Nude Turntable Project

Halcro, the can on my tt-101 is heavily damped with bituminous automobile noise suppression sheets, it is also wrapped with a fat rubber band and as I said I use a cone (more like fat cylinders with sharp points) dead center to further drain it. So while it looks primitive compared to the granite clerical collar (but far less primitive than letting it all hang out) it is actually fairly sophisticated.

I use a mu metal shield under the platter, covering the motor.

Halcro
Is there a secondary issue here?

" ..a low frequency drone begins and then increases in volume.."

Could there be acoustic feedback following the initial EMR problem?

Cheers

Halcro - if the cover is tight, then I would run an earth wire to the cover and then just push it into the cylinder leaving a gap at the top such that it doesn't touch the main TT. As long as the cover is grounded to discharge any electrical buildup it works. You could spray some damping compound on the inside of the cover if you want to get rid of any mechanical noise.

It is also possible that the tonearm & tonearm cabling could be picking up rf from the motor.

A small point on earthing - I usually find I get a lower nose floor if I run the TT earths ( i.e. chassis, motor etc ) to ground through the power cable to wall if possible and run only the tonearm earth to the phono/preamp. In a single ended system noise from grounding or shielding is effectively in the signal path.

The cover is grounded by three screws to the frame of the tt. Also, originally there was a ground cable attached to the cover. I have grounded my tt via a new 3 wire pc that replaced the original non-grounded 2 wire line. The new ground-wire is attached to the frame via the circuit-board stand-offs. Also, I highly recommend damping the cover well, including using a footer at the center to drain it.

I get zero feedback even when it is too loud to be in the room, and my left speaker is about 2 feet away from the turntable.

Richardkrebs,

Is there a secondary issue here?Could there be acoustic feedback following the initial EMR problem?

I think you're right....
When I play music at loud volume containing 30-60Hz bass drum beats (like Cream's 2005 Royal Albert Hall Concert or Copland's 'Fanfare for the Common Man' Ref. Recordings)....this 50/60Hz feedback loop can take hold.
At the same time I can feel the vibrations in the supporting shelf and in the granite cradle...😱
As the shelf is directly over the Vandersteen subwoofers, this seems like air-borne sound converting into structure-born feedback.
But why only recently...and why is the Raven not similarly affected as it is identically situated?