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Hum from Grado on LP12.. Better carts to consider?

I've had a problem with hum on my LP12 for as long as I can remember. The table (bought used) came with a Grado Signature 8MZ and I've since tried a Grado Z+ that I had from another table. Both have the same amount of hum. I have a lot of RF and noisy AC in my house. The hum is noticeable when I switch to phono and gets louder as I move the cart over the rim of the platter. From there it decreases as I move the arm towards the spindle. (The table is 80's vintage with Ittok and Circus/Lingo upgrades).

A (non-Linn) dealer said 'oh Grados do that on LP12s - lack of shielding'. My Linn dealer didn't nave a strong opinion. He suggested a Benz Ace H given my under- $700 budget. From reading the Agon forums, some think an AT150 M series has better sound for less $. I've also heard good things about the Dynavector DV-20X. Does MM/MI vs. HOMC matter in terms of hum or is the degree of 'shielding' a variable from cartridge to cartridge no matter which type? Does a good review on a MC necessarily extend to the HO version, as opposed to the LO/MO versions?

My system: ARC PH1 (48 dB gain, variable loading via soldering iron)
ARC LS2BII
PSE Studio IV/V's
Audio Physic Tempo III's
FWIW: Meridian 508 CD player is dead quiet in this system.

Music: from Joni Mitchell to Ian Dury and the Blockheads, Monk to Mozart.

Thanks for any knowledge you can impart!
geor

Showing 3 responses by atmasphere

atmasphere's avatar
atmasphere
11,574 posts
 
Grados will hum with certain 'tables, like the Rega. Usually this comes from the table not being sufficiently grounded. For example, the Rega needs to have its motor and platter bearing both grounded to the arm ground. I suspect the same is true in this case, based on the fact that if you move the arm, the hum changes. That's not a ground loop!

So this might be easy to fix- have a wire installed that goes from the motor chassis to the platter bearing and then to the base of the arm- make sure that every bit of metal on the 'table is grounded.
atmasphere's avatar
atmasphere
11,574 posts
 
Geor, they may have springs but that cannot be considered an adequate ground. The motor must have a wire that does the job, so plinth, motor, platter bearing and arm have the same ground.

The motor may not be shielded, but if you ground it that may not be important! Certainly an ungrounded, unshielded motor *will* be a problem for an unshielded moving magnet cartridge!! So get it grounded right and let's see how it works.
atmasphere's avatar
atmasphere
11,574 posts
 
If the motor is made of a metal that can be soldered, then solder it. Otherwise a wire with a lug, placed under a nut and bolt should do the job.
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