Dual 506 Hum

[oldvinyldude]

I am trying to solve a hum issue on a Dual 506 TT.

Sometimes it will be quiet for 30 minutes, but it always returns. Once the loud hum returns, it does not become quiet again, unless I mess with the grounding wire, on the preamp. Other tables do not hum when using this input-it’s specific to the table.

I have reseated the cart wires on the cart, reflowed the ground wire on the internal wiring block underneath, and reseated the spade connectors on that block.

I have also run a duplicate ground wire from the underside of the the table where the factory wire is attached to the metal frame, then directly to the preamp-same intermittent hum persists.

I note a ground wire exists at the wiring block, where the 4 wires from the tonearm meet. It then runs to the tonearm and disappears somewhere-I cannot spot where it terminates.

I also applied Deoxit to all the items I reseated above.

If I bump the table chassis, and tonearm/cartridge a bit to see if there is a loose connection, I get no change. It’s only when I touch the grounding wire that the hum changes.

I can remove the ground wire, and have quiet operation for a bit, and then the hum returns-it does not seem to alter the intermittent hum in general, whether the ground is attached or not-yet, that is the same point where the hum changes/goes away.

I am stumped

Thoughts?

 

[Hajidub]

How do the sled connections (both sled and headshell) look? Does the hum alter when you put your hand close or touch the tonearm?

 

[ranf1970]

How do the sled connections (both sled and headshell) look? Does the hum alter when you put your hand close or touch the tonearm?

This was also my initial thought.

 

[oldvinyldude]

I removed the cart from the shell, and cleaned the contacts, and found the termination of the ground wire. I resoldered it for good measure. No change. I also mounted a different cart-no change.

Still

 

[jancumps]

Does it hum at any position, or only when it's off?
2nd question: how is that ground wire connected to your amplifier?

 

[oldvinyldude]

Any position

It’s connected to the ground screw post via a fork shaped connector crimped to the ground wire.

 

[jancumps]

Any position

It’s connected to the ground screw post via a fork shaped connector crimped to the ground wire.

Is that ground wire connected to any of the signal grounds, under the TT? Ideally, all 3 grounds should go to the amp separately, when working with phono connections:

• the ground wire from the arm goes to the ground wire that you connect to the amp. There may be a 3rd wire that goes to an iron part of the TT base.
• left and right ground wires should not be connected to each other. Left signal and ground wire from the arm go to the left phono wire, signal and ground.
• Same for the right one. Right signal and ground wire from the arm go to the right phono wire, signal and ground.

No connection of the grounds inside the turntable. If you unplug the tt from the amplifier, and measure with an ohmmeter, the separate .grounds should measure infinite Ohm. Not 0 Ohm.

That way, you will not have the risk of a ground loop.

Some Duals that are imported in the USA had the grounds interconnected at the mute switch of the turntable. That's the way DIN plug connector tables in Europe were supposed to be grounded. Not correct for phono connections

 

[CrSens]

I am trying to solve a hum issue on a Dual 506 TT.

Sometimes it will be quiet for 30 minutes, but it always returns. Once the loud hum returns, it does not become quiet again, unless I mess with the grounding wire, on the preamp. Other tables do not hum when using this input-it’s specific to the table.

I have reseated the cart wires on the cart, reflowed the ground wire on the internal wiring block underneath, and reseated the spade connectors on that block.

I have also run a duplicate ground wire from the underside of the the table where the factory wire is attached to the metal frame, then directly to the preamp-same intermittent hum persists.

I note a ground wire exists at the wiring block, where the 4 wires from the tonearm meet. It then runs to the tonearm and disappears somewhere-I cannot spot where it terminates.

I also applied Deoxit to all the items I reseated above.

If I bump the table chassis, and tonearm/cartridge a bit to see if there is a loose connection, I get no change. It’s only when I touch the grounding wire that the hum changes.

I can remove the ground wire, and have quiet operation for a bit, and then the hum returns-it does not seem to alter the intermittent hum in general, whether the ground is attached or not-yet, that is the same point where the hum changes/goes away.

I am stumped

Thoughts?

I have a Dual 606, I had intermittent loud hum issues and I traced it to an RCA plug, it is sealed and it looks OK but it is not, it is a weak spot on the turntable. I twisted the wires slightly before he plug, with the turntable connected, and hum telling me where is the break. It was on left channel just before the RCA plug. I changed the plug and issue resolved. It might seem it is the ground wire, I thought that too at first, but it ended up being just the intermittent neutral at the plug.

 

[jancumps]

. It might seem it is the ground wire, I thought that too at first, but it ended up being just the intermittent neutral at the plug.

There is a difference in both hums. The hum of a ground loop is softer, in the background but hearable. Bad contact hum is more aggressive and interrupts when wiggling.
Ground loop hum can also stop when you touch the ground or insulation, but doesn't have the same on-off effect. It never cracks; it hums.

 

[oldvinyldude]

A bit late-but I fixed the hum. I bypassed the tonearm wires with another set, and concluded it was the tonearm wires.

I installed new ones- but boy was that a job. It was my first tonearm rewire, and I learned a lot. That elegant narrow low mass arm tube?-well let’s just say we are not friends. The table has been quiet since.

 

[Hanspecans]

Great work! I fear I may have to do this operation myself if my hum returns. I’m already dreading attempting to mess with the tone arm at all. Most things on this unit look easy to access and repair but the tonearm seems complicated.