A BEGINNER'S GUIDE TO GUITAR ACTIVITY. ADRIAN LEGG OUTLINES THE SIMPLE JOBS YOU CAN UNDERTAKE AT HOME TO KEEP YOUR INSTRUMENT IN THE BEST OF HEALTH.

Rule one: make sure you have the right tools — Allen keys and screwdrivers etc, that fit. You'll pay a repairer extra for time and temper if both are expended on fouled up flats and screw slots.

Pickups. The nearer they are to the strings, the more volume and attack you'll get, up to a point where the attack simply destroys tone. The closer the pickups are to the strings, the more likely it is that you'll get magnetic interference with the free vibration of the string. The pickup contains a magnet, the string is metal — get them too close and the former will pull the latter towards it (old Physics lesson) so damping its movement.

The result is a double note as the magnet tries to shorten the vibrating length almost as though it was a ghostly finger attempting to stop the string in another position. And you don't have to plug in to hear it.

Lower the pickup away from the strings, but don't undo the screws too far or it will drop with a dull clonk into the belly of your guitar. You'll have to have all the mountings off to fit it back on again.

The double note is more noticeable on wound strings (a greater mass of metal to be attracted), and used to be commoner on Strats and Teles where the pole pieces themselves were actually magnets.

It doesn't happen so much on older humbuckers, where the magnet is sited under the coils, but some recent high output humbuckers have extra magnets with increased risk. The DiMarzio X2N, for example, had those additional magnets cut away under the fifth and sixth to counteract this problem.

Strings. As they get older, so they wear and stretch unevenly and collect dirt. This makes them sound out of tune at different points up and down the fingerboard.

Boiling them is a long term waste of time, merely increasing metal fatigue. It may shift dirt, but does nothing about wear or stretching. When you fit a wound string, push it once through the hole on the machine head barrel, bring it back against the turn of the barrel (ie, if the barrel turns anti-clockwise to raise pitch, you come out of the hole and go clockwise), tuck it under the section of string that will be tight and pull it forwards, so that as you tighten up, it locks the loose end against the barrel. Tuck plain strings twice round, but don't pull up so tight so you don't get kinks. For Fender type hollow barrels, bend the string before you cut off the excess and poke it in, this will help stop the windings slipping.

Neck relief. Not an exotic massage parlour extra, but the forward curve we touched on briefly in the necks piece (April issue). It can be measured precisely with a straight edge and feeler gauges. Lay the straight edge down the length of the neck along the tops of the frets. The gap between the fret tops and the straight edge in the area around frets five to seven in the centre of the board should be between 5 and 20 thou of an inch.

The lower figure is for a very lightly played, fast action, the higher for a thicker strung thrash rhythm. Most people's ideal falls somewhere in between, and relief that is too low for you will give noticeably worse buzzes around the first two or three frets and around the sixth to eighth frets, depending on neck length.

If your guitar is brand new, "inexpensive", and still under warranty, do not touch the truss rod. Take it back if the relief is duff. Cost cutting marketing companies are having some guitars made in Third World countries by cheap labour. Some of the makers seem to know sod-all about timber and less about guitars. If your duffo shows signs of having been tampered with (by you) then you will lose your right to your money back. Think a minute about quality and inflation. Twenty two years ago, an American Strat cost £126. A retailer friend reckons that is about £2½ grand now, so what sort of mousetrap do you think you will get for £126 today?

Even on a decent quality guitar, the next bit can go wrong. To reduce excessive relief, the truss rod must be tightened up. To increase relief, it should be slackened off. Tension should be increased or relaxed a quarter of a turn at a time on the truss rod adjustment nut. Measure and observe carefully unless you know your neck intimately. It may take some time to react, so don't whack on a few more turns if nothing seems to be happening.

Sometimes, a neck that has been held back too tight may take weeks to relax forward, and ultimately might need cramping up and heating to force it forwards; needless to say, a professional job. There are other reasons why they won't move — I'll spare you the horror stories — and where once I encouraged players to look after their own necks, nowadays I am less confident about quality consistency, and so strongly recommend caution, and expert help if a neck doesn't respond simply and obviously.

Double truss rods need experience to set up correctly — unless you have it, leave them alone.

Action height. Nut end first. On an acoustic, where rattles behind the left hand can spoil the sound, the nut action is often left marginally higher than strictly necessary so that the string clears the frets between the nut and the left hand finger. If you are looking for a very clean sound on electric, then you should probably apply the same principle.

But for most rock guitars, it can go right down so that the open clearance over the first fret is the same as that over the next fret up from a stopped fret. You set this by pushing a string down to the first fret and checking its height against a good quality small rule held tip on to the second fret. This is the minimum height your open string should be over the first fret. You cut the nut slots deeper using an appropriately sized needle or feather-edge file. Make one or two cuts at a time and check: if you go too far you have to replace the nut, so it's not a bad idea to have a spare handy for your first shot at it.

The bridge action is usually very easy, simply raising or lowering individual saddles, but don't expect to take all the effort out of playing. On a nicely fretted, good quality neck and low camber fingerboard, the absolute realistic minimum height measured between the top of the twelfth fret and the underside of the string is probably about 1.3mm on the 1st string coming up across the strings to 2mm on the 6th. This will rattle if pushed, and will certainly expose any slight unevenness in the fretting. I don't think it reasonable to complain about this if your instrument cost under £500. Raise the action over 2mm on the 1st string, and you might have a reasonable case to ask a maker to adjust something. A finely set action is a function of quality, but even at two grand there are limits. It can be affected by slight contraction in a cold truss rod in winter, or even by the way you hold the guitar on a very slim neck.

If your fingerboard has a sharp camber, you probably won't be able to bend much with an action under 2mm/1st to 2.8 or 3mm/6th. Also, for the same action height you will get more rattles over wide dome top frets than over thinner ones, so there are many points to consider before getting pedantic about specific figures and stamping off back to your dealer. In general 2mm to 2.8mm is a very playable, bendable, handleable height for an electric, and if it is causing you problems, then you should look to your muscles.

Before we leave this, look out for simpler wang bars that drop action height as they drop pitch as you may have to set higher to allow for it.

Intonation. Any fretted instrument is out of tune with itself anyway by virtue of the equal temperament scale. Frets are laid out according to the "18 rule":

— scale length (nut to bridge string length) divided by 17.817 = distance from nut to first fret. Remaining length divided by 17.817 = distance from first fret to second fret, and so on up the board.

However, the note at the twelfth fret should be smack in tune with the harmonic which appears exactly over it. Assuming you've got rid of extraneous problems caused by high pick-ups or dead string, if the note is flat relative to the harmonic, then the bridge saddle must be moved forward to shorten the vibrating string length between fret 12 and the saddle and thus raise the pitch of the note. Usually, it will knock the tuning out as well, so retune on a meter before checking the adjustment. If the opposite is the case, that is, the twelfth fret note is sharp relative to the harmonic, then the distance between fret and saddle is too short, and the saddle must be moved back until note and harmonic match up.

Different thicknesses of string need different saddle settings for two reasons: One, strings bend out of tune at different rates when you push them down to the fingerboard, and two, a thicker string will start vibrating at a point further forward of the take off point on the saddle than a thin one, each string being restrained by its own mass.

Note that often moving the saddle back increases string tension as well, so slacken off before adjusting to save unnecessary strain on small screw threads.