carbon fibre and other things...
Jeff,
The stock top plate is a POS (as well as the sub-chassis, the motor...oh and the conical springs).
There are a couple of approaches regarding audio design. Er, more specifically resonant bodies and audio design. Personally I think the sub-chassis is far too weighty. I understand why it is made this way, but I think the mass itself is just to much. Think of a sprung weight in an automotive suspension. Lighten the mass of the sprung weight and the vehicle will dynamically respond better. Hence the benefit of lighter wheels (and truly proper wheels are about an improvement in handing and suspension response). Usually a larger wheel with a lower profile tire is used to allow better turn ins, but if a reduced mass wheel/tire combination is used the benefits are better handling and steering response.
The same can be said about a turntable suspension system. All things being equal a lighter sprung weight will result in a more responsive suspension. In fact a suspension can be tweaked to allow much lower spring rates to be used, while still allowing the suspension to be effective. So if the sub-chassis mass is reduced, a lighter spring weight can also be used, with an improvement in the effectiveness of the suspension. This is one of the reasons why aftermarket sub-chassis have been developed. They have been developed under the disguise of non-resonance, but it is both the anti-resonant properties and the reduced mass that makes them an "improvement". Now if a complete set of springs could be developed to be used in concert with the improved sub-chassis. The biggest concern that I see with the top plate is the fact that Linn never really developed the turntable, it was Dunlap. Linn marketed much better and Dunlap ceased. Ivor Tiefenbrun made no real changes to the turntable, because I don't believe that he saw the need.
The Khan appears to be a significant development, addressing the stiffness of the top plate and the mass/stiffness of the sub-chassis. I believe the only thing that can be done after the top plate and sub-chassis is the development of a more effective spring type. Either continue using conical springs, or develop a new spring type. Then the lowly Linn could actually begin to sing. Then we could address the motor, the drive electronics and whatever else that would be uncovered through the use of a truly non-resonant plinth/sub-chassis and suspension system.
Jeff,
The stock top plate is a POS (as well as the sub-chassis, the motor...oh and the conical springs).
There are a couple of approaches regarding audio design. Er, more specifically resonant bodies and audio design. Personally I think the sub-chassis is far too weighty. I understand why it is made this way, but I think the mass itself is just to much. Think of a sprung weight in an automotive suspension. Lighten the mass of the sprung weight and the vehicle will dynamically respond better. Hence the benefit of lighter wheels (and truly proper wheels are about an improvement in handing and suspension response). Usually a larger wheel with a lower profile tire is used to allow better turn ins, but if a reduced mass wheel/tire combination is used the benefits are better handling and steering response.
The same can be said about a turntable suspension system. All things being equal a lighter sprung weight will result in a more responsive suspension. In fact a suspension can be tweaked to allow much lower spring rates to be used, while still allowing the suspension to be effective. So if the sub-chassis mass is reduced, a lighter spring weight can also be used, with an improvement in the effectiveness of the suspension. This is one of the reasons why aftermarket sub-chassis have been developed. They have been developed under the disguise of non-resonance, but it is both the anti-resonant properties and the reduced mass that makes them an "improvement". Now if a complete set of springs could be developed to be used in concert with the improved sub-chassis. The biggest concern that I see with the top plate is the fact that Linn never really developed the turntable, it was Dunlap. Linn marketed much better and Dunlap ceased. Ivor Tiefenbrun made no real changes to the turntable, because I don't believe that he saw the need.
The Khan appears to be a significant development, addressing the stiffness of the top plate and the mass/stiffness of the sub-chassis. I believe the only thing that can be done after the top plate and sub-chassis is the development of a more effective spring type. Either continue using conical springs, or develop a new spring type. Then the lowly Linn could actually begin to sing. Then we could address the motor, the drive electronics and whatever else that would be uncovered through the use of a truly non-resonant plinth/sub-chassis and suspension system.
Personally, I think there should be more mass in the bearing, but you have to treat the sub-chassis assembly as a system. Keeping the mass low, forces the resonance frequency up.
