Getting Builds Checked for Safety

[cpsmusic]

Hi Folks,

I'm a musician (guitarist) and work in audio production and IT. I have a strong interest in music and audio technology, particularly historical stuff. Over the years I've built a few guitar pedals and a valve amplifier under the watchful eye of my father. My father was a WWII RAAF wireless tech. and spent his post-RAAF days building and repairing all sorts of things - mainly tube stuff including high-power amps, TVs, etc. so he knew a lot about working with high voltage gear. Sadly my father passed away recently (I'm currently cleaning out his electronics workshop) however I'm still keen to build gear for my home studio. My main concern is that now I don't have someone to oversee my builds, particularly from the POV of safety. For my next project (possibly a kit) I'd like to build a high quality stereo mic preamp such as this one: http://www.recordingmag.com/resources/resourceDetail/332.html

Of course this unit requires a mains power supply, supplying 48V for the mic plus whatever is needed to run the amplifier. In this case it is built as a separate unit (to help reduce noise). There are also kits like this: http://diy-tubes.ru/universal-psu-diy-kit.html

I've had a read of the ESP PSU Wiring article here: http://sound.westhost.com/psu-wiring.htm and it's made me a bit nervous! What I'd really like would be for someone to look over the build after it's finished just to make sure that I haven't done anything stupid or potentially dangerous. I'm planning on building a few other things too, most likely valve, running at high voltages. I'm in Melbourne's inner SE. Just wondering if there's anyone who would be prepared to do this sort of thing? I don't think it would take very long and at the moment I can't see myself doing more than a few projects a year so it wouldn't be too onerous.

Cheers,

Chris

[bitshift]

Hey Chris,

While there are a lot of Australians on the forum that could potentially meet up and help, there are probably a lot more people outside of Australia on the forum.

One way to get help would be to post schematics of your designs here. Since no single person is infallible, having many people look over your designs will yield a greater likelihood of discovering potential issues. When it comes to building the final product, as long as you make sure to wire everything up as per the schematics, you should be good.

[Zero999]

None of the circuits you've discussed are especially dangerous. Use an appropriately rated mains fuse, transformer and if it's a metal enclosure connect it to earth.

Another option, for low power projects, is to run it off a wall plug transformer. If you need a bipolar power supply it can be done with a voltage doubler.

[cpsmusic]

s long as you make sure to wire everything up as per the schematics, you should be good.

That's the bit that concerns me. I'm not building stuff all the time so I feel like it's possible that I could make a mistake.

[cpsmusic]

None of the circuits you've discussed are especially dangerous. Use an appropriately rated mains fuse, transformer and if it's a metal enclosure connect it to earth.

Another option, for low power projects, is to run it off a wall plug transformer. If you need a bipolar power supply it can be done with a voltage doubler.

Actually for projects like the one I mentioned I need 48V for powering the mic and then usually something like +-15V for powering the opamp. Using a wall plug might be a good option. Any idea where I can find a schematic for something like this. I've got a Silicon Chip (magazine) article that describes a 48V phantom power supply but it doesn't have power for an opamp.

[AlessandroAU]

You can do it with an AC wall-wart and avoid mains altogether! It's not legal to do your own mains wiring in AUS anyway.

Here's a supply I made a while back. You give it 12VAC plugpack and it'll give you the phantom bias voltage, a negative rail and 2 positive rails. I have mine configured as +48v, -15v, +15v and + 3.3v. It powers a mic preamp circuit for my desktop mic. (XLR condenser). It uses an INA217 opamp for the preamp.

I think we may have/had some very similar goals!

If you're super keen I think I have a spare PCB's of each left I wouldn't mind parting with. Let me know. I'm in AUS.

[cpsmusic]

It's not legal to do your own mains wiring in AUS anyway.

Thanks, I think I'll take up your offer as that power supply is just what I need. I'll PM you.

Regarding mains wiring in Australia, what do you mean exactly? I realise that it's not legal for me to wire up my own power points and lights, etc. Does this also mean that I can't build anything that requires 240V? What about people restoring vintage radios or building guitar amps?

Cheers,

Chris

[AlessandroAU]

It may surprise you just how much of a nanny state Queensland is if you've never looked into it! The rules exist but are rarely enforcd unless something happens.

Even wiring a mains plug is not OK. But you wouldn't think so when you walk down the electrical Isle at burnings. 

This is an excerpt I found on a website regarding it.

"Under Queensland’s Electrical Safety Act 2002, forbidden tasks include:

installing a new power point.
replacing a light switch.
replacing a batten holder with a new light fitting.
repairing an appliance such as a heater.
altering the location of an existing power point.
replacing a light fitting with a ceiling fan.
constructing an extension lead.
replacing a plug on the end of a lead.
 Acceptable tasks for the home owner are:

replacing a drive belt in a washing machine.
cutting openings for, but not connecting, air-conditioning units.
fitting, but not connecting, an electric wall oven in a kitchen cabinet.
You may also be able to:

rewire old-style fuses.
install garden lighting and pond pumps.
install battery-operated smoke detectors.
On top of the penalties for injury or death, The Queensland government website also has the chilling warning  that “DIY electrical work is regarded as unlicensed electrical work, which is illegal and has penalties of up to $40,000 for individuals.”

So repairing mains equipment would definitely be forbidden under the act 

Queensland has very similar laws regarding doing your plumbing aswell! Bullshit I know!

I don't mean to scare you away from your hobby, but its important to know these things.

[uncle_bob]

Hi

A *properly designed* and *properly assembled* wall wart is a fine idea. Unfortunately there is a lot of crap out there. One way around that (at least in the US) is to buy stuff from a real manufacturer rather than eBay. I'd bet it is the same in Australia. Surprisingly, the cost for the real item is not massively more than the delivered price from who knows who.

Once you get past the whole "mains interconnect" issue the rules (at least here) stop being as crazy. Put a fuse in series with the output of the supply after it gets into your gizmo. Check to see that the fuse is rated for your voltage as well as current. A 48V DC fuse is not always the same thing as a 12V fuse or a 120V AC fuse.

Once you have done all that, the chance of burning the house down (let alone injuring somebody) is pretty small. Can you still start a fire, sure, it'll likely be a small one

Bob