Low level hum only with lp playback


Basic system:

VPI Prime turntable (cart is a Dynavector 20x2L) with
Purest Audio interconnects ( with integral ground wire connected to phono pre) to
Parasound JC3+ Phono Pre with
Cardas Clear Light Balanced Interconnects and separate ground wire connected to
BAT Preamp
REL R-r328 sub

I use an Eagle PSU with Roadrunner tach for speed control. 

So I'm getting a low level hum ONLY when the record is playing. You can hear the hum on the lead in groove - the sound gets louder as the volume goes up even if the music hasn't started.  However if the needle is lifted the hum goes away. 
I played around with the ground wires locations to no avail.
I've checked the leads to the cart for tightness and to make sure they are connected completely -they are. 
I've moved the speed control equipment to make sure they are no interfering. 
All my connections are tight. 

last_lemming
Did you try to disconnect the ground wire?

I asked, because oddly enough when I upgraded from my Scout to the Prime, I also had a buzz/hum issue. I tried changing the ground around a few different ways to no avail.

Then I disconnected the ground, and total silence. I can't explain that, as the Prime is the first table that I've run, out of 5, that ran quieter with no ground connection.
 I've tried every which way - all on, all off, some on, some off, in all cases I can't get rid of the darn hum. 
Ringing platter possibly?

Quite a few yrs ago I purchased a mat from Audioquest made of sorbojel, worked great for just what you're describing, but was toxic to vinyl, ruined many of my records.

Fast forward to just two weeks ago. Experiencing exactly what you're describing and finally tired of it I thought of a possible solution. Find one of these old Audioquest mats on eBay etc and sandwich it between my platter and mat thus protecting my vinyl.

Couldn't find one of those mats anywhere so went back on eBay and found sorbothane  ( gel )  being sold in flat squares. Purchased one 12" X  12"  X 1/4', and using my mat as a template cut out a new mat. 

Should have purchased one a bit thinner as it left my spindle a bit shorter than I liked making placing the record weight a bit more difficult.

The mat along with a few other changes have virtually eliminated any and all vibrational hum.


Cartridge itself is doing funny thing?
I have a deerskin mat and my cart is I good condition as far as I'm aware 
Wow! You've had this problem for over 6 months now???

https://forum.audiogon.com/discussions/vpi-scount-to-prime-now-static

Have you contacted VPI?
Do you only experience the hum when the cart. is lowered to the record? And not when the arm is sitting in its rest? If that's the case it sounds like the problem is induced hum (is the motor nearby?) and not a grounding issue.

Jmc

to be fair that was my static issue. That was solved with the deerskin mat. The bum is new. 

john,

correct the hum only starts once the needle touches the moving vinyl. And you might be right about the hum being mechanically induced. I moved the subwoofer - only an inch - and it seems the hum is now gone. Due to my space limitations, my subwoofer is adjacent to my rack. It's never been a problem since I have a concrete floor, but a couple weeks ago I tweaked the subwoofer settings to a higher crossover point so the bass is more prominent now and I seem to get more subsonic woffer flutter. I guessing being too close to the rack may have caused a feed back issued with mechanical vibration and the TT translated that into hum. That's my best guess anyway. 
Magnetic field? Who knows, could be a lot of things...
Sounds like you’ve isolated your problem, but my recommendation for the sorbo under mat still stands. I find it dramatically deepens the sound field along with extending it vertically. For instance, now when listening to Moby Dick live on The Song Remains The Same the perspective is standing in the field center stage looking up at the band. With my 8’ ceilings the image is a quarter hemisphere extending past 90 degrees to either side arcing overhead with back hall sounds on some recordings appearing behind the seating position. Each instrument is easily defined in space to the extent you can tell when the lead guitarist for example turns to his right or left.

I’ve made other modifications to dampen the big Kenny, will share them in another thread if anyones interested, but I have to say the synergy of the Grace arm with the Grace cartridge showed it to be one of my most fortuitous purchases to date.

Martin