Part 2: Custom SP-10 Plinth

This webpage is a continuation of my SP-10 refurb project, here.

See the accompanying record cabinet here.

I considered a number of options for a plinth, but being a bit of a woodworker, I decided to build one myself, primarily using multiple layers of baltic birch plywood.  Based in part on the work by Albert Porter, whose bases are here, and described here, I used 5 layers of baltic birch, with one layer of MDF.  The latter was glued in with a soft glue to provide some additional damping.  The base also contains a 10 pound steel bar, coupled to the SP-10 bearing via brass rod, as a motor noise drain.
Layout-wise, I decided that this was to be a dedicated base for the SP-10 and an SME 312S arm combination.  I wanted to avoid the extra mechanical joint created by a separate armboard, and to me, the base also looks more finished without a separate armboard.  The top layer of baltic birch would be cut to mount the arm, and a cavity would be cut out below the arm for access to the cable and to mount the arm.

The finish will be bird's eye maple for the top, surrounded by a 1/4" trim strip of wenge, with the sides of santos rosewood.

Before deciding the dimensions of the base, I laid out the design full scale on paper, including the tonearm I planned to use: a 12 inch SME 312S.

My paper worksheet used when designing the plinth.  The planned 12" tonearm meant it had to be rather large, 22 by 17 inches.

The custom dustcover arrives.  I waited until the dustcover arrived before starting construction of the plinth to be sure the cover matched my plans.  I double checked dimensions, and it measures exactly what I specified, shown here overlaying the base plans exactly as expected.

Above: The layout transferred to the top baltic birch layer.  You may notice I made the cutout under the arm large enough for either a 12" arm or a 9" arm.

Above: Using an MDF template to route the cavity under the arm mount.  A similar template was used for the large cutout for the SP-10 base, shown below.

Above: The six panels cutout and ready for assembly, mostly upside down.  You can see the 45 degree angled cutout for the steel bar at the top, and the arm cavity cutout on the right side of most of the panels.  Note the bottom 2 panels (at the top here) are already glued together.

Above: The six panels of the base, being test fitted during gluing.  Shown in the main SP-10 cavity is the steel bar motor noise drain that will be mounted in the bottom of the base, basically below where it sits in this photo.  I drilled and tapped a 1/4"-20 hole in the center for the brass rod that will reach the bearing housing.

Above: Selecting veneers.  Bird's Eye Maple for the top, Santos Rosewood (Pau Ferro) for the sides.

Above: Bird's eye maple glued and mostly trimmed.  Test fitting Wenge strips for the perimeter.  Note the arm mounting hole is not completely cut out in the traditional SME oval.  The suggested hole is quite a bit longer than necessary (to allow arm adjustment), so I'll trim the cutout to exact size once the table is mounted to avoid the extra long cutout under the arm.

Above: Side panels added, along with rosewood veneer.  This shows the solid rosewood trim being glued to the front top.

Above: Plinth basically complete, rough sanded but not yet finished. 

Above: Plinth with polyurethane finish.

Above: Mounting the SP-10 and SME tonearm to the plinth.  I chose the SME 312S arm based on a number of recommendations, including a number of users who have paired it with the SP-10.  the 312S is a 12" magnesium arm with removable headshell (which allows azimuth adjustment that fixed headshell arms don't allow).

Above: Bottom of plinth showing the motor noise sink, bolted into the bottom of the plinth.  The brass bolt in the center reaches up to the bottom of the SP-10 bearing assembly, connecting it directly to the 10 pound steel weight.

Above: Completed table and plinth with arm mounted and aligned.

Another view of the completed setup.

...and with the dust cover.

See the accompanying record cabinet...