fluid damping for the RB300

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Eric Weitzman
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fluid damping for the RB300

Post by Eric Weitzman » 28 Jan 2010 07:00

My RB300/Shelter 901 combo has a resonant frequency of about 9Hz. Off center records and warped records play fine, but I can hear the continued effect of the undamped bouncing after the resonance gets excited. I can also see huge excursions in my subwoofer driver (which it handles unobtrusively). But I've recently learned that inaudible low frequency resonance can cause intermodulation distortion over the audio band.

Inspired by Bob Graham's short 1995 article on tonearm damping paddles I made such a device and put it on my arm last week.

The damper is made from a piece of solid 12 gauge copper wire. The last inch of the wire was hammered into a flat bar, about 3/8" wide. The other end was coiled around the end stub a few times, then reduced in diameter a bit so it could be friction fitted on the stub. The first one I made sat too close to the end of the arm. The second one goes up and over the edge of the oil pot, then extends back about an inch before going down into the oil. The flat paddle is bent so it provides both vertical and lateral (or horizontal) resistance to large excursions and then damping.

After putting the damper on the arm and filling a stainless steel food container with 5W30 oil, the resonance was definitely reduced. The subwoofer driver shows much reduced excursion on warps. However, a few records with loud bass and the tiniest warps would skip. Skipping has never been a problem before. So I reduced the area of the vertical damping part, and lowered the fluid level so the horizontal damping part wasn't so deep in the oil tray.

Highly modulated records sound much less congested now. I haven't thrown any badly warped records at it yet, but Steinberg/BSO playing Holst's Planets on DG vinyl sounds much better than it ever has. I think Jochum conducting Carmina Burana on LP may come close to the CD for clarity now.

- Eric

Here's the first one. Since it's not on the arm, I could take a closeup photo.

http://landtime.com/perm/first_try.jpg

This is the second one installed on the arm.

http://landtime.com/perm/paddle_in_action.jpg

VinylIsTheBest
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Post by VinylIsTheBest » 28 Jan 2010 22:18

I have a Fluid Damper FD-200 on my SME 3009 II Improved arm. I'm using Mugen Super Silicone #30000. I have the paddle completely submerged with the arm in the playing position. I noticed immediately more bass, bigger sound stage with every instrument having its own place. I am so glad I bought the Damper kit! The Mugen Super Silicone is for remote control cars. It is the silicone oil for the differential gear. Silicone comes in different weights so you can experiment. I bought the Super Silicone on Ebay. I wouldn't use my arm without it now, nice upgrade. Someone mentioned that they used the #30000 for their SME 3009 II Improved arm and was very happy with the results, I am too. Different silicone weights will effect the sonics of the arm. It's a matter of how much to use and what weight of oil.

Regards.

Bebé Tonto

Post by Bebé Tonto » 28 Jan 2010 22:59

Eric, you RULE!!

I love when creative people like you can solve a problem using only a simple combination of household items.

On the liquid's viscosity: Yes, silicone of more than 5000cSt is available, but i think the alternative would be to greatly increase the area of the "flat bar".

Maybe you could edit your thread title since your idea can be applied to practically ANY arm! I hope someday to try your mod!

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Post by audioorigami » 28 Jan 2010 23:55

GREAT thread!!

and well done

there is a price to pay for making the tone arm less able to move freely

but thats not to say when fluid damping is done well it really helps

i developed a damped FRONT END rega solution a few years ago....JAS was my test mule...it proved unworkable for most peeps from jas tests

i dont have any pictures now...maybe jas has some?

damping at the stub end of the arm is not ideal...the tube would benifit from damping front of the bearings more


bw
j7

abelb
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Post by abelb » 29 Jan 2010 07:48

Great idea. Maybe the arm would move a little more freely if you rotate the paddle so that flat surface is parallel to the plane of movement. It seems like it would impart some drag on horizontal arm movement. Maybe even opt for a straight paddle by removing the "L" shaped bend at the bottom to prevent horizontal drag if the arm needs to move quickly due to a warped record. I'm curious about how strongly you have managed to secure the damper to the end of the arm? Is it just the tension of the coil which holds it there?
Abel

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Post by abelb » 29 Jan 2010 07:55

Oh, and the closer you make the paddle to the end of the tonearm the less force will be required to move the paddle through the damping fluid. Having the damper too far out will act like a lever on the arm.
Abel

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Post by bauzace50 » 29 Jan 2010 08:13

Hi,
great idea! Tonearm damping is a great idea! I also feel as Audio Origami, that front of the arm's pivot can have the better effect, but it can be the most difficult to implement.

