[dgardner]

The purpose of this thread is start a DIY discussion on the design requirements to make a friendly and internationally acceptable power supply for split rail audio projects. Besides that obvious fact that international primary voltages vary (100, 120, 220, 240, etc), there seems to be a lot of products and projects out there that don't meet the EU safety standards and CE mark standards. It looks like DIY choices are limited some folks outside the US if they intend to comply with local requirements.

If anyone out there has synopsis of these requirements, please post something here. I could comb through the standards library myself, but I'm looking for some quick leads.

Earth mains grounding? Fusing? Short circuit protection? Creepage and clearance on AC lines?

 

[Dougigs]

I've lived in UK, Canada and the US during the past 10 years, and have brought literally dozens of homemade and refurbished hi-fi components back and forth across the pond. When I build things, I'm careful to make them international.

It's not very hard:

1) Almost any decent power transformer you buy these days is dual-voltage (i.e. the primaries can be connected in series or in parallel for 120/240 use -- just read the datasheets). This includes almost any toroid you can get, including the handy Talema pcb-mount units. You can make a switch. Or you can buy a premade 120-240 switch (antique electronic supply sells nice screwdriver switches made for guitar amps). Or you can just open it up and rewire it when you cross the pond.

2) Lo-current circuits such as most headphone stuff can be powered with wall warts. Change countries, just get a new wall wart (although I should note that some of the nicer ones, including most laptop adapters, produce a constant DC voltage with 120 or 240 -- you want to check this though!)

3) That safety-code stuff really only applies if you're manufacturing stuff for commercial sale. For line-powered circuits, basic safety rules apply everywhere. Yes, in the US the neutral and the ground are the same thing, whereas other countries require an earth ground. Don't get too hung up about that -- for audio circuits, you want to have chassis going to signal ground (input signal ground for some of the buffered-ground amps you'll see here), and maybe have one component in the chain connected to an earth ground if you have one

4) If you want to get fancy, think of running your audio all at 120V wherever you live. That's what I do with my 'main' system (the one I use in my office). I use a 1000VA toroid isolation transformer from Plitron and a couple of decent filters mounted in a big metal box -- when I'm living in Europe I use it as a step-down, which also isolates the line very well from all the garbage from my computers (I've mounted a couple of AC outlets on the back, one filtered and one not, so my digital circuitry such as transports and DACs can be isolated from my analog circuitry). When I'm living in North America, I rewire the primaries so it's a 120:120 isolation tranny.

 

[Garbz]

Actually regarding the safty i think the idea was general safty guidelines. I know the CE standard doesn't apply but it would be a good idea if people here designed thigns taht didn't kill them.

E.g. if you are building an amp with a metal case float the inputs and outputs and tie the case to earth. Also if you are building a balanced amp definatlity tie the case to earth and add a switch which allows you to lift the signal ground at the input / output to eliminate resulting ground loops.

 

[skyskraper]

isn't there some law in australia about only qualified electricians being allowed to work with 240v?

aside from that, great topic dan

 

[NOTHINGness]

Quote:

Originally Posted by Garbz Actually regarding the safty i think the idea was general safty guidelines. I know the CE standard doesn't apply but it would be a good idea if people here designed thigns taht didn't kill them.

I think if someone designs something that kills them, they won't be posting the design.

 

[Nisbeth]

IIRC the European standard calls for 6mm (1/4") clearance between a conductive chassis part and any part with mains potential (230VAC). The was a lot of debate about this in the STEPS discussion not too long ago and I believe Per-Anders posted some relevant information.


/U.

 

[Garbz]

Quote:

Originally Posted by NOTHINGness I think if someone designs something that kills them, they won't be posting the design.

Actually what I was referring to was advice from other people. My heat skips a beat when I see people posting a solution to ground loops being cutting the ground line to equipment!

Grounds and other safty standards are there for a reason, so obide by them. Sure you say that your equipment never gets used, but for the Californians who live on a fault line, all it takes is a small shake and a loose wire, or solder joint which was under stress could potentially turn your greatest joy into your worst nightmare.

