Please Help Me Understand Shielding & Grounding

[jtroska]

I have my Warmoth parts on order and, while I wait, I'm reading books and on-line stuff to figure out how to wire it.

I'm a little stumped on the shielding and grounding because different information sources seems to contradict each other.

OK, to shield a rear-routed body, I line the cavity with copper shielding tape and electrically connect the various strips of tape with solder.  I can also line the switch and pickup cavities and connect those shields to the control cavity shield with ground lines.

I guess the first thing I need to understand to figure out the next steps is:  What is the final "ground" that all the ground lines ultimately run to?  Is it the ground lug of the Output Jack?  Or is the the bridge wire?

Now once everything is lined with copper tape, do the potentiometers and switches sit directly on that shield?  And if the pots and switches are all sitting on the same copper shield, do I still run the usual ground wires connecting each of those pots/shields?  Or does that create a ground loop?

 

[nathan a]

The idea of a ground loop confounds me too a little, so I can't help you there. But, the copper shielding tape from warmoth is conductive even on the sticky side. No need to solder.

Highly recommend the StewMac shielding paint though.

On my project, the pots and switches contact with the shielding tape. Works great, no noise or anything. Lots of guys on here would argue though that shielding is unnecessary, and their results are essentially the same regardless of shielding

 

[jackthehack]

Based on my testing using FCC grade tape used in cell phones and RF chambers, the net effect of shielding with tape or paint is about nil. If you are playing in the vicinity of things that throw off a lot of RF like unshielded computers, electric motors, fluorescent lighting, etc. you are going to pick that RF up through your PUs, so the best thing to do is eliminate the RF sources.

You will always get some modicum of "hum" from PUs, especially single coils, and all the shielding in the world isn't going to change that fact.

As to grounds, they should ALL be tied together and run to the gnd. side of the output jack, that is the "final" ground, but there must be a circuit path to it from all other grounding points used.

 

[jtroska]

Yeah, I've heard mixed opinions on the significance of shielding.  I know my Carvin (which is shielded) is far more quiet than other guitars I've used without shielding.  But I've also been told that was probably more a result of better grounding--not necessarily shielding.  Who knows?  But I already have the shielding material and it's a hell of a lot easier to apply before the electronics go in, so I may as well do it.

So I guess, then, I just line the cavities with this stuff and wire everything as usual?  The wiring diagrams I'm looking at show all the ground wires leading to one point (usually the top of the Volume pot) and then that one point wired to the ground of the Output Jack.  Should I run a ground line from the shield to the common point at the top of the volume pot?  Or is that redundant if the volume pot os already sitting on the shield?  And--this is where I get more confused--If the volume pot AND the tone pot AND the switches are all touching this same shield, isn't that wrongly creating more than one path to ground?

 

[TroubledTreble]

A shield is used to block something. In the case of electronics the shield is actually used to "drain" something. The shield is there to provide a path to ground for any interference, thereby keeping unwanted noise from your guitar signal. If the ground path is not complete or a poor one there is little effect.

Grounding is the term used to describe the path for unwanted voltages to travel to the earth (ground). If you are a better conductor than the wire or if there is not a ground present then you will be shocked.

I have played old amps with a two prong plug, barefoot, and recieved a nice shock. Newer amps are better insullated and have better circuitry to help prevent this but it is not gauranteed. Also you may find your guitar has more buzz on an older amp. I think sheilding is a good practice even if it may only offer a small improvement. Grounding is very important! It is best practice for amps to have a 3 wire cord and the ground connected to the chassis. This will not prevent all shocks but it will prevent most and help the amp run quiter.

-TT-

 

[jackthehack]

"In the case of electronics the shield is actually used to "drain" something."

Nope. Simply there to attempt to shield RF radiation in one direction or another. Makes for shit if it's grounded or not, it's not an antenna that's RECEIVING RF signal, merely trying to block it.

 

[TroubledTreble]

Nope. Simply there to attempt to shield RF radiation in one direction or another. Makes for shite if it's grounded or not, it's not an antenna that's RECEIVING RF signal, merely trying to block it.

It does "block" it, I agree. It does this by directing the energy to ground. I always try to keep the description in its simplist terms and not confuse it with grounding which another subject. Shielding does help block signals from interfering with guitar circuits. Certianly today there are better standards and methods of construction that help electrical appliances emit less electrical noise. I remember when a vacuum cleaner would really mess up a television.

I know your not a big fan of shielding jack. This is definatley one of those things that can be a personal choice. I have shielded guitars and still get noise. I admit I haven't tried them unsheilded but I prefer, based on my background, to shield mine.

I guess we can agree to disagree on the subject of shielding. In the interest of science, the next time I build one I will play it unshielded first.

-TT-

 

[-CB-]

What jack said.  Adding, don't consider "ground loops" and other nonsense in a guitar.  As long as you have a good continual ground path - such as:

Pickup braid on the pots, and braid or wire from pots to output jack ground, and have a bridge ground, your no better or worse than any other grounding.  I personally like to run wires to the jack ground - mostly because it has a nice sturdy metal connection and a big hole to pass wires thru.  But there's not enuf current in a guitar circuit to make ground loops and daisy chained grounds an issue.... so don't worry bout it.

 

[jackthehack]

If it turns your crank to shield your axe with paint or tape, by all means knock yourself out.

I got all interested in this from posts that started on the old board, and being the Sr. Systems Engineer for a large cell phone OEM, I have access to RF chambers/rooms (will set you back around $60K for an 8 ft. empty cube) and materials used in manufacture that aren't available to consumers. so I conducted a number of experiments leaving some of my co-workers convinced that I was crazier than they already thought.

Bottom line in all the experimentation is that I could not produce any discernable difference in either a top routed Strat body with single coils or a rear routed LPS type body whether unshielded or shielded with commercial shielding tape as available from Warmoth/StewMac or higher order film used in cell phone manufacture.

So shield if you want to, but the net effects will be superfluous.