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-   -   Opus 3 Cantus parallel tracking arm (http://www.diyaudio.com/forums/analogue-source/34126-opus-3-cantus-parallel-tracking-arm.html)

Mats J 16th May 2004 01:19 AM

Opus 3 Cantus parallel tracking arm
 
Curious if anyone has used this simple looking arm?

Mats J 16th May 2004 01:24 AM

2 Attachment(s)
here's a picture and a info link:
http://www.rauna.com/cantus.html

dice45 17th May 2004 04:05 PM

All,

(admitting i did never try one) i have some objections to its design:

1st,
the tolerances between slider and rail tube could be critical, particulary if the gap becomes more and more narrow due to tar/nicotine deposit. On the VA i have read comments that this actually happens: the slider gets stuck due to deposit on the inner surface of the rail tube.

2nd,
the vertical pivot axis is way above the record surface and
3rd,
the effective arm length is small.
Those two properties together make the arm produce audible speed constance imperfections on record warps and pressing bubbles: the stylus movement is far from being (almost) vertical and the stylus height position change yields a horizontal position change. After all, relative stylus2groove velocity is all that counts and if it is not rock-solid stable, you'll hear it. Been there, done that.

4th,
to work at low friction levels, this slider bearing has to have play towards the rail tube. I do not observe anything like enough torsional inertia and/or weight and/or supporting width to let the tiny arm stabilize the cartridge against the rotation around the azimuth axis induced by the groove, particularly on rough transients.

I would expect cheap/poor sonics from this cheap/poor design.

I am just thinking about my own airless design (see website)... my ball bearings have no noticeable play, they support the slider in 4 points approx. 100 mm apart and the arm has its vertical pivot axis approximately (exactly for VTA being level and the cartridge having 17mm height) in the plane of the record surface

... and the stick/slip behaviour of my bearing structure (which has to carry 180mm effective arm length including the counterweight necessary for that and the weight of the carriage with bearings) is giving me the creeps. It is frightening me so much that i spend all my time for finding out if i can cram a Ladegaards style bearing into the same space.

I more and more get the opinion that a passive linear tracker with mechanical bearing is an inherently poor solution. Why? Because i know how sensible sonics are in respect to improper antiskating/lateral force bias balance. Because i had the great luck to obtain one of those fancy Orsonic Side Force Checkers and because i found that the side force checker's sensitivity is --just--enough to display audible antiskating force imbalances. But it is sensitive enough to get its dial needle hit the full scale stop if the cantilever is gently stroked by the tiniest artist's paintbrush available.
So:
a mechanical linear tracker will follow the groove, no doubt about this, no dicussion needed, this has been prooved. But the cartridge's cantilever will experience considerable side force all the time and the arm bearing's stick/slip behaviour will bring a side force checker mounted into the headshell to full scale reading all the time.

And i am not fine with that. I expect more from a tonearm.
Agreed, all this is theory but backupped by 1st experiments. To get a real comparison, i think, i will have to build one of each, the mechanical one and the Ladegaard one. But i already know the Ladegaard air bearing wins hands down.

fdegrove 17th May 2004 09:32 PM

Hi,

Quote:

But i already know the Ladegaard air bearing wins hands down.
Sure, all the reasoning against mechanical tangential bearings brought up in the previous post are well known and are the raison d'etre for air bearing designs and µ-processor controlled ones.

IMHO no amount of lateral compensation force will ever be right at the entire travel across the record because this is a variable angle force not a constant one, add the inertia of the bearings and you're into the deep end.

If you absolutely must use mechanical bearings than a three point design, one point making firm contact, the other two damped, provides better energy evacuation than a four point carriage but that's a fine-tune in case someone gets the thing to work properly in the first place.

For this to work it probably needs to hang off the rails, not sit on top of it, much like the Goldmund T3 design and it will still be a nightmare as the lateral forces will even try and succeed, to skew the carriage sideways.

Any way you look at it, it's a nightmare to get working and requires a dedicated masochist to design. (No offense Dice45)

So, if it makes anyone feel any better or worse about the approach I don't know but from my experience with the design of the T3 I just know this is as close to impossible to crack as I can imagine it.

Now, has anyone ever listened to that arm? :D

Cheers,;)

Nickolas K. 17th May 2004 10:35 PM

Goldmund T3
 
Quote:

Now, has anyone ever listened to that arm?
I tried once the Studio/T3F for a couple of weeks.
Build quality was beyond imagination.
The sound was very analytical and COLD
just like Goldmund electronics.
Not my cup of tea.
I decided to keep my TNT/ET2.5 and I don't regret it.

