I built my 1st air bearing arm and love it so much that I decided to build 2nd one. The construction of 2nd arm is similar to Walker Audio’s. Please see attached image.
First air bearing arm link.
http://www.diyaudio.com/forums/analogue-source/268614-diy-air-bearing-linear-arm.html
Although I still have a technical problem, I managed to play it. The sound from 2nd one is even better than 1st one. It is free of artifacts. The sound is so smooth and full 3D with the authority in bass. It even changes my impressions of some of my cartridges.
However, I still have a problem to solve.
I use two .5 inch Oav air bushings. The shaft is 11 inches long 2024 aerospace aluminum tubing. It weighs 30 grams.
The first construction I did is A in the attached image. But it bonus back and forth. I attached a video to show you that.
YouTube Video.
https://youtu.be/pEWht49wbT4
So, I tried the construction B. In construction B, I can play but there is still a tiny force to pull the shaft inwards at most outer groove. Once the needle passes certain point, there is a tiny force to push the shaft out. I had to raise the rear end of the arm a little higher to compensate the pushing force.
I have no idea what causes this. The shaft is pretty straight. Its tolerance in roundness and diameter is about .05 mm.If anyone had built similar kind of tonearm or you have the experience with air bushings, I need your advice how to solve this problem. Otherwise, I have to be very careful when I play the records. It also makes me feel uncomfortable to know there is tiny force is pulling the needle at beginning of playing.
First air bearing arm link.
http://www.diyaudio.com/forums/analogue-source/268614-diy-air-bearing-linear-arm.html
Although I still have a technical problem, I managed to play it. The sound from 2nd one is even better than 1st one. It is free of artifacts. The sound is so smooth and full 3D with the authority in bass. It even changes my impressions of some of my cartridges.
However, I still have a problem to solve.
I use two .5 inch Oav air bushings. The shaft is 11 inches long 2024 aerospace aluminum tubing. It weighs 30 grams.
The first construction I did is A in the attached image. But it bonus back and forth. I attached a video to show you that.
YouTube Video.
https://youtu.be/pEWht49wbT4
So, I tried the construction B. In construction B, I can play but there is still a tiny force to pull the shaft inwards at most outer groove. Once the needle passes certain point, there is a tiny force to push the shaft out. I had to raise the rear end of the arm a little higher to compensate the pushing force.
I have no idea what causes this. The shaft is pretty straight. Its tolerance in roundness and diameter is about .05 mm.If anyone had built similar kind of tonearm or you have the experience with air bushings, I need your advice how to solve this problem. Otherwise, I have to be very careful when I play the records. It also makes me feel uncomfortable to know there is tiny force is pulling the needle at beginning of playing.
Attachments
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Hello super10018
Watching the video, tells me that the shaft is not straight. It also rotates on its longitudinal axis as it oscillates back and forth. .05mm (.002") is not straight enough in my opinion. If the shaft is curved, it would act like a pendulum if set into motion. I would do the following:
Substitute a precision shaft of known straightness to see if it oscillates.
Take your existing tubular shaft and roll it on a clean granite surface plate to see how it behaves. Find a friendly neighborhood machine shop with a surface plate. High quality air bearings, being essentially frictionless, demand a precision shaft. If you visit the web page of the company that made your bearings, you should be able to find out what straightness and roundness tolerances they require.
There is one more possibility I just thought of:
Try rotating the tubular shaft in increments of, let's say 10 degrees, until you find a position where it won't oscillate. Good luck.
Sincerely,
Ralf
Watching the video, tells me that the shaft is not straight. It also rotates on its longitudinal axis as it oscillates back and forth. .05mm (.002") is not straight enough in my opinion. If the shaft is curved, it would act like a pendulum if set into motion. I would do the following:
Substitute a precision shaft of known straightness to see if it oscillates.
