Shielding Question

I'm not a shielding expert by a long shot. Hang around here long enough and you'll learn a lot. Just like I did.

The purpose of the tubing is to completely enclose the wire from the pickup from noise. Simply running a single conductor wire will not accomplish that. I've seen talk of using 2-conductor shielded wire from the pup through the hole and to the electronics cavity. However, I haven't seen the pros weigh in on that, so I won't suggest it at this time.

In either case, whatever shielding is there MUST be connected to the ground path of the electronics. I understand that it's best to run it to the jack's negative side, or in active designs, to the negative side of the battery connection.

Oh, and please solder together the individual foil pieces so that they are connected. That's absolutely permanent (if properly soldered). Adhesives are not, especially the contact variety used on the foil.

 

Use shielded wire instead of shielding the wire channels. That shielding absolutely IS necessary, regardless of how it is done. Think of shielding like waterproofing a submarine. If there is a leak anywhere, the submarine is useless.

FWIW, note that the tone of the pickups will change if you shield them.

 

Are you speaking of shielding the pickup cavity?

 

Shielding the pickup cavity wont change the tone, but shielding the pickup coils will.

 

I don't ever mess with pickup wires, 'cause I'm afraid I might break one of those tiny wires, and I don't think my soldering skills are up to the task of fixing one. So I shield my wire channels.

It's really easy. Wrap a length of copper tape around a straw or dowel, with the adhesive on the outside. Make sure the length of wrapped copper tubing is about an inch longer than the length of the wire channel. Slide it through the hole while still on the dowel so about 1/2" is on either side of the hole, then slide the dowel out. Cut some slits lengthwise in the ends of the copper, and then fold the flaps down against the sidewalls. Done!

Or you can use 1/4" copper tubing. I did that with my bass. Worked great.

 

^ I disagree with this.

Use good shielded wiring, and learn to solder. I don't mean to be rude, bluetalon is just trying to help. But seriously, as a professional, if I came across a copper straw in a guitar I would have very serious doubts about the abilities and knowledge of the person who did the installation.

Place the pickup upside down on the bench. Press it into a blob of blutac or tape it in place if you need to steady it. The pickup wires will come off almost instantly the iron touches the solder lug. When you go to solder the new shielded wire, pre tin both the core and the twisted length of shield and cut them to length. Use a heatsink clip on the shield so it doesn't melt the insulation and short the core to earth.

 

Robbie, do you have something against using copper tape with conductive adhesive to shield the interior cavity? I get it, you prefer to use shielded pickup wires. Bully for you. But the OP didn't ask about replacing his pickup wires with shielded wires, he asked about shielding the pickup wire channel. I don't know what you think you read in my post, but I said nothing about a "copper straw". Not to be rude, but don't put words in my mouth.

FYI, two professionals have seen the shielding job I did in my avatar bass, and both were very impressed.

P.S. If he does what you recommend and screws up his pickup, are you going to fix it for him or replace the pickup?

 

I agree with RobbieK. Proper shielded wire runs are the way to go. Not copper wrapped straws.

 

It's "copper tubing", when it's all said and done.. It's an accepted practice, just as using shielded wire is, too.

I've learned that if you use tubing through the hole, be sure to connect it to the ground plane with the cavity shielding.

Nothing special about it, just another way to get there from here...

 

If the wire channel is too small then it is better to just put a shielded wire as the pickup wire.

 

A "copper straw" or metal tube shield lining the wire hole is a perfectly good shield. For my taste shielded wire is easier to use in many cases but as long as they are all properly soldered to the cavity (or pickup) shielding at both ends all three methods will produce a good shield. If you really want the absolute best shield then a seamless metal tube is best, the shielded wire is worst, and the home made "copper straw" will be as good as the seamless tube if you solder the longitudinal seam and potentially as "poor" as the shielded wire if you don't. It is not too likely that you would be able to tell the difference between the three in this case however.

 

I'm not comfortable with using hard metal tubes.

Mechanical effects inside the bass play a big role. This could very well make a noticeable change in (non-electrical) response.

Also, movement of an unshielded wire inside such a grounded tube will induce current, this can lead to feedback, or to unwanted side sounds as the bass vibrates under string movement.

Gibson did electronics cavity shielding with a big metal box at some point. People can't rip that out fast enough, and mostly due to mechanical resonance messing with guitar. Just knock on it while the guitar is connected.

 

Shielded cable is the easiest solution. It will need to be small diameter and therefore high capacitance per foot but for such a short run any effect will be negligible.

 

nope. I use it all the time.

Yes, and so do all top pickup, amp, and audio electronics manufacturers in general. Even with shielding tape installed, as a rule of thumb, you should use shielded wire for any hi Z signal run that's more than an inch.

I'd be impressed as well. Impressed that you went to such trouble, when simply using better wire would have done. As I mentioned, it's really not too hard to solder wires on a pickup. Actually, nearly every other hand soldering job in a typical pickup/preamp install is more difficult. If you are keen to take on more diy installs, then I would suggest you get some cheap pickups and practise. Use a multimeter to check the continuity of the coil before and after. Tinning the wire first is the key to soldering to those old-fashioned eyelets in fender pickups. And using a heatsink clip is the key to soldering braided shield in general.

Of course not. When I was learning to solder I fried heaps of things. Often my fingers as well! But that's how you learn.

 

i dunno, i'd take the copper tube idea way before making a project of altering a fender pickup by adding shielded wire to it! the "first, do no harm" rule applies in guitar repair too.

i don't believe for a second that it's gonna "induce current" or cause feedback or anything like that, it's just not that delicate a circuit inside a guitar.

i have taken to spiral twisting unshielded 2-conductor pickup wires, on the idea that the ground wire serves to partially shield the hot wire; dunno how big of a difference that makes, but hey, "couldn't hoit".

the '70s gibsons with the metal can inside had a problem not from the can, but because gibson thought they could do all that shielding and then leave off the string ground

 

Twisting the 2 conductors does a lot of good in reducing noise induced into the wires. As well as reducing noise in high-current 2-pair wires, as we learned 20 years ago while wiring up amp racks. It's pretty close quarters in those amp racks full of Crown MacroTech amps, then Lab Gruppen amps, with input line, output lines, and power cables often on close proximity. Twisting the speaker cables (in raw 2-conductor form) went a long way to helping reduce the noise induced into the inputs of the amps. It happens, even with shielded balanced input cables.

To the best of my knowledge, twisted-pair w/ ground power cables are not available. They certainly don't come on the power amps. And making twisted pair w/ ground power lines wouldn't pass the NEMA codes. So we're stuck with dealing with that as best as we can.

In other non-related-to-bass-pups information....

 

oh good, so it is a thing

huh, i wouldn't have thought of speaker cables benefiting from twisted-pair! that's more about the speaker line not creating noise elsewhere, as opposed to absorbing noise itself, right? so twisting the conductors around each other actually reduces what the cable radiates outward?

 

Exactly, it works by reducing what is emitted from the speaker lines. I don't think that regular speaker cables cause a lot of problems, unless laying over lousy mic cables, but it helps inside the tight quarters of amp racks.

The "twisted-pair" shielded mic cable is always preferable.