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DIY linear tonearm
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Old 9th April 2020, 09:53 PM   #3631
warrjon is online now warrjon  Australia
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Join Date: Feb 2011
Location: Terang Vic
Hi Niffy,


I have no miss tracking with the ballrace bearings, except the occasional caused by the wiring, it took a while to get the wiring in the correct place. As my arm moves backwards and forwards to change records this sometimes moves the wiring.


As the ballrace wheels are 2.5mm wide they obviously sit higher on the rail so can disengage from the rail much easier, the 2 neodymium magnets each side I used to hold the arm forward are too strong and it almost always bounces the carriage off the rail.



You mentioned you use a periphery weight I have looked around and the only ones I can find are around $700AUD, what did you use?



I did find a problem with the pin bearing Vee mount and I am going to make a new carriage so I can use pin bearings.
__________________
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; 9th April 2020 at 09:55 PM.
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Old 9th April 2020, 10:32 PM   #3632
niffy is offline niffy  Europe
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Join Date: Nov 2013
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Hi Warrjon,

I use a screw down reflex clamp that is very effective at flattening warps. Jim uses a peripheral clamp.
I don't think that a peripheral clamp needs to be very heavy in order to get rid of even severe warps. Half a kilo total weight would probably do it, though I would recommend testing first. Commercial peripheral clamps are too heavy in my opinion. The manufacturers claiming that the increased inertia aids speed stability. What tends to happen is the high mass overloads the bearing causing more speed issues than the inertia cures. Balancing and Centring of heavier clamps is also more critical. With a deck like yours speed stability isn't going to be an issue. If I was going to DIY a clamp I would probably make it out to acrylic so that it will be impedance matched to the record and my platter.

Niffy
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Old 9th April 2020, 11:19 PM   #3633
warrjon is online now warrjon  Australia
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Quote:
Originally Posted by niffy View Post
Hi Warrjon,

Balancing and Centring of heavier clamps is also more critical. With a deck like yours speed stability isn't going to be an issue. If I was going to DIY a clamp I would probably make it out to acrylic so that it will be impedance matched to the record and my platter.

Niffy

Yes the SP10 speed stability is about as good as it gets. Some have modified the SP10Mk2 platter to increase weight by 1kg with a copper mat with no issue to the bearing.



I don't have a lot of warped LP's worst is Stevie Wonder, I had to raise the rail as the LP was hitting the rear of the carriage. I do have a 400g centre weight which made the situation worse on this LP.



I never thought of acrylic that's a good idea. I was going to make it from aluminium, but I have some acrylic that might be big enough
__________________
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 10th April 2020, 02:12 PM   #3634
niffy is offline niffy  Europe
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Hi Warrjon,

Most types of central clamp have a tendency to make warps worse. The force exerted by the clamp pushes the centre of the record into the label cutout in the platter which causes the edges of the record to rise up. A reflex clamp has a raised area around the spindle. The clamp pushes down around this causing the edge of the record to be forced down onto the platter. This both flattens warps and forces the record into a more intimate contact with the platter. Even records that look pretty flat are improved by this system. My reflex clamp is so efficient that I have to pry up the edge of the record with a thumb nail to let some air in before I can remove it from the platter. This video was originally posted to show lateral tracking but so shows how little the cartridge moves up and down due to warps.

YouTube

A peripheral clamp will definitely help with the more severely warped records or in situations where a reflex clamp can't be implemented. One important factor with a peripheral clamp is the thicknesses of the lip that holds the record down. With my arm, that only raises the stylus a couple of mm above the record when queuing, the lip would have to be very thin. I do have some 0.2mm carbon fibre that would probably be ideal.

When using arms as short as we are using a good clamp is essential. I consider the clamp to be more a part of the tonearm than it is the deck. At first glance you might expect the clamp to have the greatest impact on reducing VTA errors due to the reduction in movement about the vertical pivot. The reduction in VTA errors in actually mainly due to the reduced surface angle of the record. The effect of a good clamp on VTA is much greater than first appearances would suggest.
With a short arm with a raised pivot point the main cause for concern is warp wow. Flattening the warps has a noticeable effect on the timing of the music. Everything sounds more solid and precise.

Don't give up on the pin bearings. With home made bearings and your cartridge you should be able to get the stylus displacement down to about double that seen in this video. It took me many iterations before I got there.

Niffy
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Old 10th April 2020, 09:37 PM   #3635
warrjon is online now warrjon  Australia
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Hi Niffy,


You are correct the centre weight made the LP curve up at the perimeter. I was thinking ( a dangerous pastime I know) if I made an acrylic mat with a small dish like the in the link. The rubber mat on the SP10 has the label indent (which I think is too deep) but the mat is flat.



