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PostPosted: Thu Dec 21, 2017 3:53 pm 
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Yeah, forgot about that strap....it's been a number of years since I worked on mine.

So you're saying that strap is grounded but the arm still hums? I'm at a loss, then.... unless it's not a ground issue.

Can you check the continuity between the strap and the RCA plug?

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PostPosted: Thu Dec 21, 2017 4:25 pm 
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Any CAM vinyl guys near you that might want to lend a hand ? Also stupid of me , but the connections at the cart are nice and tight and in the proper order . It's a PIA doing carts on those fixed headshell arms . good luck


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PostPosted: Fri Dec 22, 2017 1:36 pm 
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Continuity between the strap and the ground pin is fine, but for whatever reason the wand is not sufficiently grounded through the bearings. (I'm not surprised, though—if the wand *could* be sufficiently grounded through the strap at the base, why would there be a ground wire running into the wand at all?)

The break in the wire is right in front of the end stub. Fiddling around with it, I can sometimes get it to make contact with the arm for a moment, and for those moments the wand is grounded.

Maybe you can see what's going on in the pic below? My guess is that the black wire is supposed to be soldered to the metal strap just inside the hole for the end stub (I read somewhere that this is how the ground works when the arm ships new). It's come loose, and there's not enough wire left there for me to work with. It will probably take all of one second for someone with soldering skills to fix this problem, but I think if I get in there with an iron I will likely burn the rest of the tonearm wires (the white bundle), causing a world of grief and sadness. Will try to get over to a shop sometime this weekend. Probably I should have someone look the whole thing over & set it all up right anyway.

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PostPosted: Fri Dec 22, 2017 2:34 pm 
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two2the8 wrote:
Continuity between the strap and the ground pin is fine, but for whatever reason the wand is not sufficiently grounded through the bearings. (I'm not surprised, though—if the wand *could* be sufficiently grounded through the strap at the base, why would there be a ground wire running into the wand at all?)

Can't speak for Rega's intentions, but the loom in my arm, which is based on and electrically identical to the Incognito loom, grounds the wand solely through the bearings. No hum...zero, nada. It works well enough I've rewired several other arms with the same strategy without any ill effects.

I'm wondering if the open ended ground wire in your wand isn't actually acting as an antenna picking up EMI, causing noise in the ground path. There might be something else going on I can't see from here. Noticed your other thread....as this has already been rewired there's no telling what's going on.

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PostPosted: Fri Dec 22, 2017 3:00 pm 
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ripblade wrote:
I'm wondering if the open ended ground wire in your wand isn't actually acting as an antenna picking up EMI, causing noise in the ground path.


That's a pretty interesting theory. I guess I could try clipping the rogue wire and see what happens. Still a bit of a puzzle why the rest of the arm doesn't read as continuous with the ground, though.


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PostPosted: Fri Dec 22, 2017 3:05 pm 
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two2the8 wrote:
Still a bit of a puzzle why the rest of the arm doesn't read as continuous with the ground, though.

Yes it is. Just to iterate; you're certain there's continuity between the arm base pillar (not just the strap) and the preamp ground post?

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PostPosted: Sun Dec 24, 2017 12:52 pm 
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Definitely. There does not seem to be continuity between the wand and the arm base, though, except in those rare moments that I can fiddle around & touch the busted ground wire to the wand.


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PostPosted: Sun Dec 24, 2017 1:00 pm 
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Strange.

I wonder if the bearings were swapped for ceramic ones. Steel bearings will conduct....

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PostPosted: Tue Jan 02, 2018 10:06 pm 
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two2the8 wrote:
Still a bit of a puzzle why the rest of the arm doesn't read as continuous with the ground, though.


Checked it again today, and it turns out I was wrong. There is indeed a connection between the wand and the ground post, presumably through the bearings as you said, @ripblade. Thanks for prompting me to check it again; I had trouble seeing the connection on my cheap-o analog multimeter because there's a lot more resistance through the arm than through the wires.

Anyway, having confirmed that, I'm wondering about your EMI idea again (and I'm still curious as to why there's a ground wire at all if the whole thing is grounded through the strap/base, too). Still planning to take it to a shop before long, but it's fun to poke around in the meantime.


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PostPosted: Wed Jan 03, 2018 11:27 am 
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two2the8 wrote:
Anyway, having confirmed that, I'm wondering about your EMI idea again (and I'm still curious as to why there's a ground wire at all if the whole thing is grounded through the strap/base, too). Still planning to take it to a shop before long, but it's fun to poke around in the meantime

Admittedly, I think the EMI thing is a bit of a stretch, but when I mentioned it I hadn't noticed yet that the arm had been rewired. Now I'm thinking ground loop. Do you have continuity between the ground wire at the preamp post and the RCA ground leads when they're disconnected from the preamp?

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PostPosted: Thu Jan 04, 2018 9:03 am 
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ripblade wrote:
Do you have continuity between the ground wire at the preamp post and the RCA ground leads when they're disconnected from the preamp


I'm not sure I totally understand what you're asking, but I'll try :) There is no continuity between the ground wire at the preamp post and the sleeves of the RCA plugs when disconnected. Is that what you mean?


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PostPosted: Thu Jan 04, 2018 11:28 am 
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Yes, that's what I meant.

So....no ground loop. Don't know what else to suggest. If you're handy and have 6" of 32ga wire you can use the existing wire to fish through the new wire to reconnect the ground. Though I can't see why this should be necessary it certainly won't hurt.

Where is the table and phono stage located? The signal leads not routed near any power cables or transformers? The high inductance of any MM or MI cartridge - shielded or not - can pick up stray magnetic fields. Placement is very important to minimize noise.

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PostPosted: Fri Jan 05, 2018 2:36 pm 
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I'll see about fishing a new ground wire through... doesn't seem too hard. Right now the table is apart, but I'll keep in mind what you say about placement, too. Thanks for all your help.


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PostPosted: Fri Jan 05, 2018 2:59 pm 
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two2the8 wrote:
... doesn't seem too hard.


Of course, that's the thought that got me into this whole mess in the first place! ;)


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