Thoughts On Turntable Clamps And Weights

A weight does NOT necessarily raise the outer edge of the record. A properly designed reflex clamp is a well-known engineering solution to this problem.

I use a very thin Delrin shim of about 75 mm diameter and a 2+Kg steel weight with a Delrin ring around the bottom. The result is a shim that forces the label up and a weight around the edge of the label which forces everything else down.

Benefits are improved flatness, obviously, and also an extremely good marriage between record and the 1" graphite mat, resulting in increased clarity and dynamics.

This approach is not suitable unless the thrust bearing of your turntable is sufficient for the task. My air bearing is..

Not all weights and clamps are created equal. The contact surface with the record also matters.

As the stylus moves in the groove, it causes the record to vibrate slightly. This is enough to cause detectable distortion. Therefore this vibration should be sunk into the platter and the weight. Unfortunately, all materials reflect that vibration to some extent.

The factor that determines reflection or absorption of vibration is the speed of sound in mating materials. If the SoS is close, transmission is high, if dissimilar then transmission is low. Two materials which are very close to, or within, the range of SoS of vinyl records, are graphite and Delrin. So an interface of these is best.

I use one of each.

I should also note that an intimate contact of iron (steel) and graphite or Delrin renders the pair dead to vibration. Other metals, I don't know..

True, but under the label is vinyl. That too is important, or so I suspect.

@lewm 'Darkness' makes me think of an absence of treble - yet some of the most musical of TT, IMO, can also be described this way. Like the Nottingham Analogue Dais.

Every time I've made a big improvement to my system, it's involved a loss of high frequency hash. The sound just becomes smoother and more natural, less 'hifi'.

So I'm wondering about your use of the term 'darkens'. Could it be that the Kenwood ring reduces HF distortion? Or are you using the term differently?

@pindac  I would not try to re-invent the wheel. The carbon face air bearings from New Way are near perfect IMO, and they are cheaper to buy than to make. Again, IMO.

@pindac  Suggest that you rest the record directly on the Delrin, as Delrin and vinyl couple very well (speed of sound is essentially the same). Also, you might do better with thinner Delrin, as thick pieces can be heterogenous.

Also, consider an air bearing. More trouble, but lots less noise. Best is air in all dimensions, like a thrust bushing from New Way.

Balancing is important, and easily done by machining an oversize cylinder. Thing is, it's easy to find an approximate centre of a cylindrical billet, so turn around that approximate centre, and shave off the excess to give you a perfect centre. Keep the cylinder on the lathe chuck and let it settle. Mark that point, and rotate it to the top. If it stays there, your cylinder is balanced. If not, remove a little material from the bottom, until the cylinder stays in any position. Then you have a static balance. 33 RPM is not enough to require a dynamic balance IMO.

This requires the lathe to have low stiction bearings. Also, be very careful to fit the spindle in the exact centre identified above. Repeat the balancing procedure with the spindle in place, if possible. This works with a massive platter. If the platter is light enough, go directly to turning and balancing on the spindle.

BUT - your machinist may have better ideas. It's his profession, after all, and I'n just an amateur.

@pindac

I think you mean ’thrust bushing’. Only a very few commercial TT offer an air cushion in all three dimensions, as does a thrust bushing, and they are all well north of 100K.

Their 35mm thrust bushing can support up to 60kg, so safely 45, which is what I use. Supports 60kg and resets a radial force a hundred times more than we need. The perfect solution in one piece.

I have dealt with New Way for years, and they are very good to deal with. If I were doing it again, I would get them to make the spindle as well - expensive, but guaranteed to work to the highest specification.

You can afford it when you are saving 100k !

@lewm  Understood. Thanks.

@pindac  The factory will sell to you directly, at least, they sell directly to me. Also, they give free advice. I find it easiest to buy everything from them: air fittings, shafting, end blocks to support shafting, etc. I also use their 20mm air bushing for my LT tonearm - there's a picture of it in the DIY audio thread on air bearing LT's.

IF you go air on your TT, it's natural to go with air for the TA. You'll need a good compressor - I use a stainless steel commercial unit from Werther (Italy), model CWF100 TC INOX. Only disadvantage is that it's noisy and has to go in it's own shed, outside the house. If noise is a consideration, consider the Val-air series, also by Werther.

Good luck!

@pindac If you are interested, it's on page 25 of the DIY Air Bearing Linear Arm thread at DiyAudio. The whole thread is worth reading. I learned a lot that was very useful - like the importance of 1/32" Tygon tubing.

Well said. A synchronous AC motor is a safer bet, so a good first step.