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What Really Needs Shielding?

Hues

Hues

Nov 27, 2012
10,242
31,039
#1
Question is; What components truly, truly, needs to be protected from interference?

Is it just the pick-ups themselves?...Are the pots affected at all?

I ask because I've seem some guitars were the pups and the controls are in a separate body compartments, yet the controls area is shielded anyway....Is this just OCD/overkill?
 
#3
If you think of a coax cable as being the ideal shielded component, then you want to run your signal on a wire completely surrounded by a shielded (edit:i.e. grounded) conductor. That's what I did on at least 1 of my basses.

I think shielding is more important on a passive bass, although either type will benefit. Also I have heard a few folks say that shielding the pickups changed their tone. I couldn't tell a difference but YMMV.
 
#6
Thanks,everyone.

I was thinking of making a kind of isolated cage or box just around the pick-ups...Looks like I'll go all-out.

Still, I have to wonder why they bother with the little bit of foil around the pots on the pick guard, if the waves come from all around?
 
#7
Hues said:
Thanks,everyone.

I was thinking of making a kind of isolated cage or box just around the pick-ups...Looks like I'll go all-out.

Still, I have to wonder why they bother with the little bit of foil around the pots on the pick guard, if the waves come from all around?
Click to expand...

That way, they can claim the instrument is shielded (even if poorly so), with an absolute minimum of money spent.
 
#9
Marty Forrer said:
Which begs a very good question.... why do manufacturers of quality single coil pickups not supply them with coax cables?
Click to expand...

Coax would work well here. I notice that Nordstrand ships their pickups with the wires twisted, which is another way to minimize interference (like Ethernet cables).
 
#10
Stealth said:
It's not overkill, because electric fields surround and permeate the bass at every point, controls included. It's a good idea to shield that as well.
Click to expand...

+1


You will need to shield the pickup cavity, control cavity, and pickup covers (and back of pickguard if necessary) and you will want to run a ground wire from the pickup shield to the either the pickup or control cavity, usually the pickup cavity won't have the space.

Active pickups don't hum to my understanding, it wouldn't be the first thing I am wrong about though. Passive basses, and passive pickups with active pre-amps, will require a proper shielding job.
 
#11
The point of shielding is to cover all the internal wiring with shielding so that the wire does not pickup noise from outside the grounded shield. On my bass this meant painting shielding paint in the pickup routes, the control cavity and the holes that that wires go through. I made sure there was 0 ohms from each pickup to the control cavity. The control cavity also connected to the jazz bass control plate effectively shielding the top of the control cavity too.

I also went the extra mile and grounded the metal pole pieces of the pickups. Helped the center of the pickup not pick up noise. I guess the only way to be better is to somehow shield the pickup cover as well.

Every part of the shielding needs to be grounded though. 0 Ohms to the output jack is best.

ctmullins said:
Coax would work well here. I notice that Nordstrand ships their pickups with the wires twisted, which is another way to minimize interference (like Ethernet cables).
Click to expand...

+1 the twist thing helps but the shielding does the most work.
 
#14
This is like asking what parts of your submarine need to be waterproof. It only takes one opening to defeat the purpose of your Faraday cage. The concept is that absolutely EVERYTHING up until the speaker output on your amp should be shielded. The speaker output no longer needs shielding, because the impedance at that point is too low for it to be an issue. As you can see, however, it is very difficult to keep everything shielded, since your pickups must be open and exposed. Some people do epoxy potting and cover the entire coil and pole pieces in copper tape, but be aware that shielding pickup coils influences the flow the eddy currents and changes the tone.
 
#16
DiabolusInMusic said:
Active pickups don't hum to my understanding, it wouldn't be the first thing I am wrong about though. Passive basses, and passive pickups with active pre-amps, will require a proper shielding job.
Click to expand...
That largely depends on how the active pickups are wired to work. EMG has incredible signal-to-noise ratios because their pickups work so each coil connects to one half of a differential preamplifier. Their coils actually actively cancel common-mode hum (the 50/60 Hz noise that gets sensed by both coils, hence common-mode) while actively summing the string signal, which isn't common mode because the coils don't sense the same areas of the string. In terms of signal-to-noise, that's much better than passive humbuckers can achieve.

line6man said:
This is like asking what parts of your submarine need to be waterproof. It only takes one opening to defeat the purpose of your Faraday cage.
Click to expand...
+1. Perfect analogy.

line6man said:
Some people do epoxy potting and cover the entire coil and pole pieces in copper tape, but be aware that shielding pickup coils influences the flow the eddy currents and changes the tone.
Click to expand...

Apparently a good trick is to shield the coils or pickup covers in foil, but without closing a loop - for instance, covering just three sides of the pickup. That should minimize the effect of the foil on the coil. :smug:
 
#17
line6man said:
This is like asking what parts of your submarine need to be waterproof. It only takes one opening to defeat the purpose of your Faraday cage. The concept is that absolutely EVERYTHING up until the speaker output on your amp should be shielded. The speaker output no longer needs shielding, because the impedance at that point is too low for it to be an issue. As you can see, however, it is very difficult to keep everything shielded, since your pickups must be open and exposed. Some people do epoxy potting and cover the entire coil and pole pieces in copper tape, but be aware that shielding pickup coils influences the flow the eddy currents and changes the tone.
Click to expand...

Exactly. You usually do have to leave the tops of the pickups open and even getting shielding too close can change tone. I think that's why pickup makers often don't shield them although shielded coax for the wires would be good. My experience is that just putting copper on the pickup cavities is far enough away that it doesn't change tone. And grounding poles is always a plus because usually pickup makers don't shield the coil from the poles so touching them injects hum right into the center of the coils. For example on my G&L L2500 basses I use a Radio Shack conductive paint pen that works very nicely. I run a stripe of paint from each pole down to the ground plate on the bottom of the pickup. Why G&L doesn't have these poles grounded I don't know. On those the copper bottom plate provides some shielding, but I find it's still best to line the entire cavity to give shielding on the sides as well.
 
#18
Yes - everything has to be shielded, and a small gap can actually make things worse, acting as a sort of tuned antenna. It's real important to have grounding wires from the pickup cavities to the main ground, and to be sure that the foil on the pickguard is properly grounded to the cavity foil as well - I make a tab from inside the cavity that goes under a mounting screw so it gets well connected. I have not changed out pickup leads for shielded cable, but this is a good idea - IF the capacitance of the cable is not too high. I do twist them, though. I also do the star grounding where all grounds connect to one screw in the main cavity.

There was a great thread here where the OP shielded the pup cavities and even inside the pup covers! Very amazing and thorough. I asked my brainiac engineer if you could accomplish the same thing by completely wrapping the pup in copper and grounding it, and he said yes, but it has to be done in a specific way to avoid making a 1-turn coil out of the shielding, possibly making things worse. Too complicated!!

Grounding is much more critical with passive instruments as it is all very high impedance, so it is very easy to pick up hum and RFI. Not quite as critical with active circuits.
 

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