sonddek
Trade: SUPATRAC
No, a simple aluminium finger lift will work fine, but £1.50!!!! I'm in the wrong business!
Sideways Uni-Pivot Arm, SUPATRAC Blackbird, formerly "Ekos Killer (Price?)"
- Thread starter sonddek
- Start date
No, a simple aluminium finger lift will work fine, but £1.50!!!! I'm in the wrong business!
sonddek
Trade: SUPATRAC
So far I have tried it on SL-1210 and Garrard 301. It sounded equally excellent on each. It is a stable arm design and I expect no problems on suspended decks. I intend to run one on my Sondek and Well Tempered Amadeus. I have no plans to run one on my Technics SL10 ;-)
I think it was £1.32, it is blacked and was shipped as a single item in a padded envelope, from China. It was the cheapest one on EPay.
What could we send to China for £1.32 and make a profit on? Fresh air?
jimification
pfm Member
Big props to you for getting this far - really interesting design. Personally I like the look quite a bit...Firefox with a dash of B&O!
It's quite a full-on aesthetic for something like an LP12!.... I like the string idea but it does kill the nice Firefoxy front element a bit...(tricky, as I understand you want it to sag when pushed, yet the thickness and irregularity of the string jars with that strongly geometric front element - maybe could go very thin with it in a different material to be more like an antenna visually?). The "inverted concord intakes" front elevation is nicely distinctive too but the cartridge bolts are spoiling that a bit (would countersunk heads work?) I actually think it could be a tricky design to develop aesthetically because you've established it with a very iconic primary shape language and you might find that the visual impact weakens if you don't adhere to that very closely. Really impressed to see your progress with it so far - good on you!
It's quite a full-on aesthetic for something like an LP12!.... I like the string idea but it does kill the nice Firefoxy front element a bit...(tricky, as I understand you want it to sag when pushed, yet the thickness and irregularity of the string jars with that strongly geometric front element - maybe could go very thin with it in a different material to be more like an antenna visually?). The "inverted concord intakes" front elevation is nicely distinctive too but the cartridge bolts are spoiling that a bit (would countersunk heads work?) I actually think it could be a tricky design to develop aesthetically because you've established it with a very iconic primary shape language and you might find that the visual impact weakens if you don't adhere to that very closely. Really impressed to see your progress with it so far - good on you!
sonddek
Trade: SUPATRAC
I've had an enquiry, whose answer may be of interest here:
Anti-skate
Here is a description from another forum:
The goal of the anti-skate mechanism is to produce similar anti-skate to other arms. The starting point is different though: most arms are yaw-agnostic - they do not have a favoured track position - whereas, by virtue of its suspension mechanism, Supatrac has a track position which it reverts to without other forces being applied.
This means that at track 5 the arm mostly provides its own anti-skate, without the help of the anti-skate mechanism, whereas at track one the arm has a torque towards the centre in addition to that arising from overhang/offset. Consequently the anti-skate mechanism needs to apply about double anti-skate force at track one, and almost none at the end.
This is why an unusual anti-skate configuration was required. The mechanism gradually reduces anti-skate force from about double the normal amount to almost none as it rotates through the angle of record play. It achieves this using a drawbridge type mechanism so that the standing weight gets pulled almost vertical towards end of side and the thread goes almost slack.
I will see if I have time to make an expository video today.
Effective Mass Reduction by Carbon Fibre
My approach to effective mass has been more experimental than theoretical. I use several Shure M97xE cartridges with stock and JICO styluses, among other cartridges, and these are very high compliance, hence the removable brush stabiliser, which I generally remove altogether. The original aluminium prototypes did work well with these cartridges, but primarily visual cues suggested to me that a lighter arm would suit them better, and in the event subsonic wobbles were obviously less in evidence with the carbon fibre prototype. You could also just feel the additional lightness, stiffness and deadness when handling the arm. I was a little reluctant to admit this since carbon fibre is harder to work with, but the advantage is clear and I have decided to produce no more aluminium arms.
The advantage of a very light arm is that you can easily add effective mass to suit a low compliance cartridge, whereas you can't take it away from a heavy arm for high compliance cartridges. I intend to include with each arm a 4g steel saddle which sits on the arm and can be positioned to taste for users of low compliance cartridges.
The much greater lightness also gave me the leeway to strengthen the arm while keeping effective mass low enough for a Shure M97xE without damping brush. This has been done with stiffer aluminium inserts around the cartridge mount, stiff foam in one tube, and stiffening inserts at the junction with the thrust-cage. I regard rigidity as a principle!
By nature of the design of the arm it is easy to calculate effective mass very accurately, which I will do as soon as I have some time, but for now I expect it is in the lowish range.
HTH, and thanks for the good questions.
Anti-skate
Here is a description from another forum:
The goal of the anti-skate mechanism is to produce similar anti-skate to other arms. The starting point is different though: most arms are yaw-agnostic - they do not have a favoured track position - whereas, by virtue of its suspension mechanism, Supatrac has a track position which it reverts to without other forces being applied.
