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want new plinth ideas for direct-drive turntables


By now, the idler-drive genre has enough ink on them without me adding anything new to the topic. What is little talked about is the "guts" of direct-drive tables. Many vintage DD units suffered from bad plinth design with inadequate solidity (often mounted to crappy plastic or flimsy particle-board) and inadequate isolation from resonance and interference of electronics.

I like the bare bone approach, that is, to take the motor out of the chassis/plinth/enclosure and mount it to a something solid, material of your own choice, and extend the cable by at least couple feet to the stock chassis or an enclosure that contains the electronics/motor-drive/control-console/power-supply. In fact, the Monaco Grand-Prix, Teres Certus, or early Micro-Seiki DDX/DQX-1000 takes the same approach.

Almost ALL DD tables can be improved this way. There are many other brands of superb DD tables with great potential out there can be had for very reasonable price and can be converted this way with good result. I no longer have any Technics tables on hand to experiment but I still got great results with some mid-priced JVC, Pioneer, Kenwood, Yamaha, etc... I haven't tried it on Sony and Denon tables yet because they require mounted a tapehead to check platter speed so the mounting is tricky. Modern belt-drive turntables have been doing similar things by separating the motor from the main plinth. Once again, Micro-Seiki was ahead of their time with their RX-1500 and beyond. It's only logical DD will go that direction. The days of having everything in a box for DD tables seems less attractive to me now.

If you have other ideas, feel free to talk about it here. And hopefully this will generate more new interest in the DD genre. Personally I am more interested in people's experience with brands other than Technics as they already got enough coverage in other forums and threads. Nothing against Technics, just want to direct attention to other sleepers out there. Anyway, still feel free to share ideas.

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hiho
pryso
1,947 posts
 
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.
lewm
13,303 posts
 
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.
hiho OP
451 posts
 

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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hiho OP
451 posts
 

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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mikelavigne
2,200 posts
 
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.

i've been living with the active air suspension and air bearing of the direct drive Rockport for 8 years and could not agree with you more. mass only takes things so far; ultimately any gounded tt will become a seismograph as it attains higher and higher levels of detail and tells you about how the earth sounds.

OTOH high mass plinths do yield very high performance overall. (of course, the Rockport has a 250 pound plinth, along with air suspension).

the Dobbins Technics SP-10 Mk3 with the 'naked' plinth (110 pounds) and the Dobbins Garrard 301 (80 pounds) are sitting on the decoupled Grand Prix Audio Monaco rack with Formula shelves. the GPA does offer a fairly effective passive decoupling that seems to work with these tt's. but more sophisticated active suspension would likely take things up a notch in refinement and low level detail.

i have pondered how a Halcyonics or Herzan Stable Table would do under the Mk3 or 301. would that added benefit get it closer to the Rockport?
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