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Improving a Copy Guitar (Part 2)


We gave guitar maker and repairer Stephen Delft an Antoria Les Paul copy and asked him to improve it as far as possible. This is part two of his report.

Before changes.

In this part I shall discuss some of the ways in which you can improve the performance and/or reliability of electrics inside your guitar. Let us first deal with problems of reliability.

Faulty electrics in guitars may be caused by bad design, corrosion of contacts, poor quality components, or simply wear and tear over a period of time. I do not intend to separate which causes what; all you want to know is what you can do to minimise the chance of troubles occurring, so let us start with DUST. Many guitars spend their whole lives with the electronics compartments full of a mixture of sawdust and polishing compound, left behind when they were first made. You do not need any technical ability to remove all cover plates and clean all the cavities in the instrument with a SOFT brush and a vacuum cleaner. Dust can get inside volume controls and switches and make them crackle long before they are worn out.

After changing capacitor and 'pot' on tower part of circuit.

The next thing you can do while you are inside is to gently clean any exposed switch contacts with one of the strips of impregnated pink card, distributed by Electrolube or R.S. Components. (Ask your local radio/T.V. shop). This also applies to the contacts and inside hole of jack sockets. There is an exception to this rule — if your guitar has a selector switch which works on the Fender principle, with a long, pivoted switch arm, operating a roundish flat plastic disc with connections round the edge, this sort is better left alone unless definitely noisy, as its contact springs are easily put out of alignment. You could apply a little Electronic Switch Lubricating Oil on a needle but ONLY IF IT STATES "SAFE FOR USE ON PLASTICS". If it seems strange to be cleaning perfectly O.K. switches, remember that switch oils and cleaner cards also have a preservative action against atmospheric corrosion. The other thing which will protect contacts against the sulphurous mixture we use for air in cities is a piece of old-fashioned MOTH BALL, clipped into each cavity. Remember to fasten it down firmly — if it gets loose, it may do more harm than good. It is possible to find dirty switches, even on new guitars; and it is always worth cleaning them before considering replacement.

Another thing worth checking is the fixing nuts on any controls. Apart from being inconvenient, loose controls put more strain on the wires and components connected to them.

Poor or unsuitable components generally make themselves known by faulty operation after some time. The cure is obvious, and the difference in cost between good and mediocre replacements is negligible compared with the cost in time of taking things apart to make the replacement. Always use the best quality spares you can get, but be aware that some very good volume controls are stiff to turn and may make "Violining" almost impossible.

There remains the subject of bad (or just lazy) design. Certain problems frequently occur in new electric guitars and the most common of all are tone controls which are almost like switches, and do nothing between 3 and 10, and volume controls which interact with each other and with the tone controls.

The tone control problem rarely occurs with Fender-type guitars, but as a matter of taste, you may wish to try varying the usual 0.1 tone control capacitor to 0.05, 0.22 or even 0.1. As the value is reduced, the tone control becomes less a balancer of treble against bass and more a modifier of the tone of the top two strings.

Electronic device in position.

Generally, funny tone controls occur on Gibson-type guitars with humbucking pick-ups. Most of these are fitted with 500K log 'pots' for volume and tone, (or worse still Lin pots). I believe that if the first half of a tone control does nothing, you may as well throw away that half, and spread the remainder over the whole dial. This is done by replacing the I.C. controls ONLY with 250K LOG pots. Also use the opportunity to check whether the capacitors are between 0.01 and 0.05. (Yes this is up to 10 times smaller than the recommended values for Fenders. Read the noughts carefully). My preference is 0.02 for real Gibson humbuckers and 0.01 for most copies. It varies because of a complex relationship between pick-up and tone control, and for this reason, I recommend that tone controls should generally come before volume controls in a conventional 2-tone/2vol system.

The problem of interacting volume controls is one which can only be perfectly resolved by either putting a pre-amp inside the guitar body (or using a 'Stereo' lead and doing the mixing in the two channels of your guitar amp), or by accepting a lower output from the guitar.

Guitar pre-amps are becoming distinctly fashionable, if only because they give a measure of immunity to interference from theatre lighting (later in the article, I'll describe a device of my own design which solves the problem neatly) and 'stereo' conversion (which only approaches stereo, if you use two separate amps) will be covered in a subsequent article. It is, incidentally, so absurdly simple that I find it hard to justify the extra price asked for this facility on a new guitar or bass.

Batteries in position on foam packing.

There are two accepted comprises over this problem. The first, used on most Gibsons and similar copies, is to accept the fact that, with both pick-ups on, if either volume is turned below about 3, it begins to affect the output of the other pick-up as well. It also affects the other pick-up's tone control. Strangely, I find that if a guitar with a famous name acts like this, it is accepted, on the grounds that one does not use the volume set as low as 3 because it affects the "tone". However, if one of my own guitars has the same behaviour, it is instantly noticed, and bitter complaints follow — an interesting state of affairs indeed. Strats and Teles do not suffer from volume interaction because there is only one volume control. A circuit for the first compromise is shown in Dia. 1.

1 (See Errata below)


The second compromise is shown in dia. 2 (a conversion from type one to type two is shown in dia. 2). Here you will see that the 'in' and 'out' of the volume pots are reversed. The control still operates in the same direction (and for the technically minded, forms an unbalanced T-attenuator with the internal impedance of the pick-ups).

