Slightly new take on the tonearm. The top half of the pivot has been changed-out so the wiring now comes in right on top of the pivot (easier said than done on a unipivot), reducing the lever effect (of having the wiring attach 3/8" from the pivot, and I'll admit here these are tiny/incremental changes). Also changed the arm so the stylus falls exactly inline with the pivot, provided the screws to stylus tip are very close to 3/8" (mostly a standard). Basically shifted the cartridge mounting to the right. This should make setting azimuth easier if I for some reason want to go back to an unconstrained unipivot. And I sprayed this one with some shellac. I can track at 1.25g like a boss. I hadn't realized the stylus I'm using here (ATN122EP) is supposed to work down to 1g, I didn't try that yet. These are t4p parts, so I'd probably stick with 1.25g anyhow, but now I want to try 1g and see how it tracks.
In looking for my final remaining sources of easily controlled resonance/buzzing, I zeroed in on the wiring. The original method of running the wire down the top of the arm wand and securing with cable ties was an issue that could contribute a resonance. I was aware of it and after disturbing the wire (like installing a new cartridge) would gently adjust the wire so it was only touching the wand at the points of the cable ties. I figured I should fix that, so I added a pocket for the wire which gently sort of grips the wire all the way down. Now the entire length of wire is actually touching the arm. I had all along also thought that an ideal wand material to try may be old-growth spruce, with the alternating very very hard slow-growth "rings" alternating with the softer summer growth. Nature's constrained layers, in a way. The spruce was materials on-hand, I've had it for over ten or fifteen years. I just didn't want to use any until I was further along in my wand design. These are 12" wide, 1/4" thick pieces that are left over from making veneer. Once the company making the veneer can no longer slice any further, they take what is left in their machine and sell it to fools like me. The amazing thing is that, over fifteen years, this 1/4" thick spruce that is 12" wide has stayed perfectly flat. I don't know how old it is, but the rings are very tight, and typically only the finest logs are selected for slicing into veneer. New wand is also slightly thicker (old wands were 3/16"), and the "headshell" area is slightly reduced in thickness to elevate the cartridge relative to the bearing (bringing the pivot about 1/8" closer to the vinyl's surface). It is finished in spray shellac. The extra black wire you see back at the pivot is a service loop that will allow me to cut-off the current cartridge clips and apply new ones, if necessary. It isn't unusual to bung a clip with all the cartridge swapping I sometimes do. I had previously hidden this extra wire by running it down below the wand, then back up. But in an effort to make sure there is no source of resonance or buzzing, I'm just leaving it hang, I don't really care how it looks. Still room for improvement: Easier VTA adjustment. Maybe. The current method allows me dedicate a pivot to each wand, so I can easily return to a previous VTA. But initial setup is kind of a PITA. Anyway, that is what I've been working on.
Still on the hunt for anything that may contribute unwanted coloration on my tonearm, I turned my attention to the counterweight. I spent a ton of time reading on the subject. There are obviously the coupled and decoupled camps. After trying a few different varieties and as far as I'm concerned, they each have advantages and disadvantages. The problem is really the hunk of metal that is the counterweight. Any energy passed by the cartridge to the arm travels the arm to the weight and reflects back, and decoupled arms just seem to change the nature of that reflection. What if the counterweight was really a sink for that energy? What if, I used the same Sorbothane-like material I use for my feet, for the counterweight? Oh no you didn't! Oh yes I did! The first thing I did, because I happened to have test vinyl out anyhow, was put it through its paces a little. Normally I like to listen, then test, then listen, but whatever. And what surprised me here is that tracking ability was slightly improved. This test arm has a Shure M97HE, which is known to track superbly. But I noticed I was able to achieve lower distortion on the same 80-um test tracks, at lower VTF. A good sign for sure. Also somewhat interestingly, is that the arm is quieter (vibrating less) when playing those test tracks. Remarkably quieter. 80-um can put a lot of energy into the cartridge and wand and anything connected, some arms can sound a bit like an old wind-up alarm clock with a pillow over it. Listening to some vinyl, I'd say clarity is improved overall. Piano was always this arm's forte and it just got even better. Albums I have with multiple pianos allow you to really drill down on how each piano sounds, it is a thing of beauty. Cymbals/brass also got even better. I had once read a comment from a tonearm designer that indicated one could over-damp the arm, to the detriment of the performance. So I was sort of hesitant to spend time heading down this path, figuring I'd just find that the magic was gone. MAN am I glad I decided to give it a shot.
One thing I forgot to mention, is that one thing caught me by surprise: This iteration seems to have quieted the pops and ticks some. Now, I am aware of how preamps can contribute to pop/tick enhancement, but I never in a million years would have figured the tonearm could also emphasize this sort of surface noise. My vinyl rig is already very quiet, but it did get quieter.
Nice move. But the weight still looks rigidly attached. Is this so? You're using the sorb strictly as vibration damping as opposed to isolation?
The Sorbothane IS the weight. It has a threaded inset molded into the top, the screw holding it to the bracket only penetrates about 1/4".
Great solution. Plenty of high quality arms are designed with hex/allen screw locks to both fix the counterweight in place and fully couple it to the arm stub. I don't think you could over-damp your arm - the wood is far too reactive - so the sorbothane has to be a eureka moment on your part.
Ah ok.... wasn't sure if the bolt was through or not. Are you familiar with the arm John Bicht designed for Mission, the 774? It uses a large Sorbothane bushing to isolate the weight from the arm. Similar to your idea but going back 40 yrs. Over the years the sorb has degraded in some instances, leading to some ppl replacing it with something more rigid like plastic. Some say it's better as a result. I have my doubts, but no doubt that it is different.