[DIY] TNT DIY Acrylic Turntable Mat


I have been thinking about the periphery clamp but I have not yet devised a way to machine it in the lathe, my lathe will hold 330mm but I would have to remove the gap and I don't want to do that too hard to get it back in. The commercial clamps are milled but I don't have a rotary table.


I have not given up on the pin bearings I am planning a new carriage that will use pin bearings. The mistake I made with the current one was two fold. I drilled the polycarbonate for the M3 Vees too slow and I suspect the drill wandered. I also drilled after shaping the carriage top so I had to line it up to drill with a square. It was not out by much visually it looked ok but if you put a straight edge (100mm carbide rod) between the wheels it was obvious.



This time I will machine the top of the carriage rectangular so I have the bottom perpendicular to the sides this way I can get the screws in the correct location. I'm a electronic Tech/Engineer by trade not a machinist so still learning the finer details of the art.



The RH wheel was pointing ever so slightly outwards so as the carriage moved it was trying to twist add that to the slight out of round of the carbide ring and I think these 2 things added up to miss tracking.
__________________
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 11th April 2020, 12:12 AM   #3636
niffy is offline niffy  Europe
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Hi Warrjon,

As a simple experiment you could try some different thickness penny washers over the spindle. One that is slightly thicker than the depth of the label recess would be a good starting point.

Depending on the material you want to make a peripheral clamp from you could just use a router with a circle jig. I made my platter using a router and that came out very well.

When fitting the mounting blocks, for the bearings, to the carriage I made a jig to ensure that the axles were aligned and parallel. My vee bearings were made from M3 screws. After making the mounting blocks I threaded a long length of treaded bar through both so that they were held the correct distance apart. The ends of the threaded bars were fitted into spacing blocks that made sure that the bars were parallel. Marks on these blocks also allowed me to make sure that the bars were parallel to the axis of the carriage. Whilst the adhesive, that hold the blocks in place, was curing the whole thing was clamped to a flat surface to ensure that the bars could not twist and to make sure that azimuth was correctly set.
If I was to make the carriage again I might be tempted to make the mounting blocks from aluminium rather than acrylic. Although these would be heavier they should offer slightly better coupling of the carriage to the rail. I doubt the difference would be significant.

Niffy
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Old 11th April 2020, 12:50 AM   #3637
warrjon is online now warrjon  Australia
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Hi Niffy,


My Vee's are high tensile M3 grub screws. I machined the carriage in the milling machine, which has a Digital Readout with 0.005mm precision. So I can centre the chuck and drill holes at Xmm each side of centre in X and Y axis. I used polycarbonate for the mounting blocks which did not drill well at low speed. I am going to use aluminium for the next mounting blocks.



Last time I drilled the holes all the way through from one side so the drill must have wandered. Next time I am going to drill/tap each Vee mounting hole separately.



I measured the black acrylic I have and it's 3mm thick and just over 300mm square so I might use this for a mat. I have some 10mm thick polycarbonate that is big enough to make a peripheral ring from..........I have a router circle jig - good thought
__________________
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 11th April 2020, 10:09 PM   #3638
warrjon is online now warrjon  Australia
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Join Date: Feb 2011
Location: Terang Vic
I found some 5mm clear acrylic so made this. It's the same outside thickness as the SP10 mat. I cracked it trying to machine the last little bit near the spindle.


9 steps of 0.08mm with label indent 0.1mm below the 9th step. Unfortunately it didn't flatten the 180g LP as I had hoped, but the sound was better background noise dropped and detail improved. It was a success but not in the way I had expected. I will need to make a periphery clamp.
Attached Images
File Type: jpg P_20200412_074907.jpg (394.1 KB, 244 views)
__________________
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 20th April 2020, 01:08 AM   #3639
warrjon is online now warrjon  Australia
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Join Date: Feb 2011
Location: Terang Vic
Dealing with bad warps. I had hoped that the dished mat would work but alas it still didn't flatten dished LP's and I don't have room to use a periphery weight. So after some research I decided to make a clamp and felt washer similar to the Mitchell.


I made a new mat this time flat with a 0.75mm label recess.


Here is a short video the first is with a weight the latter is with the clamp installed.

YouTube
Attached Images
File Type: jpg P_20200418_130640.jpg (622.7 KB, 168 views)
File Type: jpg P_20200418_131241.jpg (544.6 KB, 160 views)
__________________
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 22nd April 2020, 06:29 AM   #3640
nocdplz is offline nocdplz
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Hi Warren.
Warps are warps, unfortunately; but this video, showing an apparent vertical bending of the cantilever before the carriage tilting seems difficult to understand.
Since the vertical effective mass of such a short and lightweight arm should be really small, this leads to suspect a problem of excessive friction in the vertical articulation. Too much damping from the rounded section wheels while tilting on the V rail, or what ?

carlo
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