User 510's Technics SP-10 mkII
my Technics SP10 mkII while it stands in a custom plinth.
The tonearm is a Graham 2.2. Mounted to the Graham is a Shelter 501 type II MC cartridge of "low-ish" output. At first I wanted to name this plinth design the "Test Mule". But a suggestion from a friend sounds better. From here on I name this plinth style "the mule". I like that this name echos an Azimov character from the Foundation series of novels. The Mule. To see how this incarnation came to be, please read below. And it is still in the beginning stages of its journey.
The Mule 9/29/2013
Having already taken dimensional measurements on the bearing spindle shaft, the bushing bore and a visual exam of the thrust, we know that bearing wear is minimal, except that the thrust pad is in need of renewal. For this part of the project, the deck has been re-assembled. The bearing, spindle and bushing has been gently cleaned and then reassembled with fresh 20 wt turbine oil for lube.
The next step is to make a test mule to study and measure the performance of this machine. Specifically, the goal is to get points of reference for rumble and wow/flutter performance. This data will help to determine the electrical/mechanical condition of the motor unit. If there is significant wow/flutter, it will point toward problems with the controller electronics. If significant rumble is reported, it will point to excessive wear at the platter bearing. But I've already taken early listening sessions with this deck and know that the unit reproduces music quite well and with no audible evidence of low frequency rumble.
Like all my plinth designs, it starts out as a sketch, then, once I have a rough outline of the shape, I refine the shape in my 3D cad software of choice, Rhino3D.
This "test mule" plinth is intentionally light. The idea is to produce a method of supporting the motor unit and tonearm together in a single structure. But this structure needs to be one that does not depend on high mass to dampen whatever mechanical vibrations the motor unit may produce. Rather, I want to be able to readily measure for rumble and wow/flutter without having to consider that the plinth may be masking some of the mechanical noise. However the design does provide a hollow chamber in each of the 4 vertical cylindrical supports to hold a volume of #9 lead shot as a means to dampen the plinth at its support point. This idea is to help "plant" each cone foot solidly onto the support surface.
The plinth needs to be a rigid structure that can allow this player the ability to play music and sound good. The better the condition of the motor unit, the better it will sound.
3d cad quick shade. In this photo self tapping machine screw inserts will tap into the wood of the plinth, then accept the 1/4-20 threads of the allen bolt, which screws into and holds the Stillpoint cones. The advantage to this arrangement is that there is a slight range of vertical adjustment at each cone which can be used to level and stabilize the deck.
Earlier this year I purchased a used set of Stillpoints cone feet for this project. These cones are well regarded by many audiophiles in the know. However the manufacturer has replaced this model with another that claims to be an improvement. The advantage for me is that I can now purchase this old technology at 2nd hand rates, while more affluent audiophiles upgrade their equipment with the newer Stillpoint cones that are significantly more expensive. Progress is good.
Next step................... build the actual thing.
The Stillpoint cones connect via 1/4-20 threaded studs to the thread inserts that have been installed within the Test Mule plinth. This method allows height adjustment at each of the 4 cone footers for leveling.
Setup and ready to spin records
It is rough cut and unfinished. Some sanding. It has some dark brown stain. But rough.
After finish pics:
Finish coating: highly textured black enamel. Prior to paint, three successive coats of sanding sealer. Sanded between coats. Then 3 coats of the textured black with sanding between those coats.
But next I changed the pile-up method on top of the Minus-K. The TD124 slate plinth slabs were removed and replaced with an 18 x 18 x 3 inch granite inspection plate. On top of the granite is a Neuance platform. The Neuance platform will interface with the ceramic cone feet under the Mule plinth and should serve to dampen vibes coming off the sp10.
As noted in my review of the Minus-K isolation platform, there is a minimum(90 lbs) and a maximum (155 lbs) weight load requirement. That is why when I removed the TD124 slate plinths I had to replace those with something of similar weight. In this case the Granite is actually heavier than the Thorens' slate. The granite by itself weighs 108 lbs. The Mule with SP10mkII weighs 31 lbs. combined weight is then 139 lbs standing on the Minus-K. And the Minus-K happily floats the sp10 in its Mule.
