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Importance of headshell and tonearm alignment

I own a Thorens TD166MKII with an SME 309 improved arm. I haven't been able to align the arm and headshell using a protractor. The installer tried to correct the problem by cutting away the rear section of the subchassis metal base to the point of leaving the arm base supported by the two front screws. This cutting allowed the arm assembly to slide further and slightly improved the alignment but it is still off. I can get true alignment on the cartridge if I use aftermarket headshells with slots which allow the cartridge to slide at an angle within the headshell. Does anyone have experience with this type of installation and can offer a solution? Should I be concerned with the alignment of the headshell and arm or just be content with getting the cartridge aligned?
flyfisher
gregm
3,405 posts
 
I used to have exactly the same TT very many years ago!

Try reading here. While the TT is a 160 (not 166) it may help. Setting up the arm:
IF the pivot-spindle distance is indeed 215,4mm as specified here then:

effective length is: 233,19mm
offset angle: 23,6 degrees
overhang: 17,8mm and, of course,
spindle-to-pivot: 215,4mm
Null points at 66 & 120,9mm

(BTW, looking at my old notes I used to have the distance @215mm as well)

Start by getting the spindle to pivot distance right; the offset angle cannot be adjusted -- but it should be correct (sme is a very serious constructor). Then align with correct protractor at null points. If you have already tackled overhang, aligning the cartridge becomes much easier.
Cheers
Cheers!
flyfisher OP
46 posts
 
Gregm, thanks for all the added info I will verify distance more accurately and then restart the process!
flyingred
139 posts
 
My first experience of setting up an arm/cart was on a TD160 with a SME mounting board and adapter plate (in about 1980). I struggled to get the cart aligned. With hindsight, I realize that my error was in trusting the accuracy of the adapter plate - the pivot to spindle distance was off.

I suggest you measure the pivot to spindle distance and make an arm board that enables you to get that spot on. After that, cartridge overhang and alignment will be straight forward adjustments and your rig will be singing.
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