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Belts vs Direct Drive and correcting experiments

I am intrigued by the belt drive vs direct and idler drive debate.

I happen to have an amazon model one - total antithesis of a direct drive deck insofar as it is:

high mass platter
low torque motor - albeit battery powered dc
a 'thin string' as opposed to even a belt.

I am now in the process of restoring an EMT 950.

I know Albert Porter has had great success with the Technics mark 3 - which replaced a walker proscenium in his system.

David Price of Hi fi world had a shoot off between a trio L07d and a new Michell Gyro - the results went something along the lines that the Pace rythm and timing were way better in the trio, and the tonal colourig and image size was better/more pleasant with the trio.

I have had a look at a page dedicated to the trio L07d that says that the image problem tonal colouring problem can be largely addressed by the use of a sheet of copper alloy of sorts to get rid of EMI and another sheet of a cloth like material for RFI interference.

I personally think that the RFI EMI problem may well be a problem with most direct drive decks due to the fact that the motor is directly below the platter. In pursuance of this I am convinced that all direct drives can benefit from such a modification.

With my own EMT 950 - that has both a direct drive motor and a massive steel chassis with an inboard phono stage - I am convinced that such shielding would go a long way. To that end i am thinking about whielding all the electric phono stage parts etc, and also possibly the motor.

I have also discovered a spray on shield that uses an acrylic base that i may well spray onto the steel chassis before i paint it with epoxy paint.

On the belt drive front I am not sure i can do much more with my deck.

I look forward to the discussion on this topic
lohanimal
lewm
12,433 posts
 
Someone I know has installed or intends to install a shield in his Technics SP10 MkII, for the reasons you outline. I don't know how that's worked out, but I may try it on mine, now that you mention it. The only way in which this could be a bad idea is if the shield is not well fastened to the chassis, such that it is allowed to vibrate in tune with the motor/bearing energy.
pryso
1,901 posts
 
In my research for designing a plinth for my SP-10 Mk 2, I've read about and talked with Albert, and read the L-07D site. I agree that installing some form of RFI shield should be beneficial.

As Lohanimal points out DD motors are directly below the spindle, therefore will be close to the cartridge for at least the inner half of the LP during play. Belt drive tables locate their motors in a variety of positions, depending on brand and model. They may or may not be in close proximity to the cartridge during play. I believe this is why some folks experience the dreaded "Grado hum" while others have no problem with the same model cartridge.

Years ago I read an article on shielding the tt motor when hum was a problem with cartridges like the Grado. I think Albert has a much easier solution - fit a sheet of material designed to shield RFI to the top of the platter (under your mat if you use one) and this should protect the cartridge through it's entire arc of play.

Lew, I can't promise but I would expect the weight of a mat/record and possible use of a clamp would eliminate any new problems from vibration.

And Lohanimal, for the record (so to speak) Albert designed his plinth (including shield) for a SP-10 Mk 2. Recently he bought a Mk 3 and I assume he will use the same or similar set up with it.
lewm
12,433 posts
 
For my SP10 MkII, I wonder whether Albert is willing or able to sell a copy of his shield/platter mat. I will ask. That would save a lot of thinking and making.
lohanimal OP
659 posts
 
If you do a search on google and write in kenwood trio L07 D - I think you will find the website i was looking at - this shows how to make the mate - not too difficult.

I will be reporting updates on my system as and when they are mae and posting it to this thread.

My big problem with the EMT 950 is that it has a plastic/resin platter - I might have to get some sort of spray on shield - though I am willing to take suggestions to the contrary if any good ones are made.

Lohan
lewm
12,433 posts
 
I was thinking about this hypothetical problem this morning in the shower. It seems to me that the cartridge itself might provide a low-pass filter that would prevent any RFI emanating from the electronics of a DD table from entering the downstream audio system, since few cartridges can respond to anything much above ~50KHz. (As far as Grado cartridges inducing hum in conjunction with an AC tt motor, that is an entirely different problem.) Is there any concrete evidence that RFI (that's very high frequency hash, not 60-cycle hum) is a real problem with DD tables that place complex circuitry below the platter? For that matter, the (aluminum or other metal) platter itself would provide something in the way of a shield, altho imperfect. Is this a cure without a disease?
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