Topic: grounding a turntable?

[unclelouie]

I've been building a secondary system for my gf, who wanted small living room system for vinyl and DVD's.  Long story short we ended out with a Technics SA-80, and her old Technics turntable (I can't remember the model, but it was built ca. 1990) and it sounds surprisingly nice. 

There appears to be a connection for ground with a barrel connector, and I can hear a 60cycle hum through the receiver. I've got a ground on the receiver so I was going to build a cable to run from the turntable to the receiver chassis. I imagine this to be a simple build, and I'm fairly handy with a soldering iron, but I'd appreciate some instructions/advice nonetheless. A barrel connector has both tip and sleeve, and I'm unsure which one will be ground, and if the other will have voltage or be unused.

Thanks in advance

[mfrench]

does it get louder when you touch the tonearm?

[cheshirecat]

Are both plugged into the same outlet?

[unclelouie]

does it get louder when you touch the tonearm?

I assume you mean the hum - sorry, didn't try that and won't be able to for a while. Maybe I can convince the gf to try tonight, but I'm up in NH and will be away from the system for the next 2 weeks.

Are both plugged into the same outlet?

They are both plugged into a power strip, perhaps I should try the switching outlets.  I'll have her try that too.


The 60cycle hum sounds just like a loose ground on a guitar - and when I checked the turntable there was a proprietary connector for a ground - I hadn't even considered switching outlets or grounding it through me by touching the tone arm.

One thing to note is that the hum is only on the phono channel. Aux, etc. is quiet as hell - that's why I assumed the turntable needs to be grounded through the chassis on the receiver. There is no dedicated ground on the power cord.

[mfrench]

Ask her to touch the tonearm, to pick it up off its rest, touch the cartridge, and see if the hum increases. It won't shock her or anything - its safe. If the hum increases, you probably need to ground the arm or the cartridge to the preamp chassis.

You can always open the deck up, and create a ground lead from the motor for a 3-wire power connector, to ground the motor and top deck (though technics are generally plastic non-conductive top decks, so only the motor needs grounding).

I drastically improved my old technics deck by opening it, creating a new power connector installation; and, replacing the output cables with pair of nice RCA output jacks that allowed a variety of choices for interconnect cables. There should be a connector block within the deck that will allow for easy output cable replacement.

[unclelouie]

awesome, will do that tonight.

what if touching the tone arm results in no change or decreased hum?

[unclelouie]

wow - talking her through that was as difficult as herding mimes. Anyway, no change in the hum when she touched the arm and cartridge; I wonder if I've got a ground loop elsewhere in the system. 

I'm the tech-savvy one, so I guess it'll have to wait till I get back home. I'm sure she'll be thrilled when I start disconnecting stuff 

[mfrench]

yep, ground loop.

Your post caused me to relook at a nasty'ism in my own system.
I do not listen to loud music, or, listen to music loud. Its more like background noise, unless I'm ready for a critical listen.
I'd heard a buzzing in my phono circuit, but thought it was normal amplified phonostage noise (I listen at about the 9 o'clock position when I "turn it up", and don't hear the noise until its at the 12 o'clock position. 12 o'clock is at foundation shaking level).
You question had me touching and playing with my tonearms to see if what I was theorizing on was valid.
It wasn't until right then that i realized that I'd been plugged into a nasty dirty circuit. The circuit is tied to an old doorbell transformer that piggybacks off the same outlet, on the opposite of the wall.
A test with a circuit tester revealed a mis-wiring of the outlet.
So I plugged into another circuit, and the hum disappeared - but a buzz replaced it - fark! frustration runs rampant.
I was scratching my head wondering where the heck the buzz came from, when Sarge came in and turned up the kitchen lights, which turned up the buzz as if it were tied to my amplifier gain.
I'd taken an extension cord and run it off the same circuit that feeds the kitchen LED's, and the LED's were causing this new buzzing.  As soon as she turned the lights off, the buzz went away, and I have audio normalcy.
Now I just have a pending rewire of the outlet, and removal of the old transformer.

I used to have a dedicated circuit to the rack, but Sarge reclaimed the living room, and i was moved to another wall, that I just found out is nasty dirty.

[Tim]

easiest way to deal with the ground loop

[mfrench]

I gotta say thanks for starting this thread. It prompted me to look into what revealed itself to be a rather dangerous situation.
As it turns out, the prior owner of my place was one of the worst the anti-DIY'ers of all time. I've fixed his screw-ups for 15 years now, and they keep revealing themselves.
What happened:
He'd cut off the ground lead in installing a doorbell transformer (the source of the hum in my system). On re-installation, he'd reversed the hot and neutral leads.
While stuff still worked, the danger was from that I'd plugged extension cords into that outlet to work with power tools outside on the lawn.  I'll quite often do so in beach slaps, which put me drastically close to being the ground lead. I've been caught by the community sprinklers a few times out there, which now scares the crap out of me.
So, I've spent the morning removing that transformer and reestablishing a proper circuitry to the outlet in question.

I'm back to the black background of silence.

[unclelouie]

wow, that's some nasty stuff to find in your walls. I'm looking to buy a house sometime soon and these kind of stories creep me out. I spent quite last some time this past summer rewiring Stellafane, a national historic landmark up in Vermont, that had 80 years of DIY wiring - redundant and unused GFIs, loose wires, bi- and tri-wired switches, and god only remembers what else. The guy I was working with only works on wiring hot, so I was nervous as hell. Long story short, I feel your pain but in the end it's always worth it.

I'm not crazy over 3 to 2 prong adapters, and I never use them. I understand the logic behind lifting the ground  of the the offensive device. But I'd rather identify remove, repair, or electronically isolate it. Especially because lifting the ground has potential of increasing hum. My gut tells me that turntable needs to be grounded to the receiver chassis, but I haven't ruled out a ground loop elsewhere. I should probably check MY system while I'm at it.

Quick question: What is the probability that a surge protector/power strip could be the culprit?

[cheshirecat]

Re: surge protectors, anything is possible, but rather unlikely.  It should share a common ground.

Does the amp and or turntable have a polarized plug?  If no, flip around the orientation to see if running it via the other hot/neutral sovles the issue (i'm assuming that not everything is 3 prong).

Now for my next question, what all is plugged into the power strip?  If you have your cable box plugged in there, remove it since that has it's own ground and has f'ed with me in the past (isolation transformer fixed that).

[Tim]

good point, cable boxes are fairly notorious for introducing noise

[unclelouie]

there is a dtv converter box, but i think i've got video and audio devices on separate power strips.

Does the amp and or turntable have a polarized plug?  If no, flip around the orientation to see if running it via the other hot/neutral sovles the issue (i'm assuming that not everything is 3 prong).

the turntable has an un-polarized line connector so checking the polarities was the first thing i did.

[cheshirecat]

Seperate power strips but same circuit can also cause a loop.  Just a thought.  Another good test is to unplug everything else and see if you still get the hum and go from there to see if something else is unexpectedly causing some hum.