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VPI resto-mod...a tale of bastardizing my HW19
VPI resto-mod...a tale of bastardizing my HW19
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Old 13th March 2018, 04:35 PM   #41
chromenuts is offline chromenuts  United States
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Join Date: Dec 2008
Those dimensions sound about right for the magnet I was working with. As I said, it works fine now and Iím happy.

@Super...Sounds like youíre from the same area upstate I used to visit a lot when I was a kid. We had relatives from Pleasantville all the way up past Brewster. I will definitely keep in touch if I get involved in an air bearing arm. I spent countless hours in the thread devoted to them on here and other resources related to the Ladegaard experiments taking notes.
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Old 13th March 2018, 06:20 PM   #42
super10018 is offline super10018  United States
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Originally Posted by chromenuts View Post
I will definitely keep in touch if I get involved in an air bearing arm. I spent countless hours in the thread devoted to them on here and other resources related to the Ladegaard experiments taking notes.
I am not too crazy about Ladegaard's style air bearing arm personally. I would highly recommend to build a New Way air bushing style air bearing arm. High pressure air is a problem for many people so I have experimented low air pressure for my arm. My arm can run under air pressure as low as 7 psi. The arm sounded somewhat to loose dynamics comparing with high pressure, but it still sounded very very good. It is another topic. When time comes, we will talk again.

With the skills and capacity you have, I believe you can make a very nice air bearing arm.
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Old 15th March 2018, 02:23 PM   #43
chromenuts is offline chromenuts  United States
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I think I’ve gone over all the major aspects of fabrication for the project. Final set up of the table had some pitfalls.

Actually, even before I got to final set up I needed to be able to fit the plinth into the base to test clearance, height etc. I knew the plinth was quite heavy and I would need a way to hold it firmly while lowering it in place on the suspension. My first attempt was some handles that had hooks on the end and were covered with rubber tubing. They were supposed to grab the edge of the folded steel sub-chassis to help me hold and lower it in place and then pull out of the gap around the plinth.

The handles didn’t work. Actually, I ended up dropping the heavy plinth from about an inch above onto the base and damaged the oak on one of the inner edges at the top of the base. That’s why its now beveled. My plan B was two sections of copper tubing with some tough nylon string to cradle the plinth from below. It supports the plinth properly, is stable and is easily removable by using the arm board hole as a grip to slightly lift the plinth and snake the string out. I have left it in place for now in case I find I need to change something during my testing period.

The rest of the set up went smoothly. I leveled the table easily using a T handle Allen wrench from above with my new suspension design. Routing of the wiring for the controller was also easy because I only had one power source. The sensor and motor cable was easily routed as well and everything looked tidy. The tonearm was a breeze to set up. The new removable arm board made it much easier to adjust the the VTF setting of the arm to the height of the new thicker platter. I went back over the cartridge alignment, tracking force etc.

When I first set the table up I decided to test it via rim drive. This was mainly due to my experiments in the shop with the black VPI drive belts. They appeared to slip a lot and cause speed instability. There was no good reason for that as the dimensions of the table were the same and if anything there should have been more tension on the belts due to the slightly larger platter.

In hindsight, I now realize that the slippage issue may have been due to the fact that my “Super Platter” did not come with grooves machined in it for the belts. That would definitely reduce the contact area between the belts and platter and affect grip and stability. The black belts wanted to dance around on the edge of the platter. I remember contacting Harry at VPI years ago when I received the platter and asking why there were no grooves. He said they were having too many issues with loosing platters during the machining process of the grooves due to chipping. The trade-off is that I have an ideal surface to use a rim drive.

The table worked great with the rim drive. Unfortunately, there was one drawback. It was due I think to the slight imperfections in either the O-rings I was using to make contact between the motor pulley and the platter or the fact that my pulley wasn’t perfectly concentric enough, or both.

I was getting a resonance that was being amplified by the hollow walls of the IKEA bookcase I have hung on the wall that my table sits on. I tried minimizing it by adjusting the distance of the motor and platter so that it made just enough contact to maintain stable speed. It did improve things, but ultimately the resonance was still there and I was focused on it. It was being transferred down through the motor pod and into the cabinet. If I opened a door on the cabinet it would get very faint.

I couldn’t put anything under the motor to dampen the resonance because the clearance under the plinth was minimal to get a proper alignment with the pulley and platter. I rechecked the pulley and it barely measured movement on my .001 dial gauge when mounted on the motor and spinning. Perhaps using only one O-ring to engage the platter may have reduced the resonance, but then I suspect I may have started having issues with speed stability again. I will have to experiment more in the future, perhaps I need a different shelf that can absorb and dampen things better.

In the mean time I decided to try belt drive again. However, this time I used the original clear style VPI drive belt that came with my HW19. It is slightly shorter than the black belts and appears to be made of a slightly stickier rubber compound. I use all 3 belts with the clear one in the center. All the belts appear stable on the platter this way and there is excellent speed stability. There is no audible noise at all coming from the drive system this way.

