Magnets In A Circuit

[verhoevenc]

So im trying two new things on a build and had some questions. Te two new things I'm tryig are shielding the cavity instead of all the leads, and also holding the cover on with magnets instead of screws. I just realized however that the conductive shielding paint touches the magnets...

Here's the thought is my head:

1- they will cause issues, perhaps ground loops?

2- they will cause no issue, and I believe tele pickup magnet pole are ground to the pickups baseplate?

I've heard people tell me both yes and no... And both are smart sources so I'm stumped.

Chris

[verhoevenc]

Side question: for those that use shielding paint often, is it robust enough after 3 coats to use AS my grounding medium? IE: if I attach a lead to the paint and the paint touches all my components I shouldn't have to ground each component's housing? Or more importantly, maybe I SHOULDN'T wire-ground each component because it could cause ground loops if already grounded by the paint?

Thanks,

Chris

[ScottR]

I'm curious about the responses to these questions as well. I have zero point zilch expertise in things electrical....but what I did on my last build was use conductive paint inside the concavity including the cover they did make contact. I grounded all the housings to each other and to the paint. I also painted the pup cavities and grounded the pups to that. I checked that I had continuity between all housings and all the painted parts. No issues. I did not wire it up as a test without the shielding paint for a comparison.....so I honestly don't know what I gained by doing all that either.

SR

[Workingman]

my electronics abilities are modest but they exist. I see no problem with having a magnet touch a ground. I would like to know why the person who told you there will be one thinks so. They may be on to something I have not thought of.

I think the best way to go for grounding is to ground the components in a line and have a lead go from the jack ground to the shielding.

[Scott French]

Not sure about the magnets but my guess is it would not be a big deal if they touched the grounding paint. I'm pretty sure the one I did with magnets would have been touching as I have no memory of sealing them away after installation. As far as the paint goes keep mind there are different types and they will behave differently. I had a lot of problems with the waterbased stuff from Stewmac being wimpy (scrape/chip off) and in one case popping a glue joint in a hollow guitar. I moved over to the acrylic/nickel stuff and it is much more robust. I still do some form of star grounding in addition to the shielding paint as you know even the most robust paint will wear off in the area where the pot meets the hole over time. I've never noticed any negative effects from doing both.

[bob123]

*puts on nerd glasses*.

Currents are only induced when there is relative motion between current carrying conductors. A magnet touching "shielding" paint will not cause any issues at all. So, your concern of ground loops is unfounded. The only way to create a ground loop is if you used the shielding paint as the ground.

Instead, the shielding paint acts as a sort of faraday cage, blocking out external magnetic or static interference. It does not act on the circuit itself.

In reality you are better off shielding the wires, as that will produce a true faraday cage, whereas the paint will not properly disperse any external interference. (i.e. only working in one direction).

Now, to answer your side question, if you attached your ground wires to the paint itself 1) that wouldn't be very reliable, I wouldn't think, and 2) that would play more of a part in ground looping. Everything still must go to the ground wire on the input jack. So you'd be attaching grounds to the paint, and the from the paint the jack. That doesn't make a whole bunch of sense to me.

Edited February 22, 2012 by bob123

[Tim37]

the magents wont hurt any thing if they are touching the ground.

when a wire crosses a magnetic field it will produce an electric charge in the wire. so if coil up a wire (the coil is simply so you can get more wire in the magnetic field) then spin in through a magnetic field you will generate electricity. the way a guitar pickup works is you move the magnetic field across the coil and that generates electricty. the strings manipulate that field thats why they have to be made of a iron alloy.

the only thing that having a magnet on there could possibly do is distort the magnetic fields of the pickups and that could possibly cause some ouput diffences of the pickup.

[Ripthorn]

Now, to answer your side question, if you attached your ground wires to the paint itself 1) that wouldn't be very reliable, I wouldn't think, and 2) that would play more of a part in ground looping. Everything still must go to the ground wire on the input jack. So you'd be attaching grounds to the paint, and the from the paint the jack. That doesn't make a whole bunch of sense to me.

Just to piggyback on this, I have noticed that when I shield cavities with the stewmac paint, I tend to get resistances of anywhere from 20-150 ohms, so I would not use the paint as a ground connections. It will help to shield to a certain extent, but I wouldn't count on it, especially for signal grounds.

[ansil]

Side question: for those that use shielding paint often, is it robust enough after 3 coats to use AS my grounding medium? IE: if I attach a lead to the paint and the paint touches all my components I shouldn't have to ground each component's housing? Or more importantly, maybe I SHOULDN'T wire-ground each component because it could cause ground loops if already grounded by the paint?

Thanks,

Chris

i have used some really good stuff a few times but it is at my luthier friends shop and he isn't telling me whats in it as its a special mixture and was not designed for guitars. on the other side i have purchased many many products from stewmac and industrial suppliers when i ran a full size shop in the back of a record store. the short answer is this solder all ground connections to a ring and screw it through the paint to the wood. i did it in a Yamaha and it worked fine. long answer i own two Parker fly's both seem to use the same shielded paint and are relatively noise free, notice i said relatively. the green fly is now shielded with copper and by by noise. i was worried it was the active preamp going bad so i swapped them and nope. its just the paints ineffectiveness compared to the copper.