tone arm weirdness

[Br1ck]

Anyone ever have this happen?

My tone arm is a radio when the ground wire is disconnected. When it is connected to a pre amp grounding point, it hums. The tone arm tube has continuity with the end of the ground wire, and all four wires to the cart have continuity with their respective channel's RCA jacks. Grado cart. I even took the tone arm off the table to eliminate possible ground loop interaction between the table and the tone arm, so the tone arm setting on my desk or mounted on the table exhibit the same symptoms. Cart was mounted and tested by a dealer who will help, but I'd like to figure it out on my own.

 

[cgutz]

I've heard Grados tend toward hum issues. Never owned one though. Others may weigh in on the cart.

 

[gadget73]

Try cleaning the connections. A very slightly poor connection anywhere between the cartridge and the preamp can become an AM radio detector.

 

[rnorton]

Try cleaning the connections. A very slightly poor connection anywhere between the cartridge and the preamp can become an AM radio detector.

Resolder everything. Cold solder joints become diodes.

 

[marcmorin]

I've heard Grados tend toward hum issues. Never owned one though. Others may weigh in on the cart.

If it is picking up stray magnetic fields......such as a transformer, unshielded AC motor, etc.