So Weird- No Stylus Contact Woofer Pumping with Hana ML and Elac PPA-2


I observed the weirdest thing I have ever seen in audio. With the cartridge positioned above the record, tone arm locked up and platter spinning, the woofers were pumping on my system. I googled every permutation of query I could think of but came back with no hits. That’s when I decided to video the problem- link below:

Mystery Woofer Pumping

I could type out all the details but the video pretty much covers everything. I thought ya’ll might be interested in this.

 

mitchellcp

@lewm , there may be a magnet in the control loop under the platter. Very common approach. One thing is for certain. It is either something on the platter or the oscillating motor. The oscillations are perfectly rhythmic at 33.3/minute. I seriously doubt the mat. Who puts magnetic material in record mats? If its the motor that would validate my feelings about DD motors.

@dadawada , No it is not static electricity. Static electricity would not produce a perfectly rhythmic motion. Static can also not cause induction because there is no current flow to create a magnetic field. Any path to ground would short it out.   

I would be inclined to take a small magnet and run it over the platter to see if there is some point of attraction within the platter itself.  Simple test to do.  Very odd problem indeed.

@mijostyn static can build up on one section of the vinyl. As the record spins the area with static affects the magnets in the cartridge and causes the base to move in rhythm with the section moving underneath the cartridge.

As others have said, it could also be a magnet on the platter used to read and calibrate speed.