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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 8 responses by geor

geor OP
37 posts
 
I don't have cable, but I do have noisey AC power. I can hear my Braun coffee maker's thermostat cycle on and off! I also have an FM transmission tower about a mile away.
geor OP
37 posts
 
Thanks All. The Lyra sounds like a good fit, but the Dorian costs about $1100. It must have to do with exchange rates, because I remember it was around $750 a few years ago. Maybe there is presently better value in the Japanese AT for the same reason. (US Dollar) I have German speakers and had a Scottish tonearm that I bought (new) at bargain prices 5-10 years ago when the US dollar was stronger.

Also my phono pre needs higher output. I'm still wondering in general about MM vs MC and especially low or medium output cartridges. Are the advantages worth looking at a MC phono stage. There is a current thread on MM vs MC with 1000 posts but I haven't gotten much out of it yet.
Thanks again!
geor OP
37 posts
 
Thanks Coxhaus and Metralla. I did some research on hum problems and tried one suggestion with some success. That was to move the LP12 away from other components, especially their transformers. I realized the turntable motor was about 6-8" away from the preamp (ARC LS2BII) transformer on the shelf below. I lifted the turntable as much as I could - about 18"- with no change. Then I tried rotating it and the hum was almost gone.

The ARC transformer seemed to have a 2-dimensional planar beam (?) running vertically. (The transformer is mounted on the side wall of the preamp).
geor OP
37 posts
 
Thanks Sean. I do have the Lingo. I've only had two cartridges on this 'table (both Grado), so maybe it's time to live dangerously and try something new ;-)
geor OP
37 posts
 
After doing much research on Audiogon and the web in general, I am beginning to realize the problem is a ground loop hum. I have a rooftop FM antenna that is grounded to a single rebar spike. This apparently is not a good setup - too much resistance. It should be two copper clad steel rods, 5/8" x 8' long, 8' apart driven below grade, with the two ground rods connected via buried heavy gage stranded copper wire. The loop is formed by the potential difference between the ground of the FM coax (steel rod) and that of the main electrical service panel (water pipe). It seems that I should also add two ground stakes outside the main panel and connect all ground stakes with the heavy buried copper wire.
Off to the electrical supply store and not the needle shop!
geor OP
37 posts
 
Thanks Atmasphere. I'm pretty sure there is a ground wire going from the arm base to the bearing sub-chassis. The motor is attached directly to the top stainless steel suspension plate. Is there a missing connection between the top plate and sub-chassis? I thought the springs made this connection, but there are rubber washers on the springs, so I think your idea makes sense. One would think that Linn would have considered this in their design of the LP12.
geor OP
37 posts
 
Thanks everyone. Does anyone know how to attach a ground wire to a Linn motor? I'll ask my Linn 'mechanic' but I can already see the look on his face.
geor OP
37 posts
 
Thanks Atmasphere and Snfrosten. I will take my LP12 to the Linn dealer and ask them to try it on their system. I'll keep you posted.
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