A novel take on a Uni-pivot arm

[Cloclo]

Hello Cloclo,
what was your name?
Your enthusiasm would come across better with a few pictures...
Maybe I'm a bit conservative, but exuberant, unbridled enthusiasm without pictures doesn't come across that way. In my experience, the differences in sound are manageable and are linked more to the right effective weight than to minimal geometric or mechanical adjustments.
It would be interesting to see some of your tests!

With best regards

Arndt

Name is Claudio. Can be found in previous posts

I will try and upload some photos soon. However, I don't see how images can substantiate observations related to sound?
Using a decent ADC and recording vinyl drops before and after the change might be a step in the right direction
Ultimate test:  try UH by yourself and see whether you also experienced exuberant, unbridled enthusiasm or not!

[SUPATRAC]

This discussion has become confused, perhaps deliberately. When I said centripetal/centrifugal force I meant a force inwards/outwards from the centre of the record. I did not claim the arm/cartridge was spinning.

An underhung arm produces an inwards reaction at the start of a record and an outwards reaction at the end due to the direction of the drag vector relative to the position of the pivot. Unfortunately a fixed hook SUPA produces reactions in the same directions as the underhang geometry due to gravity - inwards at start of side and outwards at end of side. That's probably why underhang and fixed-hook SUPA are not a great match - they exacerbate each other's inconvenient sideways forces. That could be fixed with a clever anti-skate mechanism, but even then the geometric problems of the underhang scheme, namely that the cartridge generator doesn't align with the groove over much of the record, would still obtain. A rotating bearing at the hook should patch up the conflict between underhang geometry and SUPAs, and by several accounts it does, but the inherent limitations of the underhang scheme are still there, just as there are other compromises with the overhang scheme.

I'm really looking forward to trying a rotating hook with underhang soon - the end of my order backlog is in sight - six arms were sent today.

[TransFi]

An underhung arm produces an inwards reaction at the start of a record and an outwards reaction at the end due to the direction of the drag vector relative to the position of the pivot. Unfortunately a fixed hook SUPA produces reactions in the same directions as the underhang geometry due to gravity - inwards at start of side and outwards at end of side. That's probably why underhang and fixed-hook SUPA are not a great match - they exacerbate each other's inconvenient sideways forces. That could be fixed with a clever anti-skate mechanism, but even then the geometric problems of the underhang scheme, namely that the cartridge generator doesn't align with the groove over much of the record, would still obtain. A rotating bearing at the hook should patch up the conflict between underhang geometry and SUPAs, and by several accounts it does, but the inherent limitations of the underhang scheme are still there, just as there are other compromises with the overhang scheme.

I'm really looking forward to trying a rotating hook with underhang soon - the end of my order backlog is in sight - six arms were sent today.

Another way to look at the UH skating forces is the arm will always skate towards the tangent....wherever that is set within the grooved part of the record. It should be pointed out these forces are noticeably weaker than the inward skating force from an OH pivot arm. The standard SUPA introduces its own anomalies.

Looking forward to your UH implementation too!

Cheers

Vic

[SUPATRAC]

(BTW, I skim read the orginal and amended claims in the patent GB2599073A and did not spot a mention of bearing attached hoists or 'suspension members' as they are called in the patents.  Is it there? I might missed it - long day - or - pehaps there is a mention within the embodiments description)

You're right - it's in the embodiments:

In some embodiments, the support member further comprises a small rotating joint or bearing at the first suspension point (or, where a second suspension point is provided, both suspension points could be provided on the rotating joint or bearing). Such a joint or bearing could substitute for or supplement the suspension member at this point, to obviate torque (i.e. to prevent torque building up as the elongate member rotates around the yaw axis as it progresses across the record). In some such embodiments, the central axis of the joint or bearing passes directly through the contact point, thus maintaining the yaw axis. The rotating joint or bearing may in some embodiments comprise a ball race.

I think it doesn't matter because it's covered by the carefully-general language in the claim.

[wenig watt]

Name is Claudio. Can be found in previous posts

I will try and upload some photos soon. However, I don't see how images can substantiate observations related to sound?
Using a decent ADC and recording vinyl drops before and after the change might be a step in the right direction
Ultimate test:  try UH by yourself and see whether you also experienced exuberant, unbridled enthusiasm or not!