 

[Dougigs]

The 6mm rule is very sound and should be observed everywhere -- it's amazing how easy it is to go from "tight" to "touching" -- esp. with regard to electrolyics, whose top plates are at full potential. (Says a man who has rested his fingers on the tops of a few too many caps at 350 volt potential -- that wakes you up quick!)

3-pin grounds are a good idea, but you often only want one of them per system (usually the highest-current component). You can use one of those fancy hospital-grade plugs if you want, though these are probably only valuable if you have many hundreds of watts of poer (though I've used them just because they look neat). This approach is no less safe (as long as the chassis of all your components are connected to signal ground), and it observes good grounding practice (i.e. single point).

Things aren't as bad in California as you may think. My building there had 3-wire earth grounds, and it was a mid-'80s postmodern stucco Melrose Place horror. I think most modern building codes in the more advanced states require proper grounds (though nothing as robust as you see here in Old Europe, where massive earth cables are the norm)... I do have a house in Canada that's entirely 2-wire knob-and-tube asbestos-insluated wiring from 1905 above the second floor. I had an audio system on its top floor for a while, and I strapped the earth ground (from the amp) to the copper water pipe, which is earth-grounded (and is lower impedance than any wire). Later I had a proper 10-guage circuit wired up there, not just for audio but to keep my son from frying himself.

Keep in mind that a lot of places just don't have earth ground. From my experience this includes not only most of the United States, houses in Canada built before the 1940s, large parts of France, most of Italy, huge sections of the Middle East, most parts of Africa, Russia, central Asia, and a good number of places in the Far East. I don't know about Australia or Japan.

The point is that if you really want to make something internationally useful, it's best to design it with the assumption that there won't be a functioning earth ground. Build it so that it will be safe without one.

In other words, plastic chassis rule (actually, I'm a huge fan of clear acrylic cases these days, both for safety and beauty -- and almost every major city has Perspex fabrication shops that will build you a nice thick shiny one for almost nothing).

 

[Dougigs]

An aside, a bit OT for this forum:

Speaker design has to be radically different for North American and European houses. In NA, houses are wood-frame, and even with heavy insulation they form very serious resonance chambers. Houses in Europe have exclusively brick walls and (generally) floors, and are accoustically dead.

As the Q of your room changes dramatically, so does the sound of the speakers. Enclosures that sound great in NA are naff in Europe, and vice versa. Bass reflex sound much better Over Here, but when I bring them to North America I have to stick socks in their vents.

This almost certainly doesn't affect headphones though.

 

[Garbz]

actually the sound difference I find is not a case of good there crap here, but simply playing around with all sorts of thigns. There's no reason a speaker can't sound good if a room is decently laid out (can't be done in my bedroom

)

Also when i mentioned california I was just referring to earthquakes (bad stereotype I know, I don't live in a shaky area). As for grounded houses, I don't think it makes much of a difference. If the ground meets the neutral, eitherway if the chassis is grounded and a live wire touches it it'll trip a master circuit breaker and won't your arm fall of when you go to turn it off.

 

[Dougigs]

Oh, the earthquakes aren't just a cliche. You get them, every few months, and they're as scary as you'd think. And you have to make a good investment in blu-tak, to keep your nick-nacks on your shelf. Which is why Californians and ex-Californians know how to keep their batteries firmly in their headphone amps: Blu-tak is the stuff, man!

 

[00940]

Quote:

Originally Posted by Dougigs 2) Lo-current circuits such as most headphone stuff can be powered with wall warts. Change countries, just get a new wall wart (although I should note that some of the nicer ones, including most laptop adapters, produce a constant DC voltage with 120 or 240 -- you want to check this though!)

Most of the wallwarts which can work on both 120V and 230V are switching PS. Switching wallwarts such as laptop supplies are generally too noisy to be used for audio purposes. There are some exceptions of course.