want new plinth ideas for direct-drive turntables

DP-100 spinning tunes as I write. Love it. Only need one though so the other is going to go... :^)

One might be able to wrap the electronics in TI Shield or something similar, and leave them there (like the board in the casing of the SP-10Mk2) but if one wanted to separate the brains from the brawn completely, it should be doable with an umbilical in all but a bare minimum of cases. I recently saw that someone had taken it out and run a larger chassis cord (with larger wire count) from the motor to an outboard box). The SP-10Mk2 is eminently suited to that from what I understand of its innards. As for the Sony and Denons and the 'tapehead'... I would have to imagine one could simply take the 'brains' off-board. If one wanted to remove the entire head assembly from the mounting under the platter (as it is attached to the motor housing), and go completely naked, re-installing it correctly might be a major hassle, especially if you wanted a plinth of slate (I'd mock up the topside in MDF or plywood before doing it). Off the top of my head, I cannot remember the speed-control technology in the circuitry of the TT-71; the bi-directional-servo starts with the TT-81. I am not sure why the Pioneers would be particularly easy to do the mods on but I'll take your word for it.

In any case, your project is an interesting exercise and I expect might be worth the hassle for a DIYer. Once I get get some space, I might try doing that with a beater I have...

I know its not popular, but go and try once for heaven's sake a plinth which is suspended with low resonance frequency - below 3Hz.
It is not the plinth weight, composition or raw material - isolate it from any outside vibration and your eyes will pop wide open how the sound and stability change for an unknown quality.

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...?

______________________

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.

_______

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.