Corian Turntable Fun

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Hey Casey - hold the phone! Stop the presses! I think found a solution for you.

Seems that professional microphone cable (the type used for pa systems) is rated for 250V. Has to meet UL and CSA standards.

Most of this stuff has 3 conductors to fit a balanced XLR connector and a braided or spiral wrapped outer shield. Obviously the cable is quite small diameter, flexible and, best of all, CHEAP!

Any music store will have it and it is under a buck a foot here in Canada.

Hope this helps

Jess
 
Hey Jess,

Seems that professional microphone cable (the type used for pa systems) is rated for 250V. Has to meet UL and CSA standards...Any music store will have it and it is under a buck a foot here in Canada.

I'll give the local music stores a call, and see what they have. The nearest "big" town has less than 100k population, but there are probably enough "wannabe" rock stars populating the countryside to justify carrying some mic cable...this could be the answer, thanx for the suggestion.

-Casey
 
Well it’s Sunday, and that can only mean one thing…update time.

The pulley end of the spindle being off center had been nagging me, so I decided to spend Friday putting a sleeve on. I made a jig to hold it true center, and cut down the pulley end for the sleeve. I mounted the sleeve, and while it was still centered, turned it to .25”. I thought I had that that little irritant out of the way until I discovered that the hole in the jig was a little oversized where the set screw was, and consequently, it pushed the shaft at a slight angle. So now I have a spindle that is true at the base, but shoots up at an angle. This is not good, the top wobbles about .005”. I have a plan “B” (actually it was plan “A” until I thought of the sleeve). I will true up either the spindle or the mounted pulley with a Dremel mounted in a jig while the motor is running…similar to how I trued up the platter.

Next I made the flywheel, and drilled/tapped the holes to secure the bottom bushing. Here are the components for the spindle/ flywheel assembly…

fly-parts.jpg


…If you look close, you will notice that the very end of the flywheel has been cut down slightly smaller than the recess to the bushing sleeve. I put a small amount of grease where these two pieces would meet, and set the clearance to .005”. I was able to set the clearance accurately by shimming the spindle with .005” shim stock…

shim.jpg


…I turned it upside down, and sat the spindle in a piece of steel with a hole in it, so the weight was being carried by the spindle. I then slid the flywheel on, and while holding it down against the greased bushing sleeve, I tightened the set screw through an access hole I had drilled in the flywheel spacer…

flywheel.jpg


…I then gently removed the shims and..Voila’..005” of vertical play. The thinking here is that the grease in this small gap will provide a small additional dampening of any noise the turning assembly might have. I then mounted, and secured with 4-40 cap screws, the back of the assembly…

fly-assy.jpg


After playing with the s-m-o-o-t-h flywheel assembly for a while, I set out to re-mount the isolation assembly. I had originally used super glue for one reason, it is one of the few adhesives that will bond to Sorbothane, and boy does it bond. Super gluing Sorbothane to your finger is like gluing your finger to your finger. When I took it apart to mount the bushings, I found 2 problems. First, when I mounted it the first time, I managed to touch one of the pads to the plate off center. Naturally the super glue set immediately, and so the whole ring assembly was holding the motor off-center. This turns out to be what casued the caged bearings to be as noisy as they were..the side pull was loading them up. This set me down the path of the bushings, which turned out to be quieter than any caged bearing could be, so this was a “happy” accident. The second problem was that 2 of the four pads had already broken off from the thermal contraction of the steel plate in an unheated shop. This time around I used the superglue bonded to the Sorbathane as an intermediate layer. The super glue sticks to the Sorbathane, and my buddy JB Weld stick to the super glue…

glue.jpg


I sat the assembly on the plate with the mounted motor and alignment jig (a piece of aluminum with a 1/8” hole bored through), and marked out where the pads would sit. I the took my marking punch, and punched the steel at an angle around my markings, this gives the JB Weld an anchor. I then put the glue on the plate where the pads would sit, and lowered the assembly down the alignment jig. After the assembly was resting in the puddles, I worked the glue over the edge of the super glue that remained on the pads, giving it a finger hold on the pads. I put it aside to cure and went to work on the coupler. I started having doubts about using PVC tubing for my coupler. True, it had to work pretty hard with the screwed up alignment before, but it had turned cloudy from the stress, this got me thinking about the long term viability…after I’m done I really don’t want to go back and repair periodically. I started thinking about it, and decided to use a small spring. It would be extremely compliant side to side, but difficult to twist. I also reasoned that the “winding” of the spring at start-up would give it a little boost getting the platter going. Here are the components of the coupler…

couple-parts-1.jpg


…and here it is assembled…

spring-coupler.jpg


…I originally tried it with a Sorbothane “blanket” glued around it, but that managed to pull the centerline out, causing the motor to shimmy, so I cut that off leaving a ring of the material on the ends with the collars. Mounting it, this is the motors “eye view” of the completed isolation system…

iso-assembly.jpg


So how well does it work ?…

01snoopy.gif


moto-steth.jpg


01snoopy.gif


I put the stethoscope in the picture on, and listened to the motor…nothing. I then turned off the fluorescent over head lights to lower the background noise…nothing. I held my breath…nothing. I went and got my son with the 18 year old ears…nothing.

