[Logos]

I'm just getting started in my DIY journey, but after a couple more basic projects (mini 3, y1/2 dac) i'd like to work my way up to something a bit better. So i've been looking at something like the M^3, or the Bijou.

While looking at the kits on GlassJar, Jeff states that one shouldn't work on the Bijou unless they have experience working with lethal voltages. So my question is:

How do I gain experience? I figure i'll just have to go for it at some point. Would this be recommended as a third or fourth build? It would be my first big project so i'm not really sure what precautions to take other than the most common sense ones. I'd appreciate it if someone can chime in. I've searched the forum with keywords and have come up with little. Thanks!

 

[Spacehead]

I took apart a CD-player and found a transformer that fits my needs. Then I just took the transformers secondary , soldered it to my amplifiers dual power supply. Then I carefully added a fuse to transformers primary and soldered power cord to it.
What is very important, is to check that any wires aren't bare and everything is well insulated. And no short circuits on the amplifier or the fuse will burn.

I don't want to use that device though. If something would happen, like a fire or electric shock, I would hate myself forever. It is better to use something that is factory made.
It just feels too unsafe. But I have checked it many many times, but still.

It is the experience that would make it safe I guess

 

[whitelabrat]

I think by experience, it would mean you know what not to do. In a nutshell, being shocked by a high voltage amplifier is easy and very painful if not deadly.

This is a good read to get you started: Electrical Safety

 

[whitelabrat]

Quote:

Originally Posted by Spacehead /img/forum/go_quote.gif What is very important, is to check that any wires aren't bare and everything is well insulated. And no short circuits on the amplifier or the fuse will burn.

You don't really learn electrical safety by trial and error. When you have 470uF at 250v it's more a trial and execution.

It's not good if stuff explodes because wiring and insulation is bad. At least you're still alive.

It's unacceptable if you are any other person is able to accidentally make contact with high voltage. A lot of accidents happen while testing something that is hot. For example, ideally no part of your body is nearby when taking measurements. Likewise using appropriately rated fuses and chassis design is important too. I've seen too many tube amp PCB's just mounted on a board because it's cheap and easy. It's also stupid.

Another good example of being safe is being sure all your capacitors are drained before poking around. The power may be off, but the caps may still be charged.

Etc.

 

[balderon]

I would strongly recommend reading every word carefully on the thread HV tube amp danger and in particular the links pabbi1 posted. I have always been leery when powering up HV circuits. I typically stand away when I apply the power just to have a safety margin in case of a fireworks show.

 

[fishski13]

-common sense and presence of mind are needed with any open chassis plugged into the mains.
-don't touch anything with power applied without an insulated handle. if you need to touch any component or wire with hands make sure the power is off and caps have been safely discharged and double checked with your DVM.
-when possible, i like using a DVM probe that can be clipped to chassis ground so i only need one hand inside the chassis to take meaurements.
-clean workbench.
-take your time.

 

[Spacehead]

Quote:

Originally Posted by whitelabrat /img/forum/go_quote.gif You don't really learn electrical safety by trial and error. When you have 470uF at 250v it's more a trial and execution.

470 uF and 250 V capacitor contains lethal amount of energy, right?

I have been thinking that if I do something with higher voltages, there is no room for any mistake. So I stay at safe distance from live voltages and when I debug or handle something I always make sure I have unplugged the power cord and capacitors are drained.

Is there anything I should know about transformer safety? I now have that transformer in a plastic box, wires are soldered and taped. I don't dare to use that too much, because I am afraid that something would go wrong.

here is a picture of two amps and the transformer is also visible there.

I must say I am quite a noob in these things, but I am very interested in this DIY audio.

 

[dsavitsk]

Safety Practices, General and Ultra-High Voltage - diyAudio

 

[Logos]

Thanks for all the great replies and thread recommendations, a lot of reading ahead.

Is there a good amount of time to wait before checking caps to see if they're discharged? I read somewhere ~20mins is a good rule of thumb before testing with a DVM.

Fishski, when you say "insulated handle", you are referring to the handle of a multimeter probe correct?

 

[balderon]

Quote:

Originally Posted by Logos /img/forum/go_quote.gif Thanks for all the great replies and thread recommendations, a lot of reading ahead. Is there a good amount of time to wait before checking caps to see if they're discharged? I read somewhere ~20mins is a good rule of thumb before testing with a DVM.

A couple simple searches should answer your questions.

Need to discharge a capacitor
How to discharge caps in power supply

 

[Juaquin]

Also, those who work with HV will tell you to work with one hand behind your back (or in a pocket) at all times. If your other hand does happen to touch a live wire (or cap, etc), worst case scenario is that it travels from hand to leg on the way out, which is a lot better than hand-to-hand, which crosses the heart and is more likely to be lethal. Also, shoes are usually pretty good insulators so you stand a better chance.

 

[Squalish]

Fun link

Unplug everything.

Wear rubber gloves.

Use one dry hand.

With the other behind your back.

Do not hold alligator clips open with your finger, or stab yourself with a probe.

Assume that capacitors in circuits you build do not self-discharge at all without your assistance. Discharge them at the start of your work.

Avoid grounding yourself against anything metal, particularly against the case with your forearm.

When designing, use directly-applied bleeder resistors at any high voltage cap, so that after N hours you'll have burnt off 99% of the energy in the amp. Choose N wisely, stick to it, and observe it while working.

Respect large, heavy electrolytic capacitors, no matter their specs. When you short a capacitor, the energy has to go somewhere. If there's enough to melt solder or blow up a wire, be very careful.


That should keep you pretty redundantly safe until you get into real high voltages, where you have to worry about arcing.

 

[AndrewFischer]

Quote:

Originally Posted by Spacehead /img/forum/go_quote.gif 470 uF and 250 V capacitor contains lethal amount of energy, right?

Yes, a 470µF/250V capacitor charged up can be lethal.

Caps charged to a high voltage can store a quite a bit of energy. Energy stored in a cap increases with the square of the voltage

E = 1/2 C*V*V . C in Farads, V in Volts SO
250V
E = 1/2 * .00047F *250*250 = 14.68J

Same cap charged to 25V would have .1468J energy stored.

 

[colonelkernel8]

Quote:

Originally Posted by Squalish /img/forum/go_quote.gif Fun link Use one dry hand. With the other behind your back.

This is a myth.

Also, about caps, what's particularly dangerous is how quickly they discharge their energy as opposed to a battery or the like.

 

[johnwmclean]

Take all jewelry off your hands before working on anything.

Always have someone else around and about.

Buy specialist insulated tools that are specifically designed for HV work.

Don’t ever become complacent, always be alert.