Andre,
I think your idea has merit, and it's consistent with my theory.
If stylus drag is slowing the platter and causing your tremolo, anything which alters the amount of drag could alter the amount of tremolo.
We've established that the tremolo is worse after a large dynamic note or a warp. What is similar about these two events? Answer: both of them are trying to deflect the stylus. This requires some force. If the motor/belt aren't stable enough to overcome the resistance of the stylus/cantilever/suspension, the platter may slow.
(Bad tonearm bearings could increase the arm's resistance to rising freely over a warp. This would increase VTF and drag, which is why I thought of it. But since both your arms have the problem to some degree this seems unlikely.)
The amount of stylus drag will vary with cartridge and with setup. Here are some of the factors I can think of:
VTF - higher VTF = more friction (pretty obvious)
Compliance - the stiffer the cartridge suspension the more it resists deflection, greater resistance to deflection = more friction
Stylus profile
- fine line and micro-ridge styli cause the least friction
- elliptical styli cause more
- conical styli cause the most
This is simply a function of the contact area of each stylus type.
Anti-skate - the higher the AS setting, the more friction
Arm height
- arm tube level = normal VTF = normal friction
- arm down at stylus end = higher VTF = higher friction
- arm up at stylus end = lower VTF = lower friction
This ignores changes in VTA/SRA and any effects they may have on friction, but it might explain why you have less tremolo on 200g records than on thin ones. If you haven't raised the arm by the thickness of the record, VTF will be *slightly* reduced and therefore friction will be reduced. (I admit, this is really a stretch.) If those 200g records are less warped than the lighter ones, that would have a larger effect.
Doug