Electronics and other useful tips
When you talk to guitarplayers and mention the word electronics, or hint at the use of soldering irons, they get a faraway, zomby like look in their eyes. Still there are some very handy things to know requiring little engineering knowhow that are very very useful. I will gradually add a few of these tidbits on guitars but also on amps and other thingies.
As i wrote my books on Strat, Tele and PBass construction, subjects popped up - based on remarks, questions of readers and my own experience - that are just too much to fit in the books in order to keep them simple. I have now started a book on electronics modifications and so on, but for the time being here's some useful stuff.
0. Some stuff from my new book on electronics.
I have started work on a book on guitar electronics and modifications plus a little on sound impact of wood and paint.
As it means that i have to test a great many modified pickup circuits, 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 allowing the pickguard to be moved in and out.
0.1. Adjust pup or magnet height.
Thats easy. Either adjust the pup height with the little bolts on the pickguard or in the frame incase of a Gibson humb, 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 Phillips screwdriver, OR (some Fender) you can access the individual magnets from the underside and move them a bit up or down (very very very carefully!).
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.
0.I. Mods on one pup: Add or change tone controls
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.
Here 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.
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.
I recorded the two sounds on my iPad and you can acces the mp3 file here, to hear for yourself. In the following track you hear the first four bars with the capacitor active, and the second four bars with the cap switched off - sounds very muffled. I indeed had the pot on the Strat turned down very very low, which normally would cause the effect in the second four bars.
Here also a short clip on the subject (Youtube).
AUDIO: STRAT WITH AND WITHOUT TREBLE BLEED
Adding /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.
Drawings will follow.
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0.II. Modding with a combination of two pups
- a. Series parallel switching two 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, or also Les Paul style with simple humbuckers - rest of story follows:
The wiring of the potmeter doesnt change, just copy the one you replace.
DPDT stands for dual pole, double throw - in other words one handle acts on two switches, each switch moves between two points. The middle set of contacts normally is the common set.
Above you find the circuit 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. I will pass.
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 sound of bridge and mid pup in series:
series parallel track
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 (switchable between mod and 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. Important is how to do the physical layout, as soldering all these wires onto the tiny toggle switches is almost
- b. In phase, out phase switching (electronic)
Here a simil
ar 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 diragram.
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 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:
In the clip I used only the bridge pup with the mid pup in and outphase. Using the neck pup with the mid pup gives again a slightly different tone. As the circuit is implemented on my Labstrat, the switch dangles under the pickguard - which makes a bit of noise now and then. If you make the circuit permanent, that is a non-issue.
In the book i will add an extra potmeter for the midpup in order to determine the amount of suppression when using in a mixed mode. If you use the invertted midpup on its own, there is no difference. It only works when two signals are mixed.
C. COIL TAPPED SEYMOUR DUNCAN SL3 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 openup a SC and go for the middle, i bought a SD 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.
0.III. Modding with humbuckers
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 humbucker thats prepared for coil tap as well as split you may end up with seven wires to play with.
1. Split tapping a humbucker
I bought a very cheapo Epihone Les Paul special, very much akin to a Telecaster but then with 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, but I found the result a bit disappointing. There is a some difference in sound, but this LP does not 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 modes does sound a bit Strattisher than the Humbucker mode. And definitely, althoough not very audible on the clip the SC mode has a bit of hum whereas the humbucker is very quiet.
More on switches:
I will add here a bit more info the following 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.
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 wirth attached to it a double dpdt switch (in fact 4pdt). Applying this requires some real thought.
to be continued.
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1. Noisy pots - an annoying amp issue.
We all know the terrible noises an amp can make after a few years of service when dirty potmeters start to cause cracking 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), and a can of pressurized contact cleaning fluid with a small tube to access small dark paces.
Not many buyers will honestly tell you it takes about 10 minutes to make your crackling vintage Ampeq amp performing as new again.
REMOVE THE COVER
This specific instance is an old 30W combo of Chinese origin. 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.
I had a pleasant surprise as my old Chinese tube amp turned out to have good USA built innards
READY CONTACT SPRAY
Get your can of contact cleaner ready.
LOCATE POT HOLES
The casing of the pot will have a small hole , in which you can wriggle the little tube.
SPRAY
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.
