DIY linear tonearm

Mike, regarding P pivots, THE best way is using vintage clock balance wheel shafts and rubies.
A few years ago I found an Ukrainian guy on Ebay selling it at a very affordable price (since some of the tiny shafts were already broken).
But to be absolutely honest, I'm afraid all this parallelogram stuff is total overkill. After all, ask any decent vinyl audiophile how many badly warped records does he have in his collection... Have you seen the Portuguese two balls on rails TA in the Youtube link above? At first I almost started to laugh seeing those flimsy plastic straws. But after looking over his channel, I also found other variation involving two similar U shaped profiles. Half the balls, half the contact points so half the friction, no self-alignment needed! Simplicity at its best! diy tonearm + marantz 1060 + sony turntable + AT95e cartridge - YouTube
 
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Mike, regarding P pivots, THE best way is using vintage clock balance wheel shafts and rubies.
Would those have end vees to make sure of no side movement? the reason i ask is that all the clock mechanisms i have found only take the side load, not the end load, would be really interesting if so!
But to be absolutely honest, I'm afraid all this parallelogram stuff is total overkill. After all, ask any decent vinyl audiophile how many badly warped records does he have in his collection...
Ah, you see, i am not a decent audiophile, i know little and don't have golden ears, i have played this set up with the Parallelogram locked off with flat records and you are quite correct it works fine and sounds great, but even minor warps challenge the cantilever, so some acceptance of vertical movement is necessary, maybe 2-3mm max?
Have you seen the Portuguese two balls on rails TA in the Youtube link above?
I have taken a good look Consty and i am happy to see all sorts of aproaches, all they need to do is work and sound good. But the torque the stylus has to create to move the carriage on a pivot that long is massive and i and others like me feel we should eliminate that by having the radial rail
I also found other variation involving two similar U shaped profiles. Half the balls, half the contact points so half the friction, no self-alignment needed! Simplicity at its best! diy tonearm + marantz 1060 + sony turntable + AT95e cartridge - YouTube
But this depends on the stylus providing the stability, my aim (whether its valid or not!) is to unload the stylus of all possible spurious loads and see how good it sounds......
Great to have a discussion, may i see your previous pics of your LTA?
Mike
 
Would those have end vees to make sure of no side movement? the reason i ask is that all the clock mechanisms i have found only take the side load, not the end load, would be really interesting if so!
Those rubies, at least those that I got, are made in fact of two pieces: a flat ruby disc embedded in a brass plate (called endstone) on top of witch gets mounted a second donut shaped ruby embedded in another brass plate (called ring jewel). So this ensemble will hold both axially and radially. But beware! The donut hole and the shaft diameter fitting it has a diameter of merely 0.2mm! Any wrong handling and bye, bye shaft :)
I'll combine the second and third quote in a single answer: With this design, locking the parallelogram and having actually NO tonearm (headshell under carriage), any tiny warp (even under 1mm) will put its toll on the poor cantilever since there is no way for the cartridge to go up/down. Using a single rail and two balls doesn't necessarily mean we should use such a long tonearm as the Portuguese guy did. This is always a trade-off between low resonance/cantilever torque on one hand and ease of use on the other :)
With the fourth quote you touched a sensitive spot. At the time I built and used the airbearing TA, I did not own a smartphone or even a decent camera. That made me stay away of social media and that TA is now only in my memories :)
 
Starting at the end Consty, sorry to hear it sounds you've had difficulties, i find playing with TA's quite therapeutic in the current environment.
Join the discussions and enjoy.
Build something easy and then refine it.
There are some talented guys out there (not me!) who are a pleasure to interface with!
Enjoy
M
 
Threaders,
I have enjoyed learning what i have learnt so far (as usual i don't know what i don't know) and just recently something else has become apparent to me. I am sure its not news to lots of you out there so hope you can help me further.
I changed my Ball Bearing (BBP) based parallelogram set parallel to the grooves for the Mylar hinged one that i believe doesn't suffer from the play and vibration that the BB one has. As i set it up using the same mount point on my cart i had to add a blob of weight to keep the centre of gravity in the right place, thinking i would finalise that later.
Immediately i found better detail and much less groove noise, and particularly in the bass resonance area i have been struggling with. I am fairly sure this is a mixture of the two things i have done at the same time, so what might i learn about the desirable mass of the cart from this?
Can you help me take the next steps forward?
Maybe BBP would have been ok with the added mass?
At the moment this part is in the experimental phase and execution can be tidied up later when the principles seem correct!
M
 

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Hi Mike,

Increasing horizontal mass does improve bass response as it stabilises the cartridge in the horizontal plane. This was the largest improvement I noticed with my first DIY LTA.

Bass is cut on an LP in mono (horizontal modulation) and this modulation can be quite large. If the cartridge is not stable the horizontal modulation will effect vertical as well. IMO this is why improving cartridge horizontal stability improves micro detail, and one of the reasons oil damping is applied to pivoting tonearms.
 
Hi Mike,

Increasing horizontal mass does improve bass response as it stabilises the cartridge in the horizontal plane. This was the largest improvement I noticed with my first DIY LTA.
Thanks Warren, now for me to try and understand more please! is this simply increased mass anchoring its movement by virtue of it moving less under a given force, if so, increased lateral stiffness in the chain from cartridge to cart would do something similar?

Hi Mike,

Bass is cut on an LP in mono (horizontal modulation) and this modulation can be quite large. If the cartridge is not stable the horizontal modulation will effect vertical as well.
So, is there resonance in this or just tracing what's there and moving the cartridge instead of the cantilever alone, wouldn't the latter reduce the output in this region as output depends on the cantilever moving and the cartridge staying still

Hi Mike,
IMO this is why improving cartridge horizontal stability improves micro detail, and one of the reasons oil damping is applied to pivoting tonearms.
This effect being that removing spurious bass info or resonance stops interference with or masking of other detail?

