Fluid damping question

[diviy]

I have a Jelco sa750d fitted to my SL1210 the arm has the option to add fluid damping has anyone tried it and if so what where your thoughts ?.
Also what viscosity fluid did you use ?

[Barry]

I have a Jelco sa750d fitted to my SL1210 the arm has the option to add fluid damping has anyone tried it and if so what where your thoughts ?.
Also what viscosity fluid did you use ?

Can't say anything about the Jelco arm, but if it is fitted with a damping trough the typical viscosity of the fluid used is 30,000cS.

However SME use a very thick fluid, having a viscosity of 200,000cS.

[archiesdad]

Idiots guide answer needed, what does the fluid damping work on? Ta.

[Barry]

According to vinylengine, the fluid is applied directly to the bearings.
It would appear to be a bit of a messy process and one which needs to be maintained - the silicone oil is not very viscous (a figure of 500cS has been quoted), so will evaporate with time, as well as 'migrating' away from where it has been placed.

[helma]

I have an old Sumiko MMT which was made by Jelco and is very close to the SA-750D in design. When I searched I couldn't find what the correct viscosity is supposed to be, I used 10,000 cSt fluid, which actually seems a bit on light side for damping fluid but seems to work.

The way the Jelco design works is the fluid is added to the little "cup" on top of the arm, which is right at the pivot point. To get to it you need to unscrew the "plug" at the top, which has the "paddle" (just a cylindrical stub with a rounded end in the case of this arm), then when you reinsert it, you can adjust the amount of damping by how far you screw it in. The further in it goes, the deeper in the fluid the paddle and the greater the damping effect. The way it's designed, in the Jelco arms it damps mostly vertical movement, lateral not so much. (EDIT: if I recall correctly, there's a retaining grub screw at the side of the top cover you need to loosen to be able to unscrew the top completely, it's been a few years I played around with the MMT. If you have the instructions that came with the arm I'm sure they explain it all way better than I did here )

Fluid damping seems to be one of those things people have strong opinions on. To my understanding the way it works is below certain velocity the fluid does practically nothing, in other words it won't fight the arm movement when it's following the groove towards the center of the record, but will damp fast movement, which would be created from excited resonances. It can really stabilize tracking of warps for example, lets say you have a record with a very sharp warp which would send your cartridge flying normally - with right amount of fluid damping the same warp could be tracked without problem. Also if you have a cartridge with a compliance that's a mismatch for your arm, it can stabilize things, so for high compliance carts on a heavyish arm, it can work wonders.

Even with a good arm & cart match and flat records, I think some fluid damping provides benefits in more stable performance and cleaner sound, I can't say I've noticed any negative side effects. Some people say fluid damping tends to mess with the highs, but unless you go way overboard with it, I think it just cleans them up and what you hear is more true to record with less added 'hash' from resonances. Initially that might make the sound less exciting, I felt some of that initially when I was experimenting with it, but once I got used to the sound with fluid damping, going back to without I didn't feel like the music gained anything that belonged there - it became a bit more 'lively', but also more messy, so I came to the conclusion what was added was not recorded information but mess 'around it'. But that's largely subjective, I can't know what the record would actually sound with perfect playback, but to my ears it sounds like fluid damping can get you a bit closer to it. Mostly the effects are pretty subtle, I'd say in general the sound tends to be a bit more 'focused' with fluid damping. So I use it with my MMT and even made a DIY damping through for my Fidelity-Research FR-54 and think the arm is better for it. YMMV If you have the option IMO it's worth trying it out and judge for yourself.

[Barry]

I use the SME damping trough on my SME arms, including the viscous 200,000cS fluid. But I use the smallest paddle (coloured black) and find that to be a satisfactory combination.
Unlike you, I haven't done a 'with and without' comparison, but haven't noticed any detriment in sound quality, so appreciate the confirmation in reading of your findings.

[archiesdad]

Ta.