Take your existing tubular shaft and roll it on a clean granite surface plate to see how it behaves. Find a friendly neighborhood machine shop with a surface plate. High quality air bearings, being essentially frictionless, demand a precision shaft. If you visit the web page of the company that made your bearings, you should be able to find out what straightness and roundness tolerances they require.
There is one more possibility I just thought of:
Try rotating the tubular shaft in increments of, let's say 10 degrees, until you find a position where it won't oscillate. Good luck.
Sincerely,
Ralf
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Ralf,
Thanks for replying and suggestions!
I had checked the straightness of the shaft on glass table top. I couldn’t tell and see too much of irregularity. The tubing rolled from one side to other side smoothly. But I think it is still inconclusive since I can’t detect small irregularity by just looking. I also tried one air bearing. The shaft was moving very well. However, it may not be ideal because the needle may be off center at most inner grooves. I do think I need to find a machine shop to process the shaft.
What amazes me is that the arm is almost like immunity from pop and click noise. The background is very quiet. I remember my 1st ball bearing arm. All the pops and clicks were amplified.
What also amazes me is that the music is so smoothly flowing out from same cartridges I used for different arm. I guess it is because this kind of air bearing construction has much large of air-shaft contact area. On my 1st air bearing arm, I use .5 inch air bearing while most of commercial arms use 3/4 inch or 20 mm air bearings. Their contact area is larger than mine. But one my 2nd arm, there are two bearings so the contact area is much larger.
It also reminds me the review I read.
Kuzma Stabi XL Turntable/ Air Line Arm, Walker Proscenium Black Diamond Record Player | The Absolute Sound
In the review, the author thinks Kuzma’s arm has more hifi elements while Walker’s sounding is more real. His conclusion is consist with my experience. My 1st air bearing arm is similar to Kozma’s but 2nd one is similar to Walker’s. On my 1st air bearing arm, the sound is not as smooth as 2nd one. High frequencies are slightly edgier than it on 2nd air bearing arm, esp. under higher air pressure.
I also have the feeling that the track ability of 2nd air bearing arm is better than 1st one although I don’t do any tests yet.
If I understand it correctly, Walker audio uses carbon fiber shaft. I may try it later on as well.
On my 2nd arm, I also add a silicone oil trough for damping. The oil I use is a mixture of 20 wt and 30 wt. and the paddle is just half sunk in the oil. So, the damping is very light. Although the damping is very light, it is needed for certain cartridges and LPs.
For 2nd air bearing arm, my small fridge compressor can’t keep up. I have to order a more powerful compressor. So, if anyone wants to do an air bearing arm which is similar to the construction of my 2nd arm. You should start with a more powerful compressor. I ordered a 1/3 hp fridge compressor.
Thanks for replying and suggestions!
I had checked the straightness of the shaft on glass table top. I couldn’t tell and see too much of irregularity. The tubing rolled from one side to other side smoothly. But I think it is still inconclusive since I can’t detect small irregularity by just looking. I also tried one air bearing. The shaft was moving very well. However, it may not be ideal because the needle may be off center at most inner grooves. I do think I need to find a machine shop to process the shaft.
What amazes me is that the arm is almost like immunity from pop and click noise. The background is very quiet. I remember my 1st ball bearing arm. All the pops and clicks were amplified.
What also amazes me is that the music is so smoothly flowing out from same cartridges I used for different arm. I guess it is because this kind of air bearing construction has much large of air-shaft contact area. On my 1st air bearing arm, I use .5 inch air bearing while most of commercial arms use 3/4 inch or 20 mm air bearings. Their contact area is larger than mine. But one my 2nd arm, there are two bearings so the contact area is much larger.
It also reminds me the review I read.
Kuzma Stabi XL Turntable/ Air Line Arm, Walker Proscenium Black Diamond Record Player | The Absolute Sound
In the review, the author thinks Kuzma’s arm has more hifi elements while Walker’s sounding is more real. His conclusion is consist with my experience. My 1st air bearing arm is similar to Kozma’s but 2nd one is similar to Walker’s. On my 1st air bearing arm, the sound is not as smooth as 2nd one. High frequencies are slightly edgier than it on 2nd air bearing arm, esp. under higher air pressure.
