The Ghost of Ground Loops Past

I'm sure I'm not the only one who has experienced this: I have a system with (among other components) a Yamaha RX-797 receiver and a Stanton STR8-80 turntable.

When I set the system up, I had some horrendous problems with 60 Hz hum with several of the components. Over time, I have managed to eliminate this problem in every component except the turntable. After first determining that the house wiring itself was good (checked all the outlets), I looked at the cartridge, the wiring in the headshell...I tried tying all the component chassis grounds together, all to no avail. In fact, when I tried this last strategy, I not only failed to eliminate the hum, I actually got 120 Hz harmonics on top of it!

Recently, I read that the STR8-80 turntable had been notorious for hum. The turntable uses a two-prong AC line cord, rather than a three-prong with the earth ground pin. It was suggested that the line cord be replaced with one having the earth ground. This I did, making sure to match the hot and neutral connections of the new cord to that of the old one on the PC board, and I ran the earth ground wire to the turntable chassis ground.

Not only did this fail to get rid of the hum, it actually made it worse. Long story short, I am out of ideas. Anyone out there who knows how to fix this beast?

Thanks in advance for your help.

Hey Jack,

Thanks for the advice...I don't travel with my turntable, but what you said got me thinking, and I have a theory (which I have yet to prove out) about where I went wrong. The original line cord plugs into the unit, rather than entering through a port and a strain relief. Rather than drilling a new hole, I routed the new line cord through an existing port. This placed the line cord in close proximity to the audio cables, and I think I'm picking up the magnetic field effect from the line cord. Also, my earth ground is going to a ground connection on a heat sink, which in turn daisy-chains to the chassis ground. This is a carbord disk, concentric with the tone arm pivot, on which there is a foil backing, and all the ground wires converge there. I've been told I may have better results if I run my line cord directly to that disk. It means a longer earth ground wire, but I see the point...I may be dropping a small amount of voltage from that heat sink to earth ground (which would mean they're not exactly at the same potential).

Sorry for being so long-winded, but I wanted to post this in case anyone has had a similar experience. Thansk so much for your idea...I think you may have steered me in the right direction.

Cheers!

Alpha