So I’m new to doing electronics projects and I’m about to build two things that have a 1/4" line out, to be plugged into a mixer and/or amplifier. I was reading a book about circuit bending that said to NEVER plug one of your projects into an amp that runs into the wall unless you were absolutely sure that the amp you were plugging into didn’t have a “ground fault,” or you could get fried.
So now I’m super paranoid about the whole thing. If I’m building these projects and have the knobs and jacks properly grounded to both the package and the 9V battery they’re running off of, shouldn’t I be fine plugging into an amp that runs off of the wall?
Some ancient amplifiers were not “transformer isolated” from the AC power source. Any modern Amp with a grounding power cord should be safe, and you can be even safer by making your project in a metal box, and grounding it also.
That’s what I thought. By grounding (the project), do you mean grounding it to itself, as in using standoffs on the PCB and grounding the jacks and knobs to the metal case and the negative terminal of the 9v?
If you really want to be safe, pick up a portable GFCI at the hardware store or have a regular GFCI receptacle installed wherever you’re planning to be messing around with amps and whatnot.
Portable GFCIs come in two basic flavors:
A compact dingus like this one or in the middle of a short extension cord like this. (Note that this particular one is more for a construction jobsite as it has twist-lock plugs)
Like the GFCIs in your kitchen and bathroom, this will kell the power before any wayward watts have a chance to give you a shock.
No need to mess with trying to ground the world, which only results in heartburn, ground loops and hum.
Just make sure that the case (and anything else that you can come in contact with) is grounded. That usually means connecting the negative terminal of the power supply to the case, but not always. Some projects use multiple power supplies, and these can have positive grounds.
Thanks. These are super-simple 9V battery->one IC->a couple of resistors and caps->1/4" out noisemakers, so grounding stuff to the 9V’s negative pole should do the trick.
NO. “Grounding” your project to its battery accomplishes nothing.
The whole problem you’re trying to solve is: “What if the amplifier has a defect which pushes 120V out of it and into my project? How can I be certain to drive that current back into the wall without it going through me to the floor?”
The short answer, without opening a can of worms about ground loops, balanced lines and a whole host of other mumbo-jumbo, is “you can’t”. At least not with 100% reliability.
So put a GFCI in the power path between the wall and anything that connects to your project & relax.
Note that for 100% safety, everything that connects to your project, even indirectly, needs to be on the GFCI.
e.g. a setup like project -> pre-amp -> main amp -> powered sub-woofer plus also tv -> main amp and receiver -> main amp means all of those things (pre amp, tv, receiver, main amp & sub woofer) need to be on the (ideally same) GFCI.
Find a good ground in your house, metal drain pipe*, metal outlet box* (or if your comfortable working with electrical outlets, you could use the ground from that*) and ground to that. Since you seem to be concerend about being zapped by 120v, I would ground to a real ground, not a battery.
*by good ground, I mean, you’ve tested it to be SURE it’s a good ground. Don’t even trust an outlet until you’ve tested it.