SLATEDECK TURNTABLE PLINTHS
Arm Geometry : When a record is cut the cutter head traverses on a parallel path across the record. The information in the groove is therefore cut along a perfect radius to the centre hole. When you play back a record using a pivoted arm the cartridge traverses across the record in an arc. It will only be parallel to the groove in one or two points on this arc. For the rest of the arc the cartridge is offset from the parallel. To help counter this the cartridge is mounted at an angle to the arm in order to equalise the geometry as best possible. However this geometry is not fixed. There are several different methods of aligning the cartridge for the two points of minimum tracing distortion on the record. Normally you would cut an armboard to suit the arm manufacturer's geometry using the 'effective length' of the arm to position the pivot point. If you want to experiment with arm geometry then you can either compromise by twisting the cartridge in the headshell or drill out a new armboard. Slatedeck's Adjustable Armboard allows you to experiment and adjust the arm geometry just by rotating the armboard. For the first time arm geometry can be optimised as simply as Vertical Tracking Angle. You can download a Windows programme for generating pickup arm geometry, called armgeometer.zip, by clicking here. Pictured on the right are, from the top: SME base plate adjustment for arm/cartridge alignment. Adjustable Armboard with Rega arm Adjustable Armboard with Formula 4 arm Adjustable Armboards in detail Slatedeck 401AA with Rega Arm |
The Slatedeck Armboard |
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The standard Slatedeck plinth is ready machined to take an SME arm or any arm with SME baseplate fitting or adapter. The SME base, of course, provides full adjustment for arm base alignment and adjustment for the optimum cartridge tracking and, therefore, the lowest distortion. But what do you do if you wish to use another favourite arm which does not have an SME baseplate adapter? Slatedeck have the answer in the Adjustable Armboard. Slatedeck's Adjustable Armboard is a novel solution to a complex problem, and one that makes cartridge alignment delightfully simple. Slatedeck's 20mm or 30mm single layer plinth is also avaialble with the Adjustable Armboard to take Rega, Hadcock and Formula 4 arms as standard, or can be drilled to suit your own favourite arm by request. Like we said, the concept is complex. Cartridge alighment can often be made using slots in the headshell, whilst the SME method is more elegant providing overall adjustment by a sliding baseplate. In either case you are at the mercy of the arm designer as to the geometry you use to achieve optimum tracking across the record. If you wish to use a geometry that differs from that of the arm manufacturer, and many of us like to experiment with this, then you are forced to either build your own armboard or try and twist the cartridge in the headshell. The Slatedeck Adjustable Armboard allows you to adjust pickup arm offset in a unique way. Using this ideal method you can move both the arm and cartridge to align to any offset geometry you prefer. Slatedeck's Adjustable Armboard is the ideal solution to solving the problem of arm geometry. You fit the armbase as normal to the Adjustable Armboard and place both into the location hole in the plinth. Start by fitting the cartridge to your arm so that the distance between stylus and the centre of the armbase is the optimum effective length of the arm. This should then optimise the geometry of cartridge and arm to that which the arm designer intended. Your next step is to use your alignment protractor of choice to optimise the tracking geometry across the record. Because the armbase is offset from the centre of the Adjustable Armboard you can change the position of the cartridge on the protractor simply by revolving the Adjustable Armboard on the plinth. Using this method any type of geometry can be accommodated and you can experiment with different geometries quickly and without having to dismount the arm or build a new armboard! This really is the ideal solution to refining the performance of your turntable system. Slatedeck's Adjustable Armboard at last allows you to solve the thorny problem of which arm and cartridge geometry is optimum just by rotating the armboard. Once you have found the optimum solution then the armboard will remain locked in position thanks to the stiction of the Adjustable Armboard base. Next - Building the Twin Tier plinth system
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