Vintage DD turntables. Are we living dangerously?

04-04-14: Banquo363:
"The english flyer for the jvc ql8 has a small black and white pic of the tt81 motor. Take a look and see if you can tell whether it's a coreless motor or not."

Good find!

TT-81 motor - & - TT-71 motor

Yep, just as I suspected. The TT-81 motor is indeed a core motor, same structure as the TT-71 motor. Notice the coils wrapping around an iron core? You just save Halcro the hassle of taking apart his TT-81. :)

- - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Timeltel, I like your tinkerer's spirit. :)

______

Halcro, That's great news about your TT101, and it is useful to know yours was malfunctioning due to bad power switch. Can you describe again the symptom that it exhibited before repair? Bill Thalmann often wondered whether the switch on mine was bad as well, and that could account also for the fact that mine would work well off and on, once it had been re-capped and re-soldered. Also, it explains why leaving the Power ON is a form of solution to the problem short of replacing the switch. Where did he get a replacement switch; perhaps you can ask him what he used, just in case any of the rest of us has issues.

By Sunday, I will have completed my mods to the stock QL10 plinth. They are anti-Copernican. I will post photos, and best of all I will finally get to listen to a TT101.

Dear Timeltel, You wrote, "the 71 lacks the reverse eddy current braking both the 81 and 101 implement in regulating overshoot incurred when correcting for speed". According to everything I have read and observed, that is not correct at least for the TT101. The TT101 is unique among 71, 81, 101, in that it has a reverse servo mechanism to correct for overshoot. Nowhere have I ever seen this described as eddy current based. I have no insight on whether or how the TT81 can slow down its platter. I do know that one sign that my TT101 is running as intended is that when I press the "stop" button, the platter comes to a dead halt. When I was having problems, the platter would stop but then rotate backwards for about half a turn before lazily stopping. This indicated to me that the reverse servo was not working properly.

Someone else suggested that Exclusive P3 and P3a did NOT have a coreless motor. My information says they both DID. (They were not really two different turntables; the way I hear it, there was a change in the way rumble was measured and Pioneer re-named the table from P3 to P3a so they could claim the new re-calculated lower number for rumble was associated with something they actually did to the table to improve it.)

Also, Denon tt's were said to have an "induction motor". That would be hard to do with a servo-controlled DD turntable; so far as I know the Denon DP80 has a 3-phase synchronous motor.

Lewm: "Someone else suggested that Exclusive P3 and P3a did NOT have a coreless motor. My information says they both DID."

It does not look like the traditional pancake style coreless motor. Judging by this picture in this webpage, it might be a linear motor, which has magnets on both side of the coils like maglev train, with a cylindrically shaped stator with coreless coils, it might be a coreless motors after all. In that picture, the top motor is just an illustration what a traditional motor looks like and the bottom motor is the EM-03 motor P3 uses. It's a novel way to making the stator much like the ThinGap motor used in the VPI Direct table.

Lewm: "Denon tt's were said to have an "induction motor". That would be hard to do with a servo-controlled DD turntable; so far as I know the Denon DP80 has a 3-phase synchronous motor."

DP-80 does not use induction motor but earlier models, pre-1975, some models used magnet-less induction motors. Chronology is the key here.

_______

Regards Lewm:

Retrieved from JVC literature:

Both the TT81 and 101 utilize a servo system operating in both positive and negative directions. A disc with either (dependent on model) 180 or 90 slits is opposed to a circuit board with the corresponding number of printed-coil elements. A phase comparator circuit reconciles the signal from a quartz frequency generator with the one built into the motor.

If my math is correct, for the TT101 at 33.3 RPM, speed is sampled and corrected every 0.003 seconds. This second "negative" servo system is absent in the TT71.

Speed deviation for the 101 & 81 is given as 0.002%
Drift stated as 0.00004%/hr.for the 101 & 81. 0.0002%/hr. for the 71.

From this source:

http://audio-database.com/PIONEER-EXCLUSIVE/player/p3-e.html

"Linear torque scheme of a slotless and a coreless structure by Quartz PLL is adopted as a phone motor and a bearing structure. Furthermore, by the conventional measuring method, the impossible rotation performance of 0.001% of less (---) rotation unevenness 0.003% (WRMS, the FG method) a rotational frequency precision is realized."

http://audio-database.com/PIONEER-EXCLUSIVE/player/p10-e.html

"Rotation unevenness, 0.007% (WRMS, the FG method) 0.015% (WRMS, the Japanese-Industrial-Standard record method)."

http://audio-database.com/PIONEER-EXCLUSIVE/player/pl-70lii-e.html

"Rotational frequency deflection 0.002% or less. Time drift : 0.00008%/h."

Again relating to the OP (and I'd not wish to put it to the test) by all references Pioneer is committed to service components bearing the "eXclusive" badge.

Apparently my "IIRC" function is somewhat out of phase. Apologies were offered in advance. In view of maintaining accurate information your comments are entirely appropriate.

Peace,