I also have the feeling that the track ability of 2nd air bearing arm is better than 1st one although I don’t do any tests yet.
If I understand it correctly, Walker audio uses carbon fiber shaft. I may try it later on as well.
On my 2nd arm, I also add a silicone oil trough for damping. The oil I use is a mixture of 20 wt and 30 wt. and the paddle is just half sunk in the oil. So, the damping is very light. Although the damping is very light, it is needed for certain cartridges and LPs.
For 2nd air bearing arm, my small fridge compressor can’t keep up. I have to order a more powerful compressor. So, if anyone wants to do an air bearing arm which is similar to the construction of my 2nd arm. You should start with a more powerful compressor. I ordered a 1/3 hp fridge compressor.
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One quid:
Is your fridge compressor "oil & water free" ?
It's a must (& quasi impossible) ...
My (first) experiences with my air bearing TT (& arm) and several type fridge compressors was not a success.
Fridge compressors ... not the good solution.
If that is extruded tubing it will be anything but round. Since the mass of that part doesn't effect playback or performance I would look at getting some centerless ground tubing, possibly stainless steel. Air bearing clearance tolerances are very critical and having tubing that is out of round is going to cause all kinds of grief. Typical tolerances for extrusions are in the several thousands of an inch or more. Usually a lot more. You need tolerances held to 1/10,000 of an inch.
On the brighter side, your getting good performance on a sub-par bearing, just wait till you get a good one.
BillWojo
On the brighter side, your getting good performance on a sub-par bearing, just wait till you get a good one.
BillWojo
Carolus,
No. It is not oil and water free. The compressor uses R-134a oil. Its oil may be pumped into the line from time to time. And, water may accumulate in the line under room temperature as well. My line is about 50 feet to the arm. It is long. This is why I use a 10 micron filter as 1st phase filter and .03 micron filter as 2nd phase filter on the compressor to keep oil out of the line, and another .03 micron filter just before the line going to the arm. I check the oil level drained from the filters from time to time to make sure there are enough oil in the compressor. If not, I add some oil. The more filters you add in the line, the slower of flow is. But it is ok for tonearm. Tonearm just needs right pressure. Flow is not so critical at all.
For smooth flowing of air, I use a 10 gallons air tank. The compressor has two pressure zones to keep the motor run time shorter and down time longer.
One thing to stop a lot of people using air bearing arm is air compressor noise. It is not a problem for me. I have a large closet in my listening room and put the compressor in the closet. I can’t hear any noise.
No. It is not oil and water free. The compressor uses R-134a oil. Its oil may be pumped into the line from time to time. And, water may accumulate in the line under room temperature as well. My line is about 50 feet to the arm. It is long. This is why I use a 10 micron filter as 1st phase filter and .03 micron filter as 2nd phase filter on the compressor to keep oil out of the line, and another .03 micron filter just before the line going to the arm. I check the oil level drained from the filters from time to time to make sure there are enough oil in the compressor. If not, I add some oil. The more filters you add in the line, the slower of flow is. But it is ok for tonearm. Tonearm just needs right pressure. Flow is not so critical at all.
For smooth flowing of air, I use a 10 gallons air tank. The compressor has two pressure zones to keep the motor run time shorter and down time longer.
One thing to stop a lot of people using air bearing arm is air compressor noise. It is not a problem for me. I have a large closet in my listening room and put the compressor in the closet. I can’t hear any noise.
The problem has been solved.
First, I left a 2mm gap between the air bearings and then, flipped air bearings. I tried a couple of times. It worked. The shaft stays still wherever I move it to.
I guess the gap changes the distribution of air pressure. Flipping the air bearings may make the air bearing to fit the shaft better. And, the air bearings were not lined up properly. I still don’t know what happened exactly but it works now. The arm is very stable.
