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DIY linear tonearm
DIY linear tonearm
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Old 1st April 2020, 06:25 AM   #3601
warrjon is offline warrjon  Australia
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Join Date: Feb 2011
Location: Terang Vic
Hi Carlo,


I tried multiple ways of dressing the cable with no success. The wires are dressed to the left so if they were causing this issue the they would be dragging the carriage to the left so CL would be offset to the right.



I'm going to add a wire ring from the back of the top cross bar to hold the wires.



I'll carefully go through each system, carriage, rail bearings and test each one. I must confess I am surprised I have this problem. I have a tonearm alignment rig that I use to set the arm up it uses an M4 bolt ground to a point with a small radius. With this on a blank record the carriage moves with the slightest touch and stops.
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SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P
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Old 1st April 2020, 07:32 AM   #3602
nocdplz is offline nocdplz
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The cables often exert a resistance higher than that of the bearings (the good ones of course): therefore it is necessary to reduce their diameter beyond the limits of decency, and limit twisting as possible. On Lil Casey i came up to a double full loop around the rail which works really well. (by measures - LC has never had skipping, in normal conditions). The cable introduces variable springy stresses (if you balance it in the center it first pushes, and then pulls) - As I said several times it's not easy understandable how certain linear arms, or rotating heads, with plastic coated (!) wires can sound so wonderfully as claimed. Not to mention some pipes of the air bearings.

Imho the brush averages the stresses coming from many dozen of grooves (every bristle follows them as the cantilever does) and from the defects of the disc, clearly damping them. To do this it needs a significant amount of additional VTF. This represents a considerable help, sometimes decisive, to overcome the friction of the carriage of a linear one, which now is moved by the brush much more than by the cantilever, with a force many times higher. Unfortunately that the cantilever moves with respect to an elastic, "jelly" support instead than to the "rigid" mass of the arm, does not seem a convincing solution, almost never followed by anyone.

From the described behavior (excellent normally, but easily stumbling ) it seems like a stiction problem: in motion the friction is very low, but the start is problematic; which, with the loads generated by those micro tips is not surprising. Using very different materials, not self engaging, for the axle and the bush is probably indispensable.

carlo

Last edited by nocdplz; 1st April 2020 at 07:38 AM.
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Old 1st April 2020, 10:10 AM   #3603
warrjon is offline warrjon  Australia
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Hi Carlo,


I am using the same wire as my current LT. It is cotton wrapped litz copper and quite floppy. It does need support to stop it hanging maybe it is pulling the back of the carriage down reducing VTF. I am going to add a hook to hold the wiring similar to what my current LT has.



Stanton/Pickering are famous for the brush, as you say it provides damping of both lateral and vertical cartridge movement. The Stanton requires 1gram additional for the brush and I mostly track with the brush at 1.75 to 2.00 grams.
__________________
SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P
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Old 5th April 2020, 09:05 AM   #3604
warrjon is offline warrjon  Australia
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Found a couple of issues with the wheels.
1 - One pin was off centre. I think this happened when I machined them and turned it around in the collet.
2 The same wheel I found the carbide ring is oval by +-0.1mm



Add these 2 things together and it made miss tracking inevitable. I plan to remake the wheels this time I will make the rings from some 4140 high tensile steel I have at least this way I know they will be concentric.


Tracking is pretty good now and only the cable dressing causes it to miss track.



YouTube


Sound WOW. The first thing that is noticeable is reduced surface noise and reduction in clicks and pops on Boz Scaggs Middle Man. Then you notice the improvement in detail, the rattle of a snare and the ring of a bell.


I'll NEVER go back to a pivot arm after hearing this
__________________
SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P

Last edited by warrjon; 5th April 2020 at 09:13 AM.
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Old 5th April 2020, 12:10 PM   #3605
niffy is offline niffy  Europe
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Hi Warrjon,

Excellent news on getting your arm to track.
My first attempt at making pin bearings failed because I couldn't get them concentric. I was lucky with my carbide rings as they were only 10um off circular. I made my wheels with a slightly oversized hole and an alignment jig to get them as accurate as possible. As you are planning on making wheels from steel you could experiment with different edge profiles. I did find that the carbide wheels gave notably lower rolling resistance and did sound better. It might be worth trying a different source for the rings.

Once you hear an arm with virtually no bending mode resonances you will NEVER go back to any other type of arm.

