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Shock when going direct...grounding issue?

dwjazz54

dwjazz54

Jan 21, 2003
500
10
Jersey City, NJ
thedrunkardswife.bandcamp.com
#1
Hi everybody-
This weekend, my project was doing a gig at a party on a farm, and in our downtime we decided to do some impromptu recording. I was wandering the grounds, so did not do the initial recording set up, but when I came in, I found that there was a noticeable shock whenever I was touching metal parts of my bass. A little troubleshooting revealed that the shock went away when I unplugged the cord going from my amp's DI to the board.

Now, I typically don't like going direct, and we were able to mike the amp without any trouble. And the gigs that we do so far typically don't require going direct (and when I need to go FOH, I insist on mic'ing - I guess I've gotten lucky with soundmen!). But still, it's cause for concern, as it's a recently acquired amp (GK MB212-ii).

Do I have a grounding issue with my amp's DI? It may have even been a problem with the grounding in the space, which was essentially a fancy barn.

Any ideas? Do I need to worry?

Cheers!
-dwjazz54

PS - signal chain was Squier CV Jazz, BOSS OC-3, amp, signal going direct to board.
 
#3
1. Be sure all of the gear has a common ground.
Sometimes, building wiring can have poor grounding at branch circuits.

2. Then use the ground lift switch or ground lift input on the DI box.
 
#4
schecter5string said:
Can't you duplicate the situation at home or at rehearsal?
If you still get shocked it's your rig. If not it was the barn.
Click to expand...

Well, I would. But we didn't get back until late last night, I use a different amp in our rehearsal space, and I do not have the necessary equipment in my own home.

I just don't want to one day get to a big gig, run out of microphones (we've got accordions and horns and what-not), and find I've screwed myself...

Of course, I could buy a microphone...
 
#5
Were the mixing board and your amp plugged into outlets on different circuits? If so there may have been a voltage potential between the two circuit grounds. That's a common issue. Either run your amp and the mixer on the same circuit or use the ground lift on your DI box as suggested above.
 
#6
It sounds like a problem with the neutral (white) to the barn's wiring. Purchase one of those yellow plug-in polarity checkers. It won't solve everything, but it will tell you when wiring is crossed or there is a problem with the neutral. It won't tell you when the neutral and ground are wired together, so you still have to be careful. I call it my $5 life insurance policy.

Ground lift on a direct box is for hum suppression. It won't necessarily protect against shock.
 
#7
ganttbos said:
Were the mixing board and your amp plugged into outlets on different circuits? If so there may have been a voltage potential between the two circuit grounds. That's a common issue. Either run your amp and the mixer on the same circuit or use the ground lift on your DI box as suggested above.
Click to expand...

I have to admit, I didn't look (SHAME!). I'm not even sure that if I did have a look I'd even know what I was looking at - wiring and stuff like that is just something I never managed to wrap my head around!

Thanks for all of these quick responses, everybody - why I love TB!
 
#8
john m said:
1. Be sure all of the gear has a common ground.
Sometimes, building wiring can have poor grounding at branch circuits.

2. Then use the ground lift switch or ground lift input on the DI box.
Click to expand...

Unfortunately, the MB212-ii doesn't have one. It's got headroom, great sound, and light weight, but with that low price comes no ground lift.

On balance, though, still damn pleased!
 
#9
dwjazz54 said:
Unfortunately, the MB212-ii doesn't have one. It's got headroom, great sound, and light weight, but with that low price comes no ground lift.

On balance, though, still damn pleased!
Click to expand...

You have to clip the ground on the mic cable that you use between your amp and the mixer. Make sure you mark that cord and use it for your direct signal only. That's the quick and dirty way to do a ground lift.
 
#17
Does any of the gear that you are using have two conductor power cords? Is all the gear plugging into the same 120V circuit? It helps to use wall power receptacle tester to ensure that the sockets are wired properly. In the case of a two conductor power cord, unplugging it and reversing it can help. As can switching the polarity switch if the equipment has it.

Many DI's have an XLR ground lift switch that is used when there are audio hum issues. But this does seem like it is an equipment power grounding issue.
 
#18
When you say shock, do you mena you were getting shocked or the bass made a popping noise?

If you got shocked, you have some serious electrical issues going on.

If the bass just made a popping noise, it is a static electricity build up, I have seen it on a few basses and even some guitars. The only way to remove it that I know of is a proper shielding job, but I have also never had a bass with static build up that was properly shielded so I was shielding it anyways.
 
#19
For the last 20 years or so, I have used an outlet checker
($5) and plugged everything into a Furman power transformer (not conditioner), and used only one 110 volt outlet. Never get shocked, and never plug into faulty wiring or worst 220v on a 110 outlet.

Also, I am the only person I let check the outlet, and my whole set-up (PA and all) pulls less than 15 amps.
 
#20
john m said:
It will still work as a "regular cable" in most cases.

A factory made ground lifter is a one trick pony--- if you must, find a used whirlwind DI. If there is audio support provided, the sound company has many in their tool box.
Click to expand...
That's true...a ground lifter IS a one trick pony. That's all I need out of it, though ;)
 

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