# The basics - Current, voltage and resistance

When you deal with guitar electronics there are these three subjects that play a role - they play that role together, they depend on each other.

As follows:

Current, measured in Amperes and in circuits and formulas identified as I.

Voltage, measured in Volts and in circuits and formulas identified as V

Resistance, measured in Ohms and in circuits and formulas identified as R. ( sometimes also with the greek letter omega)

These are interdepedent,. For example if you increae V from 1,2 volts to 120 volts and leave R the same, the current I will become 100 times larger.

There is a formula called Ohms' law which lets you calculate any of these if you know the other two, As follows

I= V / R

V=I / R

R= I / V

# More basics - Switches, potmeters and capacitors

In a loaded guitar we see a few more or slightly different components.

As follows:

The resistor becomes a variable resistor, in other words the potmeter.

The battery providing V can be seen as the coil of the pups. When a string moves through the magnetic field the coil will give a tiny voltage . Minor difference is that as the string moves from one side to the other this will be an alternating voltage, givin off an AC alternating current.

The switch. Instead of scissors we use switches to open and close the circuit witout damage. There are many types, see below below.

New here is the capacitor, called C and measured in Fahrads, or F (one Fahrad is very large, so in practice we often see microFahrads).

I will not go into the theory, but take from me that the combination of a variable resistor and a capacitor will allow to adjust tone ( filter certain frequencies).

# Switches and pots

If you replace a volume pot with a pushpull pot make certain that it is an audio taper pot (logarithmic) sometimes indicated by type A, the tone pot can be linear (type B).

Although, if your ear prefers by all means use linear pots.

Switches used here are mostly toggle, either 3-pin SPDT (single pole dual throw) or 6-pin DPDT (dual pole dual throw) . You need the mini versions that can be mounted on a pickguard (not those for printboard mounting)

# The Labstrat

As i write the book i'll build and test each mod, thats the only way to verify that you dont write crap., i also use the Labstrat during the workshop.

This means that i have to test a great many modified pickup circuits. To make life a bit easier, I started with preparing a (not too expensive) body so that i can take out the pickguard leaving the guitar intact.

Here is the body, cheap but actually not extremely bad (poplar) with a big route of about half the body, allowing the pickguard to be moved in and out:

Here is the body, cheap but actually not extremely bad (poplar) with a big route allowing the pickguard to be moved in and out.

Note the extensive shielding!!

# 1 - Adjust pup or polepiece height

To be honest this is not really a mod, but more part of setup. However, by playing around with the setting you can improve your sound (or mess it up completely!)

Either adjust the pup height with the little bolts on the pickguard or in the frame in case of a Gibson humbucker (see below), or adjust an individual magnet., if one string B2 for example is a bit weak.

Individual magnets can be adjusted if they have a slot for e.g. a screwdriver (like my old SG below), OR (on some Fender pup sets) you can access the individual magnets from the underside and push them a bit up or down (very very very carefully!). The picture shows the standard Strat polepiece adjustment.

Not difficult and good experimentation to get a feel between magnet height and sound, sustain, intonation problems and other strange phenoma if you get to close.

# 2 - Mods on one pup - add or change tone control

## Treble bleed capacitor

One of a the simplest and reasonably effective guitar wiring mods is the treble bleed capacitor. If you turn down the volume pot on a guitar the sound may become muddy because of loss of higher frequecies. üÿHere a drawing how to connect a treble bleed capacitor. Mounting treble bleed capacitor between in- and output of the volume pot will maintain a certain level of high frequencies going to the amplifier and therefore keeps the sound clearer also at low volume.

Take a .001uF (micro Farad) or 680 pF (pico Farad) ceramic capacitor (the small orange discs). Try it out. Not dangerous. The only thing you need apart from the caps is a fine tipped soldering iron and a small screwdriver Phillips to open up your pickguard.

Try it out. Not dangerous. The only thing you need apart from the caps is a fine tipped soldering iron and a small screwdriver Phillips to open up your pickguard.