The reduction in surface noise is a very good sign. When the stylus hits a dust mote it produces a strong impulse. The majority of what you hear as a tick or pop is the arm resonating in response to this impulse. If you can't hear much surface noise it means that the arm isn't resonating. The same resonance is happening all the time (at a lower level) due to the modulation of the groove. This masks and veils the sound.

Niffy
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Old 5th April 2020, 09:50 PM   #3606
warrjon is offline warrjon  Australia
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Hi Niffy,
Many thanks to you for sharing your design. I'm not big on reinventing the wheel so copying your carriage initially worked well. I think I might order a couple more carbide rings and see if I can get 2 good ones.


I am going to make a new carriage that fits the Stanton better, I currently have a 1.6mm spacer under the cartridge to lower the stylus.. The rail is too close to the record surface, I will lift it up another 2-3mm. If the record has a warp the stylus drags intermittently and at the end of the LP the rear of the arm touches the record surface when cued up. I don't have may records with warps but Stevie Wonder yesterday I had to stop the TT push the arm back 1/2 way then move the carriage back to the park position.
__________________
SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P
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Old 6th April 2020, 05:40 AM   #3607
nocdplz is offline nocdplz
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Hi Warren, again congratulations for the superb realization, with a "Swiss watchmaker" level of precision.
Maybe the ideal for a perfect concentricity would be to turn between the centers a monolithic wheel, (pivots included). But for sure - apart from the difficulty - the same material would not be adequate both for wheel and pivot.
naive question: couldn't the carbide rings be rectified after they are mounted on the wheel? (running on their own pivots)
The improvements you are about to build will certainly make that residual bending on eccentricities disappear.

carlo
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Old 6th April 2020, 06:34 AM   #3608
warrjon is offline warrjon  Australia
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Hi Carlo,
Only need to turn between centres for long shafts. My wheels are made in 1 piece aluminum with rings interference fit. I just used a test indicator to true up the rings when I turned them around before I ground the second pivot, this is how I know one ring is oval.



The rings could be ground concentric but I do not have a small diamond grinding wheel to true up the ring, so I might make a new set of wheels with rings made from high tensile steel. 4140 machines beautifully and comes off the tool shiny, it's not as hard a carbide but at least I can do this immediately. If I order new rings now they will get here in June.



I played a few LP's today and the miss tracking is still there. I marked the RH wheel and the miss tracking happens at the same point on the wheel, I have turned the wheel so it is at a different point on the rail but still miss tracks at the same wheel point. So the main issue is the out of round in the ring.
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SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P
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Old 6th April 2020, 07:43 AM   #3609
nocdplz is offline nocdplz
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"Turning between centers" is said to be the best way to get no runout (oh, holy wisdom of our ancients - without our so comfortable chucks..) but I never use it because with small pieces you don't know where to put the dog. I just never remove the cantilevered part from the chuck till the end, and try to bore all the holes (even to 2 mm, with some small tools I made).

It's really strange that such a small runout can cause mistracking - the only effect should be to lift the carriage (slowly, during half a turn) a truly ridiculous acceleration. Imho there is a problem of matching between V cup and pivot. Using a material softer than the other (brass vs steel - steel vs sapphire) there is adaptation during the running-in (the harder machines the softer one), with the same material there is just reciprocal scratching (we are avoiding lubrication for known issues)

carlo
if i were you i would try to use the finest polishing powder inside the Vee and move the carriage by hand several times, then clean all and try again

Last edited by nocdplz; 6th April 2020 at 07:53 AM.
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Old 6th April 2020, 08:30 AM   #3610
warrjon is offline warrjon  Australia
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Hi Carlo,


I am only making an assumption the oval ring is the issue as the miss tracking happens at the same point on the wheel. The stylus has to pull the carriage over the hump???



My Vee's and pins are polished with diamond paste to 1micron. I took a picture of the Vee and all I could see was the reflection of the camera. The problem is not the Vee. I have swapped the wheels from left to right and the problem follows the wheel. Vee's are high tensile M3 set screws that were forged with a HSS/cobalt pin at 90deg and pins are 1.5mm HSS drills cut off and 60deg vees ground on the tip.



Plan tomorrow is make a set of wheels for the Boca bearings and install them on the current carriage. If I make the rings 2.5mm wide with 4mm diameter rail rods should work.
__________________
SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P
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