Big Bill
Summertime Rolls.....
I’m writing to share with you the story behind this Technics SP 15 and the thinking behind its current incarnation. I acquired the table earlier this year with an eye toward building a “workhorse” table for play grading “new to me” vinyl and spinning a few choice 78 RPM records.
The first thing I did was to replace all the electrolytic capacitors in the table as a prophylactic measure in order to help insure a long LSI circuit lifespan, as these are now “unobtainium”. Next I modded the main bearing by installing one of AK member “Marc Morin’s” mirror finished, hardened steel thrust plates (these things are the bee’s knee’s). I then began mulling over various plinth material options. At one point I was thinking of building a multilayered plywood plinth until I read AK member “Mister Pig’s” Technics SP 25 thread. Consequently, I decided to go “back to the well” and used a one inch thick acrylic mono-plinth for its “known to me” superior sonic attributes. I chose to radius the back left corner and to round over the top edges of the mono-plinth in order to compliment those of the sp-15’s casting.
With my plinth material and design chosen I now turned my attention to picking an arm. As some may know I’ve become quite fond of Linn tonearms lately. Since I needed an arm with the ability to swap carts on the fly, I chose the Linn LV V tonearm. While the Linn LV V series are certainly beautiful arms they unfortunately lack the quality of bearings found in the later Linn tonearm offerings. Simply put, this arm needed an upgrade! I began by removing the horizontal bearing block (which houses “loose” ball bearings in a tapered race located at each end) and machining each end of said block to receive high quality ball bearing assembly’s. For the vertical bearings Linn used self contained mini ball bearing “cups” which I chose to remove and replace with needle and jewel (sapphire) bearings. While I had it apart I also rewired it with Litz wire and internally damped the tonearm pipe with foam for good measure. I think it may just be the most tricked out Linn LV V tonearm on the planet now!
Another issue I wanted to address with this build are the reports of “jitter”, e.g., motor noise attributed to some direct drive tables. I don’t belong to either camp in the DD “jitter” debate but thought this build would be an excellent opportunity to explore the subject as it relates to this particular table.
Drawing on discussions I had with Marc Morin regarding different methods of sinking energy from AC synchronous motor assemblies, I decided on one approach in particular to incorporate in this DD build. By coupling the integrated bearing/motor housing via threaded rod to a large suspended tunable weight beneath the table, the unwanted energy should travel down the rod to the weight exciting it 180 degrees out of phase (function of distance and mass). At this point the two alternately phased wave forms should cancel one another other out at the halfway point of the motor and weight (threaded rod) and be dissipated as heat.
The following is how I went about implementing it. I drilled and tapped an additional hole in the cast integrated motor/bearing housing of the SP 15 to further facilitate energy transfer to the main bearing thrust plate (as there are only two machine screws present from the factory for securing it). Using metric studs I re-secured the bearing thrust plate and installed an additional plate about half an inch beneath it. This additional plate allows for the rod to thread through it and compress itself into the bottom of the bearing thrust plate for maximum energy transfer. The weight itself was created by fusing three spare TT platters together with the center platter (Elac) weighing in at just over eight pounds.
Now it was time for some “feet” and with the addition of the suspended weight assembly to the build I needed some serious clearance beneath the table. I choose to use some stainless steel feet like I used in the Empire build. The only difference being that these are six inches in length. I terminated the feet with some Vibracones which are secured via screws from within the feet. Since the feet I chose are hollow I was able to fill the three feet with two pounds of lead shot each for added damping. The addition of the Vibracones now brought the overall length of the feet to seven inches (leaving plenty of room for the weight).
After final assembly of the Table AK member “Fasterdamnit” (Jim) and I weighed the turntable and it weighs in at an impressive thirty four pounds. We then listened to the table with and without the weight attached using our reference album. The reduction in back ground noise and cleaning up of the soundstage were dramatic and instantly recognizable. We then “tuned” the weight by raising and lowering it for max noise reduction using a stethoscope placed on the bottom of the drive unit itself. I was fortunate in that the legs chosen were just long enough as the position of the bottom of the weight is only about an inch or so above the shelf it sits on once properly tuned.
