Reversing pickup wires will not normally damage the pickup or the preamp.

The usual issue is phase rather than damage. If two pickups are out of phase with each other, the combined sound can become thin and weak, especially with both pickups blended together.

If the sound loses bass at the centre blend position, check the pickup phase wiring.

The pot bodies need a ground connection so the control shafts and metalwork do not become a source of noise.

On plate-mounted units, the plate often provides this connection. On rear-mounted installations, adhesive copper foil on the inside face of the cavity can be used so the pots make contact with a grounded surface.

The bridge ground and the jack ground should also be connected to the same ground system.

Use adhesive copper foil on the inside face of the cavity where the pots are mounted, making sure the pot bodies contact the foil.

Connect the foil to ground, usually by soldering the loose ground wire from the jack ground connection to the foil. The bridge ground should also connect to the same ground point.

The exact solder location is not critical, as long as the foil and ground wiring are electrically connected.

It is usually better to change one part of the system at a time.

Keeping the original pickups when first fitting the preamp lets you hear what the preamp itself has changed.

If you change pickups and preamp together, it becomes much harder to know which part is responsible for anything you like or dislike.

Disconnect the pickup wires from the preamp inputs.

Fit a short piece of wire between Hot and Cold on each pickup input terminal, effectively shorting each input.

Turn up the treble and listen. There should be no buzz or interference from the preamp alone, although a slight even hiss may be normal.

Check that the jack socket is tight and does not move when a cable is inserted.

Make sure the jack has not twisted and pulled the wires tight. Gently check each wire connection to the preamp and jack.

Dirty jack contacts can also cause intermittent signal. They may need cleaning with a suitable contact cleaner, or the jack may need replacing if the fault persists.

In many cases, a damaged plate-mounted pot or a pot on a suitable assembly can be replaced by East UK.

If a shaft has been badly bent, or if straightening is not possible, returning the unit for service may be the safest option.

Do not apply sharp force to a bent shaft, as it may shear.

If the sound becomes thin or loses bass when the blend is set near the centre, the pickups may be out of phase with each other.

This can happen if one pickup uses an unexpected wire colour convention, as can occur with some Lakland installations.

Reversing the hot and cold connection on one pickup usually corrects a phase problem.

Shielding the control cavity can be useful, but it is usually more important to shield the pickup cavities first.

Most interference is picked up by the pickups themselves, especially single coils.

If pickup cavity shielding is added, connect each shield back to the instrument ground so the shielding is actually effective.

If the noise reduces when you touch the strings, bridge, jack or control plate, the upper knob may be losing its ground connection while being rotated.

In that situation your hand is temporarily providing the missing ground path, which is why the noise changes when you touch a grounded part of the bass.

A small grounding spring between the upper and lower knobs can help maintain ground contact.