Friday, 1 November 2013

The motor unit part II

Hello to everybody, sorry for a long delay with this new entry but my other activities and two fairs have  catched my complete attention within the last two weeks.

Today I will extend my former article about my motor unit for the Platine Verdier turntable with a new and easier to built round housing. A friend of mine uses two Platine Verdier turntables at different appartments in very similiar set ups. He did ask me for almost a decade to get a nice looking motor housing, similiar to mine since he followed my observations about different motor concepts. He ended up all the years with stripped down Thorens TD160 record players, without tonearm as motor units for both of his set ups. Mostly jacked up with books or card board crates to level the platter height of the Platine Verdier (minimum 22 cm, which is a lot). It looked always a bit like a neglected disaster zone beside the wonderful reduced crafted materiality of the player. Recently he burnt down his Valhalla board which I had built into his Thorens some years ago.

So when he brought the Valhalla board for repair, I thought about a way to build up a nicer looking housing as a complete integrated unit. Ten years ago I had to rebuilt my housing two times from casted concrete after accident, I decided almost never to do it again. The amount of work is just to much to make it again. Since I am in the process of bending plywoods for the front loaded funnels for my new Tannoy cabinets, I thought it might be possible as well here to bend a round housing for the motor unit, but the radius is a lot smaller. So its is a lot more difficult.

With a diameter of roughly 30 cm the wood has to be bend to its physical limits. For this reason I did use bendable plywood of 4mm thickness. In its technical specification it is determined to a minimum diameter of 26 cm. But the tension in the wood at this diameter is enormous, it can be bend but it needs to be fixed extremely solid within this position to glue. So I used the same outer round cast mold, which did use for the concrete casting a decade ago. Inside this mold I did bring three exactly cut layers of 4 mm plywood into each other, so that the single layers stabilise the others just by their own tension. It needed a lot of tests to cut the exact length of each layer so, that each layer slipped nestles into the next without any air in-between and the tensions adjust the sandwich perfectly. In order to get 9 cm height I did glue 11 cm wide stripes of almost 1 m length into each other. Finally, after drying out the wood glue, I could cut the ring on the table saw to its ideal height of 9 cm.


After building the ring I needed to to make a base and a cover to form a housing. In this design I wanted to reduce the mechanical outlay and I did it without the spring suspended subchassis my unit uses. I decoupled the main center bearing from the motor resonances just throughout the materials. The bearing is solidly set into the main construction with a massive wooden support, since the motor itself is just mounted to the 4 mm plywood top cover. Inside the housing acts like a chimney for the warm air, where the valhalla board is mounted in the center. The heat radiation of the power resistors is enormous and therefore it needs a good heat transportation inside. The most of the inner cavities can and should be filled with quartz sand in order to get mass and weight into the final unit. The filling is necessary due to the housing design, which acts more or less like a guitar or violin, with all positive and negative side effects. The unit can be adjusted to find a optimal height position for the string. A guide winded from spring steel keeps the string in central position of the platter. This guide is a must, otherwise the fine mono filament string will wander off the platter immediatly!

If somebody out there is interested to get a motor unit like this, feel free to contact me. If you are physically located close to my place in Düsseldorf I would be happy to show the advantage of this motor comparing it to your dc-motor unit, which is commonly used with such record players. Feel free to arrange a listening date.

Read on soon, Volker

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