Thanks for reading, Bill.:thmbsp:
Jim looking rather pleased.:yes:
The first thing I did was to replace all the electrolytic capacitors in the table as a prophylactic measure in order to help insure a long LSI circuit lifespan, as these are now “unobtainium”. Next I modded the main bearing by installing one of AK member “Marc Morin’s” mirror finished, hardened steel thrust plates (these things are the bee’s knee’s). I then began mulling over various plinth material options. At one point I was thinking of building a multilayered plywood plinth until I read AK member “Mister Pig’s” Technics SP 25 thread. Consequently, I decided to go “back to the well” and used a one inch thick acrylic mono-plinth for its “known to me” superior sonic attributes. I chose to radius the back left corner and to round over the top edges of the mono-plinth in order to compliment those of the sp-15’s casting.
With my plinth material and design chosen I now turned my attention to picking an arm. As some may know I’ve become quite fond of Linn tonearms lately. Since I needed an arm with the ability to swap carts on the fly, I chose the Linn LV V tonearm. While the Linn LV V series are certainly beautiful arms they unfortunately lack the quality of bearings found in the later Linn tonearm offerings. Simply put, this arm needed an upgrade! I began by removing the horizontal bearing block (which houses “loose” ball bearings in a tapered race located at each end) and machining each end of said block to receive high quality ball bearing assembly’s. For the vertical bearings Linn used self contained mini ball bearing “cups” which I chose to remove and replace with needle and jewel (sapphire) bearings. While I had it apart I also rewired it with Litz wire and internally damped the tonearm pipe with foam for good measure. I think it may just be the most tricked out Linn LV V tonearm on the planet now!
Another issue I wanted to address with this build are the reports of “jitter”, e.g., motor noise attributed to some direct drive tables. I don’t belong to either camp in the DD “jitter” debate but thought this build would be an excellent opportunity to explore the subject as it relates to this particular table.
Drawing on discussions I had with Marc Morin regarding different methods of sinking energy from AC synchronous motor assemblies, I decided on one approach in particular to incorporate in this DD build. By coupling the integrated bearing/motor housing via threaded rod to a large suspended tunable weight beneath the table, the unwanted energy should travel down the rod to the weight exciting it 180 degrees out of phase (function of distance and mass). At this point the two alternately phased wave forms should cancel one another other out at the halfway point of the motor and weight (threaded rod) and be dissipated as heat.
The following is how I went about implementing it. I drilled and tapped an additional hole in the cast integrated motor/bearing housing of the SP 15 to further facilitate energy transfer to the main bearing thrust plate (as there are only two machine screws present from the factory for securing it). Using metric studs I re-secured the bearing thrust plate and installed an additional plate about half an inch beneath it. This additional plate allows for the rod to thread through it and compress itself into the bottom of the bearing thrust plate for maximum energy transfer. The weight itself was created by fusing three spare TT platters together with the center platter (Elac) weighing in at just over eight pounds.
Now it was time for some “feet” and with the addition of the suspended weight assembly to the build I needed some serious clearance beneath the table. I choose to use some stainless steel feet like I used in the Empire build. The only difference being that these are six inches in length. I terminated the feet with some Vibracones which are secured via screws from within the feet. Since the feet I chose are hollow I was able to fill the three feet with two pounds of lead shot each for added damping. The addition of the Vibracones now brought the overall length of the feet to seven inches (leaving plenty of room for the weight).
After final assembly of the Table AK member “Fasterdamnit” (Jim) and I weighed the turntable and it weighs in at an impressive thirty four pounds. We then listened to the table with and without the weight attached using our reference album. The reduction in back ground noise and cleaning up of the soundstage were dramatic and instantly recognizable. We then “tuned” the weight by raising and lowering it for max noise reduction using a stethoscope placed on the bottom of the drive unit itself. I was fortunate in that the legs chosen were just long enough as the position of the bottom of the weight is only about an inch or so above the shelf it sits on once properly tuned.
Thanks for reading, Bill.:thmbsp:
Jim looking rather pleased.:yes:
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