My Thorens TD160 turntable came fitted with an Audio Dynamics Corporation ALT-1 Tonearm and a cartridge from the same manufacturer. The latter was toast, so I installed an Ortofon 2M Blue cartridge.
Under the close scrutiny which comes with installing a new cartridge it became clear that all was not well.
A new cartridge means lots of fiddling about and adjustment. Try as I might I could not get the alignment right. The fundamental problem was that the tonearm was mounted too close to the turntable. About half a centimeter too close.
The Thorens TD 160 turntable can be fitted with a wide variety of different tone arms. This is achieved by having an arm mounting board which attaches to the TD 160. The arm is then fitted to the board. Different designs of board accommodate different arms. Mine had the wrong board for this arm.
The board and arm were rather clumsily mounted. The wrong washers were used and the mounting hole looked like it had been “adjusted” with a rusty file.
Figuring out which board to buy was the next challenge. There isn’t a board made specifically for the ALT-1. A bit of research suggested that that the ALT-1 has similar critical dimentions to a Rega arm which used to be popular on the TD 160. Comparing pictures of the board for the Rega arm with my own board It looked promising. The hole was smaller and offset to the right a bit. I took a punt and paid my £20.
The new board was a great fit. It was also cleverly designed so that there were no mounting screws visible from above. A couple of washers from the garage and the arm was mounted sucessfully.
Alignment was now easily achieved. The cartridge is now mounted in the middle of the adjustment range on the headshell. This suggests that the arm position is now pretty much spot on.
The new board moved the arm pivot point back a bit and to the right. This solved the overhang problem. Unfortunately the counter weight now fouls against the side of the lid when the end of a record is reached. Ok, so it’s good practice to remove the lid when playing records. Meanwhile in the real world..
The counter balance weight position is critical because it balances the arm and determins the downward force on the stylus. My Ortofon 2M Blue cartridge is quite heavy for the ALT-1, so the counterweight needs to be set far back for the correct balance.
Some tonearms can be fitted with auxiliary weights to solve the heavy cartridge problem. My Dual 505 has such a weight. Can I apply the same idea here? A heavier counterweight would be positioned closer to the pivot to achieve the same balance. Maybe close enough to clear the plinth lid?
As luck would have it an M14 washer has an inside diameter which is just slightly larger than the ALT-1 counterweight mount. I could work out how much extra weight I need to add to bring the counterweight in far enough. Alternatively I could just add washers until it worked. One 7.8g washer was enough to bring the existing 56g weight in by about 6mm. Enough to prevent the lid from fouling. Another stroke of luck was finding a rubber O ring the right size to hold the washer snugly against the counterweight. It looks like it was made that way and the modification can be easily removed.
This modification is not without potential problems. It’s important to note that the calibration ring is no longer accurate due to the extra weight. This is ok as long as you are aware of it and use a stylus pressure balance to set up. The extra weigh also changes the effective mass of the arm slightly. This has an impact on cartridge compliance matching, possibly creating resonance and tracking issues. The theory around all this is complex and subject to interpretation. In pracice, it works great with or without the extra weight. I have the added peace of mind that closing the lid will not send the arm skating across my precious records.
It’s worth noting that the cable from the arm fouls the base board of the plinth. this effectively defeats the suspension so must be sorted. I made a new board to solve that problem. More on that story later..
The TD 160 is now working very well and has entered full time service as my main turntable. It is a noticeable upgrade in sound from the Dual 505 it replaces.