Some brief, subjective listening observations on how this setup sounds:
Fast. Very musical. Dynamic. Great bass. A very good sense of energetic drive. Better this way than when I had it in the earlier plinth. Detailed but not really analytical sounding. Nice.
note: this is a new reference. The Shelter 501-II was replaced with a Denon DL-103R lomc cartridge. Reason: The Shelter was producing some unwanted distortions and is now parked in its case.
Measure for Rumble and wow & flutter.
methodology: play test record on sp10mkII using a Graham 2.2 tonearm with a Denon DL 103R (with wood body/soundsmith ruby-LC cantilever-stylus) MC cartridge mounted. The SP10mk2 is mounted into its "Test Mule" plinth. The plinth stands on a Minus_K isolation platform as pictured above. Signal chain: From the Graham, the phono cables plug into a step up transformer, then into the Hagerman Trumpet phono stage. From the stage the signal is fed directly into a MasterLink 9600 hard drive recorder. The Masterlink records the test record tracks and then burns a 24-96 hi-rez CD recording. The plot spectrums seen below were developed in Audacity.
hint: to view photo full size, click on the thumbnail
But with some help from around the web, others indicate that the thrust pad is really just a cap that snaps over a knob end of the shaft. Using a pocket knife, I very gently pressed the knife edge between the pad and shaft. Very lightly. And the cap lifted off with no resistance.
It may be debatable if it is really necessary to replace this thrust cap with a new one, since it shows moderate wear at the thrust end. (wear indicator = the size of indentation made from contact with the bearing ball that the cap thrusts against as the platter shaft spins)
I will look into having another wear cap made. Perhaps I will make a small quantity and sell those at my cost to others needing a new thrust cap.
The first thrust cap is made. Here at The Analog Dept. Date: 12/30/2013
below: determining accuracy of the machining.
Above: checking pad thickness ( in inches ) This (analog) dial indicator only reads decimal inches. Its' finest graduation is .0005". slang: 5/10ths or 5 ten-thousandths
Btw. This record player was manufactured in Japan where the metric system is used for all dimensions. Given that, and where possible, all dimensional references are in the metric system. To convert from decimal inches to millimeters simply multiply the decimal inch value by 25.4.
Above: checking the outside diameter and then the length
Above: First ..........setting the Mahr gage. Then measuring the inside diameter of the thrust cap. Note: The Mahr gage is in inches while the setting micrometer is reporting in millimeters. Btw, the Mahr gage is very sensitive. Its finest graduation is 50 millionths of an inch. ( .00005" ) Zero on the dial is set to the nominal diameter. Deviation is indicated either positive or negative from that nominal.
Above: visual examination of the new Torlon 4301 thrust cap next to the old standard Nylatron thrust cap.
With Torlon 4301 thrust cap newly made and installed.
1 week after:
The next three plots (same tracks and order as above) are measured 1 week after installation of the 4301 thrust cap. Date: 1/6/2014
2nd Thrust Cap: Torlon 4203 Date: 1/6/2014
Above photos: Left: Torlon 4203 .......Right: Nylatron original equipment bearing
4203 Test Record plots:
right after installation: (1/06/2014)
1 week after: ( 1/13/2014 )
Black Delrin Thrust Cap
Above photos: Delrin cap at left, original Nylatron cap at right.
Above photos: New Delrin cap at assembly. Left; partly on.......Right; seated on
Right After Installation:
See anything different?
Only change = Delrin thrust cap
1 week after installation:
comments: Now after 1 week it appears that the Delrin thrust cap plots out just like the other cap materials. The dimple size on the cap appears normal in comparison to the other materials. But the question persists; why did the freshly installed Delrin cap plot out so much more quietly in the first place, and then what changed in the 1 week plot.
