Air bearing?
I've only just read through this thread and whilst it's only my opinion and I don't wish to detract from the work carried out already, I think the problem with this design is lack of rigidity. Pixpop has also mentioned this in a few of his posts. As I see it the mechanical connection between the platter/bearing/subchassis/arm/cartridge should be as rigid as possible. An air bearing if engineered well is capable of good rigidity at that point because air at pressure surrounds the bearing completely and gives a tight fit to the tube. The air effectively becomes part of the assembly but the bearing will still slide up and down the tube. This is how the Kuzma works and if I was going to build a parallel tracker this is the route I would choose. I did actually think about building a Laardegard at one stage but felt it also lacked the necessary rigidity.The SME 3009 suffered in this respect due to it's knife edge bearing and an Acos Lustre or RB 200 could knock the spots of it in that department.
Si.
I've only just read through this thread and whilst it's only my opinion and I don't wish to detract from the work carried out already, I think the problem with this design is lack of rigidity. Pixpop has also mentioned this in a few of his posts. As I see it the mechanical connection between the platter/bearing/subchassis/arm/cartridge should be as rigid as possible. An air bearing if engineered well is capable of good rigidity at that point because air at pressure surrounds the bearing completely and gives a tight fit to the tube. The air effectively becomes part of the assembly but the bearing will still slide up and down the tube. This is how the Kuzma works and if I was going to build a parallel tracker this is the route I would choose. I did actually think about building a Laardegard at one stage but felt it also lacked the necessary rigidity.The SME 3009 suffered in this respect due to it's knife edge bearing and an Acos Lustre or RB 200 could knock the spots of it in that department.
Si.
I am not sorry to disagree. If rigidity is your aim - bolt the arm to the platter.
I had all three of the arms you mention, and to my experince the acos and the rega (i had the rb 300) are a little too rigid for my taste - i.e. they are the *****, , and the sme 3009 and the MG1 airbearing arm play at the same level. The acos luckily burned down with my shop, the rega was sold, the sme and the MG1 remain.
Ok, so I've had a few ideas over the last few weeks...
Now for a pivot, you could use a chinese cheap as chips centre punch - it would be easy to mount and handle, and sturdy enough to avoid the flex you get with pins and so forth.
For a test arm, how about FR4 PCB... easy to build a test T section of the correct length, it's flat(ish), and easily joined together (a little epoxy, or some solder for a higher mass arm).
Counterweights have been giving me real grief, until I became inspired at B&Q (home despot equivalent) and saw some munson brass pipe fixings - these clamp on a piece of copper pipe of appropriate diameter, and allow it to be bolted to a wall or in our case tonearm.
The counterweight now is easy - a section of copper pipe with end cap, filled with something dense like lead. Slide in the munson fitting until the appropriate VTF is achieved...
To minimise the 'chatter' of the point contact bearing, make a slight depression in the FR4 using the tip of a drill, and glue a nice little neodynium magnet on the other side.
I reckon you'd be out to the tune of £10 all up for the glue, parts and so forth. certainly enough to get a more than passable arm built.
Hopefully that description is enough for most to get going and have a go...
Owen
Now for a pivot, you could use a chinese cheap as chips centre punch - it would be easy to mount and handle, and sturdy enough to avoid the flex you get with pins and so forth.
For a test arm, how about FR4 PCB... easy to build a test T section of the correct length, it's flat(ish), and easily joined together (a little epoxy, or some solder for a higher mass arm).
Counterweights have been giving me real grief, until I became inspired at B&Q (home despot equivalent) and saw some munson brass pipe fixings - these clamp on a piece of copper pipe of appropriate diameter, and allow it to be bolted to a wall or in our case tonearm.
The counterweight now is easy - a section of copper pipe with end cap, filled with something dense like lead. Slide in the munson fitting until the appropriate VTF is achieved...
To minimise the 'chatter' of the point contact bearing, make a slight depression in the FR4 using the tip of a drill, and glue a nice little neodynium magnet on the other side.
I reckon you'd be out to the tune of £10 all up for the glue, parts and so forth. certainly enough to get a more than passable arm built.
Hopefully that description is enough for most to get going and have a go...
Owen
I can't quite picture this. What is this munson thingy, and how big is it?
I like the PCB idea, especially if copper on both sides.
Re pivot/bearing/magnet: What if you start with the hole big enough so that the pivot point just touches the bottom of the magnet?
I applaud any attempt to use plumbing items for DIY projects
baggins said:
I wouldn't say it actually lifted off it's knife edges but maybe describe it as bearing chatter. However it must be said that at the time it was state of the art, in fact it defined the art, but things move on don't they. I used a 3009 quite happily for many years but with a stiffer headshell. Do SME still use knife edge bearings?
Si.
H',
I think you ought to explain exactly what you mean .For a knife edge in a v to "chatter" implies some kind of movement up the
side walls or lifting vertically clear of the contact point. The other
option is that the knife edges or the bearing suffer bending . Which of these ( or other phenomena ) do you consider was occuring?
I think you ought to explain exactly what you mean .For a knife edge in a v to "chatter" implies some kind of movement up the
side walls or lifting vertically clear of the contact point. The other
option is that the knife edges or the bearing suffer bending . Which of these ( or other phenomena ) do you consider was occuring?
Hi Baggins, Whether the bearing is suffering from bending or movement (ie chatter ) I really don't know but I believe the mechanical energy in the arm tube can exite the knife bearing and cause a raggedness at the frequency extremes.That's what it sounded like to me anyway. And as I said before it's only my opinion.However the midband improved when I used the stiffer headshell off the previous arm which was of Acos origin.I used to know a guy in Blackpool who dealt in upmarket gear. I bought a Grado cartridge from him and I when I told him I had replaced the Acos arm with the SME he explained that the bearing setup on the Acos was better in his opinion than that of the SME because of the failings of the knife edge bearing.He wasn't the only person either that held this view. I'd be interested to hear your opinion. Incidentally I think my brother still has the turntable and 3009 arm in his loft somewhere. I sold it him complete with V15 111 for £ 50 about 25 years ago.
Si.
Si.
He'd probably get more than £50 for the V15 alone on ebay !
As regards our discussion I have never even heard a sme arm in use so my opinion as regards the harshness is irrelevant. I figure that maybe the knife edge bearing is possibly too accurate in relaying plinth noise back to the cartridge, if anything.
That would make sense as a knife edge is possibly the least "lossy"
type of bearing.
As regards our discussion I have never even heard a sme arm in use so my opinion as regards the harshness is irrelevant. I figure that maybe the knife edge bearing is possibly too accurate in relaying plinth noise back to the cartridge, if anything.
That would make sense as a knife edge is possibly the least "lossy"
type of bearing.
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