Between George and LD they are costing me money! Having ordered my S-120 stylus for testing I made the mistake of re-reading George's 2007 thread on gluing his cart together and started musing about gluing my OM body to the headset. This would need to adjust postition another way, either SME style take the mountain to Muhammad or an ajustable headshell.
Blimey there are some choices out there. Having never owned a detachable headshell I didn't realise. and damn that £150 AT anniversary titanium headshell would look nice with my AT150MLx, but no way am I paying that for a headshell. But the cheaper ATs look pretty good (ok cheap being a relative term. George: would you be happy if I rewoke your old thread on that?
Back on damping, I was looking at the longhorn mod people do and thinking there must be a better way. Then I was reminded of this Mass Damper . Now that is only one dimension, but you could do 2 perpendicular to each other. The masses involved for a cart are very small, but an interesting idea and less mess than a silicone trough.
Blimey there are some choices out there. Having never owned a detachable headshell I didn't realise. and damn that £150 AT anniversary titanium headshell would look nice with my AT150MLx, but no way am I paying that for a headshell. But the cheaper ATs look pretty good (ok cheap being a relative term. George: would you be happy if I rewoke your old thread on that?
Back on damping, I was looking at the longhorn mod people do and thinking there must be a better way. Then I was reminded of this Mass Damper . Now that is only one dimension, but you could do 2 perpendicular to each other. The masses involved for a cart are very small, but an interesting idea and less mess than a silicone trough.
Yes. But Holman was interested in cartridge output in response to playback of warp, whereas I am interested in LF stability of the headshell in response to an external stimulus: in this case a friction induced impulse like tug on the cantilever due to stiction between stylus and groove. As far as the cart-arm-damping system response to an external displacement of the headshell, it doesn't matter whether damping is at the pivot end or in the suspension.
It does matter to warp/eccentricity tracking, and cartridge output though. Below the resonant frequency it is desirable for the headshell to follow the stylus with a gain of unity, and damping at the pivot end opposes; whereas cart suspension damping assists it. Above the resonant frequency it is desirable for the headshell to remain still, ie have a gain of zero, and pivot damping assists this; whereas cart suspension damping opposes it.
So cart and pivot damping aren't interchangeable except as to response to external stimulus and LF stability, where variation in stylus-groove friction is a prominent source in practice, says my thesis.
Yes, what's the chances of that ? Ha, some of that pup's stuff sure made me think.........Now of course there may be two LuckyDogs who like vinyl ... Don't really care about what happened but I must try and assemble the good stuff into one place for review. The world should not lose loading a cartridge with another cartridge!
LD
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Hi Bill, turns out that structures, including cart bodies, headshells, tonearms, often aren't rigid dynamically, despite appearing so statically.
I once did some work using 250,000 fps video, in a lab used to test jet turbines in simulated birdstrikes. I saw video footage of a gelatine pellet of a few kg, to simulate a bird, fired at a jet turbine running at full speed. A single blade from this turbine was a few feet long and so heavy and solid as to be considered statically dead rigid. When the gellatin pellet hit the blade, the pellet stayed intact, and the blade bent near double before vibrating and returning to shape. Amazing demo of what is completely counterintuitive when it comes to our concept of rigidity and flexibility in the context of dynamics.
Longhorn mods, if they are effective at all, presumably alter torsional mechanical impedance for cart body/stylus housing/headshell, and so alter dynamic torsional rigidity. If cart body/headshell/arm etc are things we consider to be rigid really might not be dynamically, I suppose anything is possible. An art that is perhaps as black as black can be...........
Attached an equation for torsion spring constant of a long hollow tube, fixed at one end, such as an armtube or cantilever, for interest.
LD
Attachments
Oh yes well aware of that. I've never had access to the really nice toys like you had there, but done enough. I'm once of the people who is quite pleased how much a 747 appears to rattle and shake as it goes down the runway, as otherwise it would crack in two.
And it's interesting to look at what has been done back in the golden age, what has been forgotten and what perhaps still needs exploring. For example I realised that having posted on the mass damper that a decoupled cantilever is exactly that, just at the wrong end. I'll have a dig on youtube to see if I can find any comparison shots of F1 cars in 2005 to show how effective the renault solution was. Of course then they went on to develop inerters (inductance for suspension) the maths for which is horrendous.
Anyway back on track. Things must flex otherwise stresses tend to infinity and bad things happen(tm). My current understanding is that only the first couple of modes of the tonearm are an issue and these can be addressed before they become less of a problem that the other issues. But you want the cartridge body to be as firmly coupled as possible to the arm to prevent additional vibrational modes (I think). We are still in danger of having a 2 pendulum problem on our hands (as in chaotic) though.
Then again, a tube is not necessarily the best shape for a tonearm
Bill
P.S. I have noted the OM series carts are effectively an I-beam construction. I have mulled gluing some additional wings on if I get a spare body for testing.
