Newsgroups: rec.audio.tech
Subject: Re: electrical question
References:   <[email protected]> 
Laurence Payne  writes:

> >>Are there any design differences between audio gear for the US market,
> >>where power grounding seems to be an optional luxury and gear for the
> >>UK, where strict regulations demand cross-grounding between just about
> >>any metal objects in premises with an electrical installation :-)\
> >
> >Newly installed wiring must be grounded, but existing wiring (some from
> >the early 20th century) does not have to be replaced. Small appliances
> >used in dry areas (stereos, small hand tools, lamps, hair dryers??,
> >etc.) do not have to include the "ground" ("earth" in the UK) wire.
> >Large appliances (washers, stoves) are grounded. Desktop computers are
> >grounded, but laptops are not.
> >
> >The ungrounded small appliances are carefully designed and tested to
> >avoid any personal or legal hazards. Other than a few screws and some
> >wire, many of the small appliances don't contain any metal that could
> >be grounded.
> 
> I was thinking more in terms of avoiding hum.  Does not being able to
> rely on having a ground connection affect audio design?  

Yes. 

> Or do circuit
> designers just assume that a ground, if available, is likely to be
> dirty, and ignore it except for safety considerations?

Some ignore, some don't. This varies somewhat form manufacturer 
to another and maybe from equipment generation to another. 
Some equipment perform better in real life situations than other. 

Ground should be considered for the safety in mind first. 
Properly grounded electronics and metacl case around them 
gives very good shielding agains electrical inteference from 
other sources. In design you must also assume that the 
ground can be dirty (ground on your quipment or the ground on 
some other equipment on your system connected to your device 
through audio cable with ground wire). Proper design will 
give safety and good performance. The for the proper design of 
the device usually takes some time and knowledge. 
And implementation of that good design can be a little but 
more expensive to manufacturer than the simplest and cheapest 
way to do things, but will keep the users much happier. 
I have used good and bad equipment. The good ones save 
you lot's of headaches and needs to do "hacks" like 
many signal isolation transformers around and "ground lifts" 
on audio cables.

Some related information can be found at 
http://www.epanorama.net/documents/groundloop/audiocircuit_grounding.html
http://www.epanorama.net/documents/groundloop/index.html



-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/