Artisan Fidelity will convert your TD125 to a Long Base that will be able to use 12" arms. Also, they will install those new dc motors and controllers in the 125's if you want. IMO, the TD520 was built at a time when Thorens was falling downhill fast in both quality and sound. Those TD520 plinths are very cheaply made in comparison to the high mass solid maple plinths AF uses. Also, they totally eliminate the old suspension which is another plus. Not too mention they just look plain incredible.
Artisan Fidelity TD125 Long Base or "LB"
http://www.artisanfidelity.com/Hardwood-Portfolio.html
The bearings used in the TD125's were tops, much higher quality that those used in Thorens models of the 80's such as the TD520.
I'd go with the AF Long base converted td125, better build and I'm sure better sound than a td520.
good luck
Artisan Fidelity TD125 Long Base or "LB"
http://www.artisanfidelity.com/Hardwood-Portfolio.html
The bearings used in the TD125's were tops, much higher quality that those used in Thorens models of the 80's such as the TD520.
I'd go with the AF Long base converted td125, better build and I'm sure better sound than a td520.
good luck