Tonearm rewire

[alcarmichael]

I have recently bought an SME V from a forum, unfortunately I believe it requires a rewire as it’s producing a hum through the speakers when the tonearm is moved with no cartridge attached. As someone who’s very busy, I was really looking forward to the festive period for some time off when I can relax and listen to some music. Might there be anyone out there who can rewire this for me before Christmas...?

[walpurgis]

Try fitting a cartridge.

[Shovel_Knight]

Agree with the post above, most tonearms will produce at least some hum when there's no cartridge attached.

[alcarmichael]

There was hum with the cartridge fitted. I removed the cartridge to prove that it wasn’t at fault.

[walpurgis]

Open the armlead phono plugs and check no wires are touching anything.

[alcarmichael]

I spent several hours last night trying everything I could think of.

[walpurgis]

Well it has to be earthing or screening related one way or another.

[alcarmichael]

Agreed. I think the internal wiring insulation has somehow worn causing the hum.

Might anyone know of anyone able to rewire the arm? I have already contacted Angus on here and J7.

[flapland]

Are you using the arm lead supplied with the arm or the one your already had. It might be worth trying a different arm lead if you have or can borrow one close bye.

Also worth checking the cartridge leads are connected correctly into the headshell end of the arm. They can come loose. Also if you have a multimeter do a continuity check of both the arm cable, the internal cabling and headshell cables. Although it could be the internal cable it could just as easily be elsewhere. Don't use the multimeter on the actual cartridge as they can damage coils.

[alcarmichael]

I will try a con check today and report back.

[Jac Hawk]

i had a similar issue with my tonearm, turned out to be the phono plugs on the phono stage were dirty, unfortunately i sent the arm away to be checked out in the mean time only to be told there was nothing wrong with it. All i'm saying is check everything else 1st, it's easy to jump to conclusions i did.

[alcarmichael]

I spent several hours trying everything I could think of. I moved equipment around. Swapped cables out. Even resorted to switching plugs off around the house. I will have another little play today though...

[Blackdog]

Do you have a multi meter than can measure continuity?
A simple check of continuity between the cartridge clips and each connection at the other end (RCA's) will tell you if the arm is at fault.

[alcarmichael]

I do have continuity from cart lead wires to phono connectors.

I also am able to play music.

I am thinking that the coating/insulation on one of the internal wires has worn...

[Stratmangler]

I do have continuity from cart lead wires to phono connectors.

I also am able to play music.

I am thinking that the coating/insulation on one of the internal wires has worn...

What about the armtube to the ground clip?
You'll need to find some bare metal or scrape back some finish on the arm (obviously somewhere where it's out of view).
If the arm has been rewired whoever did the rewire might have neglected to make sure the armtube has ground connectivity.
SME were fastidious about grounding - it will have left the factory with everything in order. If it has been monkeyed with it's another story, and a crap shoot.

[alcarmichael]

Well I’ve just installed my new cartridge ART-9xi and all my hum concerns have vanished. It sounds incredible.

[walpurgis]

Ah, that's good then. :)

[alcarmichael]

I think it’s the earth wire causing the hum. If I disconnect it from the phono and hold the connector with my fingers the hum disappears, as soon as I release my fingers the hum returns.

[walpurgis]

Try extending the earth with a bit of wire and touching it on a case screw on the pre-amp.

[alcarmichael]

That’s reduced it Geoff!

[walpurgis]

Try it on the neg (outside) of one of the pre-amp phono sockets and also on a case screw of the phono stage, do this with the gear on but volume well down. You could also try it on a turntable chassis earth if you have an accessible one. It definitely seems to be an earthing issue and they can be weird to sort.

[alcarmichael]

I already tried those options but with no real change. I’ve currently got the tonearm earth connector attached to one of the bolts on the Croft. The hum is still there but it’s much less noticeable.

[Blackdog]

The earth is basically grounding for the arm tube giving a shield for the signal wires. If that's not a good earth connection the result will be hum. Holding the wire effectively makes you earth.
To check if continuity is okay on that wire you good contact on the tube somewhere. If you look under the decorative cap on top you will see a chrome screw. That is where the earth wire connects inside the tube and is a good place to check continuity.

[alcarmichael]

https://uploads.tapatalk-cdn.com/20201214/1cf122362d79b8df05d01c8ae5b2ed04.jpg

Are we talking about this bar which mounts above the arm with the right hand bolt just next to the VTF adjuster?


