Well if youve got it tracking O.K. @ 2 gms I reckon your well on the
the way to a successful design. The vibrations you mentioned -are they at the audio frequencies because the cartridge is low compliance or are they being caused by the transport system itself?
Congratulations once again
Wilt
the way to a successful design. The vibrations you mentioned -are they at the audio frequencies because the cartridge is low compliance or are they being caused by the transport system itself?
Congratulations once again
Wilt
tubee -
I can't detect any lateral movement of the cantilever. There is no evidence of stick-slip motion, the whole thing seems to be moving slowly all the time. If in fact it is stopping and starting, the increments are too small to detect visually. Perhaps a test I could do would be to lower the stylus with the platter not spinning, and then watch what happens as it spins up.
Baggins -
I think the vibrations are due to the brass rod resonating. If I press on the rod with my finger, the vibration stops, so I don't think it's related to the cartridge or armtube. I think the rod is not rigid enough.
A solution is to use a thicker rod, and mount it more rigidly. But this will mainly serve to simply raise the resonant frequency and improve the Q, neither of which is helpful. Another solution would be to glue two rods together, one above the other, and make them of different materials.. e.g., brass and carbon fiber, to reduce the Q.
I can't detect any lateral movement of the cantilever. There is no evidence of stick-slip motion, the whole thing seems to be moving slowly all the time. If in fact it is stopping and starting, the increments are too small to detect visually. Perhaps a test I could do would be to lower the stylus with the platter not spinning, and then watch what happens as it spins up.
Baggins -
I think the vibrations are due to the brass rod resonating. If I press on the rod with my finger, the vibration stops, so I don't think it's related to the cartridge or armtube. I think the rod is not rigid enough.
A solution is to use a thicker rod, and mount it more rigidly. But this will mainly serve to simply raise the resonant frequency and improve the Q, neither of which is helpful. Another solution would be to glue two rods together, one above the other, and make them of different materials.. e.g., brass and carbon fiber, to reduce the Q.
I don't know much about physics. But my hunch is that if the only thing you change is the length, it will resonate just as strongly, but at a higher frequency. I suppose if you make it very thick and short, the resonant frequency will shift out of the audible range.
In any case, remember tat the rod is only held in place with two strips of masking tape. Worse yet, those red boxes are just empty plastic boxes sitting on the plinth. It shouldn't really be surprising that it vibrates. What should be surprising is that the damn thing plays at all
I'll do some more tests when I come up with a more rigid mounting arrangement. But having a long rail like this is inconvenient. I think the idea of a short thick cantilevered bar is more practical. I've also thought of using a tube instead of a rod, and filling the tube with some material like plaster, or epoxy. Or what about a carbon fiber tube. A 1/4 inch carbon fiber tube would be much more rigid than my brass rod, and would probably work well as a cantilever, maybe 6 inches long.
Yes, I have thought of these. Also, I've heard arrow shafts are good. Someone has given me a carbon fiber golf club. I was originally planning to use this as a tonearm, as it's tapered, and that supposedly reduces resonance in the tonearm. But that tube is too rough on the outside for the linear rail. My local hobby store carries short olengths of carbon fiber rods and tubs. I'l go in there today and pick up a few for experimenting.
Last night I had the idea to get three carbon tubes about 5-6 mm diameter, and about 200 mm long. Then I would glue them together in a bundle. Put two on the bottom, and one on the top, and glue with epoxy along their entire length. The epoxy would be in the cavity between the three tubes. Then the two tubes on the bottom would the base that the arm sits on. The carriage would ride on the top tube. I think this would be extremely rigid, and extremely low resonance.
hi pixpop, i was thinking upside down much like a "V" with the rail at the bottom, two stainless steel rods on top for rigidity and support and some nice redwood on both ends
you're doing us all a great favor with your time, effort, money, etc.
as MasterCard would put it- "priceless"
ps.
will glass tube rail ring like hell?
much like a "V" with the rail at the bottom, two stainless steel rods on top for rigidity and support and some nice redwood on both ends you're doing us all a great favor with your time, effort, money, etc.
as MasterCard would put it- "priceless"
ps.
will glass tube rail ring like hell?
I don't know, though I think glass is less elastic than metal, so perhaps it would not resonate so badly.
Stainless steel, brass, and wood look very nice together. But I'm not ready to make it pretty yet. I want to do a new version that's a bit more precise and rigid.
BTW, this thing didn't cost much. The bearings were about $5 each. The square brass, the brass rod, and the Al tube were each less than $2.
I've just noticed some ABEC-9 bearings on eBay for less than $1 each, but they are 22mm OD. Might be too heavy.
As I understand it the more rigid a material is the higher its fundamental resonance will be. I was once told by a structural engineer on a scaffolding safety course :- if you jump up and down
on a structure and it wobbles slowly get off it immediately ,if however
it just responds with a sharp sound its probably rigid-- This sounds like a pretty good way of understanding resonance . hope this helps !
On this basis glass will resonate at a higher frequency than brass or
steel.
on a structure and it wobbles slowly get off it immediately ,if however
it just responds with a sharp sound its probably rigid-- This sounds like a pretty good way of understanding resonance . hope this helps !
On this basis glass will resonate at a higher frequency than brass or
steel.
Whilst thinking with these ideas, it occurred to me that very nice precision bearings are available from dead VCR head drum motors. I've extracted a few to play with!
However, my early experiments using scanner rails suggest that the phosphor-bronze bushes used in the scanners run even more smoothly than ballraces, and of course allow full movement in both planes.
However, my early experiments using scanner rails suggest that the phosphor-bronze bushes used in the scanners run even more smoothly than ballraces, and of course allow full movement in both planes.
The combination of hard and soft materials will do the trick. The speaker Argenta from Sonics, a very good sounding speaker, is made from wood, and internally dampened with ceramic tiles. The vibrations walk dead in this compound material because of totally different transmitting velocities.
IMO thats why its not a bad thing to use a glass rod liner for the bearings, and epoxe glue a few dampening subrods on it from softer materials, eg carbon, wood, lead, or whatever you find in the garage.
IMO thats why its not a bad thing to use a glass rod liner for the bearings, and epoxe glue a few dampening subrods on it from softer materials, eg carbon, wood, lead, or whatever you find in the garage.
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