This means that at track 5 the arm mostly provides its own anti-skate, without the help of the anti-skate mechanism, whereas at track one the arm has a torque towards the centre in addition to that arising from overhang/offset. Consequently the anti-skate mechanism needs to apply about double anti-skate force at track one, and almost none at the end.
This is why an unusual anti-skate configuration was required. The mechanism gradually reduces anti-skate force from about double the normal amount to almost none as it rotates through the angle of record play. It achieves this using a drawbridge type mechanism so that the standing weight gets pulled almost vertical towards end of side and the thread goes almost slack.
I will see if I have time to make an expository video today.
Effective Mass Reduction by Carbon Fibre
My approach to effective mass has been more experimental than theoretical. I use several Shure M97xE cartridges with stock and JICO styluses, among other cartridges, and these are very high compliance, hence the removable brush stabiliser, which I generally remove altogether. The original aluminium prototypes did work well with these cartridges, but primarily visual cues suggested to me that a lighter arm would suit them better, and in the event subsonic wobbles were obviously less in evidence with the carbon fibre prototype. You could also just feel the additional lightness, stiffness and deadness when handling the arm. I was a little reluctant to admit this since carbon fibre is harder to work with, but the advantage is clear and I have decided to produce no more aluminium arms.
The advantage of a very light arm is that you can easily add effective mass to suit a low compliance cartridge, whereas you can't take it away from a heavy arm for high compliance cartridges. I intend to include with each arm a 4g steel saddle which sits on the arm and can be positioned to taste for users of low compliance cartridges.
The much greater lightness also gave me the leeway to strengthen the arm while keeping effective mass low enough for a Shure M97xE without damping brush. This has been done with stiffer aluminium inserts around the cartridge mount, stiff foam in one tube, and stiffening inserts at the junction with the thrust-cage. I regard rigidity as a principle!
By nature of the design of the arm it is easy to calculate effective mass very accurately, which I will do as soon as I have some time, but for now I expect it is in the lowish range.
HTH, and thanks for the good questions.
With a carbon armtube with no actual headshell as such, which in turn means a very modest CB weight, the effective mass should be verging on vanishingly low.
As you say, due to the reasonably simple design using very largely symmetrical component parts, working effective mass out accurately, by hand, ought to be very easy.
sonddek
Trade: SUPATRAC
You have just expressed why the string works so well: you don't have to get a finger under it.
Again, with the string you simply grip it between your fingers without having to get a finger under it, so it's just easier and safer to use. The danger you refer to is real and has happened to most of us at some point. But not with a vertical string.
Once again, your detailed description of the care that has to be taken in using a normal finger lift serves to highlight what is wrong with the design. With the string you do not have to disengage your thumb in this measured and precarious way, because the string is unable to transfer significant downforce, it just goes slack.
Precisely.
Yes indeed, and most seasoned vinyl users have done this at some point, producing an alarming noise from the speakers, possibly causing slight abrasion to the play surface, and potentially damaging a fragile cartridge in rare cases. You are making a strong case for a rethink of the traditional finger lift.
It depends how you define good. There is a lot to be said for affordability and robustness!
Agreed, and function/usability come before aesthetic concerns or status.
That seems to me to be an open question. The cartridge/headshell does a lot of buzzing and allegedly cartridges are sensitive to the echo they receive back from the arm structure. A long springy cantilever may not be the best thing to couple with the headshell.
I completely agree, which is why I have devised a type of finger lift which is more comfortable to use and probably even more inaudible than the traditional kind!
yuckyamson
pfm Member
Well that's not combative.
It would seem in terms of opinions on the queueing mechanism you have 5 FOR put in a finger lift, and 0 against. Well, 1, when you count yours.
It would seem in terms of opinions on the queueing mechanism you have 5 FOR put in a finger lift, and 0 against. Well, 1, when you count yours.
Many designs acknowledge what consumers want at the cost of a ‘better’ solution or even functionality / performance. Sometimes you just have to bite the bullet and bow to the wishes of the majority.
I’m open to the idea that the string is a better way to do this but would I want that on a tonearm? Hell no! It just looks a bit pants. Personally I find the traditional finger lift perfectly usable if sufficient care is exercised.
Also I’d worry that the material would, over time, absorb grease etc. from fingers and become, for want of a better word, manky.
All that said I’m intrigued to see how this sounds when it finally lands on an LP12.
I’m open to the idea that the string is a better way to do this but would I want that on a tonearm? Hell no! It just looks a bit pants. Personally I find the traditional finger lift perfectly usable if sufficient care is exercised.
Also I’d worry that the material would, over time, absorb grease etc. from fingers and become, for want of a better word, manky.
All that said I’m intrigued to see how this sounds when it finally lands on an LP12.
I’m looking forward to sonddek’s discussion of effective mass. I doubt very much that it will be ‘vanishingly low’.
