DIY Turntable

[dice45]

GP,

(did I hear someone fainting there ? )

no, just vomitting.
(serious now) if a direct drive i designed in a proper way, it can be terrific. All the designer has to care for is attaching proper wall thicknesses to the bearing bushing and shaft and see that no space lcaimed by the bearing is usd by the motor. Quite a task, but not impossible.

But usually DD is used for budget designs.

Belts stretchiness is also someting I had never imagined would cause a problem but if the drive motor had lots of iertia as well, then I can see a disaster just waiting to happen.

even with comparatively low inertias,
a stretchy belt eats up µdynamix, detail resolution, pace rhythm and timing. Take my word on it!

[Circlotron]

Maybe a small fluid coupling between the motor and it's pulley would damp any bad effects from belt stretchiness the same way a manual car can go jerk-a-jerk-a-jerk sometimes but an auto tranny one just won't because the torque converter slips and damps these oscillations.

You can get big ones for industrial motors that have to start high-inertia loads, but I have never heard of a flea-power one. Would be interesting I think.

GP

[AuroraB]

Drive belt discussions are as old as the TT itself..

At some instant in time, I remember an idea from somewhere, about using pure silk tread impregnated with resin ( or rosin) for friction.

A simple jig can be made so that one can "weave" a string of suficcient thickness before applying the resin..

[dice45]

AuroraB,

IMO a belt should not be sticky, quite the opposite. Look at it, any fast motor speed variation, oscillation, whatever, drowns in the belt being slippery.

Moreover, stickyness is not as uniform as you may wish it. Causing something equivalent to torque variations by this.

Have the belt slippery and under well controlled tension.

[wuffwaff]

GP,

wouldn´t the flywheel of a car do some nasty things to the tracking force when using MC´s with strong magnets?

william

[Circlotron]

It probably would. I have never checked the external field of a cartridge but I would have though for a well designed one the flux would have been almost completely self-contained. If it is not then there may indeed be problems. I'll get a very thin steel feeler gauge and wave it underneath my cartridge and see if it is attracted. But first I better see if it is not stainless and therefore magnetic!

GP.

[dice45]

Wuffwaff,

thanx alot for reminding us,
indeed a magnetic platter would influence an MC cartridge.

GP,
no, the flux is not self-contained at all, on the contrary! Best MC cartridges have non-magnetic housings or are are naked, they have no shielding for sure, and very strong magnets, SaCo or Neodymium or similar.
The magnetic field is shaped like an apple, highly non-linear and with heaps of stray field; in the region of the coils the field still is nonlinear but, by careful adjustment, symmetric.

If the platter surface is magnetic, the MC cart simply sits down on its *** and the cantilever goes CRACK!! (i once tried to find out how much spacing to record surface a used MC still had and used a 1.0mm drill bit for it --- SNAP!! the drill bit slipped out of my fingers and snapped onto the cartridge body, just oh just missing the cantilever. Phew, had it hit the cantilever, there wouldn't have been any anymore. And the drill bit was hard to remove.

So what can you do? You can put a very thick layer (say, 4", say100mm !?) of vinyl on top of your flywheel, maintaining a proper distance between cartridge magnet and magnetic part of the platter. And get sonic benefits from the mechanical impedance coupling (between record and platter) the vinyl provides.

You'll get gorgeous results! and very low surface noise.

[wuffwaff]

yes,

and after putting on the 100mm vinyl spacer you could discard of the flywheel and improve the appearance of your turntable quite a lot

william

[dice45]

William,
no, disagreeed!
He could muse about adding additional weight and approach 50kg for the platter

[Circlotron]

I rather think the flywheel would be a real conversation starter for any non-hifi person who recognised it. :-P