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  • Well, I'm trying to build a turntable

    A few weeks ago, I decided I'd like a turntable. There are some albums that belonged to my father that I'd love to hear again. I wanted to hear them with the pops and ticks, too.

    I thought a small Technics SL-6 linear was the way to go. So small (12.5" square), it would fit into my living room arrangement nicely. Push-button track selection was too cool to pass-up. The one I got on eBay arrived with a broken tonearm component. I ordered a used tonearm on eBay and interestingly enough, that same part was broken. Clearly a design issue. Of course, these turntables are 30+ years old.

    So I regrouped, and got a Technics SL-J33. Same type of unit, just an updated model. This unit had a redesigned tonearm assembly, the iffy plastic part was replaced with aluminum. Nice, a much better redesign overall. I replaced all the old grease, polished the beat-up dust cover (I'm pretty good at that now), and put it through its paces with a test album I got on eBay (Ahmad Jamal album that is nearly 65-YO, great music but the vinyl is in bad shape).

    BUT, what to do with the non-working SL-6? Well, I decided I should strip the motor/platter and build my own turntable. These are magnetic drive designs, so the motor has a board with logic that fires a ring of magnets that spin the platter. However, the SL-6 has a somewhat elaborate PCB that handles using a sensor to find the starts of the tracks, start/stop the motor, set the motor speed (33 vs 45-RPM depending on the album size), etc. So the first step was decoding the six-pin connector between the main PCB, and the motor PCB, to determine whether I could even drive it with an external 12vdc supply. It took an hour or so of head-scratching, but I was able to get the motor spinning at 33 and 45-RPM. Awesome.

    I decided to start shopping for tonearms on eBay but endured a little sticker shock. I wanted a tonearm with a built-in cueing lift, tonearm rest, and a removable head shell would be nice. Used tonearms from the likes of SME go for $400ish. I always wanted an Infinity Black Widow when I was a kid, don't even ask what those cost (they're $1000).

    So I started investigating DIY tonearms. I always wanted to make a tonearm. The two most common designs I see people making are unipivots and Schoeders (which uses string or monofilament to suspend the arm, along with two magnets underneath to provide alignment--a clever design).

    I decided to try a method I've used for low-friction joints, which is set screws and ball bearings. In doing some experiments, I found the cups on the set screws I have are less round and more inverted cone shape. So I switched to using dowel centers. The resistance is low enough that the air vent in the basement, blowing overhead, makes the arm bounce up and down.

    Next I shifted my attention to making the arm spin. I used a variation of what I saw the Technics table uses for the platter, basically a sleeve bearing is mounted inside the walnut bracket that holds my arm. A 1/4" stainless shaft fits into that sleeve bearing, and rests on a steel ball bearing at the top. It spins very freely.

    So I think I have a working model. Now I just need to figure out the details like the actual shape of the arm, how I'll run the wiring, etc.

    Likely the next step will be to mount the motor to a temporary plinth (a piece of plywood) so I can start taking measurements to make the real tonearm with proportions that compliment the overall appearance (it has to look cool, otherwise what is the point?).

    Here are a couple of short movies showing the overall performance of the moving parts. Again, this is just a proof of concept, just needed to see if I could make something that would allow a cartridge to track an album. I think this is on the right track.

    http://www.jpthien.com/temp/IMG_5095.MOV
    http://www.jpthien.com/temp/IMG_5098.MOV

  • #2
    Very cool Phil! I recently rebuilt a arxa and it is about as simple (mechanically speaking) a design as you can get. There's a guy named marc morin on various forums that is the guru on rebuilding these. He uses jewel bearings with great success. The tonearm on the arxa is a similar unipivot design, so may be worth looking at. I replaced the wand with a technics so I could fit a sme style headshell. Looking forward to seeing how this project turns out.
    Carbon13

    Comment


    • #3
      Originally posted by Carbon13 View Post
      Very cool Phil! I recently rebuilt a arxa and it is about as simple (mechanically speaking) a design as you can get. There's a guy named marc morin on various forums that is the guru on rebuilding these. He uses jewel bearings with great success. The tonearm on the arxa is a similar unipivot design, so may be worth looking at. I replaced the wand with a technics so I could fit a sme style headshell. Looking forward to seeing how this project turns out.
      Cool. That Arxa looks like an actual unipivot. Lots of DIY unipivot stuff out there. It looks deceptively simple but I decided against that design because I think to do it well requires a degree of precision I cannot achieve without a metal lathe.

