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Old 25th February 2019, 09:17 PM   #2771
Coolerooney is offline Coolerooney
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Hi all,

Question:in order to have the right mass for the TA to match the compliance of he cartridge, itis probably needed to increase the weight- does it matter where to put this weight?

Best,
Coolerooney
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Old 26th February 2019, 11:32 AM   #2772
niffy is offline niffy  England
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Quote:
Originally Posted by Coolerooney View Post
Hi all,

Question:in order to have the right mass for the TA to match the compliance of he cartridge, itis probably needed to increase the weight- does it matter where to put this weight?

Best,
Coolerooney
Hi Coolerooney,

When building your carriage there is only so much mass of material that you can use. It is best to design your carriage for the cartridge you intend to use. Doing this allows you to determine the ideal mass for your carriage. Think of this as your mass budget. You spend a certain amount of this budget on each component of the carriage, eg the headshell, the bearings, the counterweight. You want to spend the mass budget as wisely as possible, the aim being to create a carriage that is as rigid as possible with the highest bending mode resonance. Adding weighs to tune the mass of the arm to the compliance of the cartridge is a waste of part of the budget. Design the arm so that it has the correct mass in the first place.

Niffy
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Old 26th February 2019, 02:39 PM   #2773
nocdplz is offline nocdplz
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Hi C., are you asking for linear trackers? for the Vertical or the Horizontal Eff. mass?
For the Horizontal one, usually there is the opposite problem; Since it simply coincides with the whole weight of the mobile masses (cartridge + head shell + shaft + carriage + counterweight) it is rather difficult to stay well under 25 - 30 grams, at the limit of a modern - high mass-low compliance - TA.
For the vertical one it is easy to properly increase all the weights of the moving masses, as Niffy suggests. Too bad that this will further increase the Horizontal Eff. mass.
To bypass the problem someone has simply moved the counterweight away from pivot: this reduces the weight needed (and so the Hor. mass), but increases the Vert. eff mass.
If I had to say that this convinces me, I would say the opposite of what I think, and always seen on any properly designed TA

carlo

Last edited by nocdplz; 26th February 2019 at 02:41 PM.
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Old 26th February 2019, 05:44 PM   #2774
niffy is offline niffy  England
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Default Nailed it!

Hi all.

I've just spent today finishing off and testing my new idler wheels, bearings and belt configuration.

The old belt setup had a single belt that passed around the motor, both idlers and the sub-platter. With off balance records there was a slight wobble (runout) to the platter.
The new belt setup has three separate belts. One passes around the motor and the sub-platter. Each idler has its own belt that passes around itself and the sub-platter. The platter now remains level on all records (no runout). I placed a probe just above edge of the record and viewed the gap between the record and this probe using high magnification. I could not see any variation in the gap. This also means that my clamp is doing a fine job of flattening warps. I thought that fitting one belt was a PITA. Fitting three that all take different paths had me inventing several entirely new swear words. I finally found a method utilising bits of string and sticky tape.

I've also been swapping between the different bearings in the idler wheels. After much toing and frowing I have settled on the pin bearings as having the best sound. After a good run in they are much quieter than they were. The difference in sound between the different bearings is VERY slight.

The main reason for this tweek was to improve the runout of the platter which I have achieved. As my tonearm is very short it will be more susceptible to height differences in record surface than most arms. Variations in the height of the record will effect VTA errors . It will also cause something akin to warp wow. By reducing runout I should improve in both these areas.
It's different to be certain but I think that the deck now has a slightly better sense of timing than before.

Niffy
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Old 27th February 2019, 08:20 AM   #2775
nocdplz is offline nocdplz
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Congratulations Niffy, more and more sophisticated!
I'm almost tempted to put my hands back on my TT project, abandoned long ago with growing frustrations: so I would like to understand better.
In order to that, I've tried a scheme with my interpretations taken from your previous descriptions.

The old version had a single bearing, a sort of unipivot with a small diameter ball rotating on a conical seat, both made with the hardest materials. This avoids the problems of traditional or inversed bearings (noise, friction etc.) but leaves the platter free to tilt on three axes above the pivot. For sure this is limited by a relevant mass and a center of gravity much lower than the pivot.
Then there were three pulleys (1 motor + 2 idler wheels) with a single belt (flat, maybe) probably in axis with the unipivot, that stabilized the platter on three points, preventing the possible wobbling. The different traction on the three sides, due to the traction of the motor, could however allow some small residual wobbling.
The new one is the same in everything except the use of three separate belts to avoid wobbling. The motor traction is now balanced by the other two separate belts on idler wheels.

