Experience With Linear Tracking Turntables

Hi lewm.  Yes you are right and the generally accepted value is AS = ~ 0.1 (VTF).  It should be understood that there is variation in the amount of AS needed as the arm moves across the record. Also a record that is not perfectly flat will affect AS as well as VTF as the arm and cartridge travel across the record.  AS is always an approximation as you know.  Usually when too much force is applied it causes cantilever skew and resulting damage that Dover mentioned.  By contrast, I have never seen damage to a cantilever when no AS was applied.  This was true even with the very bad arm with high friction on the old AR turntable.  Another valuable lesson I have learned recently while setting up turntables with AnalogMagik is that AS can be adjusted over a fairly wide range without causing significant changes in distortion.  In other words, a little bit is enough.  There is no benefit to applying higher than a minimal amount of AS or even none at all.  To put what I mean into context, on my Technics SL1200 GAE setting up an Ortofon 2M Black LVB, VTF = 1.5 gm, set AS using the Technics scale = 1.5, I got a value for distortion of X (I am in NH, notes are in FL).  Then I set AS on Technics scale at values ranging from 0 to 2.5.  Distortion never varied by greater than 0.2% and usually much less.  I found the difference on my HW-40 (arm 10.5") to be essentially immeasurable when no AS was applied at all with a SoundSmith Hyperion, VTF = 2.0 gm.

That formula, AS = 0.1*VTF is a nice rule of thumb, if any of us could possibly measure AS in grams or any other unit of weight.  I understand that Wally Tools make a gadget for that, but otherwise the vast majority of us do not know exactly how much AS we are applying. My point was that the cure for skating is NOT to increase VTF or that cartridges requiring higher VTF are NOT less prone to skating.

I use the lowest magnitude of AS possible with a given tonearm, and I never worry about it after that. However, I do find that some AS is better than none.  As to your experience suggesting that cantilever deviation is never due to not using any AS, I was never in the business so I do not have a vast experience that could speak to that proposition. In my own private experience, setting azimuth off dead center (less than or greater than 90 degrees) has more potential to cause a deviation of the cantilever and especially aberrant stylus wear (worse in my opinion) than does too much or too little AS, unless you crank in an absurd amount of AS.  Many audiophiles seem to think that if the AS adjuster is graduated in numerical fashion (1, 2, 3...), that should correlate with VTF, which is to say that for a VTF of 2g, set AS to 2. Yet I know of no tonearm that comes with that instruction. (I know someone will contradict me, and I am happy to learn of some tonearm that does tell you what their gradations mean.)

For the moderator:  This is the fourth time today that I have had to log in to respond to a post here in the forum.  Something is amiss.

lewm, I am not in Florida so I cannot be certain, but I am going to state here with a certain level of confidence that in the manual for my Technics SL 1200 GAE there is instruction to match the setting for AS to coincide with the setting for VTF.  Frankly I am almost certain that is so.  I worked with Japanese engineers in my profession for many years and in my experience they left nothing to chance. Technics/Panasonic in particular has a reputation for being thorough and accurate in every particular.  

SME brochure for SME IV "The dial is calibrated and should be set to correspond with the VTF in use".

Jelco instruction manual for TK-950S and TK950SL

"It is calibrated from 0 to 3gr in 0.5gr increments and should be set to the same value as the tracking force setting (or somewhat less) pressure."