DIY Platter

[sq225917]

If you value your bearing this is a bad idea. Anything that upsets the balance of the platter is a very bad idea. That';s why Technics used a moulded part, so the weight distribution of it could be controlled.

[DaveK]

I'm going to expose my naivety here (again ) but I wonder how important the aspects of weight and balance are in fact. I DIY'd my Techie platter to stop ringing and any eddy currents emanating from the motor (which were once expressed here as having a possible adverse effect on the cartridge) by covering the rubber underside of the platter first with a thin layer of self adhesive copper - this was put on in at least two pieces as I could only find the copper sheet in narrow widths. I followed this up with another layer of the bitumen coated aluminium and soft 'plastic' stuff called flashing tape (from Wickes ) . This has added considerably to the weight, as you might imagine but it has certainly stopped the ringing.
It is generally accepted that the Techie is greatly over engineered to enable it to survive in it's original market, namely mobile, temporary, DJ sessions. FWIW my stock PSU has also been upgraded to an off-board Paul Hynes ancient PSR3 which was designed to be supplied by an 18v transformer but when my transformer died (of old age), with Paul's blessing it is now supplied by a 15v R-core transformer. The platter still gets up to speed 'immediately', is rock steady maintaining speed and stops 'dead' when powered down. I have run it continuously for hours just to see if anything changed and it remained cool and stable.
And, to my ears, each of these mods proved beneficial to SQ.
I have a basically original bearing housing but I have provided it with permanent support from underneath. I also have replaced the standard feet with 100mm sorbothane hemispheres - basically a very modified Techie but all DIY. The tonearm wire, tonearm itself and platter mat have also been changed, and the various layers of the deck have been bonded together to aid rigidity. Still recognisable as a Techie though .
I will now get behind the sofa to avoid the 'incoming'.
Dave.

[walpurgis]

Yes, unfortunately I also think this may not be a great idea. The Techie platter may not be a high mass item in relative terms, but platters are wide and generate significant centrifugal force and upsetting the balance even slightly may have adverse effects. Once the damping has been applied, it may be an idea to get an engineering shop to check the dynamic balance, they are equipped with balancing machines.

[Andrei]

If you value your bearing this is a bad idea.

That presupposes that it is unbalanced. The methods I have applied ensure that if there is imbalance then it will be small. Unless you have seen a white paper or suchlike to the contrary I would have thought the use of a moulded underlay would have been a necessary consequence of mass production. However, in appearance the rubber underlay appears symmetrical, is well centered and would therefore not unbalance the platter, at least while stationary. While spinning the uneven bonding of the underlay would create a tiny imbalance in centrifugal force. I'm not aware of any bearing wear put down to sideways pressure after decades of use either through this or because turntables have not been 100% level, and if that was going to happen to any turntable it would be exactly this one.

I have tried another balancing test. That was to use my spare bearing (a very good one btw, but that is another story) and spin the platters while keeping the bearing almost horizontal. I could not get any of the platters to consistently stop rotating the with a 'heavy side down'. Again not a particularly accurate test, but at least showing that any imbalance is small. The downwards force of the bearing on the base-plate would be a minimum of about 1.6kg - the mass of the platter. With mat, vinyl, and record stabiliser we could have, say 2000 grams. If the imbalance of imperfectly applied dynamat is 1 gram then that is one 2 thousandth of the downwards pressure and even that is applied over a larger area. After some period of time, maybe we are talking decades, it may be necessary to shell out $30 for a new bearing.

In the meantime I would say that if your value your sound quality you should address the standard platter. I have done most of the mods now and the platter mod is significant . Putting on isonoe feet was far and away the most significant improvement. Next would be an aftermarket power supply, aftermarket tonearm, and my platter upgrade. Those three all had an immediate and clearly audible difference. Behind that was a tonearm rewire, headshell upgrade, aftermarket platter mat.

While I acknowledge this is an issue, I presently consider it to be minor, and certainly not one of value. By way of analogy nobody fixes a fire extinguisher to the middle of their boot to ensure that the wear on the rear tires remains as even as possible.

[Andrei]

Once the damping has been applied, it may be an idea to get an engineering shop to check the dynamic balance, they are equipped with balancing machines.

Audiophiles have certainly done stranger things. I did have the idea of taking it to a Tire Shop who do wheel balancing. They have these fancy machines that check the balance of the wheel after a tire has been fitted. The interesting thing is the ease with which an imbalance can be corrected - little lead weights are attached to the rim of the wheel. I have no idea what such a piece of equipment is called but if they do have some such contraption then a couple of pre-weighed pieces (one gram, five grams etc) could be strategically placed. Come to think of it I still have four 'untarnished' platters ... will anyone offer me odds that they are perfectly balanced!

[NRG]

You could experiment by delibratley unbalancing the platter with say a gram of blue tac and use your old bearing held near horizontal as before to see how sensitive it is. Holding the bearing and spinning the platter at the same time would be interesting, I suspect you could easily feel any imbalance.....

[walpurgis]

A tire shop machine would not be accurate enough. An engineering works that balances machined parts should have very sensitive balance checking equipment.

[DarrenHW]

You could experiment by delibratley unbalancing the platter with say a gram of blue tac and use your old bearing held near horizontal as before to see how sensitive it is. Holding the bearing and spinning the platter at the same time would be interesting, I suspect you could easily feel any imbalance.....

Excellent idea! Go on Adrei, spin those wheel of steel... urm aluminum.

[CageyH]

At 33 & 1/3 rpm, any out of balance force will be minimal.
It will probably be similar to the force exerted by a 180g vinyl disc with the hole slightly off centre.
If it was me, I certainly would not worry about it.

As the original platter is also cast, I doubt that the mass and balance is very well controlled.
IMHO It's really not needed at these low speeds.

[Oldpinkman]

As noted before, the stock platter is not balanced, unlike the SP10 which is, and the need to resort to damping - which the stock platter has, is one reason for that. Damping, both standard, and yours, will have sample variation which will unbalance the platter.

Again, as previously noted (cribbing from a mate) it is unlikely to grind the bearing to dust any time soon, although will contribute slightly to accelerated bearing wear. It does affect the servo mechanism of the motor which will seek to make more corrections than with a balanced platter, and that may have an affect on sound. Car wheel balance which has been discussed, does contribute long term to bearing wear, but it has other more immediate consequences like vibration in the car and tyre wear which are more significant

But the stock platter is not balanced, and I don't see countless threads discussing its "warble" at 33 or 45 rpm. The boy is sulking at the moment, but as a lay observation its hard to see how it could be with those 2 holes unless there was some pretty cute casting compensation elsewhere, particularly given the variability that adding damping (on the stock platter) causes. Anyway, you can still pick up standard new replacement bearings for buttons so suck it and see!