I've read a little about it and other arms using the same approach. It is possible that rigid would be better than malfunctioning/sagging Sorbothane/polyurethane-based bushings. I've seen a lot of sagging counterweight stubs on eBay and via Google images, many bad enough that I think it would be audible.
In some cases it was degradation due to environment conditions, in others it was man handling the delicate suspension resulting in a tear or rip. The whole point was to remove the CW from the arm mass equation as much as physically possible. At what point is enough isolation? From the success of the aftermarket Rega CW that mostly focus on tight coupling, we know that the simple double O-ring that Rega devised is not adequate. What you've done is remove it entirely, which is more ideal than some median point acting as a tuned filter. Judging again by the success of the aftermarket Rega CW, It's either all or nothing. So what are you using for lateral balance, or is it all on the lateral restraints you have built into the pivot? They look good. Are they silicone rubber o-rings?
Thanks! Some of the stuff on bats (wood vs. aluminum vs. composites) has been very helpful. I always figured audiophiles were a bit crazy, but we have nuttin' on bat people.
Those four bands at the bottom that provide stabilization are hairbands. They're basically nylon-wrapped elastic, which is really an ideal material.
Fascinating thread Phil. I love the step-by-step development of your uni-pivot and the innovative method of roll stabilisation.
When it comes to damping a tonearm, there is a very fine line between controlling resonances, and stepping on transients. The rubber counterweight brings a lot (A LOT!) of damping to the party. I find myself reducing the damping via stabilization bands, when using the rubber counterweight. Perhaps there is an interaction between the counterweight and the bands at play, having two systems of damping may complicate matters. Nonetheless, I find myself listening via the stabilization bands and a steel counterweight the most. Using maximum damping with the rubber counterweight and bands can provide some insight into problems with recordings, though. It can sometimes feel like looking at a photo through a magnifying glass. For certain solo piano works it can be sort of captivating. I waste so much time tweaking this arm. You guys have no idea how much time I waste on this.
Another update for anyone still following along... Someone sent me some amazing 1.5mm cord to try instead of the hair bands. Just incredible stuff. If NASA wanted to make micro bungee cords, I suppose this is what they'd use. But it comes in a continuous length, not in nice little round bands. So I had to figure out a way to make it work. I also knew I wanted to return to using a bottom plate, to lock those two pillars together. So I designed a bottom plate with some notches and paths to route the cord into a double band. It allows me to achieve any tension I like, with a high degree of consistency from unit to unit. I also wanted to redo the top plate (to which the counterweight attaches) to pickup the other screw. This would yield strength as well as instant alignment without having to adjust during assembly, and also allows me to use the anti-skating hanger on either side of the arm. The arrow pointing up is the new bottom plate, the arrow pointing left is the new 1.5mm cord stabilization/damping band(s). Unfortunately a little difficult to see as the plate and cord are both black and it all blends together. So this is how I've been wasting my time. This, and listening to a ton of vinyl. I love checking my work.
The nylon or acrylic you’re using for the top plate seems like it will also do a good job of damping both minor airborne noise and minor vibration coming up from the plinth. The increase in rigidity must also be improving tracking, no doubt minutely, but improving it nonetheless. Looks better too. Any noticeable pivot bearing wear so far? Any lubricant change there? Did you bond the ends of the cords with adhesive, melt them together under heat, cold weld under pressure? What cartridge are you using right now?
Yeah that top plate is actually made of polycarbonate right now but I've used both polycarbonate and acrylic and can't decide which one I like more. I did do a little research and found that the transmission losses for the two materials are waaay closer than I had expected, which may account for my inability to actually pick one vs. the other. The bottom plate is made from acetal. That may change, as well. Funny you should mention bearing wear, I had the same question and haven't noticed any. So I just recently swapped the cup side from polished stainless steel to black oxide finished and figured I'd monitor the black oxide finish for a better wear indication. I've been trying different oils but have used the stuff I use for my air compressor a lot, which happens to be the same stuff recommended for the turntable spindle, as well as sewing machines. I'm back to using the Ortofon Super OM with a Stylus 30 a lot. Not only do I like the sound, but it is very sensitive to setup. So the cartridge/stylus can work as a bit of a feedback tool, I know if a change to the arm is causing a problem because it performs slightly less well on test tracks, for instance. I treated the cord ends with a lighter. Other cord I've tried doesn't like the lighter so much, this stuff is a dream to work with.
For my purposes in applications very different from yours, polycarbonate has proven to be somewhat more dimensionally stable than nylon or acrylic in all directions through a very wide range of temperature and humidity conditions.
Very good to know, thank you. That is a strong argument in favor of just sticking with the polycarbonate, then, as I already have seasonal issues due to humidity's impact on the wood wand. I've just recently starting keeping a spare wand on a balance so I can observe how much humidity effects the mass, and how long those changes take to migrate through the shellac finish. I don't really want MORE meaningful seasonal changes.
I've had very good luck, in a few applications, essentially duplicating a hardwood assembly or extension using billet aluminum (of the correct thickness from the supplier). Hand cutting billet aluminum is trivial, hammering (to relieve any internal stresses) the cut/filed-down piece is trivial, and grinding/sanding/polishing to various levels of finish is trivial. I have found the end result to be a better match for polycarbonate supports and attachments because both linear coefficients of expansion are much closer to each other than nylon or acrylic are to billet aluminum. Same with the specific heat capacities of billet Al and polycarbonate.Nowhere near identical, but a lot better than nylon or acrylic. Keep in mind too that acrylic block, typically, is conductive. Polycarbonate block is not conductive. If you're in any way concerned about that in your tonearm design, that's another vote for polycarbonate. Polycarbonate is also less like to trade ions with attached materials, which may also slightly help to reduce the potential for static charge buildup.
