The new mass looks and sounds much better than before. I aimed for 4.5g added mass but actually ended up with 4.7g after stacking a fair amount of hockey tape on top of the lightweight "headshell" of the Linn Ittok arm. I also removed some hockey tape from the arm which was getting too close to warped records. I added a single layer of hockey tape around much of the cartridge too (which was not easy to do) in the hopes of attenuating a high frequency resonance apparent on the Hifi News frequency sweep test.
Sonically I'm feeling I now have turntable reproduction in the big leagues, like the megabuck turntables at shows. Probably most of what they do is simply getting the basics right, such as effective arm mass for the cartridge.
In order to test turntable speed, I brought out the Feickert test record, which works with the PlatterSpeed app on my Android phone. Sadly it does not appear there is an equivalent app for iPhone anymore. The iphone apps have you place the phone on the record, which introduces a lot more weight on the platter and therefore may change the speed slightly on a Linn (which it seems to do) because the suspension is pushed down, changing the angle with the motor pulley and hence speed.
The Feickert record also has a low frequency spot frequency test which seems easier to read visually than the Hifi News low frequency sweep. The announcer announces each frequency, and it appears my low frequency resonance starts and is very intense at 8 Hz, then just a bit at 9 Hz, and gone at 10 Hz.
The previous measurement based on examining the measured response of the Hifi News test because visual inspection was not revealing, with the larger 6.1g mass, was that the lateral resonance went down to 7 Hz, which is why I decided to use less mass. But perhaps even less is called for, perhaps 3.5g added mass.
Some say 7-14 Hz is OK. Others recommend 9-11 Hz for best performance.
Here is some excellent research on arm/cartridge resonance. The usual spring/mass model is an oversimplification. Also the specs provided are not as useful as they would seem. Ultimately you must do measurements and mass adjustments to get the arm/cartridge resonance correct.
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