Hello Claudio,
I already did tests with an underhang Supa three or four years ago and was only half enthusiastic. My last tests are still running and are more successful, but I can't say that it's completely ‘better’. Anthony's measurements explain some things, but not everything.
I have tried all kinds of tonearm designs and cartridges over the years. I also have various preamplifiers and power amplifiers and finally loudspeakers that can be adjusted over a wide range with their crossover and if necessary double the number of woofers (up to 8x 38cm).
One important point is that my Supatrac clones always pick up without any problems, even if the geometry is not right at all. I think the ability to cope with the vibrations from the scanning is extremely helpful. My arms are made of Ipe or Panzerholz, both of which are materials with excellent internal damping. Nevertheless, high rigidity can be achieved, which with the Supa bearing simply guarantees excellent tracking.
I would like to see how your tonearm has developed in order to be able to judge whether something else could trigger your enthusiasm. Besides, it's always important to see other people's designs to perhaps get new ideas.
I find it pointless to compare digital recordings of other people's analogue systems. If a recording doesn't sound good to me, I can compensate a lot by choosing the amplifiers or tuning the loudspeakers. The only thing I can sometimes hear even on a tablet is the precision or lack of precision of the tracking. There is hardly a tonearm that can compete with a Supatrac. Even the best and most expensive arms often sound very nice and good, but (so far) never more precise.

With best regards

Arndt

[SUPATRAC]

BTW, it's nice to see one of the implementations which I envisaged and described in 2020, but have never had time to build, becoming a reality and delivering the goods. I wasn't sure whether the free rotating mass of the rotating bearing itself, constrained only by the hoists, would have negative/resonant side-effects, but from what has been reported it looks like that's not a big issue with small bearings.

I will say that if you assume an overhang arm, and can apply suitable anti-skate, the fixed hook junction is a more platonic solution. But with underhang it's different: applying suitable anti-skate is a headache in that case. I have some ideas, but a small low friction rotor is a good compromise.

[low pitch]

Quite often with audio innovations the original product is the most desired one later on.  Here we have introduced a bearing which gives multiple point contacts where before was only the sideways unipivot.   Not to say it doesn't improve the engineering and  sound good but it departs from the principle.

I like my top bearing because I can apply antiskate thru the hoists with a hairspring.  But if I was to buy one I would have Richard's original purist design.

[SUPATRAC]

Quite often with audio innovations the original product is the most desired one later on.  Here we have introduced a bearing which gives multiple point contacts where before was only the sideways unipivot.   Not to say it doesn't improve the engineering and  sound good but it departs from the principle.

I like my top bearing because I can apply antiskate thru the hoists with a hairspring.  But if I was to buy one I would have Richard's original purist design.

I think the sideways uni-pivot takes the heat off the swivel bearing in performance terms. The pivot is where the rigid resistance in the time axis and frictionless mobility in the yaw and pitch axes occur. The swivel bearing doesn't really interfere with those important bearing functions - all it does is neutralise yaw restitution force. Even in an overhang arm it would allow a simpler anti-skate scheme. I'm looking forward to trying it. Even today I've been explaining the variable anti-skate force to a customer and I thought I sensed his eyes glazing over, so if it saves me from boring my customers that would be a bonus. The other question is which is simpler/quicker to make and set up. I'm open minded.

[TransFi]

The other thing....for peace of mind....is you can replace the fishing line with steel cable. Fit it once & forget.

[Adelmo]

I think the sideways uni-pivot takes the heat off the swivel bearing in performance terms. The pivot is where the rigid resistance in the time axis and frictionless mobility in the yaw and pitch axes occur. The swivel bearing doesn't really interfere with those important bearing functions - all it does is neutralise yaw restitution force. Even in an overhang arm it would allow a simpler anti-skate scheme. I'm looking forward to trying it. Even today I've been explaining the variable anti-skate force to a customer and I thought I sensed his eyes glazing over, so if it saves me from boring my customers that would be a bonus. The other question is which is simpler/quicker to make and set up. I'm open minded.

