To all Ladegaard builders

[peterr]

I have been running my Ladegaard for about a year now and although it works well I am convinced things could be better than they are.
(you can see my current version here: one and two ).
Last night I tried to find out where improvements could be found and I think I have at least identified one problem. It turns out that the aircushion between base and slider is not at all uniform from top to bottom. The results is that the bottom of slider is able to move backward and forward quite a bit (see pic below).
I want to ask other users to check their arms to see if they have this problem as well.

I have been thinking about a possible solution and I can see two options that might work:
1. Drill the holes in the base in two rows instead of one (the second row will have to be a lot further down)
2. Drill the holes in one row but much further down.
I think option nr. 1 has the biggest chance to work

Reactions Please!

[J Epstein]

My only observation that relates to this is that you are better off if you can have a higher pressure and a heavier slider - you will get a "harder" air cushion and the result is a better sound. My experience is that I have been using aquarium pumps with a marginal pressure and this is less than ideal - a compressor or a compressed air source like a pressure tank would be better. Then you can pile on a litttle more weight and the sound tightens up a little.

Nice looking implementation - I like your arm lift!

-j

[livemusic]

Peter,
I would stick with the existing holes arrangement around centerline. It seems to me, the slider is more stable both statically and dynamically this way. The static air pressure under the slider within the area below the holes is maximum and equal, assuming the air flow at the slider ends is negligible. Above the holes, the pressure starts to drop towards (air is flowing from high to low pressure area). So, if you place two rows of holes, the air will tend to flow through the upper row (lower backpressure), thus increasing the total air flow and associated hiss and induced vibrations also. Placing the holes in the bottom part only may lead to dynamic instability, when the slider starts to rock due to variable stylus friction forces on loud passages.
As for making the Ladegaard better, methinks it shall be treated essentially like the Schreder arm, namely addressing the stylus induced vibrations by the armwand and counterweight proper damping, because both arms are decoupled from the armboard (no rigid mechanical bearing here). The most noticeable improvement I got was due to double damped armwand and more rigid hedshell and arm-to-slider connection.
Cheers,
Michael

[dice45]

peterr,

why not feed the air to the slider instead to the rail?
symmetric load, 100% nozzle coverage would be the benefit.

[Paul Ebert]

I've always wondered how to minimize the stiffness of the air tube to acceptable levels when supplying the air to the slider. I've seen applications (including the Kuzma linear arm), so I guess it can be made to work, but I would think you could never make it as flexible as the wires.

A possible way of making the bearing more rigid would be to change the slider to be four sided (a square tube) and put another, inverted 'base' above it (creating two opposed air bearings). This might require a change to the vertical bearing. The lower bearing would need to be supplied higher pressure to the degree required to lift the arm. The advantage would be that you could increase the pressure(s) to create a more rigid bearing while not increasing the air gap or having to increase the weight (beyond the increase caused by the square tube slider, of course). In effect, the upper bearing would load the lower.

This idea occurred to me several years ago, but I never implemented it. I ended up building an arm similar to the ET2 instead. But, I still think it's worth consideration.

Paul Ebert

[livemusic]

Bernhard,
Could you please point out any source for affordable superflexible tubes?
Thanks,
Michael

[ThorstenL]

Konnichiwa,

Originally posted by peterr
I have been running my Ladegaard for about a year now and although it works well I am convinced things could be better than they are.

I have always wondered about a "maglev" version. We know maglev is unstable, but that is what we want.

Put neodymium magnets into the sled and use electromagnets to get the sled to float, or just more ND Magnets.

Together with the Laadegard style aluminum angle you get eddy current damping for free so the lateral movement will be frictionless for slow movement but heavily damped for fast movement.

The V-Shape of the magnetic field will stabilise the system in the forward/backwards direction and the left/right movement will be in effect completely free, but damped by the eddy current damping.

Now, the question is can this be made to work?

Sayonara

[dice45]

Michael,

Originally posted by livemusic
Bernhard,
Could you please point out any source for affordable superflexible tubes?

from my calculations, there is not much air-flow needed. So i settled on a cheap silicone insulation tubing of lowest available diameter, say 1mm. I made an experiment: my comperessor could not make this tubing blow at 8 bar. I used the Coroplast brand.
Good quality, costs a joke.

You may look puzzled howsuch a weak thing as silicone insulation tubing can stadn 8 bar, but the pressure limit of a container is proportional to 1/r^3 . So, the thin tubing, having a very low r, has a high pressure limit.

How to get a terminal piece to the tubing:
take a piece of plexiglas/perspex, drill a hole with the tubing's outer dia into the perspex plate's small side, glue the tubing into the hole with cyanacrylate. Then drill another, bigger hole thru the perspex's big side, crossing (=drilling out) the tubing. Now the tubing's end should be flush with the bigger hole's surface. You can use this perspex piece to connect it via a hollow screw to the air supply.

I would expect 3 out of 4 tries to be successful if you are not extraordinarily clumsy and if you are practising a bit, you may have a 98% yield.

Having abandoned my Ladegaard project (currently designing an active linear tracker with zero lateral stylus forces) i have more tubing than i ever may need. Send me your adress via email, i send you a big sample.

[AuroraB]

Actually, - I have been pondering with the same idea for a maglev version of Ladegaard....but using ND mag's and mild steel for the lower V part.....
In theory, -it should work, but I haven't done any tests or calcs to see how much weight it will support for the sled and arm....
Wonder if the stray field would influence the PU, though....????

[ThorstenL]

Konnichiwa,

Originally posted by AuroraB
Wonder if the stray field would influence the PU, though....????

It might, but remember fieldstrength falls to the square of distance and the field is in essence static and directed not in line with the Pickups own magnets. So whatever happens there is low in magnitude and static or extremely low frequency.

Sayonara