"Cheap" bubble levels are adequate. Why do you feel the need to go more high-tech? Does your table sound bad?
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Lindisfrane, nope, turntable sounds fine :O) I have a new protractor and just thought I'd try for a "best of my ability" setup. I'm sure some of us are pretty anal about leveling and thought I'd tap in.
Schipo, My table is set up on a spiked, heavy wooden audio stand with granite inlay. Unfortunately using a pier and beam floor, but I'm not ready for a wall mount yet.
I use a bubble level to good effect.
I've got a marble slab on top of an inflatable tube. But...
I level the stand first.
Then I put the table on top of the bladder / slab combo.
Then I put the bubble level on the bare platter. I put it at several places along the arc of the tonearm, where the cartridge would read
Then I move the air bladder under the slab a little bit at a time until the bubble level reads level. The slab isn't necessarly level, and the plinth isn't necessarily level. But the platter is.
Every couple of months I add more air and repeat the last step.
Thats just me though.
I use a 12" carpenter's "torpedo" level.
Ya gotta level your platter to the best of your ability. When mine was off about 1/3 bubble, I was getting the weirdest phase anomalies and balance problems. On one mono album, the sound seemed to come from from the front window to my left--90 degrees left of the point between the speakers.
Using my trusty Sears Craftsman level to get the bubbles to level longitudinally, laterally, and diagonally fixed all this.
I used several long levels (two 4' and one 2') to check the accuracy of three 12" ones. (One of those was actually out a little.) The accurate ones are used to level the platter. Once that is done, I permanently mount a pair of custom made glass vials into the plinths of my turntables, so the user can keep an eye on it all along. To me, levelness is a big deal.
I use a cheap, 1" long bubble level (not a round one, which would be pretty useless).
To compensate for the inaccuracies of a bubble level, if any, all you have to do is spin it 180 degrees and re-check on the same axis. If the results differ, halve the difference and you're level. Nothing could be simpler.
I picking up a pair of cables at a fellow A'goner's house a couple of weeks ago and he showed me an interesting experiment relating to bubble levels. He showed me 4 bubble levels on the same surface, each of which had a different reading. He explained that these are all hand calibrated using some sort of photographic device, which explains for the discrepancies between the bubble levels. He said he uses a digital level for his turntable, which is the best way to achieve a perfectly leveled table. FWIW, he's an architect and an engineering professor at a major university.
Me, I use a bubble level because I'm feeling cheap.
Just a newbie and still working on setting my my first (real) turntable, I thought I would just put in my $0.02. Being a carpenter with extensive experience with levels, I just wanted to point out the proper use of a bubble level. Although it looks pretty simple and straight forward, it is very important that you read it correctly. Most levels have a bubble that is smaller than the lines it is to be centered in. Just because the bubble is "inside the lines", that does not mean it is level. The bubble must have EXACT spacing from the edge of the bubble to the corresponding line otherwise it will not be level. I have also seen levels where the bubble is wider than the two lines. Here you need to be sure the overhanging bubble is equally hanging over the lines. In either case, you will be surprised as to how much out of level your turntable will be if this proceedure is not followed. From all that I have been reading on setting up a turntable, it seems that this step it very important for good results.
I use the plinth because that's what the arm is mounted on, not the platter. Might not be the right train of thought, but it makes sense to me to level the surface that the arm is on. Example, say the platter is different from the plinth by a degree. Well, if you level the platter, now the plinth is off, and so is the arm. This could cause the arm to want to swing because it's off.
1. Level the TT stand
2. Level the platter top surface
3. Adjust the tonearm mounting so that its bearings are level. This is easier on some arms than others of course.
Levelling the headshell is a good place to start, but whether it should remain level varies with the cartridge. Nearly all cartridges benefit from fine tuning of both azimuth and VTA, which could result in a non-level headshell, depending on the rig.
As others have posted, I also like to use a 9" torpedo level. I like to think I'm getting a better idea of the general level-ness of the platter. My Galibier doesn't have this issue but I've had tables in the past where the platters are not flat. Some either had a convex or concave surface. This can be dealt with but it is much easier to do so when you know this condition exists before trying to level.
Many levels can also be checked for accuracy by flipping them over as opposed to turning 180. Either way gives the same indication of how accurate the level is.