Using the test Strat above as prepared for my book, i mounted this circuit with a tiny toggle switch in order to hear the sound with and without capacitor. The effect is amazing indeed. With the volume very low the sound becomes very muddy, switching in the capacitor makes a world of difference. Of course you do not need the switch, just add the cap as indicated.

Here also a short clip on the subject (Youtube).

## Adding or modifying tone controls

Look at the drawings of the Strat circuit and you will see that the bridge pup has no tone control.

By simply swapping a lead on the 5way switch you can give the neckpup tone control, by taking it away from the midpup.

For some players this is a better setup than the standard. There are a few variations to this one to get tone control on all pups.

# 3 - Mods with two or more pups

## Series - parallel switching of pups

For series parallel switching (parallel is standard) you best use a DPDT pushpull switch. A pushpull combi with a pot replaces one of your pots without any modification to the pickguard.

Here is one prewired for switching two pups in series, Strat or Tele, and also Les Paul style with simple humbuckers.

The wiring of the potmeter doesnt change, just copy the one you replace. DPDT stands for dual pole, double throw - in other words one toggle acts on two switches, each switch moves between two points. The middle set of contacts normally is the common set.

If you prefer you can also use a mini DPDT switch; this requires one small hole to be drilled in the pickguard. In some cases this is easier.

Above you find a circuit drawing to switch bridge and mid pup in series.

I suggest you try out the sound before completely replacing one of the volume pots wit the pushpull fully wired.

I wired the switch part only in order to see if i like the sound. To be honest, i dont think the difference is staggering.

The series sound is a bit fatter and louder, but not outstanding. It may be what you are looking for though - so give it a try. The result may well be different on another set.

A good exercise is to follow the connections in the drawing for both positions of the switch. If you push the switch the standard situation is active, indicated by the two little red connections. If you pull the switch the top 4 lugs are active and that means the pups in series.

Here is a Youtube clip giving the stock sound followed by the modded sound of bridge and mid pup in series.

## Parallel - all three pups in series mod

Another option is to switch all three pups in series, so you get one very hot pup. This is the Brian May red special.

In order to do this (whilst retaining the option to switch back to standard) you need a 4pdt (4 pole dual throw) switch, not available in the pushpull persuasion.

This seems a lot of hassle for just the one switching possibility.

If you want more flexibility for various combinations you get into a setup with 6 or 9 switches and a lot of wires to solder. I am working on a 9 switch mod (nicknamed the madmod) which gives all series en parallel possibilities..

## Switch mid pup out of phase

Here a similar dpdt switch prewired for switching one pup out of phase (invert phase) - for example the middle pup of a Strat.

This one creates a very different sound, much more effective than series/parallel. A bit John Scofield, BB King.

Very little low (not surprising, the lows are phased out), and a sharp biting high, quite different from the bridge pup on its own. Good for specific types of soloing.

Here is the wiring diagram.

The dpdt switch in pulled mode switches the middle pickup out of phase. Adding additional volume pots for each individual pup can change the phasing effect. I will make a demo cicruit with one extra pot for the mid pup - see what happens. It will not only change the volume, but in this case also the sound..

Here is the effect as seen on a scope. The upper channel is the standard neck pup, under is the midpup phase inverted - while sounding the open E6 string.

You can see that where one signal goes up, the other goes down. If they would be exac tly the same the result would be silence.

However, there are small differences (caused by the location of the pup for example) so there is a resulting sound , but lower in volume and thinner with some frequencies nulled out:

Here the scope view of the resulting signal of the mixed signals, looks and sounds very different.

The volume is lower (amplitude) and a lot of the low has disappeared. I will explain a bit about the use of the oscilloscope at the end of this page. I'll keep it short as not many guitar players will have one, nor have the need. I like the sound, very usable indeed. Here is the youtube clip I made to demonstrate the resulting sound:

## Coil tapped (single coil) pup

Coil tap = access (or tap) the middle of a single coil and tapping the signal there, basically gets you half a pup or the whole pup.

