2. analog
  3. 126134-46

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
jmcgrogan2's avatar
jmcgrogan2
6,346 posts
 
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?
john_tracy
341 posts
 
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.

last_lemming OP
639 posts
 
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. 
geoffkait's avatar
geoffkait
23,365 posts
 
Magnetic field? Who knows, could be a lot of things...
kingshead
44 posts
 
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
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