LP12 Grounding

[tesla13BMW]

While trying to minimise hum in my vinyl system I now realise that a systematic approach and greater understanding is needed.

 

I have fitted a Linn T Kable to my Ittok/LP12 with Valhalla power supply.  The three pin mains cable has it's earth wire mounting to one of the cross brace mounts.  I've seen photo's of other LP12's with the same wiring, but, the set up manual does not show an earth.

 

The ground wire from the T cable is connected to the centre pin of the arm via its plug and to the arm board screw which in turn goes to the other cross brace mount.

 

All this seems correct and fits my understanding of electrical reg's that all exposed steel work must be connected to protective earth.

 

BUT, last night when I plugged the LP12 into another power point (in the same room but on another wall) it was very noisy and was picking up radio - my LP12 is too expensive to be used as a tuner!

 

My Strathclyde Transcrition Development TT does not have a mains protective earth wire.  The SME 2009 is isolated from the TT and the phono cable ground wire connects to the bottom of the arm.

 

Firstly - is the LP12 wired correctly?

Secondly - should the STD have a mains earth connection?

 

Once I know these things I can then approach the SUT, phono selection switch and phono stage.

 

P.S.  At full volume the LP12/SUT produces almost twice the noise as the STD (126mV compared to 74mV of 50Hz measured at the speaker).  The phono stage with no TT attached produces 59mV of 50Hz when the pre amp is at full volume (measured at the speaker).

[DoggieHowser]

Always a pain to troubleshoot this. 

 

Was just talking to a guy who finally fixed it by wiring the earth pin on his phono preamp to the ground connector on his Thor power regulator. 

 

That and unplugging the CD player that was very close to the phono preamp. 

 

And using XLR from his phono preamp. 

[VanArn]

Use the instructions from    http://www.theanaloguedept.com/images/spp6_pics/Linn/Valhalla%20 Repair%20 Manual.pdf         The Linn Valhalla power supply/ motor should be earthed via the 3 pin mains plug. The  steel cross brace  can be connected to either the supply earth or to the arm screen earth ; but not both, to avoid a hum loop.

Edited September 12, 2017 by VanArn

[tesla13BMW]

@DoggieHowser at least at listening level it is non audible.

 

When you say "earth pin on his phono preamp" do you meant the ground post or the mains earth?  My front end equipment comes off a mains filter but the power amps and speakers come off the same power line but pre filter.

 

I find the proximity of the phono stage and pre amp has an effect on the hum.

 

I only have single ended output available on the phono pre amp.

[DoggieHowser]

It might be worth trying the power plugs on different power points.

But yeah it was the ground post - there was a second one on the Karan I think.

Another option was to try those ground lifter plugs but only as a last resort

[tesla13BMW]

@VanArn thanks for the reply.  So the short phono cable ground wire should be left unconnected?

 

This photo from Peter at Cymbiosis is principally what I have now.

 

 

[Zaphod Beeblebrox]

Linns have always been a troublesome turntable WRT earthing. I am constantly mystified that Linn managed to stuff it up for so long. I grappled with dozens of the damned things in the 1970s and 1980s. They're easily fixed though. Anyway, the mains earth MUST be completely isolated from the tone arm earth. Once you do this, you should not have any problems. If you're not certain, check for continuity with a multimeter.

[tesla13BMW]

@Zaphod Beeblebrox when you say "completely" is that just under the LP12 or throughout the entire system e.g. SUT/phonostage.  My SUT ground post is connected to the chassis but is not earthed but my phonostage ground post is connected to mains earth via the chassis.

[Zaphod Beeblebrox]

First step is to completely isolate the earths in the Linn. That should solve any issues. Beyond that, you need to apply logic and good wiring practice to sort it out.

[mitchlim]

I used to have Valhalla, very quiet with no harm. I replaced the old Valhalla with Mose/Herculus, then I started to have noise and hum, I asked Edmund (the guy who build Mose), he suggested me to move around the phono cable (better to stay away with power cord), then removed all the earth connections and only left the one connecting with tonearm and phono amp, the result was quite ok, and hum level reduced by 80% more.

 

Now i replaced the Mose/Herculus with Edmund's DC motor, and very happy with it and the hum almost can't hear it 

 

 

[tesla13BMW]

@Zaphod Beeblebrox @VanArn thanks for the advice as this would have been giving a ground loop.  I have removed the phono cable ground wire from the cross brace and hence the chassis/top plate, subplatter and platter are grounded through mains protective earth of the turntable.  The tonearm is connected to the ground wire of the phono cable and will be grounded through the "signal ground" of the system.

 

Initially this caused horrific hum until I "unlifted" the RCA grounds from the ground post on the SUT.

 

But, I still have a moderate level of hum.  However, at listening volume (9 o'clock) it is not discernible at the listening position, but, at 12 o'clock it is.  My issue is that there is a noise signal there as it can be amplified and therefore even if it is non audible it must be affecting the music at 50 Hz and its harmonics.

 

The system is dead quiet with CD selected so I believe it is in the phono system.