I have searched online to try to find a hollow aluminum shaft but no luck. I am reluctant to use solid shaft because I am afraid it adds too much of moving mass. For air bearing, adding mass doesn’t add friction, but I think it does add more inertia for given velocity. The force of inertia may disturb the needle movements.
First, I left a 2mm gap between the air bearings and then, flipped air bearings. I tried a couple of times. It worked. The shaft stays still wherever I move it to.
I guess the gap changes the distribution of air pressure. Flipping the air bearings may make the air bearing to fit the shaft better. And, the air bearings were not lined up properly. I still don’t know what happened exactly but it works now. The arm is very stable.
I have searched online to try to find a hollow aluminum shaft but no luck. I am reluctant to use solid shaft because I am afraid it adds too much of moving mass. For air bearing, adding mass doesn’t add friction, but I think it does add more inertia for given velocity. The force of inertia may disturb the needle movements.
Super10018, have you ever thought of placing the damping trough and cuing device on the right side of the arm, the counterweight side, so you wouldn't have things jetting out over the record? It would be much more convenient to change records and possibly look better.
I was thinking of the Infinity turntable.
I was thinking of the Infinity turntable.
An externally hosted image should be here but it was not working when we last tested it.
Ralf,
This is a good suggestion. I may change it later on. I don’t have any problem with silicone oil so far. However, it is safer to move the trough to other side of arm.
I have been comparing two arms during the holiday weekend. The 1st arm has very good bass. It is fast and strong. The 2nd arm has good bass as well. But it is not as fast and strong as 1st arm. However, the 2nd arm has excellent texture and micro details. The 1st arm somewhat lacks texture in high and mid-high frequencies. The moving mass for1st arm is heavier than 2nd one. I guess it is about 10 grams heavier. I think there is a sweet spot for moving mass of an air bearing arm. An air bearing arm simplifies the problem because I don’t need to worry about the friction while increasing the mass. For ball bearing arm, it is not desirable to increase mass because friction will increase in the same time. I am going to try a heavier shaft for 2nd arm.
This is a good suggestion. I may change it later on. I don’t have any problem with silicone oil so far. However, it is safer to move the trough to other side of arm.
I have been comparing two arms during the holiday weekend. The 1st arm has very good bass. It is fast and strong. The 2nd arm has good bass as well. But it is not as fast and strong as 1st arm. However, the 2nd arm has excellent texture and micro details. The 1st arm somewhat lacks texture in high and mid-high frequencies. The moving mass for1st arm is heavier than 2nd one. I guess it is about 10 grams heavier. I think there is a sweet spot for moving mass of an air bearing arm. An air bearing arm simplifies the problem because I don’t need to worry about the friction while increasing the mass. For ball bearing arm, it is not desirable to increase mass because friction will increase in the same time. I am going to try a heavier shaft for 2nd arm.
I replaced aluminum shaft with stainless one. The aluminum shaft is 33 gram, which is almost same as a 1/2 inch air bearing. The stainless steel one is 76 grams. So, the moving mass is more than doubled.
The cartridge I installed on is Dynavector 17D3. 17D3 is usually weak in bass, but not on my 2nd arm with stainless steel shaft. At first, the bass was a bit too much and I had to turn down the subs. After carefully adjusting the damping, its sounding is wonderful now, especially for classical music.Again, I learn that how critical damping is. Damping is a must for all air bearing arms.
The stainless shaft is still a hollow shaft without any internal damping. Once if I feel everything is settled, I may use insulating foam or high viscosity silicone fluid to fill inside of the shaft to further dampen the vibrations.
I also upgraded the compressor. I bought a 1/3 hp compressor and run two fridge compressors together. It takes only less than 5 mins to pump up to 90 psi. The arm sound best under 50 psi. I also modified the inline filters so the most of oil pumped out of the compressors will be recycled back to the compressors.
