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A Papst in a Thorens?
The story goes something like this:
In 1977, ten years after the TD124 had been discontinued, Thorens management worried that it could no longer supply new replacement motors for their once top-of-the-line player. The solution turned out to be the subject of this article. Thorens contracted with Papst to adapt one of their "Aussenlaufer" motors to function in the TD124.
above photo: the 60 hz Papst Aussenlaufer motor is wired and ready for use.
The Papst motor, unlike the Thorens E50* motor that it was to replace, is an Eddy Current motor. The relative contributors to the Papst motors' speed regulation are: mains frequency (97%), torque load (2-3%) and drive voltage (<1%)
The Thorens eddy brake is still functional and does offer a means of fine pitch control. An important detail that should be mentioned is the fact that this Papst motor is a three-phase ec motor. Generally, 3-phase electrical power is used in industrial settings, not residential, which is single-phase. To get the motor to run on household current, a capacitor is connected across two of the three leads and "fakes" the motor into working.
Another important detail is this; the rotating part is the outer casing, while the stator, the part with the windings, remains fixed. This design results in a relatively high moment of inertia at the rotor, giving a flywheel effect. When turned by hand, the turn of the rotor exhibits no magnetic cogging as does a more traditional synchronous motor such as those found on Thorens' belt drive models. This is an interesting turntable motor.
Here's a detail shot of the hook-up. With this scheme, the strobe will not
light. I could find no alternate means of including a lit strobe in
combination with a functional, switched Papst motor. However, in the other
important way, this motor did power the Thorens platter, operating from the
speed switch and with some considerable driving force. More about the
sonic character further down the page.
Here's Figure #2 from the Thorens service bulletin No. 22 . It is a
schematic of the wire-up. The image quality of the photo makes it almost useless
but the schematic illustration is useful. I've made minor
translations into English for those of us who aren't fluent in
German.
note: click on thumbnail to view full sized image
Thanks to Schopper, and courtesy of Octave Audio, Schopper's distributor in the USA, I have new motor grommets to help isolate the Thorens from the motor vibes produced by this high inertia motor. Schopper also offers a "kit" that can adapt an early (mk 1) E50 motor, with the shorter grommet poles, with longer ones to allow use of the double grommet scheme. This will further reduce motor vibes. More about that in an upcoming article.
Here's a detail photo of the E50 wire-up...should you ever need a map to make
the correct connections. I'm glad I took the photo since after a few days
of listening to the Papst, I returned the E50 into its rightful place.
What was life with the Papst like, you ask?
Unlike the E50, the Papst gets up to correct operating speed right away and locks in. I did mention above that the eddy brake fine pitch adjuster is fully functional with the Papst and provided a precise means of dialing in pitch. Very nice, that part of it.
I also used my stethoscope to listen for motor vibrations at various points in the cast chassis of the Thorens. Even with the double grommet isolation kit, there was more vibrations heard throughout the chassis than is heard from the E50 using only the single grommet isolators. This is significant.
I had setup my Expressimo RB250 with the Ebony bodied ( by Uwe) Denon DL-103R MC cartridge. After careful alignment and a vta adjustment session I began listening to some Lps. First up was, Paul Simon's "There Goes Rhymin' Simon". This is an Lp that gets frequent play in my room. Right off I noticed a strong rhythmic drive but also noticed a loss of upper frequency detail. The cymbals were almost entirely missing. The acoustic guitar notes had significantly less air. Tone and texture seemed to take a back seat. Ambience was duller. Now it was about the rhythm section, which was strong and moving my feet.
Just to make sure, I spent some more time dialing in VTA. Also, I experimented more with VTF adjustments and found a slightly more open sound while tracking at 2.3 grams rather than the nominal 2.5. Then I played from my list of titles currently in rotation. War, Brian Auger, Paul Simon, Horace Silver, Herbie Hancock, Cannonball Adderly, Miles Davis, Santana, Sonny Rawlins, Joni Mitchell, ELO, Clapton, Steely Dan......
In every case, the driving rhythm was excellent and moving while tones, textures, fine details and ambience seemed to have been covered with a blanket. Not distorted, just not alive or present. This must be why the Papst Aussenlaufer motor is not generally regarded as any kind of upgrade for the TD124. I was privy to some here-say to this effect going into it, but I also knew something else.
That something else is that -if- the Papst were to be operated on a true 3-phase power supply, it would become a much smoother running motor. Then, I suspect, the turntable motor would offer the best of both worlds; a strong rhythmic drive while providing details, air and ambience. More on this theme later.
Other notes: During the process of installing and figuring out the wire-up I spent some time listening to my Teres 145. At one point later it occurred to me that if I had to choose between the Papst/TD124 or the Teres, I would have gone with the Teres. However, if it becomes a choice between the E50/TD124 or the Teres, I'll be listening to the Thorens, thankyou please. The Thorens TD124 gives a nice blend of details, air, ambience while providing rhythmic drive that will lift your feet.
At the time of this writing I have the E50 back in the Thorens. Now that's better!
Footnotes:
* The original Thorens E50 motor is classified as a shaded pole induction motor. According to one expert source I know its speed regulation contributors are: mains frequency (85%), torque load (10%) and drive voltage (5%). This category of motor is of a type that is often used in electrical fans. Of course the E50 is a well built and long lasting "fan motor" and so owners should not become suddenly upset at this disclosure. :-)