Jazz Shielding Pictorial (Big Images Warning)

[Lyle Caldwell]

Originally Posted by Modern Growl

Thanks for the info.
quick question though. Why would you soder the wall to the floor of the cavities if the copper is already touching, or making the connection between the wall and cavity floor? whats the deal? seems redundant, but i'm probably wrong.

also

isn't shielding the pup cavity going to reduce some top end as well, being its so close the the coil? or does the shielding have to be like...... right next to the coil to reduce top end?

I use the solder at the seams because I don't like to rely on the adhesive being a good conductor. The wall pieces are separate from the floor pieces, and where they overlap, there's a layer of adhesive between them. Now, the adhesive is conductive to a degree, but using solder assures complete conductivity.

As to shielding proximity, some say that any copper should be 1/8" away from the coils, so they'd suggest trimming the copper walls of the pickup cavities so the copper stops 1/8" below the bottom of the coil.

In my experience (and I've tested it both ways), there is either no difference or the difference is so slight as to be unnoticeable. However, with the walls cut lower, there is a bit more noise.

So you trade the potential of slightly fewer highs for the increase in noise reduction. And remember, if the signal has less noise, you can turn the treble control of your amp up without getting hiss, so this is a good tradeoff.

However, when I've shielded the insides of pickup covers, the treble loss was very apparent. The shielding on the inside of a cover is much closer to the coils (and goes over the top as well) than the shielding on the cavity walls. In my experience, this was tonal degradation and not worth the slight reduction in 60 cycle hum.

[Lyle Caldwell]

Thanks, Eric!

[Lyle Caldwell]

I'd like to mention that there are different kinds of "noise" produced by bass circuits/pickups, and that each has a different cause and cure.

First, there's higher pitched humming caused by a badl ground- this can be as extreme as an instrument with no ground or the "normal" kind with stock instruments, where as soon as you take your fingers off the strings/other metal parts you hear a high pitched hum. With a good shielding job, the circuit doesn't need your body to provide a good ground (for techies reading this, yes, it's more complicated than this, but I'm typing on my lunch break so bear with me). So after a bass is properly shielded with a star ground, there will be no high pitched hum even if you aren't touching metal (in fact you can remove the bridge ground completely).

Then there is induced noise, from lights, dimmers, CRT monitors, TVs, and transformers. This can be a combination of hum and hiss. This is picked up along the path from the pickups to the output jack. Shielding eliminates this, but this noise can be present even if you're using humbuckers or other noise-cancelling systems. This noise is introduced after the pickups.

Next, there's 60 cycle hum, which is a low hum (on guitars you hear the octave above at 120Hz since guitar amps don't do much at 60Hz, but with a bass amp you hear both). This is just part of single coil design, and you can't eliminate it with shielding, though shielding does reduce it a bit. As above in the thread, you can reduce it further by shielding the inside of the pickup covers, but there is a tonal tradefoff. John Suhr has an upcoming system that will eliminate this, but as of this writing it's only available in his factory guitars, not aftermarket or for bass, but in the future this may be an option.

Last, there's what I called "filtered" 60 cycle hum, which is often present in humbuckers where both coils aren't exactly equal (few are). In this case, some of the hum is eliminated but some isn't, and the phase of the hum is altered, causing cancellations. This results in a lower level and higher pitched hum, but it's still 60Hz hum. Just like single coil hum, this is impossible to truly eliminate but you can minimize it. But at least this is low enough in level that in a well shielded instrument it's not a problem.

Not all of the above applies to active pickups, though it all applies to active preamp circuits. Every instrument can benefit from shielding.

Last, I was recently raked through the coals on another forum for recommending copper foil. The guy said in effect "no professional luthier uses copper."

Aside from that being total BS, I'd like to talk about copper vs conductive paint.

Both work. The paint is easier to work with, though slower (takes many coats with long drying times). The copper is harder to work with, though faster to apply. The copper gives a better shield, but the paint gives a very good shield. Paint is more expensive in small quantities, but if you're doing a lot of guitars, paint is the way to go. Copper is removeable, paint isn't (not at all easily, at least).

So Sadowsky uses paint in his production instruments. But if a client wanted him to shield a 50s Strat, I'd bet Roger would use copper since there would be no permanent change to the instrument.

I use copper as I only shield an instrument when I buy a new one (typically one every few years, though I've been buying a bit more than that lately). Each time I get a new instrument, I order $20 worth of copper shielding and spend an hour shielding the instrument. If I were doing all my instruments at once, I might spend $60 for the paint and give the whole project a few days to allow for drying time.

So there's the whole copper vs paint dilemma. Beyond that, some people just like to argue.

[Modern Growl]

Lyle,
thanks for all that info, but now there's one more question that comes to mind. I'm going to be wiring my pickups with the standard Vol/Vol/Tone (Fender Jazz Bass), using this exact wiring diagram:

http://www.fender.com/support/diagra...131800APg2.pdf

Now, is this good enough, along with copper shielding in the pickup cavities and control cavitie, connecting the two? Or do I need to add another ground lug somewhere?