With the exception of the Cetec carbon comp. sub-chassis, I believe the machined aluminum pieces come pretty close to the stock weight. It's more a function of stiffness-mass ration as well as damping.
I would take it one step further and decouple the motor from the top plate.
It already does, so it's all gravy from here on.
jeff
Jeff...
you Linnie, you.
Firstly, Merry Christmas to any reading this, and in particular to various folks I consider friends: Pano, Jeff, Dave, Chris. et al on the island, TerryO and Pano from the US, kevinkr and others I've only had contact with over the Internet...
I agree completely with your comments generally, but specifically I have small "issues". Reduction of mass in and of itself as long as stiffness and strength are maintained does result in moving the frequency up, but the amplitude down (all else being equal).
When I rebuilt an Ariston RD11S (that I thought turned out pretty good), I used cork between the top plate and the motor and didn't cinch the motor right up against the top plate. A rubber band around the motor can do wonders for helping to reduce the magnitude of the apparent motor resonance. When I actually get to building my take on an LP12, I'll include monor improvements to the design and will post the results in a new thread for those that may be interested.
Jeff what's your LP12 set up? LP12, Hercules PS, Tiktok (Ittock) arm, cartridge? mods?
Regarding the top plate diagram, if it is helpful I'll redraw it in sketchup and upload a standard measure and metric drawing if any want. I'll also include the optional 7 o'clock mounting position. One thing that does frustrate me a little is the lack of contact that the belt makes with the drive portion of the platter. One can "mimic" the Funk Firms "vector drive" by simply mounting a good idler pulley as close as possible to the drive portion of the platter. A longer belt would be required but the additional contact can help increase the amount of power (and hence torque) applied to the platter by the drive motor.
I'll upload the pix to my photobucket albums and will post the link in this thread.
you Linnie, you.
Firstly, Merry Christmas to any reading this, and in particular to various folks I consider friends: Pano, Jeff, Dave, Chris. et al on the island, TerryO and Pano from the US, kevinkr and others I've only had contact with over the Internet...
I agree completely with your comments generally, but specifically I have small "issues". Reduction of mass in and of itself as long as stiffness and strength are maintained does result in moving the frequency up, but the amplitude down (all else being equal).
When I rebuilt an Ariston RD11S (that I thought turned out pretty good), I used cork between the top plate and the motor and didn't cinch the motor right up against the top plate. A rubber band around the motor can do wonders for helping to reduce the magnitude of the apparent motor resonance. When I actually get to building my take on an LP12, I'll include monor improvements to the design and will post the results in a new thread for those that may be interested.
Jeff what's your LP12 set up? LP12, Hercules PS, Tiktok (Ittock) arm, cartridge? mods?
Regarding the top plate diagram, if it is helpful I'll redraw it in sketchup and upload a standard measure and metric drawing if any want. I'll also include the optional 7 o'clock mounting position. One thing that does frustrate me a little is the lack of contact that the belt makes with the drive portion of the platter. One can "mimic" the Funk Firms "vector drive" by simply mounting a good idler pulley as close as possible to the drive portion of the platter. A longer belt would be required but the additional contact can help increase the amount of power (and hence torque) applied to the platter by the drive motor.
I'll upload the pix to my photobucket albums and will post the link in this thread.
Thanks Stew, Merry Christmas to you and your family.
At the moment; Herc II mounted in external box/AT33PTG/Jelco370H/Sowter 7136x trans for step-up, Baltic Birch arm-board, underside of sub-chass. treated with SR500 anti-vibration compound, and of course the top-plate flip per your recs.
Next up will be a DIY Sole with custom bearing. Just have to finagle some lathe time at the shop. Sole will be a 1/8" Al.-12mm BB-1/8" Al. sandwich.
PS: I have a top plate drawing sitting on my old HD, just have to re-connect it, which means a temp. shutdown.
jeff
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Hi Jay,
I like the 33PTG more, but the 103R I have is stock. With a wood body and SS ruby cantilever/LC stylus, I might not be saying that.
jeff
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