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
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
unchilled
15 posts
 
HI,
I had VERY similar problem, 120 Hz predominant noise + ONLY when record playing.  Turned out to be mechanically induced -- by vibration from the motor pod (physically separate) transmitted by the underlying shelf to the turntable/tonearm.  Banished by a mousepad under the motor pod; recently replaced the mousepad by Herbie's thick Grungebuster dots.
Good luck,
Harvey
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