As it is fairly difficult to open up a SC and go for the middle, i bought a Seymour Duncan pup which has this feature wired in. The trick is that the full pup is very hot, around 20 kOhm, the tapped mode provides a pup of around 10 kOhm - still hot but a lot less so. See scan from the leaflet above.

## Stereo Stratocaster and no-load effect

An interesting effect is to make a Strat stereo, for example the neckpup left and the midpup right or vv. Obviously you need a stereo mixer or two amps or something like that. The sound is quite broad and has a lot of depth.

An interesting feature is that in stereomode the Strat can also be in 'noload' mode, i.e. volume and tone are bypassed if you add another little switch (this is also called the 'solo' switch as you're suddenly very loud when flipping the switch).

For any mod i make the design principle is that you can go back to standard Strat mode at the flick of one switch.

What you need is:

- stereo jack (receptacle)

- stereo cable or stereo to two times mono splitter

- stereo mixer/PA or two amps

- a few pieces of flexible wire, solder etc.

- a 3PDT switch (or DPDT plus SPDT)

- possibly a spare pickguard and a Strat with no guarantee!

Drawing 4 shows the stereo switch leaving the volume/tone circuit connected.

I have drawn the extra little switch, but not connected. In practice you will hear that in stereo mode for one channel volume and tone are still active, the other channel (pup) is noload. The effect is that you can turn down the volume on side of the stereo sound. Something you possibly can play around with

Drawing 5 shows the circuit with the volume pot disconnected in stereo mode. (and solo mode).

So stereo mode here is now full no-load.

Here's a few pics to illustrate the proces

Note that i used a a DPDT switch here. The SPDT switch to cut out the volume control is connected, but dangling out of view and outside the labstrat. If I would make this a permanent mod i would use a pushpull switch replacing one of the pots

This mod places the strat in 100% stereo mode, i.e. no panning/mix between left and right. I may add yet another version (6. probably) with two pots (concentric) allowing the mix between left and right to be changed. I will place the sounds in a clip for you to hear, although the effect is much clearer if you sit directly between two big amps. The stereo mode results in a very broad sound with lots of depth (like perspective in a drawing)

# Mods with humbuckers

Above mods are mainly about single coils. Humbuckers offer different possibilities as a humbucker is in fact already two pups in one

But first, whats the diff between COIL SPLIT and COIL TAP? If you follow the various fora (more than one forum) you see the terms used ad random or randomly (in english). Confusion galore. I use the term as follows:

Coil split = splitting a humbucker into two separate coils (switches the guitar to single coil sound with either coil, or humbucker mode)

Coil tap = access (or tap) the middle of a single coil and tapping the signal there, basically gets you half a pup or the whole pup.

Coil tap = tapping a humbucker between the coils. Leave the connection between the coils, you only litterally tap it.

The pic below illustrates SC coil tap:

If you have a humbucker thats prepared for coil tap as well as split you may end up with seven wires to play with!

## Coilsplit a humbucker

I bought a very cheapo Epihone Les Paul special, very much akin to a Telecaster but then with two humbuckers.

Each humbucker can fairly easily be opened. Carefully take of the insulation tape around the coils. Then you see a wire (this case white, but can be any colour), which connects one coil's mass side (but used as serial connection in humbucker mode), to the hot side of the second coil.

The mass side of the second coil is soldered to the baseplate i.e. mass or ground. You now have a choice:

a. to tap: leave the connecting lead, only take away a bit of insulation and solder a lead onto the blank. The lead goes to the control cavity and gives you the possibility to switch between SC and Humb modes.

b. to split: This is what I did in the example as you have more flexibility. I Cut the white lead between the coils (see picture) and extended each with a lead that i brought into the control cavity. Then I added the little switch as in the drawing.

At this stage I used the coilsplit as coiltap - confusing?

Look at the drawing. I could also bring out the mass wire from the second coil to the control cavity in which case I would have had access to both sides of both coils. In that case you have an extra choice, i.e. use either coil as SC.

It does work fine. There is a difference in sound, this LP does sound like a Strat or Tele in split mode.