Some of you may know that I bought a Rabco active arm to do some modifications. But now, I am seriously doubt how much a modified Rabco can be better than my air bearing arm. So, I may give up the project.
The cartridge I installed on is Dynavector 17D3. 17D3 is usually weak in bass, but not on my 2nd arm with stainless steel shaft. At first, the bass was a bit too much and I had to turn down the subs. After carefully adjusting the damping, its sounding is wonderful now, especially for classical music.Again, I learn that how critical damping is. Damping is a must for all air bearing arms.
The stainless shaft is still a hollow shaft without any internal damping. Once if I feel everything is settled, I may use insulating foam or high viscosity silicone fluid to fill inside of the shaft to further dampen the vibrations.
I also upgraded the compressor. I bought a 1/3 hp compressor and run two fridge compressors together. It takes only less than 5 mins to pump up to 90 psi. The arm sound best under 50 psi. I also modified the inline filters so the most of oil pumped out of the compressors will be recycled back to the compressors.
Some of you may know that I bought a Rabco active arm to do some modifications. But now, I am seriously doubt how much a modified Rabco can be better than my air bearing arm. So, I may give up the project.
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I bet that the stainless shaft is much rounder than the extruded tube so the air bearings are working a lot better now. Do you think that the higher mass of the tube is making the cartridge track better? Now when the stylus is moving back and forth in the groove, all the energy is going into the cartridge instead of moving the light weight aluminum tube. I bet that is why it sounds better. What is your clearance in the air bearing? I would get a real air compressor, one drop of oil in those bearings will be a problem. Look on CL for a used one.
Glad your making real progress, sounds exciting.
BillWojo
Glad your making real progress, sounds exciting.
BillWojo
BillWojo,
The tolerance of roundness is almost same. It is 0.003 inch for stainless shaft. But I think the fitting is tighter now. There is smaller gap between the bearing and the stainless steel shaft.
I can’t tell better sounding is caused by heavier mass or tight fitting. However, I do learn that heavier mass is fine for air bearing. I understand why most of commercial air bearing arms use 20 mm or 3/4” bearings now. I am also thinking of changing my 1st arm which has 1/2” bearing to 3/4” bearing. I may also try to add some mass on counter weight side of shaft so the weight distribution is more balanced.
If I just started from beginning, I might think to get a commercial compressor because my diy compressor is not cheap. It is about $400 now. But my diy compressor has two pressure zones and a large air reservoir, a 10 gallon tank. I have two filters on the compressor. First one is a 10 micron filter and second one is a 0.3 micron coalescing filter. The tubing from compressor to the air bearings is about 50 feet long. It runs from ground level to ceiling which is 10 feet high. Then it comes down from ceiling to the arm. I also add another 0.3 micron coalescing filter just before the air line going to the air bearing. So, it is impossible for oil to reach the air bearings.
Thank you for your inputs!
The tolerance of roundness is almost same. It is 0.003 inch for stainless shaft. But I think the fitting is tighter now. There is smaller gap between the bearing and the stainless steel shaft.
I can’t tell better sounding is caused by heavier mass or tight fitting. However, I do learn that heavier mass is fine for air bearing. I understand why most of commercial air bearing arms use 20 mm or 3/4” bearings now. I am also thinking of changing my 1st arm which has 1/2” bearing to 3/4” bearing. I may also try to add some mass on counter weight side of shaft so the weight distribution is more balanced.
If I just started from beginning, I might think to get a commercial compressor because my diy compressor is not cheap. It is about $400 now. But my diy compressor has two pressure zones and a large air reservoir, a 10 gallon tank. I have two filters on the compressor. First one is a 10 micron filter and second one is a 0.3 micron coalescing filter. The tubing from compressor to the air bearings is about 50 feet long. It runs from ground level to ceiling which is 10 feet high. Then it comes down from ceiling to the arm. I also add another 0.3 micron coalescing filter just before the air line going to the air bearing. So, it is impossible for oil to reach the air bearings.
Thank you for your inputs!
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