      I'm not sure what my pivot type would be classified as. Mixed, I guess.

      I was contemplating ways to improve what I've got last night, but realized quite a bit of my ideas would increase the mass @ the pivot, and some of them would make it look neater but would actually reduce functionality. I've come up with a couple of ideas I can use, but it is entirely possible my final result is going to look a lot like what I have here.

      My overwhelming problem now is, determining how long to make my final arm. I need to know how long the arm should be, from pivot to stylus. I know there are somewhat standard tonearm lengths. I'd like to keep it as short as possible to keep this turntable as compact as possible. I've done some googling but it would be nice to find some general design guidelines.

      Comment


      • #4
        You may want to download some alignment protractors that are available online as that may help with determining your overall length.

        Marc morin reccomends getting the counter weight close as possible to the pivots to allow the arm to be more "lithe"

        And yes, although mechanically simple, these designs are brilliantly engineered and alot of incredible design is incorporated. Just like a good athlete always makes it look easy
        Carbon13

        Comment


        • #5
          Originally posted by Carbon13 View Post
          You may want to download some alignment protractors that are available online as that may help with determining your overall length.

          Marc morin reccomends getting the counter weight close as possible to the pivots to allow the arm to be more "lithe"

          And yes, although mechanically simple, these designs are brilliantly engineered and alot of incredible design is incorporated. Just like a good athlete always makes it look easy
          It is stuff like that, that I need to know. I wouldn't have necessarily thought of it myself, but once told, yeah, that makes a ton of sense.

          Comment


          • #6
            There's a thread on AK forum called "I Am Thinking I Really Like Uni-Pivot Arms" that has a ton of interesting info, particularly from marc. I think you'll find it very informative.
            Carbon13

            Comment


            • #7
              Originally posted by Carbon13 View Post
              There's a thread on AK forum called "I Am Thinking I Really Like Uni-Pivot Arms" that has a ton of interesting info, particularly from marc. I think you'll find it very informative.
              This evening I found some small ball bearings with flanges on Amazon, I ordered some to try.

              The problem I'm having with the method I've been trying is the trade-off between friction and play, which is fairly well documented.

              I'll go find the thread you reference, thanks!

              Comment


              • #8
                Just an update if anyone is following along...

                I decided I'd try my hand at a unipivot.

                This arm has the SME V measurements. So pivot to stylus, and cartridge mounting angle, are the same as an SME V. I picked the SME V because of their reputation and at $10k, they should have gotten some stuff right on this one.

                I'm waiting for some parts from McMaster. I'm going to use a stainless rod end to fashion my counterweight axle. It should look pretty much like the eye bolt I have there, except the eye is 1/4" ID and 5/8" OD, which means I'll be able to squeeze it between two spacers. Which means I should be able to rotate it left/right to accommodate azimuth adjustments.

                I'm also getting aluminum and stainless spacers in two sizes, so I'll be able to do 1-1/2" and 2" heights. The two different heights with two different weights of materials should allow me to change the performance characteristics quite a bit.

                If this works out I can try different materials for the wand. Carbon fiber comes to mind. Different types of wood, as well.

                The slots in the wand are for securing the wiring. I have some shielded four conductor mouse wire to try (don't laugh, it is suggested at DIY tonearm sites). If that doesn't work, I can order some stuff on eBay, it isn't expensive.

                I haven't given up on more conventional gimbal type arm, just rethinking construction methods.

                Comment


                • #9
                  If you are going to use carbon fiber, the shafts from arrows work extremely well.

                  There are quite a few DIY tonearm build threads all over various forums using arrow shafts.

                  I was very close to starting a tonearm build myself, but then I discovered this retired engineer selling his own uni-pivot arms online. I bought one of his 12" models, and it has been fantastic!

                  For about $300, I now have a tonearm that is as good as many much more costly arms. Easily betters $1000 arms. As much as I enjoy the hell out of DIYing, it was just not worth the time and effort, for inferior results.

