A question I am asked a lot is what are the differences between a TD-125 and a TD-125 MKII.
Some general information first. The TD-125 was introduced in 1968 and was the replacement to their top-of-the-line turntable the TD-124. Unlike the TD-124 which is a hybrid belt-idler wheel turntable, the TD-125 is belt driven. To my knowledge, it was one of the first turntables where the speed was controlled electronically rather than just an AC synchronous design. The speeds on the 125 were 16, 33, and 45 RPM. A strobe was included to dial in the speed. Some were sold with a stock arm, but it appears at least anecdotally that many many more were sold with SME tonearms or other brands. Finally, unlike many of the other suspended turntables on the market, in this case the whole top plate floats on three springs, rather than using a sub chassis design. The top plate isolates the platter system and the tonearm from the energy vibrations produced from the motor and also the environment. The 125 gave way to the 125 MKII in 1972.
In terms of differences between the two, let me start first with the similarities. Each uses an identical 10 mm drive platter. To my knowledge, all of the TD-125 turntables used a captured ball bearing design. I’ve seen early TD-125 MKII turntables, also with this captured ball bearing design. However, that is the minority. Far more have a conical designed bearing. As someone who has worked on these turntables for 20 years, I don’t see one advantage over the other. Both are very quiet and made with high-quality materials. One thing I do like about the design of the TD-125 platter system, is the shaft well itself is removable with three screws that are triangulated around the well opening. It’s great to be able to remove that both to work on the well and to clean in that area. The outer platter itself is identical on each turntable. The platters are identical and they are made of zamac.
The plinth design is identical. They are veneer over a particleboard of some kind. The bottom portion is a black strip that in some cases was painted, and another cases seems to be ironed on vinyl strips. Over the course of time, Thorens used different screws to mount the chassis to the plinth, but they were all identical in terms of the thread size. Both plinths use a fiberboard bottom plate, and the originals came with felt pads as feet. It seems that the armboards changed over time in terms of materials. I’ve never done a study of that or taken them for analysis. Some appear to be a painted plywood where you can easily see the layers on the edges, and others appear to be a wood composite, where the finish is more smooth on the edges. Both MKI and MKII utilize the same dustcover and hinge design. (Though I believe the “bubble” set on style cover came out later, just for MKII, but will also fit MKI.)
The most significant difference between the two turntables is in the motor design and the electronic speed control. With the TD-125 MKII, Thorens introduced a clutch into the pulley which takes up slack in the belt at startup so that a steady speed is achieved more quickly. The 125 has a one piece pulley. In my experience, with a fresh belt on each turntable, it takes approximately 3 to 4 more seconds for the 125 to achieve a steady speed on the strobe. If your belt is brand-new or very old, there is sometimes slightly more noise at startup on the TD-125. That’s belt slippage and lasts 1-2 seconds as it gets the torque to spin that heavy platter system.
In terms of the electronic speed control board, for both models it is really not something for the do-it-yourself novice to take on. For someone who has a little bit of experience, the design of the board on the MKII is slightly easier to grasp and to work on. However, if you are buying either turntable from Vinyl Nirvana, that is a moot point because in either case the board will have been completely updated.
Another small difference is the way the switches are designed/attached. Most of the body of the MKI switch is metal. Additionally, it is attached with a flat end machine screw into a machined metal hole. It has a nice solid feel to it. The MKII switch body is almost entirely plastic (except for metal top plate) and is attached with a pointed screw that just by design could strip more easily. Finally, for whatever reason, some of the MKII switches have bowed over time. (That could never happen with the MKI.) Unfortunately, there is no easy way to swap a MKI switch into a MKII.
Finally, the TD-125 MKII seems to have been sold much more often with the TD-16 tonearm already installed. Those with that arm installed, feature a third switch on the front fascia plate that operates the cueing for the stock arm. In those cases where someone is removing that stock arm and installing an aftermarket one, you are left with that third switch as a vestige. As someone who frequently modifies these turntables, it’s generally easier to find a front fascia plate for a TD-125 that has two switches versus a TD-125 MKII.
In terms of performance, though I have never done it personally, I’m sure if we mounted the same tonearm and same cartridge on these turntables and A/B-ed them for a room full of listeners, almost no one would be able to tell the difference between the two. In terms of usability, it’s just that extra three or four seconds for the platter to attain a steady speed on the strobe.