Jimmy Page Les Paul Wiring
Preventing Ground Loops
I have made a few modifications to the wiring in the diagram. I have 2 major reasons:
- Basically, I wanted a wiring version that did not require soldering to the pot’s shell. I found that most guitar projects don’t turn out as well as they should because most people do not have a soldering iron powerful enough to solder a ground wire to the pot shell. Usually, the pots get overheated and do not work as well as they should or they end up with a cold solder joint.
- I separate the signal ground from the chassis/mechanical ground. This is an excellent way to make the guitar even quieter. Since I shield the control cavity, the guitar gets the added benefit of eliminating 60 cycle hum.
What is the difference between signal ground and mechanical/chassis ground? Let’s keep things simple, maybe overly simple.
First, what is the signal ground?
The signal from the pickup start wire (+) wants to get to the (+) terminal on the output jack. If we wire the pickup start wire (+) directly to the (+) terminal of the output jack, then we get the maximum output from the pickup. If we want to control the volume, we put a volume pot in the signal path. When we turn the volume pot down, part of the signal goes to ground (the (-) terminal on the output jack). The path from the volume pot to ground is part of the signal ground. If we want to control the tone, we put a tone pot and a capacitor in the signal path. When we turn the tone pot down, some of the signal goes to ground (the (-) terminal on the output jack). The path from the tone pot to ground is also part of the signal ground.
What is the mechanical/chassis ground?
Any metal parts of the guitar that are near the signal path, need to be grounded. If not, there is potential that they will cause noise. This noise is usually hum. If the metal part is not connected to the (-) terminal on the output jack, then you become the ground when you touch it. That is why some guitars get quieter when you touch the strings.
Mixing grounds and ground loops
The classic way guitars are wired is to have a common ground for both the signal ground and the mechanical/chassis ground. The lug of the volume pot is soldered to the shell of the pot. The pots are soldered together. Eventually, all the grounds are connected to the (-) terminal of the output jack. Mixing the two types of ground can introduce hum.
A ground loop occurs when a signal ground has two or more paths to the (-) terminal of the output jack. This is most obvious when the guitar has the pots connected to a metal plate or metallic foil. Since the ground signal travel from pot to pot over both the wire connecting them and also over the metal plate connecting them, it causes a ground loop. Ground loops can cause hum.
Take a look at the lists:
Signal grounds
- Bridge pickup volume pot lug 3
- Bridge tone .047 capacitor lead
- Bridge tone push/pull switch lugs C & D
- Neck pickup volume pot lug 3
- Neck tone .047 capacitor lead
- Neck tone push/pull switch lug D
Chassis/Mechanical grounds
- Bridge pickup bare wire
- Bridge volume pot shell
- Bridge tone pot shell
- Neck pickup bare wire
- Neck volume pot shell
- Neck tone pot shell
- 3-way switch
- Ground wire from bridge
- Output jack sleeve and jack plate
- Insulation on wire from switch
- Control cavity shielding
During the wiring of the Jimmy Page modification, the signal ground will be separated from the mechanical/chassis ground.
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Bob Pittman
Brookline, MA
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article
01.01.2009
- Introduction to Jimmy Page Les Paul Wiring
Preventing Ground Loops
Getting Ready, Tools, Parts
Pre-Wiring: The Workboard
Pre-Wiring: Prep the Pots
Pre-Wiring: Pots and Output Jack & Signal Wiring
Pre-Wiring: Signal Ground Wiring Wiring
Pre-Wiring: Three-Way Switch
Shielding the Guitar Control Cavities
Install Switch, Pickups and Pot Assembly
Wire the Switch & Chassis/Mechanical Grounds
Wire the Output Jack & Pickups
Testing Your Work
- Introduction to Jimmy Page Les Paul Wiring
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