want new plinth ideas for direct-drive turntables

Travis, the TT-71 is the typical servo quartz lock type right before JVC went bi-directional but TT71 and TT81 do share the same motor. So after the mod, if I ever find a TT-81, I can always plug the umbilical cord to it as an upgrade.

Yes, the SP-10 family is easy for this type of mod, just to note that the MJX-12A motor is pretty wide diameter (6 inches) compare to other DD motors, so you need to cut a pretty big hole. Here's an example of the Kaneta style:

http://homepage2.nifty.com/~mhitaste/audiotop/audio_apparatus_page/sp-10mk2.html

Yes, as I said, the Sony and Denon are doable but the requirement for precise mounting of the tapehead is a hassle so I leave them alone. But I am attracted by the nice motor in the PS-8750... and it's a beater. Hmmm...

Typical Pioneer motors from, say, PL-500, PL-600, PL-L1000, have a flat bottom so one can simply mount them on a flat surface without cutting a big hole. The earlier models such as PL-550, PL-570, require a 4" diameter hole on the plinth for mounting. All their motors contains the speed control requirement so no external hardware like tapehead is required like Sony and Denon. Admittedly, their sound to my ears is not as smooth as JVC stuff but perhaps with a plinth overhaul will push their performance a notch. Or maybe not. I did try their cheap models with coreless motor like the PL-300 and it has a smoothness reminds me of the JVC, so I am very curious about their later models like PL-70L that switched to coreless motors. Of course, they continued to use the superb Stable Hanging Rotor(SHR) bearing.

You have TWO DP-100?!! Wow. Lucky man. You have owned just about every top of the line Japanese DD tables in the golden era (1975-1985). What's your next conquest? Vintage European DD tables now like the EMT 950 or Goldmund Studio, etc...? Or the new generation of DD tables like the Teres Certus, Monaco Grand Prix, Brinkmann Bardo, etc...?

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Dertonarm, yes a DD tables are very suitable for suspended plinth. Unlike some belt-drive suspended tables that the motor is fixed and the platter and arm is suspended that creates speed issue. I believe the Goldmund Studio was one of the first expensive tables to employ suspension in the DD genre. It's definitely worth investigating. Thanks.

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Need some 'splainin' here, as Desi Arnaz used to say.

I don't know all that much about electronics and I'm only familiar with the SP-10 Mk 2 series of DD tables. But since the motor must remain attached to the spindle and platter, how much benefit can be gained by moving the circuit boards outboard? It seems to me the biggest potential problem could come from the current field of the motor itself, rather than the circuit board(s). For this reason the addition of an EMF/FRI shield such as recommended for the Kenwood L-07D, suggested by T_bone above, and implemented by Albert Porter in his SP-10 tables, would be as good an upgrade and far simpler and cheaper.

Concerning Dertonarm's suggestion for suspension to isolate outside vibrations, would not the high torque motor of the better DD tables be the largest source for micro-vibrations in most set ups? How would suspension address that?

Thanks for any more light on these thoughts.

Dear Tim, I think the business of torque is over-stated both for its virtues and its problems. The motor, any motor, does not use its full torque unless or until there is an equal force opposing its rotation. So if you turn on your turntable and prevent the platter from turning with your hand, then and only then does the motor develop its full torque. In real life, this only occurs for a brief moment at start-up, when the motor has to move the platter from rest. Once things are up and running, the torque necessary to keep the platter in motion at a constant speed will be determined at any given micro-moment by a number of other parameters, which have been discussed here and elsewhere ad nauseam, but IMO huge amounts of torque are not necessary when playing an LP and are not generated either. So in fact it could be argued that a DD motor might present less of an endogenous vibration problem vs belt-drive or idler-drive motors, because it is spinning at a much slower rpm compared to the other two. Nevertheless, I think your point, so far as we limit the problem to vibration rather than high torque, has validity in that one cannot decouple the motor from platter in DD, whereas such strategies do work and are feasible with belt- and idler-drive types. So if the motor is inevitably closely associated with the platter, then there must be limits as to what can be achieved by isolating the entire tt with a suspension. This is what bugged me when I started to think about using a heavy, dense plinth in the first place for dd tables. But it does seem to "work". I will say one thing - I never liked the "sound" of the Goldmund Studio back in its day.

I did not say taking the electronics out. I only want to take the motor (and platter) out of the stock chassis so it can be mounted on something more solid - Mike Lavigne's Steve Dobin plinth works the same way. The Kaneta approach is a radical one as it keeps only the motor from stock form and redesigned all the electronics from scratch using new circuits and power supply. I am not suggesting that and I simply do not have the knowledge nor resource to do that. Taking the motor and platter out of the stock turntable makes it flexible to implement new plinth design. The original electronics remains in the stock plinth/chassis/enclosure/whatever or you can house it in a different box. Yes, it will require extending the motor wires to reach the electronics.

I hope the "splainin" helps. Thanks for the interest.

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one cannot decouple the motor from platter in DD

It is possible to decouple the motor from the platter in DD. I was thinking about that the other day. Here's a concept turntable. The problem is that such design will have two layers and it will require having two bearings. One for the platter above and one for the dd motor underneath. Think of the EAR Disk Master turntable by having non-contact magnetic drive in concept but instead of having gear belt driving the subplatter underneath, simply use a direct drive motor. Another way of looking at it would be having a platter/bearing assembly at the top layer with a with a contact disc at the bottom of the bearing to make contact with the dd turntable at the bottom. Make sense? Here we can take advantage with decoupling and direct driving at center of the platter. Again, it's just a concept, whether that's practical to make or not is another issue. The Clearaudio Statement is similar concept except the lower platter belt-driven and again using non-contact magnetic pull to rotate the top platter.

Lot of fun ideas in the head. :-)
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