it is a difficult one, but you may get away with two pieces glued together to get the 50 mm, but have the top piece drilled for the arm, and the bottom piece drilled to allow the large nut to be tightened. Should work well enough (although not 100%, see above about chasing numbers!).
My RTA has undergone many iterations and is playing quite nicely these days.
I made the hinge away support by iterative experiments, stiffness was very significant, so i have a very large bolt ground to a taper working with Avonite parts as can be seen in the picture.
I already imagine that moving the pivot to reduce the free length of the rails should stiffen and raise the resonant frequency to benefit.
What else might help in designing new parts here please?
M
I made the hinge away support by iterative experiments, stiffness was very significant, so i have a very large bolt ground to a taper working with Avonite parts as can be seen in the picture.
I already imagine that moving the pivot to reduce the free length of the rails should stiffen and raise the resonant frequency to benefit.
What else might help in designing new parts here please?
M
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I don't see any materials you have use in the construction (except the added lumps of plasticine type) which may (will) cause problems.
Many thanks Cats, the Blu tack are little damping experiments, the aluminium rods seem better with that damping than without, then the pieces on the cartridge side or balancing weights.
of course its difficult to be sure as i cannot have one without the other.
I intend to try a shrink sleeve on the aluminium at some point instead.
I assess such experiments with measurements.
Here attached are how that lot plays a 1000hz tone.
However, reading your informative thoughts about materials i hoped for some suggestions for further improvement, where might i start looking please? - all ideas much appreciated!
M
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Hi Hugh, no, these are stainless tubes, i dress them for straightness and polish them. These have been damped internally in three different ways, a foam rubber insert, sand inside and blu tack, they currently have the blu tack, the sand may have been very marginally better.
Using a stethoscope i listen to taps on the various parts, and also cartridge on record through the speakers.
The rods give a dull thunk, the carriage sounds more lively...........this may also be because it is closer to the cartridge.
Making everything really stiff was the main route to improvements and the side bands you can see in the measures are much reduced as a result, damping the parts is less predictable.
What form is your LTA?
M
Mine is built in the Niffy style. Tungsten carbide rings rolling on TC rods mounted on a stiff piece of aluminum channel. I used Ductseal and strips of vinyl to (I think) damp it a bit. I'll take some pains to measure it later.
I also sandwiched layers of vinyl between most Aluminum pieces. That seemed good, but again, I did not measure it (so cautious about offering advice). I will measure it on this next one.
Hugh
I also sandwiched layers of vinyl between most Aluminum pieces. That seemed good, but again, I did not measure it (so cautious about offering advice). I will measure it on this next one.
Hugh
Clearly the Niffy style is an interesting development.
BTW, the measurement set up was daunting to start with but now very simple.
Mine is a result of many iterations Hugh, i have learnt a lot and many offered advice and help. I was initially reluctant to go to the complexity of measuring but can now see i regularly confused what i could hear, believing i suspect that because i thought it would be good and i put a lot of work in that it was! - auto suggestion is very powerful! often measurements proved otherwise and i have a box full of failed experiments!
I wonder how many folk believe rather than measure. I do take a few other screenshots but this series, now at the 1000 mark are mostly measures of my RTA journey.........
I found that following stiffness in importance is the route to carry vibrations away from the head shell piece. i try and minimise components and give firm contact, so for example i would ask about the vinyl between pieces if they are on that route, measure with and without in such a joint.
The paralelogram pivots are carbide tipped (glass cutter spikes) and there is nothing soft on the route between the headshell and the TT base that the arm is clamped to.
I agree with you about measurements.
Here's some shots of what I mean about layers of Aluminum and vinyl. 1/8" Aluminum, 1 or 2 layers of Vinyl tile, then 1/8" aluminum all bolted together. It'in the base as well as the supporting structure for the rails. It'll be quite a while before I get around to measuring it and seeing if I can do better.
https://www.diyaudio.com/community/threads/diy-linear-tonearm.238027/page-184#post-6215783
Here's some shots of what I mean about layers of Aluminum and vinyl. 1/8" Aluminum, 1 or 2 layers of Vinyl tile, then 1/8" aluminum all bolted together. It'in the base as well as the supporting structure for the rails. It'll be quite a while before I get around to measuring it and seeing if I can do better.
https://www.diyaudio.com/community/threads/diy-linear-tonearm.238027/page-184#post-6215783
Thanks Hugh, i took a look and understand, so that method of construction comes directly back to my question about
Thanks, Link got me there OK!, i used some Ball bearing hinges for a while but they still had play........sorry about the previous part complete answer above! i intended to go on to ask about that sandwich structure, is that an optimum arm base? - i will shortly build a new base and would be intrigued to know, thanks, mike
Mike,
I found an older file. It was two layers of vinyl tile sandwiched between two 4"x4" x1/8" Aluminum pieces all bolted together. It sounds fairly dead when tapped - better than Aluminum alone for sure. But there's a big resonant peak around 3 khz, so there's better combos.