Nick

fdegrove 17th May 2004 10:43 PM

Hi,

Quote:

I tried once the Studio/T3F for a couple of weeks.
Actually I meant that other arm, the Opus 3 Cantus.

Quote:

The sound was very analytical and COLD
I suspect that's more to do with the cartridge and electronics.
The arm is not without flaws but I would most certainly not accuse it of being cold and lifeless.

Problem is you'd probably need a training course to set it up properly and extract the best of it.

Cheers, ;)

Nickolas K. 17th May 2004 11:17 PM

T3f
 
Quote:

I suspect that's more to do with the cartridge and electronics.
Cartridge was a vdH Grasshopper White Beauty SPX custom made to work on a parallel tracking arm (stiffer suspension, shorter cantilever, shorter coils and an output of 0.3mV).
MC-prepre was a diy Threshold M1.
Preamp was an ARSP15 and power amps were 2 diy ML monoblocks.

So, where was the COLD coming from?

Nick

fdegrove 17th May 2004 11:35 PM

Hi,

Quote:

So, where was the COLD coming from?
Maybe someone forgot to close the door of the fridge?

Seriously, short of trying out a dozen of combinations with that gear you mentioned and some other stuff in an attempt to isolate the source of this cold sound, how can one tell?

A tonearm, like anything else in the reproduction chain, should be neutral in sound.
I know, nothing ever is but saying a T3F is a cold sounding arm?
Don't think so...

Kali nichta,;)

innernerd 18th May 2004 12:44 PM

I saw and heard the Cantus arm in operation at a show (Manchester). I didnt listen long enough to really pass any judgement on its sonic abilities - afterall the whole system was unknown to me - other than to say it didnt sound at any disadvantage to the other vinyl systems there (Blue Pearl aside).
One thing of interest though, the record being played had a badly offcentre hole and the lateral deviation per rev was quite severe - it had no percievable effect on the sound or visual effect on the stylus cantilever.

dice45 19th May 2004 11:55 AM

fdegrove,

Quote:

Originally posted by fdegrove
IMHO no amount of lateral compensation force will ever be right at the entire travel across the record because this is a variable angle force not a constant one, add the inertia of the bearings and you're into the deep end.

If you absolutely must use mechanical bearings than a three point design, one point making firm contact, the other two damped, provides better energy evacuation than a four point carriage but that's a fine-tune in case someone gets the thing to work properly in the first place.

For this to work it probably needs to hang off the rails, not sit on top of it, much like the Goldmund T3 design and it will still be a nightmare as the lateral forces will even try and succeed, to skew the carriage sideways.

Any way you look at it, it's a nightmare to get working and requires a dedicated masochist to design. (No offense Dice45)
i don't agree with you completely.
1st,
the arm should not hang like the Goldmund or the Cantus. The arm should have its vertical pivot at record level and how then can it hang?

2nd,
probably a lateral force compensation cannot ever work properly and the lateral force will vary due to the groove being variable, agreed. But this is no reason to skip the task.
TME a pivoted arm needs skating compensation: the lateral force vector has to be either zero or very small but in any case the cantilever has to be deflected edgewards as few as possible but not spindlewards.
The force vector pointing spindlewards (equivalent to skating overcompensation) IMO leads to a dead sound without any perceivable µdynamics.

The cartridge cannot tell if it is mounted in a pivoted or linear tracking arm, it just experiences lateral force, period.
So if it is mounted in a classical passive linear tracker like the Air Tangent, its stylus experiences a lateral force deflecting the cantilever spindlewards. And it will punish you most probably by the mentioned dead sonics.
If now the linear tracking tonearm is able by any means to provide a lateral force biasing, one can adjust this bias force to a value a little bit more than compensating the transport force:
the tonearm's slider then always is a little bit more eager to approach the lead-out groove / spindle than the (variable) groove pitch wants to permit and as a result the stylus puts a bit more pressure on the inner groove wall and on the outer one and the cantilever is a teenyweeny bit deflected edgewards.
No question i want this pressure difference to eb as small as possible but i want the inner groove to win. As i do with the pivoted arm.

So: a lateral force compensation which is a little bit overdoing its task is just what i want.
Oh and before i forget it: what i described above is a systematic imperfection inherent to passive linear trackers. No matter if they work with an air bearing or with a mechanical bearing ... just the needed forces are different.


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