2. analog
  3. 1160709105

Vintage Problem

Confused about this...Recently had a mint Scott 340 tube receiver restored and found a Fairchild 412 turntable and a NOS Fairchild 500 tonearm. This is a system I first had in the early 60's. I'm using a Shure 44E cartridge. Problem is I have a hum using the phono input only when I place the arm on a disc. The tomearm has a four prong plug-in cable and no separate ground wire. When I use another table, an Acoustic Research which has a ground wire, there is no hum. Should I try to ground the chassis/motor of the Fairchild table to the ground screw on the receiver? If anyone has an idea I would love to hear from you......
lovesmusic
bdgregory
1,712 posts
 
I have a hum using the phono input only when I place the arm on a disc
does this mean you don't have the hum when the cartridge/tonearm are resting on the tonearm holder, but the power is turned on? If you can power the system on and there's no hum except when the cartridge is placed on the disc, I don't think this is a grounding problem. It may be a problem of feedback from the motor through the cartridge - which is the same problem I have with a Grado cartridge on my Heybrook table. It increases in volume the closer the cartridge gets to the center of the platter (and the motor). Does this sound familiar?

maybe it's also possible that there's a short in your tonearm wiring that results from binding as the arm is moved??
fatparrot
1,314 posts
 
Bdgregory...BINGO! Same problem with a Grado on a Linn LP-12. Actually, even at the innermost grooves, the hum was not really annoying...and I'm pretty picky!
lovesmusic OP
34 posts
 
Well, I have a partial solution: Ran a ground wire from receiver chassis to table chassis. No hum if table is running, hum when turned off. Also hum (different) when arm is lifted with finger, goes away when arm/cartridge on disc. Strange huh?
More to discover