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Springs under turntable

I picked up a set of springs for $35 on Amazon. I intended to use them under a preamp but one thing led to another and I tried them under the turntable. Now, this is no mean feat. It’s a Garrard 401 in a 60pound 50mm slate plinth. The spring device is interesting. It’s sold under the Nobsound brand and is made up of two 45mm wide solid billets of aluminum endcaps with recesses to fit up to seven small springs. It’s very well made. You can add or remove springs depending on the weight distribution. I had to do this with a level and it only took a few minutes. They look good. I did not fit them for floor isolation as I have concrete. I played a few tracks before fitting, and played the same tracks after fitting. Improvement in bass definition, speed, air, inner detail, more space around instruments, nicer timbre and color. Pleasant surprise for little money.
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mijostyn's avatar
mijostyn
8,152 posts
 
Lewm, You put a record on the turntable with any record weight type device you use then press the turntable down evenly to stretch or compress the springs equally then let go and count. 3 hz is very slow and should be fairly easy to count. If the turntable bounces so fast you can't count it then you need to use springs with a lower rate or add mass to the turntable.
When I hit my Sota with a hammer I am not hitting the suspended part of the turntable. That is inside the plinth. If I abruptly jerk the outside of the turntable (moving it say 1/4") the suspended section will start bouncing at 3 Hz. The tonearm will not skip. If I jerk it hard enough to bottom out the suspension in any direction then the tonearm will skip in a major way.
indranilsen
113 posts
 
@rixthetric- Yes I tried using rubber band on the footer which was at the top point in a triangular configuration to increase the spring rate. This indeed help me with balancing the turntable better w/o hitting the bottom but it didn’t resolve the footfall issue. In fact adding spring rate led to more frequent bouncing of the spring as I anticipated and that was counterproductive when isolating vibrations in the sub sonic domain...
@mijostyn- None of the footers including Solid Tech as I experienced could bring the natural frequency down to 3hz. I initially thought that these footers were isolating footfalls but I was wrong. I had a low pass filter on the Luxman phono pre amplifier which was turned on by mistake... When the flipped the switch back to no filter the woofers started moving...
indranilsen
113 posts
 
Hello,
I was thinking of sharing the spreadsheet that I put together to design a spring with a targeted natural frequency with this group. You might already be doing it but just thought of sharing...


Item- Clearaudio Turntable

Total Load (3 Springs) = 23.79 lbs

Item No (Century Spring)-S942


Spring Rate (Lbs/Inch) = 2.75

Spring Rate (N/M) (k)= 612.94

Spring Outer Dia = 1.39 inch

Spring Wire Dia = 0.07 inch

Spring Total Coil = 5.75

Spring Free Length = 2.75 inch

Spring solid Height = 0.40 inch

Load (m)= 7.93 lbs

Spring height at the load 7.93 lbs = 0.48 inch

Spring Natural Frequency = 2.077 hz by using the below formula

Formula = 1/(2*Pi)*SqRt(k/m)

Excel Formula = =((0.5*(1/PI()))*SQRT(k/(CONVERT(m,”lbm","g")/1000)))


Another point that I wanted to highlight here is the importance of load and spring rate to get a spring natural frequency, something like 3hz. In this example, I needed to load each of the three springs to a compressed height of 0.48 inch leaving only (0.48-0.40) = 0.8 inch from the base to get a natural frequency of 2.1 hz. This also shows the degree of difficulty in arranging these springs under the turntable such that each one has a compressed height of only 0.8 inch from the base platform, something @mijostyn has pointed out earlier. 

Apologies for dumping a lot of numbers here but I thought this might be interesting to this audience.

Thanks.



mijostyn's avatar
mijostyn
8,152 posts
 
Nice work Indranilsen, That is about as far as the Sota springs will compress before the chassis hits its stop. Remember the Sota subchassis hangs from its springs. This is the best picture I could find of it
https://hometheaterhifi.com/reviews/vinyl/turntables/sota-nova-turntable/.
If you hung a platform with springs you could put your turntable on it. If the springs themselves were hung from a threaded rod you could adjust them for turntable level and any mass configuration of the turntable.
lewm
12,429 posts
 
This is why I use Delmonte Mandarin orange slices in water, in small cans, as my turntable isolation devices. I use three of them to support a slate slab containing a turntable chassis, either Denon DP80 or Lenco. I support the weight of the slate on the outer rim of the unopened can, and I support the base of the can at its center using a black diamond racing cone, away from the outer rim, so the outer rim never touches the shelf. The springiness comes from the flexing of the top of the can inside its stable outer structure. Someone gave me the black diamond racing cones, and I paid two dollars each for the cans of mandarin orange slices in water.
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