Ooh yes, do not do this if you still have warranty on your guitar. That will defintely be void now.

Here a clip to let you hear the difference between the two modes. The difference is more subtle than overwhelming, but definitely the SC mode does sound a bit Strattisher than the Humbucker mode. And definitely, although not very audible on the clip the SC mode has a bit of hum whereas the humbucker is very quiet.

## Humbucker split switch parallel, phase

Now we have done the difficult part, i.e. cracking open and destroying a humbucker above, its easy to use the same thing with a slightly different DPDT switch confifguration to do the following interesting things:

a. switch the primary coil from series (normal) to paralell operation

b. switch the primary coil in reverse phase, i.e. swap the leads.

First two simple drawings, text and pics later.

A completely bonkers modification with nine switches that will give all posssible series and parallel combinations as well as the normal Strat mode.

This is just the idea, it works on paper but i havent had the time to test it.

As soon as i have tested it in reality i'll place it here on the site. The complexity is not so much the amount of switches but more the amount of soldering, the limited place under the pickguard and the type (brand) of switch to be used.

## The mono jack connector - receptacle

It is important to know how the jack connector (the thingy where you plug in your cable). One of the common errors is to mix up the signal and mass connections.

Looking at the cable's jack or plug, the tip always is the signal carrier (or hot or +), the remainder is connected to the metal mesh sock which is connected to earth.

There are two soldering lugs,, the signal is connected through the long spring to the lug right accross (most of the times), the other lug therefore is earth. In case of doubt take a multimeter, plug in a cable and measure which lug connects to the tip.

A stereo connector is slightly different - there are three soldering lugs - but you can figure that out easily with a multimeter stereo type jack.

I will add here a bit more info on various types of switches, which may make the issue a lot more confusing. Not to be helped though, they exist.

MEGASWITCH - a real 5way switch (not a a 3way with stops in between), otherwise a more or less direct replacement.

DPDT dual pole double throw, schematic

Pushpull DPDT dual pole dual throw integrated with potmeter.

SUPERSWITCH - this is a 4 layer 5 way switch which can be used to add a lot more confusion, i mean possibilities like phase switching, coil tap etc.l etc.

S1 SWITCH - this is a pushpull pot with attached to it a double dpdt switch (in fact 4pdt). Applying this requires some real thought, as the number of possibilities is rather confusing..

Les Paul 3way switch. This is a DP3T switch (at least behaves like one). Another name for this type of switch is on/on/on. The picture under shows how you can emulate a LP switch with standard DPST toggle switches. More about it later.

## A nineties vintage Vantage T50R tube amp - noisy pots, an annoying common issue

We all know the terrible noises an amp (or any other volume or tonepot) can make after a few years of service when dirty potmeters start to cause crackling sounds that disturb everything with ears in the area.

Many a player sold  his amp in desperation for cheap, not knowing  how very easy it is to overcome. You need only two things, an appropriate screwdriver (mostly Phillips or Pozydrive), and a can of pressurized contact cleaning fluid with a small tube to access small dark paces.

This case is a vintage amp produced as brand Vantage, or also as Samick. It is a surprisingly loud tube amp; really nice, apart from the creaking and sizzling pots. The electronic innards are from the well known Seymour Duncan club.

Not many buyers will honestly tell you it takes about 10 minutes to make your crackling vintage Ampeq amp performing as new again.

Here are the steps to follow for an old sick amp i had. With a few variations the steps willl apply to any old amp - including yours.

### Remove cover

A closed  top will not be much different. They all have some form of a cover, back or side, that can be unscrewed in order to reveal the amplifier chassis with the trafos, tubes, resistor pcb's and potmeters and switches.

Be certain that the amp is NOT connected to the mains and has not been connected for a while. Unless you are suicidal that is.

Large capacitors (electret) on the chassis may hold a nasty surprise if you don't give them time to lose their charge. Steer clear from the capacitors anyway.

### Unfasten chassis screws

You will also be able now to locate the (probably) 4 bolts that fix the chassis to the casing.

