Shielding

Providing for additional shielding of single-coil pickups is highly recommended, and humbuckers can also only benefit from it. A single-coil pickup will always produce a certain amount of hum - if it was fully shielded, it would not give any output at all. So for reasons of sound it may not even be desirable to shield a guitar all too well. Shielding always increases capacitance, and the closer the shielding is to the pickup the stronger its influence on the tone will be. Capacitance always lowers a coil's resonance peak and makes the sound less trebly and more lifeless. Taking off the metal cover of an old pickup improves the sound and is therefore very popular.

Using shielded wires only makes sense with wire lengths of at least 15cm (6"), as a few inches or centimeters of bare wire ends will always be needed for making solder connections. A shielded wire consists of conducting wire surrounded by braided wire.

Cheap shielded wire often has a very poor braided shield which is very patchy and therefore remains ineffective. Quality wire has a tightly-woven braided shield. To be effective the braid has to be connected to ground. The braided wire can also be used as a pickup lead.

Apart from using braided wire, lining the pickup and control cavities with thin copper foil also helps to minimize hum. Cut the thin copper foils to the sizes required and glue them to the wood with spray glue. To be effective they have to be grounded. Using conductive shielding paint is another option provided it is connected to ground.

All pot casings should also be shielded by connecting them to ground. Some manufacturers even have the pots entirely encased in grounded metal containers.

Grounding the strings is an absolute necessity with single-coil pickups if you want to keep humming noises to a minimum. This can be achieved by means of a wire which connects the metal of the bridge to ground. On tremolos the ground wire is soldered to the metal plate that holds the spring. When the guitar is played the strings are almost constantly touched by the player so that the electronic circuits of the guitar are grounded and shielded via the bridge, the strings and the body of the player.

In the past there have even been casualties because amplifier casings became part of the electrical circuit. Theoretically, this can, of course, always happen. But normally electrical installations have a mains trip system that interrupts the circuit if such a situation should occur. If, however, there is no such switch or the amplifier is not properly grounded, the current flowing through the cord can become fatal if it reaches the strings. To be on the safe side connect the strings to ground via a high-ohm resistor and a capacitor switched in parallel. With such a precautionary

measure any current that, if things went wrong, would flow through the player's body is weakened and the voltage is brought down to unharmful, no-longer-fatal levels (around 40 volts, depending on the individual body resistance) while still providing sufficient grounding of the strings. The capacitor used should have a value of 0.001mf (1nF) and be able to withstand not less than 500 volts. Use a 220K-ohm resistor. Both building components should be protected against short-circuiting by surrounding them with insulating tape or - which is even better - a piece of heat shrink tube. Although this doesn't provide 100 per cent protection as the metal jack plate will still remain ungrounded, the light electric shock you will receive as a result should be a strong-enough warning to make you immediately unplug the the amplifier from the mains. On occasions such as big concerts experts are specially employed to check the grounding and other safety measures before anybody goes on stage.

And finally, a few hints for wiring. Wiring diagrams may look very simple and clear, but when it comes to soldering you can easily end up with a chaotic tangle of wires. To prevent this, work systematically: always tick off finished connections on the diagram; try to minimize any hum potential by keeping wires as short as possible; use colored wires to facilitate keeping track of individual wires and checking faults - use “warm” colors such as red, orange or yellow for signal-carrying (“hot”) wires and “cold” colors such as black or blue for ground wires.

Crackling sounds in the speaker are mostly due to poor-quality soldered connections. To repair them, reheat those dull-looking, lump-shaped connections and add a bit of tin. When turning a pot produces a crackling sound, replace it or spray it with contact spray. If a logarithmic pot works the wrong way round, interchange its outer connections. And finally: if a guitar remains silent, make sure you first check whether the guitar cord is working properly before you start disassembling the guitar's electronics.