Like this diagram (#17)

http://www.fender.com/support/diagra...193400APg2.pdf

[Lyle Caldwell]

The first diagram will be fine, so long as you have the copper contacting the control plate like in my photos on the first page of this thread.

[Modern Growl]

Originally Posted by Lyle Caldwell

The first diagram will be fine, so long as you have the copper contacting the control plate like in my photos on the first page of this thread.

thanks man!!

so whats the purpose of that solder lug w/ screw (#17) anyways? to throw people off? lol...

also, the only way I will be able to connect the 3 cavities is by a wire, soldered to each. I'm assuming thats going to be fine, but figured I'd ask since you ovbiously know alot about this.

BTW (i'm going to be using a shielded lead/cable from Pups to pots) sortal like what EMG pickups leads look like. So the leads will also be shielded, just in case you were wondering.

[Lyle Caldwell]

The ground lug is there in the Fender PDF because that bass has conductive paint in the control cavity, and that wire and lug connects the shield to ground.

With copper, you can bypass that if all your wires connect to the controls rather than to the cavity, as the copper can just contact the control plate.

You can just connect the shielded routes with wire - it works fine, but there won't be shielding between routes.

On that note, if your wire is single conductor with shield, it won't do as good a job of shielding as two conductor with shield, where one wire carries positive, one negative, and the shield is connected to ground at only one end. If you have the latter style, then the cavity shielding is less necessary, but if you have the first (regular) style, you may want to try shielding between cavities.

[Modern Growl]

Originally Posted by Lyle Caldwell

The ground lug is there in the Fender PDF because that bass has conductive paint in the control cavity, and that wire and lug connects the shield to ground.

With copper, you can bypass that if all your wires connect to the controls rather than to the cavity, as the copper can just contact the control plate.

You can just connect the shielded routes with wire - it works fine, but there won't be shielding between routes.

On that note, if your wire is single conductor with shield, it won't do as good a job of shielding as two conductor with shield, where one wire carries positive, one negative, and the shield is connected to ground at only one end. If you have the latter style, then the cavity shielding is less necessary, but if you have the first (regular) style, you may want to try shielding between cavities.

The single wire carries the positive and negative. I will connect the negative to the back of a pot (grounding it) and connecting the hot lead where that goes.

SO your saing because of me having the single wire w/ both positive an negative in one, that I won't have to shield the cavities?

[Modern Growl]

I believe my Fender jazz has conductive paint then in the cavities. Will this be considered double shielding and actually increase hum?

[Lyle Caldwell]

Won't increase hum, but there's no point in shielding an already shielded cavity. Just tie the copper to the paint with a grounding lug.

[Lyle Caldwell]

Or if all of your cavities are already painted, just verify that each cavity is connected to the others.

[Modern Growl]

Originally Posted by Lyle Caldwell

Or if all of your cavities are already painted, just verify that each cavity is connected to the others.

cool. thanks agian...

I just got off the phone with Mike Lull and he mentioned I should connect all the cavities, and then use one of those same connections to the back of a pot.

did you do that?

[Lyle Caldwell]

No, I connect the cavities, but then I connect the cavity shielding to the control plate rather than to a pot.

Mike usually doesn't use a control plate on his basses, so the pot makes sense for his use.

[Modern Growl]

gotcha, thanks man!

[TheEmptyCell]

Excellent pictorial, I'll be tackling the shielding and grounding of my Jazz soon.

Now, I'm a little stumped. I opened up my bass, and found that there is a black wire running off of a pot (like in the Fender daigrams above) to the bridge. Now, I'm assuming that is the ground.

So, when I shield, I can install the lug, and then just run that one wire to the lug, right? And will that mean that I will get zero noise when I'm not touching something metal?

[Lyle Caldwell]

Once the bass is shielded, you could remove that wire and still get no noise when you aren't touching anything. But if you want the bridge grounded, yes, attach it to the ground lug.

[TheEmptyCell]

Thanks for a quick response! I just find it very annoying to be playing, and then get that nasty little fizzly noise when I let go. I'll be doing this to my fretless then as well.

[Lyle Caldwell]

Soon you won't have that problem anymore.

[Modern Growl]

Originally Posted by Lyle Caldwell

No, I connect the cavities, but then I connect the cavity shielding to the control plate rather than to a pot.

Mike usually doesn't use a control plate on his basses, so the pot makes sense for his use.

it certaintly wouldn't hurt it to make that extra ground connection right? perhaps streighthen the ground connectivity ????


I will have the copper lead up to the control plate just like your picture, but why not have the cavity copper also be directly connected to the back of a pot ?? nothing bad will happen, right?

[Lyle Caldwell]

You don't want two paths to ground - that's how loops occur. Either a wire or the copper. Not both. If you attach copper to the back of a pot, well, aside from being hard to take the plate off, I don't know how you'd attach the copper to the pot with the plate off to begin with.