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Grounding of switches


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I'm wiring up a Strat in a different way. No volume or tone pots. I'll have a Fralin noisless single that has two wires AND a shielded ground wire. I'll also have one Suhr humbucker with four wires AND a shielded ground wire. The humbucker will first go to a on/on switch for series/parallel operation, then to a three-way pickup selector. The Fralin will go directly to the three-way. From the three-way pickup selector, the signal will go to a kill switch and then to the output jack. My question is about grounding. Does the three-way need to be grounded? And does the kill switch need to be grounded? IOW, does everything need to be grounded (the bridge will be grounded too)? Should they all tie together before going to the output jack ground? The kill switch has no lug for grounding so if that needs to be grounded I assume I will ground to the body of the switch.

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Another question about grounding, this time about the pickups.

Both pickups have a shielded wire. It's the third wire on the Fralin and the fifth wire on the Suhr. From what I've seen online they both go to ground. So each pickup has two wires going to ground. Why are there two grounds for each pickup? What is the purpose of this extra shielded wire?

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Since I haven't seen your schematic, I cant tell you 100% on everything here but for most situations, you do use ground for many situations you mentioned.

 

First the reason your pickups have the extra wire is for situations where you may want to run pickup coils in different configurations.

Ground always has to be connected to shielded cable to prevent hum. You can also choose to ground one coil leg early on in the wiring or in cases with 4 conductors, you way want to swap coil phasing or run series parallel, or use splits in different ways before you ground a coil. You can ground the coil before the switch or after, it doesn't matter so long as the braded wire that surrounds the 4 conductors (the 5th wire) always remains grounded. All that 5th wire does is connect to the shielding and the pickup covers to remove hum. It doesn't connect to any coils till you actually ground both.

 

The plastic kill switch, One wire connect to the hot wire and one connects to ground. When you flip the switch it ground your signal down completely the same way as you get when turning the volume down.

 

Kill switches should NOT be put in series with the hot wire Make a contact. It would remove the signal that way but it would hum like a SOB. Its like unplugging your guitar jack with the amp on and having it hum. The switch connects the two terminals of the output jack and creates a dead short to kill all output. Because the switch is plastic and not metal its casing cant be grounded to reduce hum so it will simply be a possible source of hum. If it has three terminals, use the and end terminal for the hot wire. That will have the shortest length of exposed metal. The ground will connect to the rocker and provide a little better shielding internally.

 

As far as the 3 way goes its going to depend on what kind of three way and how its wired. If the switch has a metal casing, soldering a grounded wire to it shields the connections inside to prevent hum. You have to watch out soldering cause heat can melt many of these switches instantly. Always use a heat sink to remove heat before it gets to plastic components, A pair of forceps or alligator clips can work well for that.

 

You can switch pickups in two ways. You can use the switch make/break contacts to the coils or you can have the pickups wired and functioning with the switch in the middle and toggle to short one or the other out.

 

Some manufacturers like Gibson, uses a make contact switch. In the middle its two sets of contacts are closed and both pickups are seeing the hot wire. When you toggle you break a contact to one or the other coil. The base of the switch is grounded to remove hum but it isn't grounded for any reasons involving the switch operation. Of course if the switch wasn't grounded and you touched the metal the hum level would go up instead of down.

 

Since I don't know what switch you're using I can only guess weather you're using a signal contact or signal to ground to control the pickups. There are many ways of doing things in electronics and being specific is important.

 

Ground has a dual purpose. It shields the hot wire from magnetic waves that can induce hum, and it also provides the second connector for your pickup signal. Most guitar amps use unbalanced high impedance designs and to save on cost and wiring the chassis is one gig conductor you can use to connect all your negative power supplies to. It also acts as a shield for all the components inside the chassis

 

This is where the term common ground comes in. Its common to the signal coming in and in many cases the signal leaving the amp to the speaker, as wall as for removing hum by grounding the chassis to the earth.

 

You need two wires to conduct AC waves from your pickups. The hot wire I one, the other is your ground. Guitars are therefore called Unbalanced because the ground conveys noise to earth ground and it also carries the negative AC potential.

 

In Balanced applications like Low impedance mic cords, the two signal wires are normally independent from the ground wire. This allows the use of transformers or circuits to step the voltage up and current down so there's less loss in fidelity using long wires needed for mics. That why they use three wires instead of two like your guitar cord.

 

I should mention there are some guitars that do use low impedance like the Les Paul Recording model, but they weren't huge sellers.

They are great for maintain pickup fidelity recording directly through a mixing board on long runs to a PA but guitarists usually have more then enough fidelity running unbalanced and given the fact they usually use dirt boxes to kill fidelity, a little signal loss from a cable is unnoticed.

 

Anyway, you'll need to give me switch types and wiring schematics for me to be any more specific.

Your strings do get grounded wither through the bridge posts or tail piece. When you touch the strings your body becomes grounded acting like a big metal plate to absorb magnetic waves before it gets to the circuit and causes hum. The strings carry the waves your body collects to ground through the strings. If the strings aren't grounded, your body acts like a gig collector dish and when you get close to the guitars wiring the hum actually goes up instead of going down. The body contains mostly salt water which is a very good conductor and magnetic wave collector (nerves in your body transmit electrical pulses all the time) The key is to make it work in your favor by grounding it.

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