for me)
Once you have a decent platter bearing, you don't need 2 additional pulleys as the bearing ignores the tiny lateral belt force.
Once you have sufficient mass accumulated in your subchassis, the same: the subchassis' suspension will ignore the belt force
I have no objection against a direct drive, provided it is an asyncronous drive. Provided the bearing gets all necessary space and wall thicknesses etc. . Better design the motor around the bearing.
Unfortunately, doing so is not suitable for small production numbers as the motor then is no catalogue item anymore and cost is prohibitive if not preventive.
Thank you!
to put it a lil' bit more in technical terms: you have n rotational inertias connected by n flexible ropes (the belt trums) which never are indefinietely stiff against elongation: they will oscillate transversally and longituninally as well. Doing so, they transmit rotaional energy from one rotational inertia to the other one.
The more rotational inertias you have, the more complex (and chaotic) the oscillating ssystem will be. Means: goodby to reliable dynamic and static platter speed constancy.
For a given transient, it may well happen a phase situation such that all motor inertias are in fact pulling the platter. This transient will sound shockingly dynamic.
The opposite may happen for another given transient: platter pulling all motors.. which will make the transient sound unbelievably lame.
Or something in between. You never will know, never will be able to predict.
To me this appears not as a proper technical solution. The opposite to the KISS principle.
I once talked to a design engineer skilled and experienced in designing speed-controlled drives for e.g. hard disk drives.
His experience: for a fixed speed belt drive, speed control works best if rotational inertia of motor/pulley and driven cylinder is within a factor of 2 in either direction.
But if you want to have a wide band of speeds (as is the case with TT drive: 33 ( 16 ?) to 78, eventually to >100), he warned me from having the motor's rot.inertia singiificantly influencing the equation; he recommended having as few rotational inertia for the motor as even possible. And having the motor have a speed as low as possible to store less energy in the motor's rotation.
That's why i am so fond of maxon and Faulhaber motors. Using one motor only of course. And to get farther away from the oscillation problem, i do not only use stiff belts but also ones as slippery as possible.
And as a high motor torque always improves sonics, i prefer the rare earth version of the maxon: enough torque at a managably low speed. Say 1200 for 33rpm.
maxro said:
Once you have a decent platter bearing, you don't need 2 additional pulleys as the bearing ignores the tiny lateral belt force.
Once you have sufficient mass accumulated in your subchassis, the same: the subchassis' suspension will ignore the belt force
I have no objection against a direct drive, provided it is an asyncronous drive. Provided the bearing gets all necessary space and wall thicknesses etc. . Better design the motor around the bearing.
Unfortunately, doing so is not suitable for small production numbers as the motor then is no catalogue item anymore and cost is prohibitive if not preventive.
EC8010 said:
Thank you!
to put it a lil' bit more in technical terms: you have n rotational inertias connected by n flexible ropes (the belt trums) which never are indefinietely stiff against elongation: they will oscillate transversally and longituninally as well. Doing so, they transmit rotaional energy from one rotational inertia to the other one.
The more rotational inertias you have, the more complex (and chaotic) the oscillating ssystem will be. Means: goodby to reliable dynamic and static platter speed constancy.
For a given transient, it may well happen a phase situation such that all motor inertias are in fact pulling the platter. This transient will sound shockingly dynamic.
The opposite may happen for another given transient: platter pulling all motors.. which will make the transient sound unbelievably lame.
Or something in between. You never will know, never will be able to predict.
To me this appears not as a proper technical solution. The opposite to the KISS principle.
I once talked to a design engineer skilled and experienced in designing speed-controlled drives for e.g. hard disk drives.
His experience: for a fixed speed belt drive, speed control works best if rotational inertia of motor/pulley and driven cylinder is within a factor of 2 in either direction.
But if you want to have a wide band of speeds (as is the case with TT drive: 33 ( 16 ?) to 78, eventually to >100), he warned me from having the motor's rot.inertia singiificantly influencing the equation; he recommended having as few rotational inertia for the motor as even possible. And having the motor have a speed as low as possible to store less energy in the motor's rotation.
That's why i am so fond of maxon and Faulhaber motors. Using one motor only of course. And to get farther away from the oscillation problem, i do not only use stiff belts but also ones as slippery as possible.
And as a high motor torque always improves sonics, i prefer the rare earth version of the maxon: enough torque at a managably low speed. Say 1200 for 33rpm.
I once talked to a design engineer skilled and experienced in designing speed-controlled drives for e.g. hard disk drives.
His experience: for a fixed speed belt drive, speed control works best if rotational inertia of motor/pulley and driven cylinder is within a factor of 2 in either direction.
In control systems design you select a gear ratio between the motor and driven load using the formula GR=SQRT(JL/JM) where GR is the gear ratio, JL is the load moment of inertia and JM is the motor moment of inertia. That way the transformed moment of inertia seen by the motor is the same as the motor moment of inertia. In other words, the gear ratio equalizes the inertias. This allows maximum acceleration of the load.
As an aside, the last control system I worked on was to drive 50 hp motors on a telemetry tracking antenna. Our power amplifier put out +-400 volts at 200 amperes. We had a 10kW dummy load for testing. You had to be real careful working on that amplifier.
Regards,
Ray
His experience: for a fixed speed belt drive, speed control works best if rotational inertia of motor/pulley and driven cylinder is within a factor of 2 in either direction.
In control systems design you select a gear ratio between the motor and driven load using the formula GR=SQRT(JL/JM) where GR is the gear ratio, JL is the load moment of inertia and JM is the motor moment of inertia. That way the transformed moment of inertia seen by the motor is the same as the motor moment of inertia. In other words, the gear ratio equalizes the inertias. This allows maximum acceleration of the load.
As an aside, the last control system I worked on was to drive 50 hp motors on a telemetry tracking antenna. Our power amplifier put out +-400 volts at 200 amperes. We had a 10kW dummy load for testing. You had to be real careful working on that amplifier.
Regards,
Ray
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.