I can say that no part of my methodology, in these tests, has changed. The only apparent difference between the before and after on the Delrin cap is the small evidence of wear at the thrust. At this point I will refrain from speculating and just let the evidence lie, while continuing these material tests.
MDS filled Nylon Thrust Cap
Above photos: The new replacement Nylon cap on the left. The original nylatron cap on the right.
Note on machining nylon. The material cuts cleaner with very, very sharp cutting edges ground with extreme rake angles. Any further production of Nylon thrust caps will include greater attention to producing cleaner cuts than I have done on this first sample.
Test plots conducted just after assembly of the nylon thrust cap:
Silent groove notes: appears to compare with all previous material test plots except to the fresh Delrin plot, which may be in error.
Test tracks after 1 week of normal use
Kevlar Filled Nylon
product name: Hydlar Z
Material Manufactured by: Ensinger
Above: Left: new replacement Hydlar Z thrust cap; Right: original Nylatron thrust cap
Above: Left. new replacement Hydlar Z thrust cap parked loose on the shaft knob end. Right: Seated on.
Test Record plots with the new Kevlar filled Nylon thrust cap (Hydlar Z)
After 1 week (Hydlar Z)
note the inclusion of unknown material. I can't say if this happened because of the machining process, or if the inclusion was within the material prior to the machining. Then consider that I have machined three caps from this same stock and neither of the other two have the inclusion.
Test plots 1 week out.
No difference noted. Minimal
Cap Material Summary:
Instrument in use: a 10x Loupe with reticle manufactured by Peak (Japan). This reticle is in decimal inches and resolves to .005 graduations.
(note: this symbol Ø is gd&t for 'diameter'.)
Other notes: The test record report graphs were produced before and after the 1 week period on each cap material. I saw no appreciably change between fresh and 1 week in this reporting. Except for the Delrin results which I'm tempted to toss out as an unexplained anomaly and I doubt its validity. Also it is useful to take note of the test record reporting on the original equipment 37 year old and well worn cap compared to any of these new materials.
Apart from the test record plots, listening sessions did not truly indicate any audible difference in sound quality between the above thrust cap materials. In each case sound quality was as good as I'm used to hearing from this player. Next step; the thrust bearing ball that the thrust cap spins on. Will a difference in material and quality of this bearing ball make a measurable or audible difference?
Does it make sense to try different materials and grades of the bearing ball in the thrust end of the platter bearing? Let's see if we can't prove it one way or another.
Ceramic: 9/32" SiN4 Ceramic grade 5 (sourced from Boca Bearing Company)
Prior to assembly, the ceramic ball is perched in the cup end of the thrust cap that will be used. Looking close, the ball has a highly polished finish. And also tiny bits of dust clinging tenaciously to its outer surface. I wiped the ball with a chamoise several times to no effect.
Exterior detail. The Torlon 4203 cuts fairly clean with commonly used lathe tool bits of carbide and high speed steel. A hand held metal file was used to apply edge breaks while the part was turning in the lathe. The part was cut complete in a single setup. Turning the OD. Facing off the open end. Drilling with a center drill to open up for the boring bar, which was used to cut the ID for size and also used to cut the interior face to depth. To establish the length of the part, a parting off tool was used. To finish it, a secondary operation was applied using a bench lap to lap the thrust face of this part into a smooth condition. This process has been used on all of the above thrust caps, including this one.
Replacing the plastic thrust cap at the tip end of the bearing shaft is somewhat simpler than replacing the bearing ball. For the cap all one needs to do is leave the player upright and disassemble the platter from the motor unit, then remove another 'gazillion' machine screws an assortment of keepers and cover plates......and a platter brake assembly. After than we can gingerly lift the rotor, the very valuable rotor, up out of its bearing housing. To understate it, Technics has their player securely buttoned up and held together tight.
