Linn LP12 ground

Hello everyone,


I know this has been done to death, which is exactly why I'm unable to sift through the interwebs on this one. There is simply too much.


Here goes. I own an older Linn LP 12 with a Valhalla that I don't use very much. It has a Linn Troika MC. I had to replace the Valhalla a while back, but shelved the unit.


I reconnected it over the weekend. As the amplifier does not have a MC input, I use a Pro-Ject Phono box DS+ with amplification set to 60 dB. The amp is earthed.
Unfortunately, it hummed like a SOB. I started searching the 'net, and it appears to be a problem that's been around for decades. Funny, it hadn't bothered me when using direct amp connections (different amps). Or at least I think it didn't. Equally unfortunately, the solutions proposed in many many posts on various websites and forums sound like snake oil proffered by people who seem to lack a basic understanding of electricity.


So I opened it back up, and noticed a really funky earth/ground arrangement. The ground wire from the plug is connected to the metal cross brace where the Valhalla is mounted. OK. There's a thin black wire connecting the metal bearingplate to the brace. OK. The signal ground is run from the arm plug outside with the RCA's for connection to the phono pre-amp, which is also standard fare. But now, there is a small black wire with an eyelet - I assume is the arm ground - that is also connected to the chassis ground, which I find mightily strange. Especially since the arm is mounted on a wooden armboard and thus isolated from the metal frame. As soon as I disconneced this wire the hum all but disappeared. When I disconnected the signal ground from the phono pre-amp it became very quiet.

I am now contemplating extending the 'arm ground' to go outside with the signal ground and both connecting them o the pre-amp to there is equipotential on everything coming from the arm.


Your thoughts ? Thanks, Pete
 

warrjon

Member
2011-02-04 10:10 am
Vic
I had a1983 LP12 Ittok and Troika these are a pretty good rig. If it's quiet lifting the ground wire leave it.


Grounding and hum can be individual to the setup. The mains earth for instance can be a source of grounding back to the amp. Having multiple paths with different potentials is where the problem lies.


I changed the tomearm on my current rig (Technics SP10) and the thing BUZZED like crazy getting worse to the centre. Adding a ground to the TT frame tamed the buzz. This ground was not needed with my EPA100.