2 (See Errata below)


With the type 2 circuit, the volume controls are largely independent of each other, but low volume settings may seriously affect the tone on the same pick-up, and at high volume settings, both tone controls affect both pick-ups. Yer pays yer money and yer takes yer choice.

For reasons I have already explained, some makers of 'one-offs' prefer to use circuit two, but I feel type ONE is the lesser evil. However, both circuits suffer from an interaction between guitar and amp, which causes a change in tone between (say) volume 10 and volume 8.

The difference in tone is small enough to be compensated for by most amp tone controls: the problem is that the tone varies, and by an amount which depends on the particular amp in use at the time — hardly a satisfactory situation.

The problem arises because most pick-ups work best when they "see" a certain value of load resistance connected to them. This is called the Optimum Load, and is tolerant of small variations, depending on how you like your tone.

It appears that most standard (high impedance) pick-ups are happy with a load between 150K and 500K. If that sounds confusing, all will be explained in future articles.

3 (See Errata below)


With either system, when a volume control is on full, the pick-up sees a load which is a little lower than the "input Impedance" of the amp. (You may think of this as an imaginary resistor across the amp's input jack) and this resistor may easily be as low as 33K — considerably lower than the recommended 150K minimum.

The device I mentioned above runs off two small batteries, is small enough to fit in most guitars without modification, and which gets between the guitar and the amp and ensures that the pick-up never sees a load less than 150K. It does this without lowering the output, by drawing a little power from the batteries (2 milliamps) to make up any losses. This device should be used with the type one circuit (dia. 4).

4


Its second advantage is that the output to the amp is at a relatively low impedance, which means you can use really long leads without the usual loss of treble, the leads don't crackle, and you are less likely to pick up interference from mains or lighting cables. The only component not included within the device is an output coupling capacitor, which for most purposes need not be larger than 0.1 microfarad, but some cheaper effects pedals may require you to fit a larger one of about 1 or 2 microfarad (as used in last month's hum loop isolator) if you lose a lot of bass. In either case, the capacitor should be a non-electrolytic type, rated at 30 volts or more.

I have used a Rendar one make/one break Mono Jack Socket Type No. R 32621 (available in small quantities from Rendar Instruments Ltd., (Contact Details), for 29p each inclusive of tax and post) to switch on the batteries when the guitar lead is inserted, but you could use a different switched socket or a separate switch. Remember that the battery Positive (plus) goes to the 'Earth' connection (dia. 5).

5


Removing difficult knobs.

Finally, a few hints on tools. To change controls, you must first remove the control knobs. These come in three varieties: those held on by a grub screw, or collett fixing under a centre cap, those which pull off, and those which should pull off but don't. For these you use a piece of twin figure-8 mains flex, split in the centre just enough to slip under the knob each side. Hold both ends and the guitar and pull.

Examples of tone pots with long and short threaded fixing bushes. Also note plain and splined spindles.

The simplest way of getting replacement pots which will fit push-on guitar knobs is to buy spares for American guitars. It is also the most expensive way! Take care that the pots you buy have a long enough threaded fixing bush for your guitar. (Some are meant for fixing to a thin plastic panel only — for a pot fitted from the back you may need 9 or 10mm of thread). You may have difficulty obtaining 250K pots with long threads. The other solutions are used to pots with round or D-shaped spindles and either fit new screwfixing knobs, or drill out the originals and glue them on. By the time the pot wears out, the knob is generally worn out too. You cannot solder to the case of most English pots without filing RIGHT DOWN TO THE STEEL INSIDE FIRST, and you will need a minimum 25 watt iron.

Tweezers and non-melt silicone rubber sleeving are useful aids in confined spaces. Take care not to burn the guitar body or other wires when soldering and don't drop solder on the back of the guitar. Tubular spanners are the safest way of dealing with control fixing nuts. Pliers tend to slip and gouge the guitar top.

Draper no. 5225 10/11 mm, also 5/16" and 1/4" Whit hexagonal, and 1/2" A/F. These fit most nuts.

I believe this is the first ever article on a do-it-yourself basis covering electronics fitted to standard guitars. I hope to keep you in touch with further developments in this field.

ERRATUM AND ADDENDUM

Re: Fender-type guitars: You may try varying the usual 0.1 capacitor to 0.05, 0.02 2, or even 0.01.

Re: Funny tone controls: by replacing the tone controls only with 250 K log pots.

The first diagram is DIA 2, below it is DIA 1. Conversion from type 1 circuit to type 2 is shown in DIA 3.

Bottom of column 3, page 12 ; some makers... prefer... circuit 2, but I feel type ONE is the lesser evil [amended in text.]



Previous Article in this issue

Emerson/Moog

Next article in this issue

Albums


International Musician & Recording World - Copyright: Cover Publications Ltd, Northern & Shell Ltd.

 

International Musician - Jun 1975

Donated & scanned by: Mike Gorman

Topic:

Maintenance / Repair / Modification


Series:

Improving a Copy Guitar

Part 1 | Part 2


Feature by Stephen Delft

Previous article in this issue:

> Emerson/Moog

Next article in this issue:

> Albums


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