DIY Platter

[dimkasta]

I understand what has been done there, but static balancing is not the same as dynamic balancing. Would you balance a car wheel with a spirit level, and why do manufacturers usually take such trouble to carry out dynamic balancing of platters? The potential out of balance forces may be relatively small, but in vinyl replay the displacement and forces involved at the stylus are tiny.

I don t know if TT companies claim to dynamically balance their platters, but my guess is that it is either marketing BS or just something to care for a public opinion creating problems.

Static balancing balances a rotating object on its X axis, taking into account weight differences around the nominal disc surface.
Dynamic balancing also balances it on its Y axis, caring to separate balance inconsistencies scattered on the Y axis and account for them individually on the X axis balance.

The smallish speed, the shallow height, the rigid and consistent material and the static Y axis makes dynamic balancing rather irrelevant on a TT platter.
Car tires is a different thing because we have a highly elastic material with inconsistent density and significantly bigger height, spinning on high speeds and alternating Y axis.

Anyway, to my knowledge, the SL1200 platter is not even statically balanced, so even statically balancing it should be enough and a big improvement as it is...

We can statically balance the platter by tilting the TT at around 40 degrees, and slowly spinning the platter. The heavier side should slide at the down side and the platter should swing a bit on that spot before stopping rotating. We need to add some weight on the opposite side. We repeat that until we have no swinging effect because of heavy areas drawn to the bottom by gravity.
Careful no to damage your spindle with the side forces.

[sq225917]

Your cartridge traces paths measured in microns, do you not think the best balancing possible should be a gold standard, especially given the effects on speed stability and bearing noise that imbalance in the platter could potentially cause?

[dimkasta]

Applying the entire gold standard for tire balancing to my platter? Not really. they have different properties and different degrees of freedom to move.

Considering the slowish speed and the single axis of movement, static balancing should minimize all those effects to the point where they are a matter of bearing tolerances.

Oh and not to mention the top rubber mat, which would make every attempt to balance the platter a joke, unless we glue it to make it a permanent component of the balancing act.

[RickeyM]

You can see here that there there are large places where the bonding agent has not connected with the rubber under-mat. Clearly the rubber mat does nothing for the structural integrity of the platter.

The original platter is not good. If you hold it by the magnet and tap it with a spoon you can hear it rings like a gong. Incidentally If you do the same test after you have stripped the rubber it resonates about twice as long. so I estimate that the rubber damping is about 50% effective ... pretty useless. The same tapping test after the Dynamat is in place produces no ringing. It is almost as dead as Monty Python's Parrot. In terms of sound difference it worked really well and I felt the base tightened up nicely.

I always wondered why the platter on my SL-1200 rung like a struck gong even with that nifty Technics rubber mat under there. For the $15 that I can get some for on eBay, it's definitely going on the underside of my platter. If you think damping sheets (Dynamat or Cascade) have many audio uses, do a Google search on "Magnepan Razor Mod". And yes, my Maggie MG-2.5R's have been treated as well

[Mr Kipling]

An alternative way to kill a ringing platter is to attach lead stripping that can be used on glass windows to the inner edge of the outter platter. And a two-piece platter can be "glued" together with a thin layer of vaseline.

[Qwin]

My view has allways been that balancing is a waste of time on the Technics and similar platters for the reasons allready given relating to speed, matt and also the fact that the platter sits on a tapper and will never sit in the same position twice making the process redundant. Any accurately machined platter will be good enough for the speed it rotates at. The variation from true is not going to be enough to cause audible speed fluctuation and there are many factors which have a far more dramatic effect on sound which should be addressed before getting to that level, weakest link first etc. If you are looking at that level of detail you should not be using the stock platter and bearing anyway, bit like doing engine mapping and full rolling road tune on a Nissan Micra used for commuting to work. The acuracy of the hole positioning in the centre of the record will have a greater effect on the sound due to speed fluctuation on the eccentric groove diameter.

So there are many factors to consider and although in principle we should allways strive for the optimum, I wouldn't get too concerned about balancing.

[Oldpinkman]

Anyone reading this thread could be forgiven for thinking Technics employed kids from the street to design their products. The SP10 has a balanced platter and a certificate to say it is balanced. Platter balance will affect speed stability and impact on the servo mechanism in the electronics and motor control.

Lack of resonance and damping are not a panacea. I have heard an MDF platter, (AK's original idea for the LSD) and it was dire. Dead - in every sense of the word. Certainly ringing like a bell is not a good thing, but simply damping it is not a perfect solution. Balance, rigidity and structural integrity are important too.

As for a damped platter rendering the termination of a mat redundant - well. only maybe. Just because any energy from the stylus isn't exciting a ringing in the platter, doesn't mean it isn't being reflected back from the platter into the vinyl itself. A damped platter won't transmit energy away, nor absorb it all.

If a bit of gunge on the underneath of a platter is the ultimate last word in platter design, a couple of rubber bands wrapped round the outside of a tonearm should achieve the ultimate tonearm design. And to think people waste time with engineering solutions

[Andrei]

I always wondered why the platter on my SL-1200 rung like a struck gong even with that nifty Technics rubber mat under there. For the $15 that I can get some for on eBay, it's definitely going on the underside of my platter. If you think damping sheets (Dynamat or Cascade) have many audio uses, do a Google search on "Magnepan Razor Mod". And yes, my Maggie MG-2.5R's have been treated as well

Interesting results on an image search - you would think Mag would incorporate it into their design, it probably would not be expensive to them.
Have you used Cascade before? I have tried an alternative to Dynamat but it was not as effective, but it wasn't Cascade as I would have remembered that name (it is a bridge partner's online handle).

[RickeyM]

Interesting results on an image search - you would think Mag would incorporate it into their design, it probably would not be expensive to them.

I guess Magnepan isn't treating their speakers for the same reason other speaker makers aren't treating the baskets of their drivers. Probably too labor intensive as I don't see any way it could be automated. I used some DYNAMAT EXTREEM on the cross bars of the woofer/mid drivers along with strips of it around the perimeter of the driver frame. It did sound better but not as dramatic as when I put the drivers from my MMG's into hardwood frames. I'll have some time Sunday to finally apply the DYNAMAT to the bottom of my Techie's platter and I'll post back on the results. I agree with you Andrei, damping the underside of the platter may make whatever mat you use on top of the platter less critical. Or maybe even more effective. We'll see.

[Mr Kipling]

If a bit of gunge on the underneath of a platter is the ultimate last word in platter design…

I haven't read anyone saying it is. What it is is a cheap, simple and effective way of killing a ringing platter. It works - well it did with a Thorens 160 B MK II and original AR turntable, when I tried damping both platter and sub-chassis on them. Indeed, at one point Thorens' importers Cambrasound, made available a tune-up kit for the 160 which included damping panels after it was seen there was a market for it. And what about Max T. using carpet to damp his Glastonbury speakers?

What would your solution be?