 

If I am to work backwards from the input to the pre amp do I just unplug cables or should I build grounding RCA plugs and sockets to check components and cables.  Does a load need to be present?

 

When I talk "phono system" it consists of LP12 with 100uV MC into SUT into phono switch, there is also a Strathclyde with MM connected to the switch.  The switch feeds the phono stage.  Shielded cables are used with the shield connected at source.  The TT ground wire is connected to the SUT ground post, the ground post is connected to the ground of the RCA's via a lift switch within the SUT (all RCA grounds in and out of the SUT are common).  No further ground connections are installed between the SUT, switch and the phono stage i.e. uses the RCA grounds.  RCA grounds are connected to protective earth in the phono stage.

 

All components are powered from the same outlet except the right hand side speakers and power amps are supplied form a different wall outlet, although next to each other on the wall.  All front end components are powered form a power filter.

 

Any methodical checks to perform or things to try would be greatly appreciated.  This weekend may be a matter of unplugging everything and "reset" the whole system including cleaning all RCA plugs and sockets, checking all protective earth connections and power leads.

 

Cheers, Chris. 

[andyr]

Mmmm, frustrating, Chris! 

 

Reading what you (and others) have written can I suggest:

• if your CD is silent then yes - you have a problem somewhere on the vinyl side. 
• don't waste your time cleaning RCA plugs & sockets until you've sorted the hum.
• having a phono switch is a distraction - remove it and try your VLOMC+SUT into phono stage and MM into phono stage, separately.
• you said "RCA grounds are connected to protective earth in the phono stage".  If by this you mean "RCA grounds are not isolated from the phono stage's case" then I think you need to try having them isolated.  If this is impossible with your phono stage ... borrow another phono stage - which has isolated RCAs - and see whether you still have hum.  If you pay postage, I can send you up a Hagerman Cornet 2 MM phono stage, to try.  I built it deliberately (as I normally do) with RCA sockets isolated from the case.

 

Regards,

Andy

 

[Telecine]

Try running a ground wire between the phono stage and the preamp. You may also need to run a ground wire between the SUT and the phono stage.

 

The other possibility is the cart. Grado carts hum on some decks.

[tesla13BMW]

Hi Andy

 

Thanks for joining in.  From your knowledge of the LP12 do you agree on keeping protective earth grounding and phono cable grounding separate within the LP12"

 

With the SUT the RCA's are isolated from the chassis but internally the -ve RCA goes to protective earth.

 

With the phono stage the RCA's are isolated from the chassis but through the PCB and a ground wire are common with protective earth.

 

I'll have a look at the Graham Slee Reflex M tomorrow and see what arrangement it has.

 

I am guessing your comment is such that there aren't two pathways to ground I.e. through the chassis and through the circuitry?

 

P.S.  The hum is at a similar level with the reflex M and the PH16.  I can put in a Bugle I purchased of @Batty (his two box bugle build) and se how it fairs.

 

Cheers, Chris.

[tesla13BMW]

@Telecine I will try these options again and make notes and measurements, but, my feeling is the different combinations had little effect.

 

However, the ground wire from the LP12 included with the Linn T kable runs to the case of the SUT i.e. the ground post and the -RCA (isolated from the enclosure) are grounded to the ground post internal to the SUT.  Therefore wont a ground from the SUT to the phono stage give two earth paths and a ground loop?  Or is it only if they go to different ground points?

 

Hard to find a good definition / description of ground loops

[Telecine]

You will need to try different options. It is hard to know how effective the grounding solution is on various devices. I have found the chassis of preamps to generally be a reliable option.

[Batty]

15 minutes ago, tesla13BMW said:

Hi Andy

 

Thanks for joining in.  From your knowledge of the LP12 do you agree on keeping protective earth grounding and phono cable grounding separate within the LP12"

 

With the SUT the RCA's are isolated from the chassis but internally the -ve RCA goes to protective earth.

 

With the phono stage the RCA's are isolated from the chassis but through the PCB and a ground wire are common with protective earth.

 

I'll have a look at the Graham Slee Reflex M tomorrow and see what arrangement it has.

 

I am guessing your comment is such that there aren't two pathways to ground I.e. through the chassis and through the circuitry?

 

P.S.  The hum is at a similar level with the reflex M and the PH16.  I can put in a Bugle I purchased of @Batty (his two box bugle build) and se how it fairs.

 

Cheers, Chris.

How is that going for you? Good value for money?

 

[tesla13BMW]

Hi @Batty excellent value for money with looks to boot.  I run it on the office system from the CJ Walker into the Earle Western Troubadour feeding a pair of Image 402's.  I have no reason to fault it at all.

 

Never run it on the main system so that will be interesting!

[Batty]

So proud that you think it capable of being run in the company of something Earle built.

Nice to hear of something I made being so well accepted.

 

Go on give it a serious work out, hope it holds it's own.

[djb]

@Point source might care to comment be is currently running my ( loaner) Strathclyde. .

neither he nor @jamesg11 who used it for a year had issues .

 The switch between peons seems a likely cause of the problem 

@VanArn might have a suggestion