The housing/casing will probably have some provision that prevents the chassis to fall down when the bolts are out. In my case there were some wooden supports which allowed the chassis to be lowered a few cms, but not drop all the way.

That would be goodbye to the tubes and thus eliminate the problem in a more permanent way..

### Take out the chassis

Carefully now take the chassis out and place in a good viewing position on a workplace.  You can leave the wiring to the speaker in place, it will be long enough if there is no provision to unplug the speaker.

In any case you want the speaker connected to test a bit while you still have access..

## Get the spray and locate holes in the pots

I prefer the vers

The casing of the pot will have  a small hole , in which you can wriggle the little tube.

Insert it in the offending potmeters. Spray whilst turning the pot's shaft a number of times. Now you have access, treat the other pots and switches if any,  as well.

If you are confident with electricity and electronics you can switch on the amp and check if the pots behave nicely. There is high voltage on several parts of chassis contacts and the like.

There shouldnt be a problem though if you follow the next rule: Don t touch anything with your bare hands, while the mains are on! Except of course the nobs on the pots, which are insulated anyway. You may need to repeat the treatment a few times.

Disconnect the amp from the mains each time as you do so. As far as I know the fluid has no conducting properties, but be on the safe side and let it dry a bit before re-connecting the amp.

Now follow the steps  in reverse order to reconstruct the amp.

BTW, noisy pots on a guitar can be treated in the same way.

# Repair dents and scratches

Here a suggestion made by a reader who is also a pro carpenter (furniture).

Old trick to repair a dent in wood (including painted wood) is to apply steam. I haven't tried it yet (i like dents), so test it on a piece of scrap. On thing for sure is not to place the guitar over a pot of boiling water. The steam must be applied locally, so make something with a small flexible tube that you can fit on a kettle or something.

Not difficult. If you want to approach it pro, go to StewMac.com, they have this sort of thing with which you can unglue a neck from an acoustic guitar (you drill a small hole in de position just over the body neck connection mostly a position marker, and insert the tube, it will dissolve the glue and you can take out the neck - don't do this at home with a valuable antique Marttin or a Les Paul Gold Top 1953!)

Now we are on the topic, repairing (provisionally) an ugly scratch, where the blank wood shines thru - that ugly - get a felt pen (permanent) in roughly the same color and apply sparingly. Test the colour first. This I have done with a green Fender Highway body that came in with a very ugly scratch - instant success.

Obviously it doesnt take away (fill ) the scratch, but it becomes invisible except for close inspection. A bit more expensive are the special pens in the right colours from luthier shops.

All books on guitar electronics refer to the use of the multimeter to check shorts, nonshorts, resistance or whatever. However, if you have no clue what a bloddy multimeter is this may be somewhat of a mistery and sometimes misery. Have no fear, it is a very useful device and easy to use for our purpose here.

It deserves a bit of theory, bear with me.

In electronics there are basically three phenomena that frequently require a measurement. They are:

a. resistance, measured in Ohms

b. voltage , measured in Volts

c. current , measured in Amperes

The relation between the three is that if you take a battery (Volts) and connect the two contacts with a wire (resistance) the result will be a flow of current thru the wire that is dependent on the resistance of the wire. If the wire has a low resistance, current will be high (you will burn your fingers), if the wire has a high resistance current will be low. There is an easy formula if your're interested :.

current = volts / resistance

or

I=V/R

which is referred to as Ohm's law. Enough. Thats all you need.

There are a few other units such as for impedance (very similar to resistance), capacitance (Farads for capacitors, requires different eqt), and some values (Henry) to do with coils, magnetism etc. which is more advanced.

On the standard device in the pic above (=low cost) with the lower rotating selector chose between what you want to measure, Ohms, Amperes, or Volts - here kOhms.

In the pic above the testpins are held against each other which means that the device sees a very low resistance. Indication gives a outcome of zero Ohms.

With guitar electronics you use the multimeter mostly to check if there is yes or no resistance between points - no resistance often means there's a short - which could mean no sound, or terrible noise. Therefore a cheap one is more than good enough.