Hi,

In my imagination I would select a design that do not need at all to adjust the hoist threads and that could be set from the manufacturer. Therefore a solution with blades rather than threads and without threads spools which ensure also the H alignment between pivot and  low hoist holes.  What would remain to adjust would be something more close to a standard TA adjustment and perhaps also my wife could easily do from zero. The hoist bearing/rotating ( there is space to also use something without spheres )  also would enable a more simple setting of the TA Bias. I imagine a kind of triangle made with thin CF blades with fixed 3 edge position regarding all the correct levelling and alignments.

Best regards

Adelmo

[SUPATRAC]

The other thing....for peace of mind....is you can replace the fishing line with steel cable. Fit it once & forget.

Is that good advice?

[low pitch]

Not in my opinion, there are so many fibre strings to choose from with the strength needed that surely have better sonic properties than steel strands.  Maybe a single strand of nylon isn't the best over a sharp edge, but fibre hoists will be OK and provide flex at very low mudulus.

[SUPATRAC]

Not in my opinion, there are so many fibre strings to choose from with the strength needed that surely have better sonic properties than steel strands.  Maybe a single strand of nylon isn't the best over a sharp edge, but fibre hoists will be OK and provide flex at very low mudulus.

I agree. Strong waterproof braids last a very long time. They give you a lot of strength at a tiny diameter. They flex very well without memory. They are extremely light which is good from the point of view of resonance. They don't suffer from fatigue like metal flexures. I've never had a hoist break in four years. I don't believe steel would flex as well - it's bound to be more springy, and I don't think hooks and rings are as simple to implement well without compromising the geometry or making it less reliable.

[TransFi]

Is that good advice?

I can only speak from my experience. These are the hoist materials I have tried:



I think the Dorisea & Hercules 20lb - 50lb waterproof nylon braids are what Richard recommends.

However, they are not chafe proof, and I notice the chafing start within a short time of use. Granted, during the time of use the arm was subjected to some manhandling. I had the hoist break while the arm was actually in my hand (luckily). Sharp edges from the flex holes & hooks initially were to blame....but as I became aware of this, deburred, smoothed & polished the affected components, I still did not rest easy using these hoists. Richard also suggests the hoists be changed after 2 years. I would not trust this task to the types of clients I have had in the past. I actually had one client return my Terminator Air-arm because he could not get it to track. When I opened the box, the aquarium pump was dripping wet. I asked him why this was so. The answer was he a submerged it in an aquarium tank! I have many similar stories.

Once I sorted my arms regarding the sharp or rough points, I noticed the hoists furring up around the hook where the hoist cross-over occurs.
Maybe I am using the wrong hoist material?

So, when I eliminated the cross-over with the bearing mod, I reasoned a flexible hoist was no longer necessary, as demonstrated by Adelmo's fine blade mod. I went with the 0.3mm stainless steel vinyl coated braid which jewellers use. This was easily flexible enough to wrap around my guitar tuning pegs, and indeed, around the 2mm hoist retaining pin that fits through the bearing core.



Sonic tests have proved absolutely no detriment to sound quality. I dont want to suggest the quality actually improved as this could be considered cognitive bias. Suffice it to say, I rest easy with this stainless steel braid.

So Richard.....to answer your question 'is this good advice'......yes indeed. If it was my arm, I would not trust the nylon/kevlar braid to break at a most inopportune moment, and take my stylus with it. It is not a 'fit & forget' solution, as pointed out in your manual:



......not a gamble I would take running a £5k cartridge!

My design has evolved since the days of hook & rings. I think the solution I now use is much simpler & more elegant as illustrated in the above Blackbird instructions

[TransFi]

I think the sideways uni-pivot takes the heat off the swivel bearing in performance terms. The pivot is where the rigid resistance in the time axis and frictionless mobility in the yaw and pitch axes occur. The swivel bearing doesn't really interfere with those important bearing functions - all it does is neutralise yaw restitution force. Even in an overhang arm it would allow a simpler anti-skate scheme. I'm looking forward to trying it. Even today I've been explaining the variable anti-skate force to a customer and I thought I sensed his eyes glazing over, so if it saves me from boring my customers that would be a bonus. The other question is which is simpler/quicker to make and set up. I'm open minded.

Richard.....here you have reasoned a positive case for the adoption of the swivel bearing.
Now....just open your mind to replacing the fraying string with steel cable. Dont adopt the closed mind attitude of some of our forum members. Try it then comment. I can certainly envisage a much simpler & reliable way to string the hoists without using complicated knots