Not everyone is focused on magnetism. Have you read any of my posts? I’ve just grown weary of contradicting Holmz, who IS focused on magnetism. I let his last fantasy stand as is, because I did not want to appear to be picking on him.
Like I have said three or four times, my best guess is that the system is oscillating at a very low frequency when the preamplifier is hooked to the cartridge output in balanced mode. When the OP switched to single ended mode, the problem went away. The bit about the platter mat and LP is a red herring, as per my earlier definition. The fact that it seemed to make a difference can possibly be due to the fact that when you power down an oscillating electronic device (in this case, the preamplifier or the amplifier would be oscillating due to input from the TT), the oscillation of course ceases. When you then restart or power up the same electronic device, even with the same input and output loading, the isolation may or may not reappear. In order to remove the platter mat and LP, in this instance, the OP had to shut down power to the TT and then power it up again in order to demonstrate the "no platter mat, no LP" condition. So lets say the cartridge is picking up something from the TT motor that intermittently causes either the preamp or the amplifier to oscillate but only in balanced mode. The intermittent nature of an oscillation is what confounds the investigation of its cause, let alone trying to fix the problem. And beyond that, we really do not have enough data to speculate further. Maybe the OP will eventually come forward with some additional information, but I don’t blame him if he does not want to be bothered and is perfectly happy to operate in SE mode.
Magnetism, shmagnetism.
Yeah @lewm I am guilty as charged.
Your posts are usually pretty thoughtful, so I would probably be OK with being picked on.
WRT the air currents and wind, just blowing on the stylus would be more that it would see from currents, and if that does not move the stylus then to get LF movement would be pretty hard.
And resonance of the stylus/cantilever should be much higher freq, that the <1 Hz.
So I am thinking the causal mechanism is doubtful to be mechanical… which leaves electrical and magnetic as two forces.
@mitchellcp I have lost that ball a bit, but we may want to see of it pumps moving the TT patter by hand, or as the thing is spinning down right after the motor stops getting power.
If it does it with only the motor being on, or regardless of whether the motor is powered, then that would be “more clues.”
@lewm I am starting to come around to your hypothesis, as it seems like it what is known as motorboating.
It looked like it was sync’ed to the platter position, and platter speed.
I am wondering if the pumping is faster at 45RPM than at 33-1/3?