                  Also let me add, make sure that the center of gravity at the pivot point is low, in relation to a high pivot point. Also, uni-pivot arms are susceptible to something called "bearing chatter", which causes audible mistracking. Many uni-pivot arms use oil damping to remove chatter, but there are other methods.

                  You'll notice, on the temaadadio arm, the pivot is at the top of the cone, where the nob is, and the cone itself is quite heavy. This is what keeps the center of gravity low, and pivot point high. Also notice, the counterweight has its center of gravity low, and has those "outriggers" are important for setting cartridge azimuth.
                  Attached Files

                  Comment


                  • #10
                    OK, so I just wrote a long reply, and during an edit, it all went away.

                    So, to recap:

                    Carbon fiber arrow shafts work great for DIY uni-pivot arms.

                    But, there is a retired engineer, that sells his own uni-pivot arms for about $300. They will easily compete with arms at $1000 or more.

                    I love to DIY all sorts of stuff, but it hardly seems worth it in this case, for resulting in an inferior arm.

                    Comment


                    • #11
                      Originally posted by Simon Moon View Post
                      OK, so I just wrote a long reply, and during an edit, it all went away.

                      So, to recap:

                      Carbon fiber arrow shafts work great for DIY uni-pivot arms.

                      But, there is a retired engineer, that sells his own uni-pivot arms for about $300. They will easily compete with arms at $1000 or more.

                      I love to DIY all sorts of stuff, but it hardly seems worth it in this case, for an inferior arm.
                      I wish your message hadn't been lost.

                      His arm looks fairly typical of 99% of DIY unipivot designs out there. I've tried to address many of the issues in those arms, in my design.

                      My pivot is lower, relative to my stylus. I think I can get them pretty closely aligned by the time I'm done. I'm accomplishing this by dropping the center of gravity for my counterweight.

                      My azimuth adjustment and weight setting are two different operations. Setting weight and azimuth simultaneously by offsetting the counterweight while you tighten it isn't easy, I've tried. This is a real issue for people that really know their arms.

                      My counterweight is threaded to make adjustment (including fine adjustment) very straight-forward.

                      My arm is CNC pre-drilled for perfect cartridge alignment for all cartridges with a 3/8" stylus projection (this is how SME does it). No fiddling around there. Setting my arm height is very simple, too, I'll post pictures once I have my other parts.

                      Due to the way his cartridge is mounted, it doesn't look possible to easily add a finger lift, whereas I can make one as pictured and use the screw holes for the cartridge. I'm not interested in grabbing wands and dropping into the groove, I want a finger lift.

                      My arms wands are fairly easily interchangeable, if I want to use a longer arm (for instance).

                      I'll be able to somewhat easily add mechanical cueing, which is even better.

                      And after my McMaster order is here, I'll have about $50 invested in two different arm concepts. This one is nearing completion, the other needs work.

                      It is all about having fun, and learning something, too, though. I'm learning more about CAD/CAM, about the abilities of my CNC router, how to start over from scratch, etc.

                      Comment


                      • #12
                        Let me add some more of the things I stated in my lost response.

                        If you are going to DIY, make sure that the pivot point is as high as possible, and the center of gravity is as low as possible. Uni-pivot arms all already a bit 'wonky' feeling, but if the pivot is not high, and center of gravity os not low, they will just not track very well at all. Inner groove distortion will be quite bad.

                        Here is the pivot of the above mentioned Temaadaudio arm. The pivot is at the top of the cone, and the weight and arm is well below it. Also notice that the counterweight also has a low center of gravity.

                        Also, at the top of the shaft that support the pivot (hidden by the cone) is a reservoir that gets filled with oil. The oil drastically reduced bearing chatter, which will also cause mistracking.

                        So, even though uni-pivot arms are quite easy to build, they are a bit tougher to make sound good.


                        Comment


                        • #13
                          Originally posted by philthien View Post

                          I wish your message hadn't been lost.

                          His arm looks fairly typical of 99% of DIY unipivot designs out there. I've tried to address many of the issues in those arms, in my design.

                          My pivot is lower, relative to my stylus. I think I can get them pretty closely aligned by the time I'm done. I'm accomplishing this by dropping the center of gravity for my counterweight.

                          My azimuth adjustment and weight setting are two different operations. Setting weight and azimuth simultaneously by offsetting the counterweight while you tighten it isn't easy, I've tried. This is a real issue for people that really know their arms.