P.P.S have a cheeky bid on ebay for a pair of super-OM bodies. If I win will sent you one as interested to see if you can measure any difference with the split-pin body.
And it's interesting to look at what has been done back in the golden age, what has been forgotten and what perhaps still needs exploring. For example I realised that having posted on the mass damper that a decoupled cantilever is exactly that, just at the wrong end. I'll have a dig on youtube to see if I can find any comparison shots of F1 cars in 2005 to show how effective the renault solution was. Of course then they went on to develop inerters (inductance for suspension) the maths for which is horrendous.
Anyway back on track. Things must flex otherwise stresses tend to infinity and bad things happen(tm). My current understanding is that only the first couple of modes of the tonearm are an issue and these can be addressed before they become less of a problem that the other issues. But you want the cartridge body to be as firmly coupled as possible to the arm to prevent additional vibrational modes (I think). We are still in danger of having a 2 pendulum problem on our hands (as in chaotic) though.
Then again, a tube is not necessarily the best shape for a tonearm
Bill
P.S. I have noted the OM series carts are effectively an I-beam construction. I have mulled gluing some additional wings on if I get a spare body for testing.
P.P.S have a cheeky bid on ebay for a pair of super-OM bodies. If I win will sent you one as interested to see if you can measure any difference with the split-pin body.
But maybe a good excuse to get a ruby cantilever & Paratrace stylus from Expert Pickups
Thank you Ricardo. Lack of funding will save me from the dilemma (buy a new one or fit a better cantilever)
Thanks Lucky. See also pages 23-28 here:
http://www.bostonaudiosociety.org/pdf/bass/BASS-03-04-7501b.pdf
Go ahead Bill. (under one term: Don’t spend much money on vinyl playback
)https://www.youtube.com/watch?v=rSafRuLB0c0
https://www.youtube.com/watch?v=851y6F79Qtk
These birds have the habit to eat small stones.On top of the damage due to their own mass, when they are sucked into the core of the engine, these small stones impinge on compressor blades. Half of the borescope field inspection requirements on turbine engines is due to birdstrike.
Most probably this is what happens (on the 'to do' list)
Page 8-9
http://avahifi.com/images/avahifi/root/audio_basics/ab_pdf/ab1982.pdf
George
Go ahead Bill. (under one term: Don’t spend much money on vinyl playback
Too late! Ebay is bad for me. esp as I have just sold my old car. But I have resisted so far an ortofon MC70 anniversary. The MCx000 series were the only super cartridges I really lusted after, mainly because they were bonkers. However.. I do have a Rohmann on the way in need of repair that was very cheap. That will sit on a shelf until I have money or until I give up and sell it on
. At least I have parked my arm worries, so its getting approval from the wife as to where to put the shelf for my Kenwood then I can start playing. That is the link that got me thinking about mass dampers. Still can't find a video showing how effective they were in action, but an F1 car hitting the curbs and a lump of grit displacing a diamond have some similarities. But a silicone trough does the job. At some point the turd can be polished no more
There's actually 2 simple methods to damp nearly all the mechanical resonances of a tube.Then again, a tube is not necessarily the best shape for a tonearm
One, not so simple, is to taper it, which is SME IV & above.
The other is to simply bend it.
So don't be too contemptuous of detacheable headshell arms ... which are usually bent twice.
The headshell joint is usually the weakest point and some attention to this is always worthwhile. Of course, a detacheable wand like the 3009 Series III and the Thorens is a better mechanical and acoustic solution.
__________________________________________________________
http://www.bostonaudiosociety.org/pdf/bass/BASS-03-04-7501b.pdf
Thanks for this George. Loadsa arcane paraphernalia for us devotees (& pseudo devotees) of da Ancient arts.
I note Mr. Schwarz ex CBS & Micro Acoustics is a believer of vinyl/tip mass resonance too
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And the RB300. I like my SME. Couldn't afford one now!
But (and this is the core of my irrational fears) solid cast straight, vs bent car aerial. The cure may be worse than the illness.The other is to simply bend it.
well my 345 DOES have a detachable headshell, so I should have clarified that it was SME bayonets from the 50s that concern me.
But the series III headshell isn't acually fixed on. I realised this when looking at the unit on ebay and reading the manual section for azmiuth adjustment! You just twist it, not even a fixing screw.
Heroic cartridge stiffening attempt of the day http://www.lencoheaven.net/forum/index.php?PHPSESSID=enc9v6p13897fecis61ttaije6&topic=5044.0
.. and so does Series II detachable headshell
The original SME version of their detachable headshell was certainly not the best implementation. Some of the copies were better but all could be improved.And BTW, if you want a bend with the "resonant damping" advantages, you have to make sure you don't kink it .. ie no bent car aerials
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I think that sums it up, in reality. And no 2 situations are quite the same. Personally, I think that simplicity lends itself to analysis, but might still get beaten by luck or art, and in practice the popular stuff empirically is proven good.