It is unwise to speculate, as we do not have dimensions and masses, but I expect this arm to be in the lower medium mass range.
It is unwise to speculate, as we do not have dimensions and masses, but I expect this arm to be in the lower medium mass range.
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I am unure why you would suggest it unwise (or wise) to speculate. It is no more than speculation, the fate of the nation, or anything else, does not depend on it.
In conventional tonearms (i.e. the competition), the very great majority of the effective mass is contained in/produced by two parts - the headshell and the CB weight. The rest is all but irrelevant. The headshell of the SupaTrac almost does not exist, as that is so, the mass of the CB weight must inescapably be low. VERY simple maths.
In conventional arms, the reason that the headshell is so significant is that it is so far from the fulcrum. The reason that the CB weight is so significant is that it is so heavy.
Effective mass is really what the rest of the world calls inertia.
Also, damping troughs are just a way to modify inertia (increase it). FAR more convenient and FAR less messy to go with the proposal of a saddle to fit the armtube as in umpteen other tonearms.
Vinny, what you have posted is totally incorrect.
Re. effective mass (let’s call it em): even a tube with no head shell contributes to em. Recall that the moment of inertia of a tube of mass m and length l pivoted about one end is ml^2/3, so the tube’s contribution to em is (m front) /3 for the front part and (M rear) /3 for the stub on which the counterweight goes. To first order, small appendages can be treated as point masses and their contributions to em can be easily calculated. In order to calculate the contribution of this arm’s counterweight to em it can be treated as a block. As you will appreciate, unless we know the positions of masses, dimensions, magnitudes , etc. an estimate of em is not possible, hence my comment on speculation.
Re. damping: it is a velocity dependent *force*. It DOES NOT modify inertia in any way. The purpose of a damping mechanism is to damp the LF resonance due to arm em and cartridge suspension compliance. Ideally, this LF resonance should be over 12 Hz.
Re. effective mass (let’s call it em): even a tube with no head shell contributes to em. Recall that the moment of inertia of a tube of mass m and length l pivoted about one end is ml^2/3, so the tube’s contribution to em is (m front) /3 for the front part and (M rear) /3 for the stub on which the counterweight goes. To first order, small appendages can be treated as point masses and their contributions to em can be easily calculated. In order to calculate the contribution of this arm’s counterweight to em it can be treated as a block. As you will appreciate, unless we know the positions of masses, dimensions, magnitudes , etc. an estimate of em is not possible, hence my comment on speculation.
Re. damping: it is a velocity dependent *force*. It DOES NOT modify inertia in any way. The purpose of a damping mechanism is to damp the LF resonance due to arm em and cartridge suspension compliance. Ideally, this LF resonance should be over 12 Hz.
Unfortuantely what I said is CORRECT - I would refer to to a very neatly and accurately worked example over on Vinyl Engine. I am merely quoting from it.
Pick holes in the maths there, no-one else could or did for the few years that it has existed, barring minor nit-picking - posted originally April 2015.
The very great majority of inertia in a conventional arm is due to the headshell and the CB weight. Fact.
As for damping troughs - if the paddles were locked solid to the tonearm.......... but they aren't.
Rosewind
Lost in Translation
If you wanted to you could use a straight pin with a grip at the top - sort of like this one.
It is from a Chromatic harmonica but I hope you get the idea.
The design both resembles the NAD tonearm and the Scheu Classic unipivot. I find the Scheu design a little more elegant, but I must say that your tonearm looks interesting.
I own a Kuzma Stogi S 12 VTA and I feel it is a little wobly when I use the finger lift pin. It makes it tilt to the right and perhaps a way could be found to balance a unipivot better when handling it.
It is from a Chromatic harmonica but I hope you get the idea.
The design both resembles the NAD tonearm and the Scheu Classic unipivot. I find the Scheu design a little more elegant, but I must say that your tonearm looks interesting.
I own a Kuzma Stogi S 12 VTA and I feel it is a little wobly when I use the finger lift pin. It makes it tilt to the right and perhaps a way could be found to balance a unipivot better when handling it.
I really don't think you're listening but it's your call. It's like when you see people on Dragons Den who've invested so much time, effort and money into an idea that they are blinkered to how dumb it is. Just stand there looking gormless while the dragons shake their heads.
And the string is a dumb idea. If it sticks straight up it will foul the lid on some turntables, a point you didn't reply to. Even if the lid only hits it while it's on the rest it'll bend the string over, unless it's a spring string? If the string is sticking sideways instead of straight up you won't be able to lift it without pulling the arm sideways as you do.
You can't rest your hand on the plinth as you cue. The string is not going to stay clean, there is a reason why porous materials are used for Hi-Fi control surfaces by no one ever! It's just a crap idea.
But what is concerning me now is wondering what else you're being blinkered about? You insist the string is a much better solution than a traditional lift because you thought of it. Not because it actually is. Is this the case for the entire arm?