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Earthing issue.....


MoJoKe
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Can anyone help please? I posted this in the amps/cabs sectioin yesterday, but perhaps should be here...

Lakland 5502, new planet waves lead into a Markbass CMD151 with a brand new power lead. If I touch the strings I get earth buzz.

Yesterday at rehearsal I connected my HTC phone using spotify, to the practice room PA with a microjack to 2 phono lead, and when I picked my phone up while holding bass with fingers on strings I got a small but significant shock.

Both MB amp and PA amp on the same ring main....

Ouch... hheeelpp!

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Are there any extension cables or 4-way mains blocks involved ? You need to check that all the earths are in place on all mains cables or extensions. If the 13 amp plugs are the type that can be opened up (i.e. they're not molded ones that don't open) then have a look inside each and ensure that they're wired correctly - paying particular attention to the earth wire (the green/yellow one) which should be connected to the largest pin in the plug.

Does the buzz happen in other rooms, or just the rehearsal space ?

Simplify your setup to test it - plus the amp directly into a mains socket (no extensions). Plug the bass directly into the amp with no effects. Does it buzz ? Try a different mains cable. Does it buzz ? Try the same in a different room.

You need to establish if there's a fault in the mains cable, the amp, or the room.

Avoid touching any other equipment while doing this.

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Thank you for your help. I have just tested the setup with my other 55-02 which is fine, so it looks like its the Bass...!

I've had the cover off and there doesn't appear to be an earth connecting the foil strip (which has bridge and both pickup earths connected) to the rest of the earths, and certainly not the jack ring. Is this correct? I have poked around with a meter and getting 1 or less (with meter set to 2000ohm) on all other earthed components, but 90 or more when between jack socket sleeve and the bridge earth.

That cannot be right?

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Resolved!

The foil strip in the control cavity had earths from the bridge and pickups, but this wasn't connected to anything else! A quick soldering job to earth it to the jack socket ring (via one of the pots) and the probelm is solved....

However, why the guy who did the final checks on the bass before it was shipped didn't spot this heaven only knows!!

In investigating it I compared the wiring from my older Bart pickup'd 55-02, which was beautifully neat and tidy, the newer bass wiring is an absolute mess by comparison. Rather than being encased in plastic like the older one, the preamp has two strips of insulating tape on to stop the PCB shorting on the foil of the cavity plate, and the wiring is a tangled mess.... not impressed...

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