However here are my doubts: the three belts can not be co-planar, so the tractions generate different momentums on the pivot. (upper - aligned - lower)
How is it possible to have a correct and stable regulation of the three belts over time? (pulley shafts mounted on eccentric spring bases?)

carlo
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File Type: jpg TT SCHEME.jpg (89.3 KB, 184 views)
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Old 27th February 2019, 10:27 AM   #2776
Hiten is offline Hiten  India
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will...

1) an extended tube on sub platter main bearing which extends to bottom and on that end has magnet
and
2) a grooved marking on main platter on outer surface and use of a round shape belt

further stabilize the things ?

Regards
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Old 27th February 2019, 10:46 AM   #2777
Hiten is offline Hiten  India
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how about a three internal contact point nylon washer as shown in the pic in red ?
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Old 27th February 2019, 11:03 AM   #2778
carolus is offline carolus  Belgium
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Quote:
Originally Posted by Hiten View Post
how about a three internal contact point nylon washer as shown in the pic in red ?
Good idea (perso opinion) ... it's like the concept "well tempered TT" (three points centering).
Three points centering is near the absolute center ...
(My experience in air bearing TT)
Karel
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Old 27th February 2019, 12:56 PM   #2779
niffy is offline niffy  England
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Hi Carlo, Hiten,

One of my original designs had the belt run around the periphery of the platter level with the contact point of the bearing (gyrodeck style) . This setup offered very little stability, the platter would precess and would require some form of sleeve to stabilise it. This is because a large tilt of the platter will have very little effect on belt tension so there is little to prevent the platter from tilting.

In my design I have the bearing contact point as close to the surface of the record as possible and the center of mass of the platter as far below this as possible. The belt/belts are also positioned as far below the pivot as practically possible. In this way a small tilt of the platter will result in a larger change in belt tension. This also has the advantage of allowing a smaller sub-platter to be used than running the belts around the periphery of the platter, which in turn allows for a smaller sub-chassis as the idlers are mounted on the sub-chassis. In general the smaller the sub-chassis the better its resonance characteristics. Also a smaller sub-platter allows for shorter belts which gives the motor more direct control.

With a single belt the sub-platter can move around a bit without actually stretching the belt all that much. With three belts the same amount of movement of the sub-platter will result in a much larger amount of stretch in at least one of the belts. Although the belts do have to run at different heights they are still quite close to each other and a long way below the pivot. The aim of this approach to the way the bearing and drive systems interact was to be able to dispense with the need for any form of sleeve to the bearing. (a three internal contact point nylon washer is still a sleeve of sorts). The sleeve seems to be the part of the bearings that causes the biggest problems, has the largest negative impact on sound quality and is the most difficult and expensive to manufacture. The primary role of the sleeve is to keep the platter centred and level. The small diameter ball running in the tiny pit that my bearing uses keeps the platter well centered. The belt configuration and dynamic stability of an inverted bearing keep the platter level. In combination these points eliminate the need for any bearing sleeve.
Even with the old single belt setup the runout on the worst off balance record was still mild. Most platter mats, especially felt ones, will introduce more height variation than this system did. The improvement going to the three belt system is only slight as the maximum level of improvement possible was slight. It's very much a case of me being a perfectionist and having a slightest imperfection bugging me.

I got the idea for eliminating the sleeve from the days when I owned a pink triangle anniversary deck. This used an inverted bearing and a Teflon washer in very much the same way as Hiten suggested. I found that removing the washer gave a large improvement in sound quality even though the platter wobbled all over the place. The negative effects of this simple sleeve were still greater than a couple of millimetres of runout. Don't get me wrong, the anniversary is still one of the greatest decks ever made.

Attached is a photo showing the new belts.

IMG_20190227_120124_crop_372x318.jpg

Niffy
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Old 27th February 2019, 02:13 PM   #2780
Hiten is offline Hiten  India
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OK I understand. I was thinking on the lines of... Washer being thin and contact points surface low. This will only help in consolidation of already stable system.
Regards.
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