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[Blackdog]

Under that bar. Remove the two screws and you will see a chrome screw. That's where the ground wire connects to internally.
DO NOT remove or loosen any other screws.

[alcarmichael]

Thank you. I’ll have a look after work.

[alcarmichael]

OK, so the resistance from the screw at the top to the earthing connector on the tonearm lead is all over the shop.

Can I remove that screw to try and sort or is that a bad move?

[Barry]

I would be very reluctant to touch that screw until you have eliminated all other causes. For example:

[1] is the connection between the min-DIN connector of the arm cable and the earth lead sound?

[2] is the connection between the screw and the plug (at the base of the arm) also sound?

[alcarmichael]

[1] Yes

[2] No

[Barry]

Are you able to examine the connections within the mini-DIN connector at the arm base?

[alcarmichael]

If you mean a visual examination of the connector here it all looks good:https://uploads.tapatalk-cdn.com/20201214/0a34b69e326996f2c54e053941cb009d.jpg

Or do you mean remove this cover to see how the wires look:
https://uploads.tapatalk-cdn.com/20201214/5b4c9940810bf98f1c2f590063f573ce.jpg


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[Blackdog]

I would be very reluctant to touch that screw until you have eliminated all other causes. For example:

[1] is the connection between the min-DIN connector of the arm cable and the earth lead sound?

[2] is the connection between the screw and the plug (at the base of the arm) also sound?

I agree, don't touch that screw. It not only holds the ground wire, but is also part of the rear weight assembly. There is a disc inside that has a threaded hole in the center where the weight shaft threads into.

If there is a break in that earth wire, most likely at the DIN. You can remove that back cover at the base and see if the center wire is still soldered. It will have a white rubber sleeve over it. Chances are if you try to lift that sleeve you WILL break the solder. Just give the wire a very gentle pull. It breaks very easily. So I can't stress enough. Be gentle.
If all seems well, then you are past the point of DIY.
These are not difficult arms to work on, but one slip and it is re-wire time. They also scratch very easily, and the bearings are delicate.

The only other place I have seen a break is at the vertical pivot. This is usually caused by somebody trying to take the arm apart.

[alcarmichael]

Earth wire seems to be connected fine here

https://uploads.tapatalk-cdn.com/20201214/207b0811eaa49400cbdc749268051ac5.jpg


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[Barry]

What is the resistance between the earth connection at the mini-DIN and the chrome screw under the bearing housing?

[alcarmichael]

I couldn’t get a good reading. The four wires were all steady at around 0.6 ohm. The earth lead was jumping around all over the place, it did get quite low at around 1. something ohms but was also up in the 20’s and above.

[Blackdog]

Just to verify the readings. See if you can get good continuity at another spot on the arm. Possibly under the headshell, or some other clear spot. Could be the contact point of the screw, so we just want confirmation.

[Barry]

I couldn’t get a good reading. The four wires were all steady at around 0.6 ohm. The earth lead was jumping around all over the place, it did get quite low at around 1. something ohms but was also up in the 20’s and above.

Those figures are rather high, but if consistant, 0.6 Ohm should not cause any audible problem (unless the coil resistance of your cartridge is very low).

Of much more concern is that of the earth lead; even 1 Ohm is very high for such a short length of wire. The intermittent readings suggest a loose or corroded contact. Since the connection at the mini-DIN end is more accessible, check the integrity of the connection of the wire with pin (bearing in mind Dan's caution concerning the fragility of the soldered connection).

If this connection is sound, then it strongly suggests the problem lies with the connection between the wire and the arm (under the bearing yoke cover).

Whilst I have plenty of experience with the Series II arms and with the M2 -12R arm, I have no personal experience with the Series IV or V, so cannot advise you further. There are however a few companies who can repair and fettle arms, Audio Origami and Phonomac, being two I can name. I have used Audio Origami a couple of times and can vouch for their professionalism. SME themselves may be able to help, even though they are now no longer willing to sell any of their arms alone.

[AJSki2fly]

I would send it to SME, I was told in the past by a dealer that knows that SME V's are very tricky to set up. I believe SME are still doing service/repairs for existing owners. I have used them in the past and they were extremely helpful. Give them a call and ask for the arm service dept.