Thursday, 21 November 2013

Sony PUA-114 Tonearm converted to 12''

Hello to everybody. My speakers are still in work, so they are not ready for the public viewing. Instead I want to show a conversion of a unknown high quality japanese 9 inch tonearm into a 12 inch version. For this conversion I did use one of the arm wands from my SME conversion kit.

I had this japanese Sony tonearm lying around for years. I did buy it once because it has a mechanism to adjust the vertical tracking angle on the fly, it can be made during the pick up process. There is a knurled round plate just under the bearing to operate a thread, which will rise the whole bearing shaft up and down. Only a few very expensive tonearms give this luxury extra as option. So, what is the idea behind such a mechanism? If you use different moving coil cartridges, each needs to be exactly mounted into its perfect position to give its best result. Perfect geometry of arm and cartridge is the one thing to reduce errors of the pick up process. But the vertical angle varies the angle of the diamond tip in the vinyl groove. This angle has some influence into the ability of the best high frequency response which is obtainable with a given angle. So a changeable angle will result in more or less a perfect position of the diamond, i.e. in a more or less better defined high frequency response of a cartridge.  All cartridges are normed for a 15° angle in relation to the record surface. So this option gives some extra opportunity for adjustment of the response of each cartridge. If a tonearm has this option it will be very easy to match a pick up into a system just by listening evaluation. The classic heavy arms from SME, Ortofon, Fidelity Research and Ikeda do not offer this option.

This extra was my basic interest when I bought this arm some 10 years ago. But I never tried it with my turntable. Since I have the conversion kit to offer, I was thinking I should try this tonearm once. But first of all it needed to be converted into a 12 inch length.
For that reason the original s-shaped 9 inch aluminum arm wand got detached. The most japanese tonearms do fix the arm wand to the bearing house with one or two screw, here it is made with two worm screws from underneath. The SME armwand has a outer diameter of 9.5mm, almost all tonearms did follow more ore less this size, only a few tonearms use thinner tubes of 8 to 9 mm size. As well here the 9.5mm did perfectly fit into the bearing house. This is milled from solid aluminum with more than 2mm material surrounding the tube fixing.
When I dissembled the bearing house, I was surprised about the built quality of this arm. A lot of japanese mass arms incorporate the two tipped bearing principle with steel tips. Here the tips are counter positioned into micro ball bearings with stainless steel end caps. These little bearings (2mm outer diameter) are precisely positioned in caves, which are milled into the center shaft. So the depths of the tips need to be fine adjusted with a tension tool. The tips itself are made from chrome plated polished steel. This mechanical principle is only found in fine crafted tonearms, other than ordinary tonearms mounted on turntables from the typical mass suppliers.

The headshell connector on the other side of the arm wand is fixed with a little screw from underneath, similar like the typical SME arms from the 1970ties, but the screw is positioned some millimeters closer to rim of the tube. This made a cut necessary to adjust the difference, which will result in a 3mm shorter arm geometry, comparing the SME 3012 size. The effective length between center of the shaft and pick up diamond is now 302mm instead of 305mm of the 3012. I think it can be lived with that loss...

Another problem might be the new heavier weight of the arm tube. So the counterweights are a bit underrated for that tube, but if necessary, it is possible to add extra weights for compensation (Sony did offer a additional weight in the 1970ties). Of course I did use the balsa inlay to damp any ringing in the tube and I did use silvered copper litz for the signal connections inside. For a propper set up it would be necessary to make a solid base, where the shaft will be clamped in and were the whole arm will be mounted to the player. If made from a round bronze bar, like used for heavy metal shaft bearings would be the ideal choice.
I did some test without this stage of perfection, just to figure out were this arm will find its ideal use. It was no surprise that it would give a extremely precise imaging of the music, comparing it with more simple designs (like the knive edge of the SME). The other side of this medal is always a bit of the lack of sheer dynamics other arms can show. This arm might improve in this discipline with a better base construction. But never less, it is a 12 inch tonearm. It has a wide stereo image and a giant depth of stage illusion, 9 inch arms don't come by. Together with its possibility of VTA adjustment on the fly, it is the perfect tonearm for people which want to evaluate several different cartridges in their system. To find something similar in terms of comfort and in this range of quality, you need to spend some more thousand dollars.

If there is somebody out there, who might have an interest into that rare tonearm, I will be open for any reasonable offer to sell it, of course without the nice bakelite headshell and the pickup.

Stay tuned, Volker

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