Main > Main Forum
Questions about grounding a cab
(1/5) > >>
jimmy2x2x:
After fitting an IEC socket to my cab I have started to notice an occasional buzzing from the speakers when I touch certain parts of the cab.

There are various metal parts on the cab that are not currently grounded, control panels, cocktail legs, glass clips, large speaker/ air intake grill etc.

If I make a ground loop, connecting all of the metal parts (or as many as practicle) would it be best to connect it to the ground pin on a mains plug (in UK here)?

Not really sure about this, never done this before.

Thanks
mgb:
Yeah, everything metal should be grounded together and bassically you want it to go back to the ground of your power plug.
BobA:

--- Quote from: mgb on August 14, 2011, 08:10:28 pm ---Yeah, everything metal should be grounded together.

--- End quote ---

The purpose of this is to GET RID OF A GROUND LOOP that can cause interference when grounds are at different potentials.
MonMotha:
Here's the thing to remember about "ground".  The word "ground" is commonly used, especially in the US, for two things: power "common", and earth ground.  I'll attempt to carefully distinguish between them using these terms here, even though many people just say "ground".

Earth ground (often just referred to in Europe as simply "earth") is a safety thing.  All the externally accessible metal bits of your cabinet should be tied together and connected to earth ground to prevent touch hazards between these metal chunks and, well, the earth.  "Earth ground" is the 3rd prong on your IEC inlet.  It's somewhat preferable to run dedicated, heavy gauge wires from each metal chunk back to a central point, but that's often impractical, and just daisy chaining them together is fine, too.

Power common, aka "the black wire", is something else.  It's simply the return path for electric current from your DC supplies.  All your signals and such are also referenced to this "common" line.  This includes not just button signals but also your video signal as well as single-ended (non-balanced) audio lines like the line level audio outputs from your PC.

There's two common schools of thought on how to address this.

A common thing to do is connect these two "grounds" (earth ground and power common) together AT ONE POINT ONLY.  No other connections are allowed as this results in "ground loops" which can cause audio hum, interference patterns in video, etc.  Your PC will do this internally in its power supply.  If any other connections exist, and there's even the SLIGHTEST bit of potential difference between them (which can happen for lots of common reasons), current will want to flow on your signal wires between all these connections to equalize things out.  That's what causes the interference and creates the "ground loop".

The other option is to provide no path at all between the power common line and earth ground.  This will work fine as long as absolutely no paths exist.  However, the way switch mode supplies, like PC power supplies, are built, there's a small amount of current that wants to "find" earth ground, and it's surprisingly easy to create a "weak path" to earth such as through a person if they happen to touch both a connector and a chunk of metal.  It'll also tingle (quite a bit) should you do this, but it's not particularly hazardous.

One thing to note is that arcade monitors will generally provide a tie between power common and earth ground.  This is in a generally undesirable place and is difficult to avoid (since, for safety reasons, the monitor frame really should be grounded), but it's in a place that doesn't generally cause many problems.  I have actually seen commercial arcade designs that don't ground the monitor frames for this reason, though.

The Wikipedia article on "electrical grounding" will explain some of this in more detail.  You can kinda think of the "power common" within your PC and/or cabinet as a "technical ground" as would exist in a TV/radio studio or a "signal ground" that might exist on a circuit board.
SavannahLion:
If I may....

I'm just adding to what MonMotha has said. He just overlooked a couple of minor details.

First off... Check to see if you even have an "Earth Ground" on your socket, your power strip, or whatever you're plugging your cab into. I spent a mighty long time figuring out why I was constantly getting shocked and getting weird behavior from my PC (in my old apartment) until I realized the landlord was too cheap to do a proper (Earth) ground at the socket. I add a ground myself and those problems went away.

Second... Make sure your socket is wired correctly in the first place. I discovered one socket where the ---uvula--- (same apartment) flipped the hot and common lines. Those sockets are polarized for a reason. If your system is tying the Common and Earth together and you plug in to this socket. Good Luck. I caught it while looking for groundless sockets with one of those chintzy plug "checkers" from Rat Shack.
Navigation
Message Index
Next page

Go to full version