Regards, and thanks for the photos and comments!
bauzace50

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Post by cats squirrel » 29 Jan 2010 10:03

maybe what is needed as a damping fluid is a thixotropic material? This would allow rapid movement, but damp the low frequency vibrations.

Eric Weitzman
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Post by Eric Weitzman » 29 Jan 2010 20:35

Thanks for the kind comments.

Regarding the sound:

So far, I've only noticed improvements in clarity on highly-modulated passages and warped or off-center LPs. Everything else seems unchanged.

@VinylIsBest and @Bebé Tonto

I'm not sure what the ideal fluid viscosity would be. There would be a tradeoff between paddle area and viscosity. As it is, I cannot take the oil pot out without rotating or removing the paddle (and having to reset VTF afterwards), so trying different fluids will be a pain. Nice to know that silicone fluid might be available at hobby stores.

@Bebé Tonto

I get a big kick out of making things from common and obscure but available materials. This made great use of a left over piece of buss wire.

@audioorigami

There would seem to be two effects at play.

1. The initial impulse from a warp, or the impulse at each off-center lateral extreme when the arm changes lateral direction, would move the arm up/down or left/right LESS because of the resistance of the arm/paddle combo to large forces or excursions. This should cause a LARGER electrical signal because the needle/cantilever/coil assembly will move more relative to the more stable cartridge body.

2. The subsequent vibrations (or ringing) would be reduced by the damping.

I'm only seeing #2 (as reflected by the subwoofer driver excursion). In fact, I think that the opposite of#1 may be happening and don't understand this. I need to record some warped records both with and without the damper and look at the waveforms.

I can see some benefits of having the damper in the front of the arm: Fewer resonant parts, perhaps less increase in effective mass, more rigidity in the damper itself.

By using such thick wire and short lengths, I hoped to keep spurious vibration in the damper to a minimum.

@abelb

The position of the paddle is as close to the arm as I could make it without touching the oil pot's sides or edges. I have some hardware affixing the armboard and wiring which limits my choice of containers for the oil pot. I could move the screw shown in the second photo in my first post and get the oil pot a tiny bit closer to the arm stub, or make room for a wider oil pot, but it's not worth the hassle right now.

BTW, it took some eagle-eyed shopping to find an oil pot that would fit in the limited space behind the arm. The one in the photo came from a Daiso store in Cupertino.

http://www.daisojapan.com/images/Produc ... m/2062.jpg

The paddle acts as a frequency- or amplitude-dependent lever. Resisting torque is the third parameter besides fluid viscosity and paddle area. Cartridge compliance should be thrown in there too. If only I had paid attention in first year physics.

I made the L shape intentionally to provide damping in both planes. LPs with the slightest off center spindle holes cause trouble, not just warps. I have a friend with a HFNRR test record that's off center and the buzzing on the trackability test tracks moves from left to right and back as the arm sways side to side because of the centering problem! I have an old (but mint) CBS STR112 test record with two sets of progressively hotter 300Hz bands. The arm has improved from playing the +12db band with no buzzing to playing the +15db band on the lateral cut series (+6db, +9db, +12db, +15db, and +18db). It could already play the complete vertically cut series (+6db, +9db, and +12db) without buzzing.

The copper wire is twisted ~1.5 turns around the end stub. It is very tight. It can be rotated with some force, but is very hard to remove by pulling it axially. After forming the wire around an old endstub, the loops were carefully reduced in diameter a bit with pliers to make it fit tight. There are traces of copper left on the steel armstub from putting the damper on a half dozen times.

@cats squirell

"Thixotropic" fluid? I'll have to look it up. Then maybe find sources for some.

This will bump "triboelectric" as the newest concept discovered while trying to understand LP playback.

- Eric

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