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Something Cool
Since this just came up again I think it's better to have it in one place.
Short version:
Long version:
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Concept of shielding:
List of shields in humbucker guitars:
List of shields in traditional Fender single coil setups:
Shields in both humbucker and fender style guitars:
FAQ:
Short version:
- Everything that acts as a shield needs to be grounded.
- If your pickup wire has a shield, ground it. In a so-called 4-conductor wire you need to ground the bare wire, in addition to one of the leads. It actually has 5 conductors, that's where the confusion is from. That grounds the pickup's baseplate and the wire shield.
- Most guitars want you to ground the strings so that your body acts as a shield.
- If there is shielding foil or conductive paint, it needs to be grounded to be effective.
- Ground the casing of all the potentiometers.
- Use shielded wire inside the guitars for any long connections, such as toward a LP switch. Using shielded wire for short distances such as to the output plug helps quite a bit, too.
Long version:
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Concept of shielding:
- A shield is a grounded conductor around a signal-carrying wire.
- Examples are foils or meshes around a wire (inside shielded wire), foil or conductive paint in a cavity or the foil on a Strat's pickguard.
- It does not matter how thick the shield is, any thin foil will do. You can use gold rolled so thing you can see through it. However, thin foil such as kitchen aluminium foil is harder to work with and breaks easier afterwards.
- It doesn't matter whether the ground is a "real" solder point. Things touching each other with decent pressure are sufficient. If it conducts it'll do.
- Additionally, things that conduct a little are commonly abused as shields.
List of shields in humbucker guitars:
- The pickups have either "2-conductor" wire, which is hot and shield. Easy, you must ground the shield for it to work anyway.
- ... or "4-conductor" which is 4 leads plus shield foil plus bare wire. You must connect the bare wire to ground, along with one of the leads. I you don't then the shield in the shielded wire doesn't shield, but what is worse is that the pickup baseplate wouldn't be grounded. This is a common mistake.
- The pickup wires are shielded, but you must also use shielded wire to go to the switches, especially to a switch far away like a LP switch. Common mistake, too.
List of shields in traditional Fender single coil setups:
- Since the pickups hum like mofos anyway Leo didn't bother with shielded wire either.
- In Leo's defense, his idea was to have a metal dome around the whole thing including the strings (think Jazz bass). We removed those and now we need to deal with the noise.
- There often is a foil shield inside the pickguard. It needs to be grounded to have an effect. It is usually grounded via the grounded pots that are screwed into it.
- You can improve noise by shielding the pickup cavities but see "eddie currents" below. Myself I wrap some grounded foil around the unshielded wires between the Strat style pickups but leave the pickup area itself alone.
Shields in both humbucker and fender style guitars:
- The potentiometer housing is grounded. Theoretically it is incorrect to solder to be back but it does the job well enough.
- Since manufacturers are too lazy to shield all the cavities they abuse the player's belly (or in the case of Les Paul players the balls) as shield, by grounding the strings via the bridge. This is IMHO life-threatening nonsense and can be cut if shielding is otherwise complete.
- The output plug can be connected using shielded wire. There's no downside to doing that and it cuts back on some noise.
FAQ:
- Conductors near oscillating magnetic fields induce eddie currents, which dampen the amplitude of the resonance peak. In other words, they cut off some treble the same way that lower value pots do. Humbucker covers do this. Myself I tend to keep shielding in cavities away from Strat pickup cavities, although I am fine with the shield in the pickguard. I have not done and I am not aware of any specific testing that was done on this topic.
- Heavy constructions like Gibson's old brass box can resonate mechanically and that will be audible.
- You can't produce "ground loops" inside a guitar. The distances are too short to have enough potential difference as long as nothing is broken. Just don't use half-broken wires or solder points that conduct but at a couple megaohms or so.
- You can remove the ground wire to the bridge and strings after you shield everything else. You can build a complete shield pretty easily.
- Humbuckers don't need more shielding (such as conductive paint in the cavities) because, well, they buck the hum. The hum canceling is complete. The only exception is that there is a short distance of bare wires between the shielded wire and the coils. That is shielded in a pickup with cover and unshielded without the cover. I doubt that shielding the cavities will help here or that it makes enough of a difference. Remember the baseplate is grounded so I doubt a shielded cavity will improve things.
- There are symmetrical music cables such as used for microphones. They carry the signal separately from the ground in a twisted pair. This helps cutting back on the noise from the long cable. The same principle would work for guitars, too, but since the pickups have much higher output than a microphone it is not generally considered worth bothering with. You can't use the microphone cable material for passive guitar anyway since the capacitance of such a cable is too high.