This is true. Well, it sort of scrambles available vibrational modes and frequencies.There's actually 2 simple methods to damp nearly all the mechanical resonances of a tube.
One, not so simple, is to taper it, which is SME IV & above.
The other is to simply bend it.
So don't be too contemptuous of detacheable headshell arms ... which are usually bent twice.
Leigh Phoenix's article is just great, and the maths works out: I love it. He considers that cart suspension and pivot damping coefficients can be combined by addition, for simplification, if they are small. IMO this is fair. The typical cart suspension damping factor Phoenix quotes holds good IME, c 0.12, but perhaps a bit skinny typically for good stability I think.
LD
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I should admit that your comment about putting the mass at the cart only just clicked with me. I was thinking too much about inertia and not about the simple cartridge model.
Did make me realise the best arm is probably ceramic foam with a CF or Al skin. slight challenge for DIY. Much as I love Aerolam its orthogonality is not great.
Did make me realise the best arm is probably ceramic foam with a CF or Al skin. slight challenge for DIY. Much as I love Aerolam its orthogonality is not great.
Hi George, they seem perhaps naïve now, like exploratory stuff I feel. It's good to think about stability and such things in this way, but maybe as a stepping stone. I think there were later, and better, versions, but the basics are prob correct..... (?!)
LD
I make plans for using dried common reed
Thank you Lucky.
I can’t remember when had I downloaded those. It’s a subject worth revisiting
George
You're welcome, George.Thank you Lucky.
I can’t remember when had I downloaded those. It’s a subject worth revisiting
George
Yes, it's easy to think of VTF as being 'constant', whereas in reality it varies greatly whilst tracking warp, platter/spindle vertical run-out, etc. A lot of the trackability budget can be consumed simply by keeping the headshell following the record surface in practice.
This confirms something about surface noise, especially crackle-pop, which generally does not vary on a once per revolution basis. Whereas VTF does vary, even for normal records with typical amounts of warp/run out. I think this tells us in a very evident way that this type of noise does not typically vary with VTF.
Another aspect, from looking at headshell displacement response in the time domain, is just how long it takes for a headshell to settle after encountering an external event such as stylus jumping dirt/noise, or a stiction tug on the cantilever perhaps. Looking in the frequency domain, as is so common, doesn't make it obvious that what is really important is the settle time. The role of damping then becomes clear, and its easy to see how this aspect is important, but very neglected, when matching carts and arms. And how some forms of surface noise might unavoidably evoke unwanted displacement of the headshell, which its desirable to settle quickly.
LD
Reed could be a good starter. Bamboo also if you can get it lined up in 2 directions.
https://www.youtube.com/watch?v=xzB6KSlD6ec shows on a motorbike what is happening with the cartridge. Interestingly the frequency range is about the same as well. They have the advantage of a controlled valving steering damper, but the tail can still wag the dog. Of course the short wheelbase doesn't help. Maybe dynavector aren't onto something
https://www.youtube.com/watch?v=xzB6KSlD6ec shows on a motorbike what is happening with the cartridge. Interestingly the frequency range is about the same as well. They have the advantage of a controlled valving steering damper, but the tail can still wag the dog. Of course the short wheelbase doesn't help. Maybe dynavector aren't onto something
Did you know that effective mass of a tonearm tube has nothing to do with it's length ?
Tonearm tube, length L, mass m has Moment of Inertia mL2/3 about the pivot (1)
MOI of effective mass M at distance L from the pivot is ML2 about the pivot. (2)
Equating(1) and (2) M = m/3 ...... nothing to do with length then, only total tube mass.
Since effective mass of the headshell and cartridge is pretty much simply it's mass too, the effective mass of a tonearm has pretty much nothing to do with its length, only armtube mass and headshell/cart mass. (!!!)
So, if one can tackle armtube self resonances and keep armtube mass low, there's no reason long arms shouldn't have low effective mass. Long arms minimise offset angle, minimise skate torque arising from friction surface noise in principle, IMO. Better headshell stability and so better pitch stability is the outcome.
LD
Tonearm tube, length L, mass m has Moment of Inertia mL2/3 about the pivot (1)
MOI of effective mass M at distance L from the pivot is ML2 about the pivot. (2)
Equating(1) and (2) M = m/3 ...... nothing to do with length then, only total tube mass.
Since effective mass of the headshell and cartridge is pretty much simply it's mass too, the effective mass of a tonearm has pretty much nothing to do with its length, only armtube mass and headshell/cart mass. (!!!)
So, if one can tackle armtube self resonances and keep armtube mass low, there's no reason long arms shouldn't have low effective mass. Long arms minimise offset angle, minimise skate torque arising from friction surface noise in principle, IMO. Better headshell stability and so better pitch stability is the outcome.
LD
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