I felt (didnt know) that the bass output from little if any modulation was a resonance, and maybe the mass has changed that resonant frequency?
 
You probably need some mass near the cartridge to create enough inertia to stabilize and let the cantilever operate properly. If the mass near the cartridge is too low the cantilever will appear as a stiff rod pushing the cartridge up down or left right.

I once build a super light tonearm (light wood and bamboo skeleton and the arm won't
track until i added some weight to the front.

Fel.
 
You probably need some mass near the cartridge to create enough inertia to stabilize and let the cantilever operate properly. If the mass near the cartridge is too low the cantilever will appear as a stiff rod pushing the cartridge up down or left right.

I once build a super light tonearm (light wood and bamboo skeleton and the arm won't
track until i added some weight to the front.

Fel.
Thanks,
I think that is what i am wondering, but it tracks fine, no skips, no problems in that respect.
But does it need some mass/inertia to work against, and why does this materialise as bass noise/resonance?
M
I expect someone has some figures that might confirm or deny this idea?
 
Thanks Warren, now for me to try and understand more please! is this simply increased mass anchoring its movement by virtue of it moving less under a given force, if so, increased lateral stiffness in the chain from cartridge to cart would do something similar?

In simple term the additional mass is preventing the stylus throwing the cartridge back and forth with horizontal modulation. The amount of mass will be dependent on the cartridges lateral compliance. Experimenting and measurement here is the key.

So, is there resonance in this or just tracing what's there and moving the cartridge instead of the cantilever alone, wouldn't the latter reduce the output in this region as output depends on the cantilever moving and the cartridge staying still

Yes there will be resonance involved and this can be complex to model. The cartridge is moved along the rail by the horizontal drag force inline with the stylus (quickly put my flameproof vest on). Let me explain, the stylus has positive castor meaning the pivot is behind the contact point, opposite to shopping trolley wheels, so the cartridge will move along the rail as a direct result of this horizontal force. Optimising mass in the horizontal (with the rail) plane with very low drag/stiction will mean the cartridge will follow the stylus with little side force on the groove.

This effect being that removing spurious bass info or resonance stops interference with or masking of other detail?

If the stylus is resonating it will struggle to stay in contact with the groove wall. Any resonance will modulate onto the audio signal smearing the sound, this can manifest as lack of detail and/or muddy or harsh sound.


I felt (didnt know) that the bass output from little if any modulation was a resonance, and maybe the mass has changed that resonant frequency?

That is quite possible and reducing unwanted movement in the cartridge body will have a positive effect on the sound.
 
Thanks All, i have spent quite a few hours experimenting and trying to find a promising route, but nothing so far...............

The noise is a low frequency gentle rumbling noise from the speakers, its not turntable rumble but a similar frequency. Its about as low as any frequency in music. it sounds maybe like a big jet taking off 1km away?
The symptoms are.
Stylus off the record, turn it up full volume (and the stylus off the record) and you just have the quiet “shush” noise like the sea 100m away from all three drivers, i.e. nothing, at normal listening levels complete silence. Tap anything except the stylus and still nothing.
Then with Stylus on the record, stationary, turn it up full volume and tap any part with a finger gently and there is a low frequency thud/dunk noise (same frequency as when playing), fades quite quick, (before it resonated and sometimes made a loop of feedback and you could see the bass speaker excursion). Tap horizontal on anything excites less than vertical, the further up the chain from plinth towards cartridge the louder the result.
Cue onto a moving record on the intro track and the stylus excites the same frequency, probably slightly increased with warp or eccentric.
I can hear it more upo behind the speakers where there is bass build up in the room corners.
As soon as there is any music its drowned out but i know it will be modulating the music.
When the intro track is cued hold on to any part from plinth to rails and it gets louder.
As experiments I have added mass to all sorts of things on the arm and it’s not changing it………

Yesterday it seemed wonderfully silent.
I adjusted VTA and VTF (VTF always at 1.85 but it is changed by the VTA adjustment) and now i have the noise, related, i don’t know, but i cannot get rid of it by going backwards on that route it seems.
Any thoughts for diagnosis or cure most welcome
 
Dear Mike56,

Your arm is reacting (resonating) to the low frequency of the record.
Similar to tonearm cartridge resonance problem at really low frequency.
Try add some slight damping to the pivots.

BR, Fel

Good evening All,
I wasn't at all sure how this happened because i felt that i had not changed anything significant to "gain" this problem. however when doing checks and videos etc, i happened to tap the isolated counterweight when the stylus was on a stationary record and it resonated visibly and audibly. i suspect that previously it had been close to a resonance but was working ok and some small adjustment to VTA/VTF brought it into that range. to prove the point i went back to my coupled counterweight today and all is clean and light again.
At some point i will try again the isolated counterweight because i felt there was a benefit to opening out the sound, but i will design it with a more tolerant hinge perhaps and different ratios of length and weight to be well away from this resonant set-up.
So for now, once again i have something that is notably quiet and plays nice music.
Thanks for the input, always interested to have feedback. latest pic attached, please forgive the blob of blu tack, it puts the centre of gravity of the cart in the correct place....
M
 

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Good evening threaders,
I have had useful input from a number of you, many thanks as always.
I split the counterweight total across the two parallelogram horizontals both to lower overall COM and to reduce the individual load on each hinge and it seems to work.
Grumble is dispelled and this is now sounding (to me) notably clean, low background noise, detailed and smooth, tight full tuneful bass, fun to listen to.
I am not saying it cannot be improved but if someone (me eventually) built a tidy version of this i think you would have something quite rewarding for a simple low material cost arm.
Pics show the details of the new work
M
 

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