The only noise is air born from the motor itself (my new Hurst motor has a small “scrub”), but with the bottom covered…nothing. This thing is “graveyard” quite. Sitting on the table there is NO discernable vibration/noise.

This problem had been kicking me in the hind quarters for a l-o-n-g time, but not only have I finally overcome it, I may have set a new standard for a motor of any kind..unless there is another motor that’s truly silent.

I am freshly motivated to get the motor finished, and will be spending the next couple of days thinking about what I need to do to true up the spindle/pulley.

Later,
Casey



 
A quick update...I left it running for several hours (killed power just before going to bed), and no new noises surfaced. In fact, the "scrub" in the motor itself has reduced quite a bit. As I mentioned above, this noise is eleminated by covering the bottom of the housing, but it still torques me that a new motor makes ANY noise.

-Casey
 
Hi Guys,

Re-reading my post, I realized I didn’t give some specs on my noise isolation system I had intended to share in case anyone wanted to try something similar. First was the flywheel weight of 71 gm., or right at 2.5oz. This seems pretty small until you consider the motor has about 2in-oz. of torque. The spring I used in the shaft coupler has an OD of approx. ¼”, a length of 1/2” between the collars , and is the “return” type. That is, it was intended to be extended rather than compressed. The coils were originally wound tight together, but I stretched it slightly. It goes side-side quite easily, but it’s not so easy to twist. The first couple of degrees of twisting rotation requires very little force, but applying the approx. force of the motor with my hand (simulating a stall condition) I could only twist it maybe 5-10 degrees. The force required to twist it is progressive.

Even though the airborne noise of the motor is somewhat academic, since it is completely contained in the housing, it was still bugging me. A brand new motor shouldn’t be that noisy. When I got home today, I went out to the shop to investigate. I noticed that depending on how I sat it down (with the bottom over the edge of the TT or bench to clear the wires), the level of noise changed rather dramatically..hmm. I found that pulling the wires side to side did the same thing..hmm again. I lifted the motor up and applied light pressure to the bottom of the motor and the noise all but disappeared ..A-HA! I didn’t have any pre-load on the motor bushing. When I assembled it, I simply tightened the spring collar down while the spring was relaxed. So, as the coupler vibrated (as intended), it was bouncing the motor bushing. I pre-loaded the sprng/bushing .03” (one turn of the 6-32 nuts holding the motor), and now the airborne noise is what one would expect from a motor free mounted in a steel pipe. Kind of a hum mixed with the “shu-shu-shu” of the bushing. You have to have your ear within a few inches of the open bottom to hear it..which as I have pointed out, won‘t be open.

I made a less pleasant discovery as well. In the process of setting the motor on the TT, I accidentally sat the motor on the wires. The kinetic energy passing through the four 24ga. tinned wires from the motor was enough to vibrate the bottom plinth to the point of hearing and feeling the hum!! I have built a freakin’ sounding board tuned somewhere around 60/120 Hz, and called it a plinth...not exactly the plan. Compounding the problem, the motor shelf sticks out about 6” from the nearest support (foot). The top plinth isn’t a problem (thank God), it has a solid ½” aluminum core along with the reinforcement from the cap screws, as well as the mass of the platter. I have a few ideas on how to address this, but would love to hear any thoughts anyone would like to share on how best to attack this.

The above dilemma puts a couple of things in context. First, my previous motor attempts, under “normal” circumstances, would probably have been adequate (other than my belt vibration), and secondly, it illustrates just how absolutely silent my new motor is. Believe me, if it vibrated in the least, my mechanical amplifier of a plinth would reveal it. I know I have spouted off before about how I had solved the noise problem (and then later finding I had come up short), but, this is the real deal folks.

IT-IS-DEAD-QUIET!!!

Every couple of hours I call BS on myself, and try in vain to hear ANYTHING with my stethoscope…there simply is nothing to hear.

I have kept enough notes on it’s construction that I could draft a reasonably accurate CAD if enough folks are interested. I believe that a working version of this design could be constructed with basic tools (hacksaw, drill, etc) and off the shelf parts. If you need quiet…this will get you there.

-Casey
 
Hi pixpop,

I'm not certain I understand the question, but if you are refering to the noise transmitted to the plinth, I discovered this before I tightened the nuts. Besides, you need to realize "tighten" in this case means squeezing soft rubber .03"..you cant tell anything was tightened.