                          My counterweight is threaded to make adjustment (including fine adjustment) very straight-forward.

                          My arm is CNC pre-drilled for perfect cartridge alignment for all cartridges with a 3/8" stylus projection (this is how SME does it). No fiddling around there. Setting my arm height is very simple, too, I'll post pictures once I have my other parts.

                          Due to the way his cartridge is mounted, it doesn't look possible to easily add a finger lift, whereas I can make one as pictured and use the screw holes for the cartridge. I'm not interested in grabbing wands and dropping into the groove, I want a finger lift.

                          My arms wands are fairly easily interchangeable, if I want to use a longer arm (for instance).

                          I'll be able to somewhat easily add mechanical cueing, which is even better.

                          And after my McMaster order is here, I'll have about $50 invested in two different arm concepts. This one is nearing completion, the other needs work.

                          It is all about having fun, and learning something, too, though. I'm learning more about CAD/CAM, about the abilities of my CNC router, how to start over from scratch, etc.

                          Your process looks very good, for sure!

                          Keep up the great work.

                          There are accessories available for the arm I mentioned, for cueing and such.

                          Comment


                          • #14
                            Originally posted by Simon Moon View Post
                            Let me add some more of the things I stated in my lost response.

                            If you are going to DIY, make sure that the pivot point is as high as possible, and the center of gravity is as low as possible. Uni-pivot arms all already a bit 'wonky' feeling, but if the pivot is not high, and center of gravity os not low, they will just not track very well at all. Inner groove distortion will be quite bad.

                            Here is the pivot of the above mentioned Temaadaudio arm. The pivot is at the top of the cone, and the weight and arm is well below it. Also notice that the counterweight also has a low center of gravity.

                            Also, at the top of the shaft that support the pivot (hidden by the cone) is a reservoir that gets filled with oil. The oil drastically reduced bearing chatter, which will also cause mistracking.

                            So, even though uni-pivot arms are quite easy to build, they are a bit tougher to make sound good.
                            My center of gravity is lower (due to the offset) than can be achieved by drilling a counterweight with an off-center hole. I'm hoping this allows me to keep my pivot point somewhat more in line with my stylus while maintaining stability.

                            If it doesn't work, I honestly haven't lost much.

                            Comment


                            • #15
                              My DIY tonearm project continues.

                              I got my parts from McMaster. Right now I'm using the aluminum spacers (instead of the stainless I also ordered) because they're light. The overall height of the arm is 1-3/8" but you need some clearance at the bottom for pivoting action. I'm trying to keep the height down because my platter/motor won't be too terribly high (they are pulls from an old Technics SL-6, if you recall).

                              I'll likely replace the screws with flat-heads to reduce the overall height and compensate for the tonearm wiring having to clear that front screw on top. My tonearm material is just 3/16" thick, so I might end up needing to order undercut screws (should have thought of that). I'll try countersinking carefully.

                              The wire I'm using is from a travel mouse, it is very fine, probably nearly 32 AWG. You can't tell from the pic but the section of wire with the insulation still in place has the shield wire running into the same hole as the rest of the wires, and then it wraps around the top part of my pivot component. So ground will be carried down through the pivot. I don't know at this point whether I'll even need a ground, but this is my pending/untested solution if I do.

                              The counterweight idea worked out extremely well. I can adjust weight and azimuth (because the counterweight can be shifted left/right). Right now I'm using washers and a nut/wingnut as my actual counterweight. Once I get further along, I can come up with a properly-sized more elegant solution.

                              The entire thing is very light, and extremely responsive without being wobbly. I think I could further lift the "headshell" area to do an even better job of aligning the stylus with the pivot, due to my low center of gravity counterweight method, without making for a wobbly unit.

                              The steel nut you see where the cartridge should go is my attempt at approximating the weight of a cartridge. It is just 2-sided taped in position.

                              I need to find a very inexpensive cartridge and screws to mount it to my tonearm for initial testing. Also the proper clips to go on the end of my wire (the ones there were from a shell for the mouse connection, and I can't make them work for a cartridge for reasons I won't bore you with).

                              I'll keep watching eBay for a crap cartridge and screws and cartridge clips. The little things start to add-up, as the shipping starts to eat into the cost on this stuff.

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