Mounting an SME 3009 'improved' to a TD160
The SME 3009 S2 Improved fixed headshell tonearm. Not everybody likes this arm. SME had redesigned their vintage S2 series arm to become a better match to the popular high-compliance, low-tracking-force, phono cartridges of that day. SME also reduced the length from the pivot rearward, making the arm a better fit on smaller belt driven suspended turntables of the time. Perhaps the biggest area of concern is the nylon knife-edge bearing. Previous models had used a steel knife edge bearing.
Detractors aside, there are plenty of these arms in circulation and available second hand. The going prices aren't terribly high for all the work that goes into the production of this arm. I thought I might try one and see for myself. Fortunately I was able to find one that was still sealed in its box. NOS (new old stock) as they say. Fresh pivot bearings.
Here are some more reasons I choose this arm.
1) The pivot to spindle requirement for the SME is the same as for the Thorens arm. This means that the tonearm should fit within the port opening in the top plate of the Thorens. Well....you'd think it would, anyway. More about that below. Besides, SME makes an arm-board for this particular application.
2) I already had a Shure V15VxMR cartridge. The effective mass rating for the fixed head version of this arm is 6.5grams. This arm will make a satisfactory match up to the Shure with it's compliant cantilever.
3) All (most) SME's are lovely to lay your eyes upon, including this one. It just doesn't hurt to look at from any angle.
Locating the pivot
The SME 3009 Improved does not allow adjustment for effective length. This may seem somewhat odd to many. Often times, it is the effective length that is adjusted in order to achieve correct overhang. Not so with this tonearm. Instead, effective length is a fixed distance and overhang is aligned by adjusting the pivot to spindle distance. This is fine as both effective length and pivot to spindle distances are merely adjacent sides of the same triangle. Given this, it will be important that sufficient room for maneuvering the pivot to spindle distance is found within the tonearm mounting that will be arranged.
above photo #1. An early version of the armboard using inexpensive materials to test fit and function. The trammel (A very handy device for measurement of pivot to spindle distance. This being the trammel portion of the Clearaudio protractor ) is used with an extended pointer. Centered to the pointer is a paper disk the same diameter as the outer body of the pivot bearing of the SME. By setting the trammel to the specified 215.4mm length, it can be seen in the photo above and those below that there is indeed open space for this bearing to locate to. There will be no need to grind away any material from the sub-chassis to fit this tonearm. However, the "can" will need to be disassembled from the SME tonearm to make this possible.
Photo #2a: location for pivot bearing for standard arm, #2b.
Photo 3: Arm board #2 will use this location for pivot bearing of the SME.
Should this be a one-piece armboard, or could one take a constrained layer approach...? Answer below.
Brian Kearns sent a drawing. This becomes armboard #2 using inexpensive materials to test fit-and-function.
Arm board #5:
Above: a 3d model based on an 'SME manufactured' arm board for this very application. Soon a "real" part will be produced and tested.
Weight. The SME arm, less arm-board, cartridge and screws weighs in at 15.5 oz. Notice the black oval 'can' over the lower portion of the bearing. That will be removed and so will the rearward mounting post for clearance reasons.
The Thorens arm, a TP16 mk 1 complete with arm-board and cueing assembly, but without cartridge or screws, tips the scales at 15.5 oz. And that is with the underneath cavity of the plastic arm-board stuffed full of Blue Tack putty and a control cable hanging off the side. The Thorens arm is definitely lighter than the SME but by less than 2 ounces give or take a pinch of Blue Tack. I guess I can retain the standard Thorens suspension springs for now but it is necessary to adjust the elevation upward at this corner.