Same for a guitar:
BTW, noisy pots on a guitar can be treated in the same way of course, after all, a pot is a pot is a pot. Take off the pickguard and spray.
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One of my customers (Hans Brinkman) came with the following simple and elegant solution to make an adjustable shim.
More detail will follow (measurements etc).
When youj do this dont forget a metal plate in the neck if it doesnt have one already, otherwise you will destroy the neck at that point.
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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 you can buy these feltpens at luthier shops, available in most popular colours.
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I often get a question "What the heck is a scalloped neck".
Without going into whys and wherefores, here is a pic.
Don't do this at home.
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5. A very noisy Telecaster pup?
I worked on a Tele mounting a very nice pup set but got a lot of noise in addition to the sound you would expect.
On closer inspection I suddenly realised that the bridge pup was mounted on rubber tubings instead of small springs and thereby was very well insulated from the rest.
Adding a lead from one of the potmeter casings (the black one) with an "mounting eye" (i have no idea what its called in english) and fixing it to the 
shielding solved the problem.
Great Tele, immediately confiscated by my son.
In general improving a mass connection can reduce noise.
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6. Building a piezo transducer into a Martin DXM
My Martin DXM (the budget model but a great guitar nevertheless) came without pickups or whatever.
Although the guitar has an amazing volume, this is not always enough.
I acquired a lowcost set as urgent solution for a gig and here is how I mounted it..
To the left Step 1. Think, am i really going to try this?
Step 2. Take the plunge and first remove the strapholder. Carefully wriggle it out.
I will write some more about this one when i have a USB audio card/mixer (one or two channel) hooked up.
I tried it with the built in apple mic, which works fine but I would like to have guitar input as well.
Step 3. Take the whole set and place it on top of the guitar. Connect to an amp and determine the best position of the transducer.
This roughly as on the photo, a bit more to the side as it conflicted with a brace inside.
Step4. Very, very carefully englarge the hole to the size of the strapholder interface - often around 12mm.
I use two bits one like here and a normal 12mm wooddrillbit.
Step 5. This drillbit must be the exact size of your new interface strapholder
You cant use this in step 4 as the bit will slip and make a very nasty hole.
Step 6. Now you place the jack and the transducer inside roughly at the spot you measured earlier.
I attached it using the self adhesive tape that came with it, as its easier to remove than glue.
Put the strings back on and go. .
7. Introduction to the electronic Multimeter
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.
It deserves a bit of explanation.
In electronics there are basically three phenomena that frequently require a measure ment. 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.
There are a few other units such as for impedance (very similar to resistance), caqpacitance (Farads for capacitors, requires different eqt), and some values to do with coils, magnetism etc. which is more advanced.
On the standard device in the pic above (=low cost) you see the lower rotating selector chose between what you want to measure, Ohms, Amperres, or Volts - here kOhms. In the pic above the testpins are not held against each other which means that the device sees a very high resistance. Just left of the three zeros there is a flashing three, could be an E or whatever to indicate that the resistance is near infinity. The pic was just taken when it flashed off!! An analog device will show the needle right to maximum indication.
With guitar electronics you use the multimeter mostly to check if there is yes or no resistance between points - no resistance normally means there's a short - which could mean no sound, or terrible noise.
In the picture at the left the pins are held against each other (shorted), the device sees a resistance of 0 Ohms.
You may also wish to check for example if a Strat volume pot you have lying around is 250 KOHM or 500, here's how to do that., i.e. measure a resistance.
In the picture at the left the pins are held against the outer lugs of the potmeter, which reflects the total resistance of the pot. - correcty in this case 250KOhm.
(The middle lug is the variable, shown below)l
Here we look at the restance of the potmeter output = the middle lug (the variable connected to the runner).
I have placed the runner roughly in the middle and you can see that this is less than 250 but not asyou would expect 125. This is good, as these potmeters are logarithmic, not linear. So dont panic, this is ok
Resistance here is about 160 kOhms.
Be aware that if you measure a potmeter like here, but mounted in circuit on a guitar,the measurement is not only the pot but also (a kind of average of) the rest of the components such as the pups.
Now, if you want to measure voltage for example, turn the selector to Volts and connect the testpins or test clips tot the poles of whatever you want to measure voltage between.