But to remove the bearing ball at the bottom of the bearing housing, one needs to hold the motor unit upside down safely and securely, then unscrew another gazillion machine screws to remove the bottom cover. Having done that it exposes the main-board circuitry and the all important platter bearing thrust cup sticking up in the middle of it all. But one needs be careful not to disturb the printed circuit boards and the small city of electronics parts attached to them. Or perhaps it is better to remove the printed circuit board prior to removing the bottom bearing thrust cup. The parts on this player are rare and valuable. See elsewhere in this article ( Disassembly photos ) for some details on removing the platter bearing thrust cup. It is held on by threads and a generous amount of thread sealer. Care needs be taken. Care and technique...if you want to avoid damage.
Looking into the thrust cup. Notice the threads, the spot face at its bottom and the prominent crater that indicates previous use. The bearing ball holds a fixed position, does not turn and is held in firm contact with both this cap and the side walls of the bearing housing where it resides. click the photo to view it full size. Then notice two bits of annotation. A number 1, indicating the spot face surface, and a number 2, indicating a wear spot where the bearing ball makes firm contact with the cup.
Let's measure the wear spot to see how deep the crater is:
A granite based drop indicator is used to measure the wall thickness at the cup bottom. This shot shows the indicator almost set to zero. This was adjusted prior to making measurements to exact zero on the big dial. Also take note of the smaller dial within the face of the indicator. It is also set to zero. That smaller dial counts revolutions of the large needle. One rev is .050 inches.
Checking in the center of the wear crater. What's the reading? Look at it two ways. Compare this reading to the previous reading taken on the spot face surface to get a simple depth read. Just subtract the smaller value (crater read) from the larger value (spot face read) to find depth of the crater. I get just a touch over .001" of depth in that crater. Not very deep. You can also figure wall thickness at the crater bottom simply by reading the dials. For that I get .095 inches. Isn't this fun.
While I've got the thing apart let's take a look at some other sizes.
I'm using a Mahr gage to find the size of the bearing housing ID. I used the Mahr gage to scan up down and around within this housing. The gage indicates a straight through bearing bore with no relief areas, that is straight and round. Variation of the readings was less than .0002 inches.
Using a micrometer I'm gaging the diameter of the original equipment thrust bearing ball. Guess what; the .2815 inch ball is closely size for size with the bearing housing inside diameter. This also works out to a fractional inch size; 9/32". Go figure. A Japanese manufacturer, where the metric system dominates, choses a 9/32 inch bearing size for their top of the line record player. What this leaves us with is a bearing ball that is size for size with the bearing housing it must fit into. A small amount of force is used to assemble and disassemble the ball from the housing each time. That way the ball is not allowed to move, not even slightly, while doing its job at the bottom of the platter bearing.
Checking the new SiN4 Ceramic grade 5 bearing ball. Funny, it checks .0013 inches larger in diameter than the oem ball. And this is over the nominal 9/32" stated size for this bearing. What it means is that if I use this bearing ball it will need to be pressed into the bottom end of the bearing housing. Should I do that or should I find another ball? As it turned out I just placed the ceramid ball on the opening end of the bearing housing, then screwed the bottom cup down over it to press the ball into position. The required force did not seem excessive to my calibrated wrist as I wrenched the threaded cup down over its fitting.
Test Record Plots for the ceramic ball:
As I review this group of test plots and compare against previous plots from the different materials while using the oem bearing ball, I see that there are some small differences in the measurements. In particular as I look at the silent groove plot exclusively I can find differences between them on the order of 2 to 3 db. And that is all. This is not significant.
After 1 week: 2/9/2014
Wear rate does not stand apart from the previous group when using the standard issue hardened steel bearing ball.
Test record spectrum plots after one week
I heard no overt differences in this configuration than I had previously. Perhaps, there were some subtleties to be appreciated. Inner details seem nicely rendered. I can't say that I did not notice this in any of the other cap/ball configurations. Nonetheless, sound quality is as good as I have heard it over the duration of this bearing cap/ball test session. As good as I've yet to hear out of this motor unit regardless of configuration.