Turntable Ground Loop remedy?

A few years ago my father’s old Lenco 75 was reconditioned (tonearm rewire/updated v-blocks etc.) and brought back to like by Deco Audio. They did a great job and to my ears it sounds very nice - I also like the looks and it fits well on my Solid Sounds rack. However, there is a ground loop hum (occurs circa 60hz) when it is on and the phono input it selected on my amp (Arcam A28). When reconditioning, at my request they changed the output leads from DIN to stereo RCAs + a ground wire which, when in use, does help lessen the hum but it does not go away. I’ve tried the TT with different amps and an off-board phono stage and all have hummed through the speakers - the A28 less so than the others.

I have tried moving cables etc. and it does lesson the impact but it is still present when music is not playing/during quiet passages. The level of hum changes with the volume on the amp.

Both the amp and TT have a ground/earth wire attached to the UK 3 pin plug and I have tried using different sockets/both using the same power strip without any success.

What I am wondering is whether something like the ifi Audio Ground Defender would do the trick? It seems like a safe way of removing the ground connection of the TT to hopefully eliminate the ground loop. Has anyone used one or had any experience of chasing grounds loops, specifically with a TT.

It’s not the end of the world as I don’t use the TT that often but it would be good to get it sorted out if I can - I would then use it a bit more as a result!

Did you means 60 Hz - and not 50Hz, which is UK Mains frequency…?

What Cartridge are you using…? Could it simply be the cart picking up noise from the motor…?

If you move the Arm closer to the Spindle, does the hum get worse, or stay the same…?

Realistically it could be 50hz - I’m not sure the app I used for the FR is that accurate.

The Cartridge is a Goldring Elan which was already installed and Deco tested it and we’re happy with it. Nothing fancy I admit. Ref the noise/distance from the spindle, it seems pretty constant to me - certainly does not increase or decrease when I reseat the arm after playing a record.

I would suggest you look into Earthing a bit more. You may have a Ground Loop. Difficult to say. Depends how/where the Ground wire was attached.

The way it should be - IMO - is that the cart and all its wiring should be fully floating - not tied to either the Main earth or the Ground wire.

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It was a long time ago but I remember playing with ground loop issues on a Garrard SP25 MK3 and I tried lots of things including different carts and new connections both at the cart / headshell and from the T/T to the amp. I think I remember eventually solving it by running an extra ground wire (or wires) from the turntable chassis and or arm to a separate grounded earth - not on the amplifier. I’m sure some experimentation will provide success. Good luck.

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Thanks for the replies. When I get a chance I will look into options. I’m assume the cartridge is currently grounded through the wire to the amp’s ground. Using this wire does improve things but does not eradicate the hum.

What do Deco say? can you go back to them and see if it hums there as then you can track the fault to your set up or the deck I guess

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I had the same issue donkeys years ago with a Rega P3, Tube Box, and SN2. Tried all sorts of things… the fix was a separate earth wire from the phono preamp to the earth pin on a mains plug. BINGO… problem gone.

No, thats not possible. You don’t want the cart to be grounded at all. You do want the metalwork of the deck and motor to be grounded - but only once. If they are somehow grounded twice, you get an earth loop - and hum.

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Get a multimeter and check to see if any of the connections to the cartridge are connected to the drain wire or to the mains earth connection. If so break the connection.

Check to see that the arm tube is ONLY connected to the drain wire and not to the mains earth connection.

Check to see that the external casework is ONLY connected to the mains earth.

Sorting out these last two may be more problematic, as the connections may require the motor / power supply to be double insulated. This is getting to the point where, for safety reasons, I can’t make any specific recommendations.

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Thanks for the replies. Lots to go at there. I will unearth the info on Lenco Heaven ref wiring and earthing as this might help me trace the issue. It’s a couple of years since the work was done (Covid occurred so I never really chased it up) but Deco are based in Aylesbury so quite a long drive for me (North Lincs) to sort out unless going in that direction. If I could sort it using any of your collective advice above or using a relatively inexpensive ‘gizmo’ that would be preferable.

Hi @AlexP , how did you resolve this issue? (if at all?)

Any update, please?

I don’t have this issue, but was recently reading the documentation with my old 1960’s Thorens TT.
It mentions, with schematic/diagram, the option of cutting and adding wires here and there, to isolate arm ground from PE.
So this is a topic I have recently been interested by…

It would be nice to hear if you discovered a ground loop, or how you may have resolved your issue?
Particularly regarding whether you isolated the arm ground?

In fact, my Thorens specific “connection options” would probably be a topic for a seperate thread.
Pehaps I’ll do that…


Sorry I have not updated the thread recently.
So far I have tried disconnecting the amp chassis ground (no effect) and trying common plugs for TT and amp (no effect). I have checked and this is definitely a 3 pin plug TT with chassis earth wire fitted - some were 2 pin apparently.

The hum was similar with a different amp and when using an external phono stage so I don’t think it is specific to the amp. The hum remained no matter where the external phono stage was located.

I checked my correspondence with Deco and all seems to have been done on accordance with the recommendations on Lenco Heaven.

I have attached pictures of the ‘terminal block’ under the platter: the grey wire in the middle replaced the yellow ‘arm ground’ that was definitely in place before it went to them - I managed to dislodge the arm end of the yellow wire before I sent it to them so I definitely know what it was for.

They returned the original yellow wire (pictured) and also the original arm/cart signal wire that was removed when they swapped the 5 pin din to dual RCA + ground wires.

From what I can tell things are as they should be. In their correspondence they did mention that the motor sometimes ‘buzzed’ during soak testing but I’m not sure how this would manifest itself through the speakers as a ground loop hum?

I do wonder if I should temporarily disconnect the Earth wire within the TT wall plug to see if this stops the ground loop - I will only need do this for a few seconds!.If so I’m pretty certain that the IFI ground defender will do that task safely and I will get one ordered. The one complication is that the TT has a captive mains lead so I will need to purchase two IEC adapters, one to go into the IFI defender from the wall and one to go from the defender to the TT. I think places such as Farnell sell them.

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