Coupling platter bearing to plinth

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Phillyboi
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Joined: 13 Jan 2019 19:09

Coupling platter bearing to plinth

Post by Phillyboi » 13 Jan 2019 23:19

Hi Everyone,

I was just wondering if anyone has tried to couple the platter bearing to the plinth of a 301 or 401 instead of having it just hang inside the plinth cutout. The idea is to mount a large (approximately 1"x4"x6") piece of steel under the plinth. The steel will have a threaded hole under the bearing so a bolt could be screwed into it. The end of the bolt will contact the bearing. This is similar to what Albert Porter did to his Technics SP10. He said this about the design:

"The design is simple, the iron block is fixed (recessed) into the plinth bottom with stainless steel screws and has a threaded hole, bored very offset from center.

A large brass rod with polished end threads through the iron block, passing through the plinth, coming to rest against the bearing well of the MK2 or MK3.

Not only does this stop any tendency of the turn table frame to flex vertically, it offers a direct connection-drain point for vibration to flow into the massive iron block. The iron block is probably 15 pounds, it's a lot thicker than you think.

Iron is near the top of the heap in it's ability to absorb energy, making it ideal other than it's magnetic properties. Those magnetic properties are why it's very offset, on the opposite side of where the phono cartridge traces the LP."

So, has anyone tried this with a Garrard? It would be very easy to test once installed by listening with the bolt installed and coupled to the bearing or unscrewed one turn to decouple it.

Spinner45
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Re: Coupling platter bearing to plinth

Post by Spinner45 » 14 Jan 2019 04:16

I assume Garrard did their homework for those units, and with their popularity and reputation, I wonder why you'd think their equipment would need such a drastic modification.

DSJR
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Re: Coupling platter bearing to plinth

Post by DSJR » 14 Jan 2019 12:15

Below is as objective as I can make it. Apologies if it doesn't come across too well...

The noise in a 301 and 401 is more in the motor and idler drive principle rather than the high-drag main bearing. If you want total silence, seriously, buy a top 70's Jap direct drive (I know the top Sony and Technics decks and the short lived Pioneer PL71 and it's 'armless' version that barely made it to the UK and these can sound stunning). These are silent in quiet grooves and if properly plinthed and sited, will out-perform any 301 or 401 if truth to the mastering session when the acetate was cut is wanted (about as far back as we can go with vinyl as the mastering engineer had the final say in how the end pressing was going to sound). For smaller Uk rooms, these solid plinth 'Japanese made' decks could feed back and this was the issue as feedback messes with the sound long before howl begins. It was suggested a carefully sand lined outer-box worked wonders on some of these and bass reproduction improved a lot...

The 301 and 401 were designed primarily as broadcast decks spinning 24/7 for months on end and I believe that's why the main bearings were designed as they are. PLEASE don't try modifying the stock bearing with thrust balls and so on, as the main spindle shaft wasn't designed or case-hardened for this type of use and will wear rapidly if you do this. Replacing said bearing with a complete third party type designed differently for general domestic use may be a costly option though.

One of the UK established way of dealing with the 301 and 401's excesses and one that works in my experience is to make a multi-layered plinth of marine ply, jigging each layer so there's no cavity to speak of inside under the deck. The first of these was the 'Martin Bastin' plinths and with a darned good overhaul of the drive, these machines were substantially quietened down, the motor 'drone' reduced almost to inaudibility.

A properly sited and plinthed 301 or 401 can be very effective in a 'convex centre image' kind of way, but they do have oodles of added sonic character too, so not really 'high fidelity' in the purest sense. I love the 401 styling as I grew up in the 60's and loved the sharp corners and grey/black-silver decals, but please don't think you can better what came after. Supporting the bearing from underneath may well Help the structure as a whole, but not the bearing as such, which is the lreast of its issues in my experience.

Miles and Lee
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Re: Coupling platter bearing to plinth

Post by Miles and Lee » 18 Jan 2019 01:53

Hello Phillyboi,
Sounds like a great experiment to tryout. Here's another approach you may be interested in, proposed by Vinylista. They call it a tuning bow I plan on building a plinth for my 301 using their plinth design ideas.
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Good luck with your build.
Regards,
David

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