Ungrounded power leads?

[duuuhhh]

Hi guys,

I have a question that might sound stupid... I hope it doesn't.
I used to think the power "ground" or "earth" was somehow related to the "shield" or "neutral" or "ground" in audio cables/connections, was I wrong? Yeah, obviously I'm not an electronics guy, so could someone help me out here? I got a bit confused about it after finding some mic preamps/converters on the market (check the links below for example) that don't have a grounded power lead, but at the same time claiming to have all "balanced" ins and outs... Is that actually possible? How does that work?

http://www.sweetwater.com/store/detail/DigiMaxFS/ --> this one has just an external supply with an ungrounded lead;
http://www.sweetwater.com/store/detail/OctoPre2dy --> while this one's actually written "This equipment must be earthed by the power cord" on the back panel.

Cheers!

[rick]

the power ground on a box is there to save your life if something goes wrong its not part of the audio circuit on purpose

the audio ground which is often tied to the box at the same place as the power ground is for a different purpose it "shields the audio cable" from hums and buzzes and stuff .

you can have a balanced audio connection without the ground being connected .

all boxes should have a power ground connected ( even though some dont ) .

dont be confused , read up on this stuff , ask about it learn about it it may save your life one day when your doing something dumb

[stosostu]

Any mains powered electrical equipment, that complies with Australian Standards, that doesn't have an earth connected or doesn't have an earth pin on the plug has to be double insulated. What this means is that there has to be two levels of insulation barrier between the user and any electrical terminals within the equipment. In fact, fitting an earth to this type of equipment (which is illegal) will breach this double barrier, since there is no longer a double insulation to the terminals.

If the equipment has a ground for shielding purposes on audio connections, this will be isolated from the mains power.

[rick]

If the equipment has a ground for shielding purposes on audio connections, this will be isolated from the mains power.

you know bob your right i agree with what you have written and i found it pretty hard to make a simple bullet proof explaination myself , as long as we identify your statement as being correct for modern two prong power devices only

but because i can think of a dozen boxes i have that dont agree with the rules - things can and do get confusing for the novice and pro alike
we are talking about POWER to KILL YOURSELF here folks , dont assume because you read something on the net that its safe or it will be ok
if in doubt .. dont etc etc

i reckon the op was asking about a concept , the concept is that power earth(grounds) and signal earth are technically different things
but they sometime share the same connection point thus his confusion ..

[stosostu]

You're right Rick, I was talking about compliant, modern equipment, which is why I made the point about Australian Standards compliant..

There are, of course, all the older US items, particularly guitar amps, that only had two pins and WEREN'T double insulated. In that case, use an isolating step down transformer (NOTE: they are not all isolating) or have it rewired with an earth by a licenced electrician.

As Rick says, this stuff can and will kill you.