-Casey
 
Hey pixpop,

so.. when do you hear this vibration? If you hold the motor in your hand, it's quiet. But if you let it rest on the plinth you can hear the vibration? Or is it only if it rests on the wires?

Believe me, I understand how hard this is to grasp...watching first hand still causes me to shake my head.

If I hold it in my hand..silence. If I set it on the bench with the wires free..silence. If I sit it on the wires on the bench..silence. If I sit it on the plinth with the wires free..silence. If I sit it on the wires on the plinth..its loud enouph to hear standing over it, and you can easily feel the vibration. The plinth is setting up a resonance from the energy transfered frpm the wires...unbelievable I know.

-Casey
 
Yikes.

If you put the motor on the bench, but then have something else compress the wires against the plinth (something heavy.. e.g. a 1 pound bar of gold bullion) what then? I.e., does the vibration originate in the wires or in the motor? From your description, it sounds like it originates in the wires. But that's hard to believe with the low current you have.

I have a 300 watt floor lamp. The ac wiring enters at the base, then runs up 6 feet through a metal tube to the light at the top. When it's running, if you touch the metal tube you can feel slight vibration caused by the magnetic field surrounding the wires. But that's about 3 Amps.

Since your motor case it ferromagnetic, I guess its possible that the alternating field surrounding the wires could vibrate the motor casing. The wires might be vibrating each other as well, but you should be able to hear that with your stethoscope.
 
pixpop-


I know :mad:

I.e., does the vibration originate in the wires or in the motor? From your description, it sounds like it originates in the wires. But that's hard to believe with the low current you have.

Guess I wasn't clear enough (big suprise ;) ) my motor is essentially (as far as vibration is concerned) hanging in free space..it is allowed to physically buzz along to its hearts content. It is the physical excitation of the wire from the vibrating motor thats being transfered by the wires (think the can & string intercom), not the miniscule induced hum from the current.

As I said..unbelievable :eek:

-Casey
 
Hi Nordic,

Maybe try decoupling that last bit of wire with some thin flexible wire... or hotglue them down?

That is one option I'm considering. My first plan is to roll the leads into a coil (spring), and loose couple it to the housing with a Sorbothane grommet. Decoupling the wire from the housing really isn't a big deal...I was just trying to illustrate what a "stink bomb" my bottom plinth turned out to be :rolleyes:

Or is there a way to damp the plynth?

That is the question of the hour. I'm looking at some struts to stengthen it, and possibly some pockets of lead shot,and skinning the bottom with Sorbothane.

My motor effort shows, if nothing else, I'm tenacious :)

-Casey
 
valveitude said:
I'm looking at some struts to stengthen it, and possibly some pockets of lead shot,and skinning the bottom with Sorbothane.

I assume you have some short legs underneath the plinth. Easiest thing to try is to reposition the legs so that they are not uniform distances apart. This will help break up resonant panels. Also you can add an additional leg or two. But don't space them evenly. If you bond a layer of material to the bottom, with the new layer being a different stiffness and/or density, this will also break up harmonic nodes. Can use constrained layer damping, i.e., thin layer of flexible material between the layers. Sorbathane is one such material, but even a thick flexible glue or caulk will help.

Sheldon

edit: Play guitar? You know then that if you touch a string halfway and pluck it, you will ring one octave higher than the open string. If you touch it just a little bit off, you will damp it almost completely. Different affect with a hard slide, BTW - it's not damped, but acts like a fret instead. So a little dampening between feet and plinth, and uneven spacing (not divisions of two or four, etc.), should help.
 
Hello Sheldon,

I assume you have some short legs underneath the plinth.

Yep.

Easiest thing to try is to reposition the legs so that they are not uniform distances apart. This will help break up resonant panels. Also you can add an additional leg or two.

Actually, this would be extremely difficult. The bottom legs are part of the lead shot pods for the top plinth legs..fortunatly I don't need to move them, as they are already un-evenly space. I am considering adding a foot directly under the motor shelf though.

If you bond a layer of material to the bottom, with the new layer being a different stiffness and/or density, this will also break up harmonic nodes. Can use constrained layer damping, i.e., thin layer of flexible material between the layers.

You have basically described the construction of the plinth.

1st layer=Corion
2nd layer=aluminum
3rd layer=lead
4th layer=aluminum
5th layer=Corion

Sound like it would be pretty inert eh ? What a drag :mad:

I believe it is the assembly as a whole, rather than the material, resonating, as it is sitting atop a "spongy" bench. I think it's a question of geometry, in that, the motor is hanging out on a shelf approx. 6" from the nearest foot. I believe it is using this as a fulcrum (sic) to flex the rest of the plinth. It actually feels like its vibrating harder the further you get away from the motor. I think I will try the bracing first..this may cure it. If not...:xeye:

Congrats on your phono pre by the way ;)

-Casey
 
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