I'm sure I'll have something to suggest in several months.
Hugh
I found an older file. It was two layers of vinyl tile sandwiched between two 4"x4" x1/8" Aluminum pieces all bolted together. It sounds fairly dead when tapped - better than Aluminum alone for sure. But there's a big resonant peak around 3 khz, so there's better combos.
I'm sure I'll have something to suggest in several months.
Hugh
Mike,
I take that back about having nothing to recommend yet. It dawned on me that the layers of Acrylic I'm testing probably would do very well as a base.
Are you able to acquire GB (brand) Ductseal? Two layers of Acrylic, Ductseal in between and finger tight Nylon bolts to keep the layers together. 3 or 4 layers is more effective, but it's diminishing returns.
Hugh
Hey Pyramid, I really enjoyed your research and ultimate building of your plynth - well done and the test jigs are great. During your investigations, did you look at the characteristics of any wood products such as maple, walnut etc. I build many turntables and like the aesthetics of wood. I tend to build them thickly and introduce N0. 11 lead shot into the mix as a dampener. Any thoughts on that approach? Regards John
Hi, to all out there, i tend to do experiments with things i have.
At the moment my TT and TA are mounted on separate sheets of Avonite (Corian alternative) the TA is bolted to its one and the TT rests on its own.
Then these sheets sit side by side on a sheet of Mass loaded vinyl around 4mm thick (the black layer in the picture) which sits on another sheet of avonite.
This whole sits on a shallow sand box on a wall shelf.
My feeling is that the weight of the top lot connects the top sheet quite firmly to the MLV and so to the bottom sheet of avonite, maybe this works like CLD?
My question is simple, would it be better to
1. Leave as is
2. Bond with bitumen roofing glue (viscoelastic?) the top and bottom avonite sheets to the MLV
3. Remove the MLV and bond one sheet of avonite to the other with bitumen glue
Obviously i only get one chance at this as bitumen glue is sticky stuff!
M
Nice looking work Mike.
I suspect some sort of viscoelastic might work better than the MLV between the layers, but I really don't know for sure.
The Roofing goop scares. Anything I've used on shingles stinks for a long time. Not good indoors. And, like you say, one chance with that stuff.
I like GB Electrical Ductseal because I can pull it apart if I don't like the results. It cleans up with Varsol. If it's a success, finger tight nylon bolts helps keep the "bond".
Some types of Plumber's putty might be similar (but some dry out and get a bit hard after a few months). Blue Tack, Modelers clay, Stretchy acrylic caulking, butyl tape - lots of choices.
I also bought a can of Butyl sealing goop that I've not tried yet. I'm not sure if it stays soft.
If the Ductseal is of interest, I'll post some photos of how to apply and compress it.
I'm interested in how this works out. I have some Corian to use up.
Hugh
I suspect some sort of viscoelastic might work better than the MLV between the layers, but I really don't know for sure.
The Roofing goop scares. Anything I've used on shingles stinks for a long time. Not good indoors. And, like you say, one chance with that stuff.
I like GB Electrical Ductseal because I can pull it apart if I don't like the results. It cleans up with Varsol. If it's a success, finger tight nylon bolts helps keep the "bond".
Some types of Plumber's putty might be similar (but some dry out and get a bit hard after a few months). Blue Tack, Modelers clay, Stretchy acrylic caulking, butyl tape - lots of choices.
I also bought a can of Butyl sealing goop that I've not tried yet. I'm not sure if it stays soft.
If the Ductseal is of interest, I'll post some photos of how to apply and compress it.
I'm interested in how this works out. I have some Corian to use up.
Hugh
Thanks Hugh, i shall have a look at Ductseal, interested in your methods and any test results, blu tack over that area is too large, but i have lots of success with it locally and you can often see local blobs around as experiments.
Any other input please gents?
M
Mike,
You got me wondering why I never tested any Corian. So I did. It'll be quite a while before I calculate any DF numbers, but these charts show part of the story....
This first one is a large 1/2" (12mm) thick piece of Corian. It's resonant frequencies will differ a little from your big pieces of Avion, but you get the idea.
Hugh
You got me wondering why I never tested any Corian. So I did. It'll be quite a while before I calculate any DF numbers, but these charts show part of the story....
This first one is a large 1/2" (12mm) thick piece of Corian. It's resonant frequencies will differ a little from your big pieces of Avion, but you get the idea.
Hugh
Attachments
Thanks Hugh, i am not familiar with these plots or their interpretation, does it demonstrate that Corian/Avonite might be a good or poor start point please? - how does it compare? - for a while Corian was thought to be a good start point.
Meanwhile i "dolloped out" some bitumen glue to see what i have, to be honest the smell/volatiles wasn't so bad as the warnings!
It stays liquid a couple of hours and starts to set, question is, is it a V.E. layer at the end, do i aim for a couple of mm? i could fence the edge of the avonite, level it and make a pond before adding the second sheets, i see it as quite practical if its a sound idea!
M