There is a definite “warm up” period for the drive system. I don’t know exactly what factors cause it, but the speed wants to very slowly creep up over a 30 minute or so time period. This is being measured in thousands by the RoadRunner. Perhaps it is friction on the belts, lubrication in the motor, performance of components in the control circuit under different temperature or all of the above. I have tried to set a compensation into the frequency that drives the motor so that if I wait ten minutes or so after starting the table the speed has already climbed to within an acceptable tolerance (acceptable based on my mood). It is easy to compensate by adjusting the frequency by .01 if I’m feeling impatient and anal and then just wait to reduce it after I’ve played a side or two.

Last edited by chromenuts; 15th March 2018 at 02:27 PM.
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Old 15th March 2018, 02:54 PM   #44
Packgrog is offline Packgrog  United States
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I'm perplexed as to why you have the monstrously heavy turntable on a piece of flimsy Ikea furniture instead of that beautiful, sturdy Flexy rack right next to it! I get wanting to have your RCM at a lower height for easier use, but why on earth would you want it that close to your audio gear, and on a rack so clearly ideal for your turntable!? I also do question the choice of feet for the lower part of your plinth. Either extra-firm Tenderfeet or spikes would probably be better there. And why don't you have a platform between the lower half of the plinth and the cabinet, like you have for everything on the beautiful Flexy rack? Everything else you have done here looks so well thought out, but your most vibration-prone components (tube amp, turntable) are still missing the most common tweak!

On the subject of belts, have you considered trying a flat belt? While your pulley does have grooves, a flat belt might reduce/eliminate the drift issue that you describe here since the pulley is single-speed anyway. Or you could make another pulley without grooves.

Last edited by Packgrog; 15th March 2018 at 03:09 PM.
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Old 15th March 2018, 03:20 PM   #45
Pyramid is offline Pyramid  United States
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Originally Posted by Packgrog View Post
On the subject of belts, have you considered trying a flat belt? While your pulley does have grooves, since it's single-speed anyway, it would reduce/eliminate the drift issue that you describe here.
In order to use a flat belt, the motor will need a crowned pulley, otherwise the belt will migrate up or down and fall off the pulley.

The speed drift chromenuts observed is fairly typical and is the reason why I created the feedback loop between the PSU and the tach. I initially created the tach to measure the PSU performance, but no matter how accurately I set the speed initially, it would always drift upwards over 30-45 minutes. The tach had a serial output (initially USB), that was intended for logging the speed readout on a computer. The solution became obvious once the symptom appeared: connected the serial output of the tach to the PSU to compensate the drift in speed.

There are no changes in the electronics causing the speed drift, it is purely mechanical (bearing oil viscosity, belt diameter and Young's modulus changes with time/heat). While the motor RPM is constant with time, the platter speed will vary with small changes in drag manifested as belt creep. Unlike belt slippage which can be cured with correct tension, belt creep cannot be cured, it is an unintended byproduct of torque. It can however, be compensated for with feedback, and if done correctly, is inaudible.
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Old 15th March 2018, 06:35 PM   #46
chromenuts is offline chromenuts  United States
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@Packgrog

It’s all about circumstance. Everything you see is in flux. The “flexy” rack as you describe it is nothing more than one of my experiments that didn’t turn out the way I had hoped. It is in fact flexible...and not the way I would want it to be in terms of being able to reset shelf height as is required. I made it from materials I had lying around because I was running out of space. It is some 3/8” stainless rod and MDF. There aren’t any isolation platforms. There are just some cross braces glued and screwed to the bottom of the MDF shelves to reinforce them. I wanted some more space quickly and it wasn’t well thought out. It actually sways easily side to side because the 3/8” rod is too “flexy”.

Until now the IKEA shelf that I hung and anchored directly into my wall studs to isolate it from the floor vibration from footfalls or otherwise has actually worked very well. I often put music on for my kids and my daughter is a very enthusiastic dancer. Never had a skip.

I agree that there needs to be some kind of damping platform under the table if I want to continue to experiment with the rim drive option. I’m not a huge fan of cone feet, and actually got rid of the cone feet that were originally on the table. I think once the table is in its permanent home it will be fine.

My hobby has outgrown the space limitations of my living room and I have been unhappy with the situation for a while. I am in the process of planning my biggest audio project ever which will be tearing down an old sunroom on the back of my house and rebuilding it with the priority of having a better listening space.

@Pyramid

I suspected the creep was part of the reason for the feedback feature between the RoadRunner and Falcon you developed. Obviously the Falcon was a dead end for me personally because I wanted to use a motor that was beyond what it was originally designed for.

The SG4/M3D project has been a dream come true and really was the reason I even considered going forward with this project. Thank you for that. If there was a way to take advantage of feedback from the RoadRunner with the SG4 I would probably go for it. However, its not something I can’t live without either.



P.S. No tube gear running in that pic...just my stereo Gainclone project that I fabricated so the transformer was outside the case and had a cover.

Last edited by chromenuts; 15th March 2018 at 06:39 PM.
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Old 16th March 2018, 06:46 AM   #47
coolmaster is offline coolmaster
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Originally Posted by chromenuts View Post

The SG4/M3D project has been a dream come true and really was the reason I even considered going forward with this project. Thank you for that. If there was a way to take advantage of feedback from the RoadRunner with the SG4 I would probably go for it. However, its not something I canít live without either.
I second on what you said and all cheers to Bill. At the back of my mind, was hoping Bill or someone else can invent another tt platter feedback thing to connect to the SG4 for speed control. Hope I described it right.
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